[Federal Register Volume 73, Number 140 (Monday, July 21, 2008)]
[Rules and Regulations]
[Pages 42444-42504]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: E8-16084]



[[Page 42443]]

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Part III





Department of Transportation





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Federal Aviation Administration



14 CFR Parts 25, 26, 121 et al.



Reduction of Fuel Tank Flammability in Transport Category Airplanes; 
Final Rule

  Federal Register / Vol. 73, No. 140 / Monday, July 21, 2008 / Rules 
and Regulations  

[[Page 42444]]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Parts 25, 26, 121, 125, and 129

[Docket No. FAA-2005-22997; Amendment Nos. 25-125, 26-2, 121-340, 125-
55, and 129-46]
RIN 2120-AI23


Reduction of Fuel Tank Flammability in Transport Category 
Airplanes

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Final rule, request for comments.

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SUMMARY: This final rule amends FAA regulations that require operators 
and manufacturers of transport category airplanes to take steps that, 
in combination with other required actions, should greatly reduce the 
chances of a catastrophic fuel tank explosion. The final rule does not 
direct the adoption of specific inerting technology either by 
manufacturers or operators, but establishes a performance-based set of 
requirements that set acceptable flammability exposure values in tanks 
most prone to explosion or require the installation of an ignition 
mitigation means in an affected fuel tank. Technology now provides a 
variety of commercially feasible methods to accomplish these vital 
safety objectives.

DATES: These amendments become September 19, 2008. Send your comments 
by January 20, 2009. The incorporation by reference of the document 
listed in the rule is approved by the Director of the Federal Register 
as of September 19, 2008.

FOR FURTHER INFORMATION CONTACT: If you have technical questions about 
this action, contact Michael E. Dostert, FAA, Propulsion/Mechanical 
Systems Branch, ANM-112, Transport Airplane Directorate, Aircraft 
Certification Service, 1601 Lind Avenue, SW., Renton, Washington 98057-
3356; telephone (425) 227-2132, facsimile (425) 227-1320; e-mail: 
[email protected]. Direct any legal questions to Doug Anderson, ANM-
7, FAA, Office of Regional Counsel, 1601 Lind Avenue, SW, Renton, WA 
98057-3356; telephone (425) 227-2166; facsimile (425) 227-1007, e-mail 
[email protected].

SUPPLEMENTARY INFORMATION: Later in this preamble under the ADDITIONAL 
INFORMATION section, we discuss how you can comment on a certain 
portion of this final rule and how we will handle your comments. 
Included in this discussion is related information about the docket, 
privacy, and the handling of proprietary or confidential business 
information. We also discuss how you can get a copy of this final rule 
and related rulemaking documents.

Authority for Rulemaking

    The FAA's authority to issue rules regarding aviation safety is 
found in Title 49 of the United States Code. Subtitle I, Section 106 
describes the authority of the FAA Administrator. Subtitle VII, 
Aviation Programs, describes in more detail the scope of the agency's 
authority.
    This rulemaking is promulgated under the authority described in 
Subtitle VII, Part A, Subpart III, Section 44701, ``General 
requirements.'' Under that section, the FAA is charged with promoting 
safe flight of civil aircraft in air commerce by prescribing minimum 
standards required in the interest of safety for the design and 
performance of aircraft; regulations and minimum standards in the 
interest of aviation safety for inspecting, servicing, and overhauling 
aircraft; and regulations for other practices, methods, and procedures 
the Administrator finds necessary for safety in air commerce. This 
regulation is within the scope of that authority because it prescribes
     New safety standards for the design of transport category 
airplanes, and
     New requirements necessary for safety for the design, 
production, operation and maintenance of those airplanes, and for other 
practices, methods, and procedures related to those airplanes.

Table of Contents

I. Executive Summary
    A. Statement of the Problem
    B. Reducing the Chance of Ignition
    C. Reducing the Likelihood of an Explosion After Ignition
II. Background
    A. Summary of the NPRM
    B. Related Activities
    C. Differences Between the NPRM and the Final Rule
III. Discussion of the Final Rule
    A. Summary of Comments
    B. Necessity of Rule
    1. Estimates/Conclusions Supporting Need for Rule
    2. Additional Research Needed
    3. Consistent Safety Level With Other Systems
    4. Human Errors
    5. Explosion Risk Analysis
    6. Special Certification Review Process vs. Rulemaking
    7. Flammability Reduction Means (FRM) Effectiveness
    C. Applicability
    1. Airplanes With Fewer Than 30 Seats
    2. Part 91 and 125 Operators
    3. All-Cargo Airplanes
    4. Specific Airplane Models
    5. Wing Tanks
    6. Auxiliary Fuel Tanks
    7. Existing Horizontal Stabilizer Fuel Tanks
    8. Foreign Persons/Air Carriers Operating U.S. Registered 
Airplanes
    9. Airplanes Operated Under Sec.  121.153
    10. International Aspects of Production Requirements
    D. Requirements for Manufacturers and Holders of Type 
Certificates, Supplemental Type Certificates and Field Approvals
    1. General Comments About Design Approval Holder (DAH) 
Requirements
    2. Flammability Exposure Level Requirements for New Airplane 
Designs
    3. Flammability Exposure Requirements for Current Airplane 
Designs
    4. Continued Airworthiness and Safety Improvements
    E. Flammability Exposure Requirements for Airplane Operators
    1. General Comments About Applicability to Existing Airplanes
    2. Authority to Operate With an Inoperative FRM, IMM or FIMM
    3. Availability of Spare Parts
    4. Requirement That Center Fuel Tank be Inert Before First 
Flight of the Day
    F. Appendix M--FRM Specifications
    1. Fleet Average Flammability Exposure Levels
    2. Inclusion of Ground and Takeoff/Climb Phases of Flight
    3. Clarification of Sea Level Ground Ambient Temperature
    4. Deletion of Proposed Paragraph M25.2 (Showing Compliance)
    5. Deletion of ``Fuel Type'' From List of Requirements in 
Proposed Paragraph M25.2(b)
    6. Latent Failures
    7. Identification of Airworthiness Limitations
    8. Catastrophic Failure Modes
    9. Reliability Reporting
    G. Appendix N--Fuel Tank Flammability Exposure and Reliability 
Analysis
    1. General
    2. Definitions
    3. Input Parameters
    4. Verification of ``Flash Point Temperature''
    H. Critical Design Configuration Control Limitations (CDCCL)
    1. Remove Requirement
    2. Clarification on Responsibility for Later Modifications
    3. Limit CDCCL's to Fuel Tanks That Require FRM or IMM
    4. STC Holders May Not Have Data to Comply
    I. Methods of Mitigating the Likelihood of a Fuel Tank Explosion
    1. Alternatives to Inerting
    2. Inerting Systems Could Create Ignition Sources
    3. Instruments to Monitor Inerting Systems
    4. Risk of Nitrogen Asphyxiation
    5. Warning Placards
    6. Definition of ``Inert''
    7. Use of Carbon Dioxide
    8. Environmental Impact of FRM
    9. Current FRMs Fail to Meet Requirements

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    10. FRM Based on Immature Technology
    J. Compliance Dates
    1. Part 26 Design Approval Holder Compliance Dates
    2. Operator Fleet Retrofit Compliance Dates
    K. Cost/Benefit Analysis
    1. Security Benefits
    2. Likelihood of Future Explosions in Flight
    3. Costs to Society of Future Accidents
    4. Value of a Prevented Fatality
    5. Cost Savings if Transient Suppression Units (TSUs) are not 
Required
    6. Corrections About Boeing Statements
    7. 757 Size Category
    8. Number of Future Older In-Service Airplanes Overestimated
    9. Revisions to the FRM Kit Costs
    10. Revisions to the Labor Time to Retrofit FRM Components
    11. Retrofitting Costs per Airplane
    12. Percentage of Retrofits Completed During a Heavy Check
    13. Number of Additional Days of Out-of-Service Time to Complete 
a Retrofit
    14. Economic Losses From an Out-of-Service Day
    15. Updated FRM Weight Data
    16. Updated Fuel Consumption Data
    17. Updated Fuel Cost Data
    18. Cost of Inspections
    19. Inspection and Maintenance Labor Hours
    20. Daily Check
    21. Spare Parts Costs
    22. Air Separation Model (ASM) Replacement
    L. Miscellaneous
    1. Harmonization
    2. Part 25 Safety Targets
IV. Regulatory Notices and Analyses
V. The Amendment

I. Executive Summary

A. Statement of the Problem

    Fuel tank explosions have been a constant threat with serious 
aviation safety implications for many years. Since 1960, 18 airplanes 
have been damaged or destroyed as the result of a fuel tank explosion. 
Two of the more recent explosions--one involving a Boeing 747 (Trans 
World Airways (TWA) Flight 800) off Long Island, New York in 1996 and 
the other, a Boeing 727 terrorist-initiated explosion (Avianca Flight 
203) in Bogot[aacute], Columbia in 1989 \1\--occurred during flight and 
led to catastrophic losses (including the deaths of 337 individuals). 
Two other recent explosions on airplanes operated by Philippine 
Airlines and Thai Airlines occurred on the ground (resulting in nine 
fatalities).\2\ While the accident investigations of the TWA, 
Philippine Airlines and Thai Airlines accidents failed to identify the 
ignition source that caused the explosion, the investigations found 
several similarities. In each instance:
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    \1\ Although it was determined that a terrorist's bomb had 
caused the explosion of the center tank in the Bogot[aacute] 
accident, the NTSB determined the ``bomb explosion did not 
compromise the structural integrity of the airplane; however, the 
explosion punctured the [center wing tank] and ignited the fuel-air 
vapors in the ullage, resulting in destruction of the airplane.''
    \2\ Philippine Airlines Boeing 737 accidnet in Manila in 1990, 
and a Thai Airlines Boeing 737 accident in Bangkok in 2001.
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    1. The weather was warm, with an outside air temperature over 80 
[deg]F;
    2. The explosion occurred on the ground or soon after takeoff; and
    3. The explosion involved empty or nearly empty tanks that 
contained residual fuel from the previous fueling.
    Additionally, investigators were able to conclude that the center 
wing fuel tank in all three airplanes contained flammable vapors in the 
ullage (that portion of the fuel tank not occupied by liquid fuel) when 
the fuel tanks exploded. This was also the case with the Avianca 
airplane.
    A system designed to reduce the likelihood of a fuel tank fire, or 
mitigate the effects of a fire should one occur, would have prevented 
these four fuel tank explosions.
    A statistical evaluation of these accidents has led the FAA to 
project that, unless remedial measures are taken, four more United 
States (U.S.) registered transport category airplanes will likely be 
destroyed by a fuel tank explosion in the next 35 years. Although we 
cannot forecast precisely when these accidents will occur, computer 
modeling that has been an accurate predictor in the past indicates 
these events are virtually certain to occur. We believe at least three 
of these explosions are preventable by the adoption of a comprehensive 
safety regime to reduce both the incidence of ignition sources 
developing and the likelihood of the fuel tank containing flammable 
fuel vapors.

B. Reducing the Chance of Ignition

    To address the first part of this comprehensive safety regime, we 
have taken several steps to reduce the chances of ignition. Since 1996, 
we have imposed numerous airworthiness requirements (including 
airworthiness directives or ``ADs'') directed at the elimination of 
fuel tank ignition sources. Special Federal Aviation Regulation No. 88 
of 14 Code of Federal Regulations (CFR) part 21 (SFAR 88; 66 FR 23086, 
May 7, 2001) requires the detection and correction of potential system 
failures that can cause ignition. Although these measures should 
prevent some of the four forecast explosions, our review of the current 
transport category airplane designs of all major manufacturers has 
shown that unanticipated failures and maintenance errors will continue 
to generate unexpected ignition sources. Since manufacturers completed 
their SFAR 88 ignition prevention reviews, we have had reports of 
potential ignition sources (including unsafe conditions) that were not 
identified in the SFAR 88 reviews. For example:
     We issued AD 2006-06-14 to require the inspection of fuel 
quantity indicating probes within the fuel tanks of Airbus A320 
airplanes to prevent an ignition source due to sparks that could be 
created following a lightning strike. This failure mode was not 
identified as a possible ignition source in the SFAR 88 analysis 
presented to the FAA.
     We issued AD 2006-12-02 following a report of an 
improperly installed screw inside the fuel pump housings of A320 
airplanes that could loosen and fall into the pump's electrical 
windings. This could create a spark and ignite fuel vapors in the pump. 
The ignited vapors could then exit the fuel pump housing, enter the 
fuel tank through the hole created when the screw fell out of the 
housing, and cause a fuel tank explosion. This failure mode was not 
identified as a possible ignition source in the SFAR 88 analysis 
presented to the FAA.
     We received an in-service report on a Boeing 777 that was 
operated for over 30 days with an open vent hole between the center 
wing fuel tank and the wheel well of the airplane. During maintenance, 
a vent hole cover used to facilitate venting of the tank was 
inadvertently left off. This was not discovered until a flight occurred 
where the tank was fueled to a level where the fuel spilled from the 
tank into the wheel well during pitching up of the airplane for 
takeoff. Since the airplane brakes routinely exceed temperatures that 
could ignite fuel vapors and the wheels are retracted into the wheel 
well, the open vent port could have allowed ignition of fuel vapors in 
the center tank and a fuel tank explosion. This type of maintenance 
error was also not identified as providing a possible ignition source 
during the SFAR 88 safety reviews.
     On May 5, 2006, an explosion occurred in the wing fuel 
tank of a Boeing 727 in Bangalore, India, while the airplane was on the 
ground. This event occurred after a modification to include special 
Teflon sleeving and recurring inspections had been implemented to 
prevent possible arcing of the fuel pump wires to metallic conduits 
located in the fuel tank. Initial information indicates that the 
identified

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AD action was inadequate to prevent the formation of an ignition source 
in the fuel tank and that the change intended to improve safety caused 
premature wear of the sleeving and an unsafe condition. Premature wear 
of Teflon sleeving on the Boeing 737 has also been reported, resulting 
in AD action to modify the design and replace the existing sleeving. 
This failure mode was not identified as a possible ignition source in 
the SFAR 88 analysis presented to the FAA.
     We also received a report that during a recent 
certification program test, an ignition source developed in the fuel 
pumps causing pump failure. These pumps had been designed to meet the 
most stringent requirements of SFAR 88 and Amendment 25-102 to 14 CFR 
25.981 (issued concurrently with SFAR 88), yet the pump failed in a 
manner that allowed a capacitor to arc to the pump enclosure and create 
an ignition source. The applicant has since conducted a design review 
that has resulted in numerous modifications to the pump's design.
     Following the TWA 800 accident, the risk of uncontrolled 
fire adjacent to the fuel tanks causing a fuel tank explosion was 
identified as an unsafe condition. In 2006, we issued a MD-80 AD (AD 
2006-15-15) to prevent worn insulation on wires from arcing at the 
auxiliary hydraulic pump, which could result in a fire in the wheel 
well of the airplane. The AD required inspections to validate the pump 
wire integrity as well as incorporating sleeving on portions of the 
wires. In April 2008, we received reports of improper means of 
compliance being used regarding the requirements of AD 2006-15-15. 
Human error in completing the procedures required by the AD resulted in 
airplanes being operated without the needed safety improvements.
    Based on the above examples, we have concluded that we are unlikely 
to identify and eradicate all possible sources of ignition.

C. Reducing the Likelihood of an Explosion After Ignition

    To ensure safety, therefore, we must also focus on the environment 
that permits combustion to occur in the first place. Many transport 
category airplanes are designed with heated center wing tanks in which 
the fuel vapors are flammable for significant portions of their 
operating time. This final rule addresses the risk of a fuel tank 
explosion by reducing the likelihood that fuel tank vapors will explode 
when an ignition source is introduced into the tank.
    Technology now exists that can prevent ignition of flammable fuel 
vapors by reducing their oxygen concentration below the level that will 
support combustion. By making the vapors ``inert,'' we can 
significantly reduce the likelihood of an explosion when a fire source 
is introduced to the fuel tank. FAA-developed prototype onboard fuel 
tank inerting systems have been successfully flight tested on Airbus 
A320 and Boeing 747 and 737 airplanes. We have also approved inerting 
systems for the Boeing 747 and 737 airplanes, and two airplanes of each 
model type have performed as expected during airline in-service 
evaluations. Boeing plans to install these systems on all new 
production airplanes.
    Given that ignition sources will develop, the chances of a fuel 
tank explosion naturally correlate with the exposure of the tank to 
flammable vapors. The requirements in this final rule mitigate the 
effects of such flammability exposure and limit it to acceptable levels 
by mandating the installation of either a Flammability Reduction Means 
(FRM) or an Ignition Mitigation Means (IMM).\3\ In either case, the 
technology has to adhere to performance and reliability standards that 
are set by us and contained in Appendices M and N to Title 14 Code of 
Federal Regulations (CFR) part 25.
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    \3\ FRM consist of systems or features installed to reduce or 
control fuel tank flammability to acceptable levels. IMM is based 
upon mitigating the effects of a fuel vapor ignition in a fuel tank 
so that an explosion does not occur. Polyurethane foam installed in 
a fuel tank is one form of an IMM. See AC 25.981-2 for additional 
information.
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    This final rule amends the existing airworthiness standards 
contained in 14 CFR 25.981 to require all future type certificate (TC) 
applicants for transport category airplanes to reduce fuel tank 
flammability exposure to acceptable levels. It also amends 14 CFR part 
26 ``Continued Airworthiness and Safety Improvements'' \4\ to require 
TC holders to develop FRM or IMM for many large turbine-powered 
transport category airplanes with high-risk fuel tanks. Finally, it 
amends 14 CFR parts 121, 125 and 129 to require operators of these 
airplanes to incorporate the approved FRM or IMM into the fleet and to 
keep them operational. We estimate that approximately 2,700 existing 
Airbus and Boeing airplanes operating in the United States as well as 
about 2,300 newly manufactured airplanes that enter U.S. airline 
passenger service will be affected. Fuel tank system designs in several 
pending type-certification applications, including the Boeing 787 \5\ 
and Airbus A350, also have to meet these requirements.
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    \4\ Part 26 was added to the Code of Federal Regulations to 
include all requirements for Continued Operational Safety. See 
Docket number FAA-2004-18379 for more information on this subject.
    \5\ This airplane model already includes a FRM in its design 
that the applicant intends to show will meet today's final rule, so 
no additional modifications will be required.
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    We acknowledge that these requirements are costly and have adopted 
these steps only after spending several years researching the most 
cost-effective ways to prevent fuel tank explosions in cooperation with 
engineers and other experts from the affected industry. Those efforts 
have resulted in the development of fuel-inerting technology that is 
vastly cheaper than originally thought.
    In contrast, the loss of a single, fully loaded large passenger 
airplane in flight, such as a Boeing 747 or Airbus A380, would result 
in death and destruction causing societal loss of at least $1.2 billion 
(based on costs of prior calamities). We estimate that compliance with 
this new rule will prevent between one and two accidents of some type 
(for analytical purposes we assume the accidents would involve 
``average'' airplanes with ``average'' passenger loads) over 35 
years.\6\ In addition to the direct costs of such an accident, we now 
recognize that, in the post-9/11 aviation environment, the public could 
initially assume that an in-flight fuel tank explosion is the result of 
terrorist actions. This could cause a substantial immediate disruption 
of flights, similar to what occurred in Britain on August 10, 2006, due 
to the discovery of a terrorist plot.\7\ This could have an immediate 
and substantial adverse economic effect on the aviation industry as a 
whole.
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    \6\ Although Boeing has committed to installing compliant FRM in 
all future production airplanes, regardless of this rule, operators 
could deactivate the systems unless this rulemaking is adopted. The 
final regulatory evaluation includes the costs and benefits of these 
actions for newly produced Boeing and Airbus airplanes.
    \7\ Flight schedules in Britain were significantly disrupted due 
to flight cancellation of all flights into Heathrow Airport and 30 
percent of all short-haul flights out of Heathrow Airport for one 
day (according to Secretary of State for Transport Douglas 
Alexander). The day after the event, the crowds and lines that log-
jammed British airports the day before were largely gone, he said. 
British Airways stated that it cancelled 1,280 flights between 
August 10-17 due to the discovery of the terror plot and subsequent 
security measures. EasyJet said it was forced to cancel 469 flights 
because of the disruption caused by the terror alert. Ryanair said 
it cancelled a total of 265 flights.
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    The FAA's safety philosophy is to address aviation safety threats 
whenever practicable solutions are found, especially when dealing with 
intractable and catastrophic risks like fuel tank explosions that are 
virtually certain to

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occur. Thus, now that solutions are reasonably cost effective, we have 
determined that it is necessary for safety and in the public's best 
interest to adopt these requirements.

II. Background

A. Summary of the NPRM

    On November 23, 2005, the FAA published in the Federal Register the 
Notice of Proposed Rulemaking (NPRM) entitled ``Reduction of Fuel Tank 
Flammability in Transport Category Airplanes'' (70 FR 70922). This NPRM 
is the basis for this final rule.
    In the NPRM, we proposed steps to be taken by manufacturers and 
operators of transport category airplanes to significantly reduce the 
chances of a catastrophic fuel tank explosion. The proposal followed 
seven years of intensive research by the FAA and industry into 
technologies designed to make fuel tanks effectively inert. Inerting 
reduces the amount of oxygen in the fuel tank vapor space so that 
combustion cannot take place if there is an ignition source. Although 
the NPRM did not specifically direct the adoption of inerting 
technology, it did propose a performance-based set of requirements for 
reducing fuel tank flammability to an acceptably safe level.
    We proposed regulatory changes to require manufacturers and 
operators to reduce the average fuel tank flammability exposure in 
affected fleets. The main premise of the proposal was that a balanced 
approach to fuel tank safety was needed that provides both prevention 
of ignition sources and reduction of flammability of the fuel tanks. 
While the focus of the NPRM was on airplanes used in passenger 
operations, we requested comments on whether the new requirements 
should also be applied to all-cargo airplanes.
    We also proposed changes to expand the coverage of part 25 by 
making manufacturers generally responsible for the development of 
service information and safety improvements (including design changes) 
where needed to ensure the continued airworthiness of previously 
certificated airplanes. This change was proposed to ensure that 
operators would be able to obtain service instructions for making 
necessary safety improvements in a timely manner.
    As to fuel tank flammability specifically, we proposed to require 
manufacturers, including holders of certain airplane TCs and of 
auxiliary fuel tank supplemental type certificates (STCs), to conduct a 
flammability exposure analysis of their fuel tanks. We proposed a new 
Appendix L (now Appendix N) to part 25 that provides a method for 
calculating overall and warm day fuel tank flammability exposure. Where 
the required analyses indicated that the fuel tank has an average 
flammability exposure below 7 percent, we anticipate no changes would 
be required. However, for the other fuel tanks, manufacturers would be 
required to develop design modifications to support a retrofit of the 
airplane fuel tanks. Under the NPRM, the average flammability exposure 
of any affected wing tank would have to be reduced to no more than 7 
percent. In addition, for any normally emptied fuel tank (including 
auxiliary fuel tanks) located in whole or in part in the fuselage, 
flammability exposure was to be reduced to 3 percent, both for the 
overall fleet average and for operations on warm days.
    We also proposed to set more stringent safety levels for certain 
critically located fuel tanks in most new type designs, while 
maintaining the current, general standard under Sec.  25.981 for all 
other fuel tanks. The expectation was that the design of most normally 
emptied and auxiliary tanks located in whole or in part in the fuselage 
of transport category airplanes would need to incorporate some form of 
FRM or IMM.
    In Appendix M to part 25, we proposed to adopt detailed 
specifications for all FRM, if they were used to meet the flammability 
exposure limitations. These additional requirements were designed to 
ensure the effectiveness and reliability of FRM, mandate reporting of 
performance metrics, and provide warnings of possible hazards in and 
around fuel tanks.
    We also proposed that TC holders for specific airplane models with 
high flammability exposure fuel tanks be required to develop design 
changes and service instructions to facilitate operators' installation 
of IMM or FRM. Manufacturers of these airplanes would also have to 
incorporate these design changes in airplanes produced in the future. 
In addition, design approval holders (TC and STC holders) and 
applicants would have to develop airworthiness limitations to ensure 
that maintenance actions and future modifications do not increase 
flammability exposure above the limits specified in the proposal. These 
design approval holders would have to submit binding compliance plans 
by a specified date, and these plans would be closely monitored by the 
design approval holders' FAA Oversight Offices to ensure timely 
compliance.
    Lastly, the proposal would require affected operators to 
incorporate FRM or IMM for high-risk fuel tanks in their existing fleet 
of affected airplane models. The proposal would have applied to 
operators of airplanes under parts 91, 125, 121, and 129. Operators 
would also have to revise their maintenance and inspection programs to 
incorporate the airworthiness limitations developed under the NPRM. We 
also proposed strict retrofit deadlines, which were premised on prompt 
compliance by manufacturers with their compliance plans.
    The NPRM contains the background and rationale for this rulemaking 
and, except where we have made revisions in this final rule, should be 
referred to for that information.

B. Related Activities

    On November 28, 2005, the FAA published a Notice of Availability of 
Proposed Advisory Circular (AC) 25.981-2A, Fuel Tank Flammability, and 
request for comments in the Federal Register (70 FR 71365). The notice 
announced the availability of a proposed AC that would set forth an 
acceptable means, but not the only means, of demonstrating compliance 
with the provisions of the airworthiness standards set forth in the 
NPRM. On March 21, 2006, the FAA published a notice that extended the 
comment period as a result of an extension of the NPRM's comment period 
to May 8, 2006 (71 FR 14281).

C. Differences Between the NPRM and the Final Rule

    As a result of the comments received and our own continued review 
of the proposals in the NPRM, we have made several changes to the 
proposed regulatory text. The majority of these changes will be 
discussed in the ``Discussion of the Final Rule'' section below. The 
following is a summary of the main differences between the NPRM and 
this final rule.
    1. Design Approval Holders. The design approval holder (DAH) 
requirements proposed in the NPRM as subpart I of part 25 are now 
contained in new part 26. This was done to harmonize with the 
regulatory structure of other international airworthiness authorities. 
We also revised the applicability for the retrofit requirement so the 
DAH requirements do not apply to airplanes manufactured before 1992. 
The effect of this change is that DAHs will not have to develop FRM or 
IMM for many older airplane models that do not have significant 
remaining useful life in passenger operations. We revised the 
compliance times for DAHs to

[[Page 42448]]

develop and make available service instructions for FRM or IMM by 
replacing specific compliance dates with a compliance time of 24 months 
after the effective date of this rule for all affected airplane models. 
We have also made some changes, discussed later, to the compliance 
planning sections of the DAH requirements.
    2. Auxiliary Fuel Tanks. We have learned that few auxiliary fuel 
tanks installed under STCs and field approvals remain in service, and 
we need to obtain additional information to decide whether the risks 
from these tanks justify retrofit requirements. Therefore, we have 
removed the requirements for an FRM or IMM retrofit for these tanks.
    3. Impact Assessments. We limited the requirement for impact 
assessments for auxiliary fuel tanks to airplanes with high 
flammability tanks for which an FRM is required (i.e., Heated Center 
Wing Tank airplanes).
    4. All-Cargo Airplanes. We retained the proposal to exclude all-
cargo airplanes from the requirement to retrofit high flammability 
tanks with FRM or IMM. However, we added a requirement that when any 
airplane that has an FRM or IMM is converted from passenger use to all-
cargo use, these safety features must remain operational. We also added 
a requirement that newly manufactured all-cargo airplanes must meet the 
same requirements as newly manufactured passenger airplanes. We revised 
Sec.  25.981 to remove the exclusion of all-cargo airplanes so that any 
newly certificated transport category airplane, regardless of the type 
of operation, must meet the same safety standards.
    5. Part 91 Operators. The proposed rule would have applied to 
operators under part 91, which is limited to private use operations. 
However, the final rule does not include part 91 requirements.
    6. Retrofit Requirements for Operators. We have added a provision 
for air carrier operators that allows a one year extension in the 
compliance time to retrofit of their affected fleets if they revise 
their operations specifications and manuals to use ground conditioned 
air \8\ when it is available. Instead of requiring retrofit for all 
airplanes with high flammability fuel tanks, we revised the operating 
rules to prohibit operation of these airplanes in passenger service 
after 2016 unless an FRM or IMM is installed. This approach gives 
operators the option of converting these airplanes to all-cargo 
service. We also prohibit the operation of airplanes with high 
flammability fuel tanks produced after 2009 unless they are equipped 
with FRM or IMM. This requirement parallels the proposed production 
cut-in requirement, but also applies to foreign manufactured airplanes. 
Finally, instead of requiring retrofit of high flammability auxiliary 
fuel tanks, we prohibit installation of auxiliary fuel tanks after 2016 
unless they comply with the new requirements of Sec.  25.981.
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    \8\ ``Ground conditioned air'' is temperature controlled air 
used to ventilate the airplane cabin while the airplane is parked 
between flights.
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III. Discussion of the Final Rule

A. Summary of Comments

    The FAA received over 100 comment letters to the proposed rule and 
guidance material. These letters covered a wide spectrum of topics and 
range of responses to the rulemaking package, which will be discussed 
more fully below. While there was much support for the general intent 
of the rule changes and the guidance material, there were several 
requests for changes and for clarification.

B. Necessity of Rule

1. Estimates/Conclusions Supporting Need for Rule
    In the NPRM and its supporting documents, we noted several 
estimates and conclusions that we used to determine the necessity and 
content of this rule. We received comments on the following 
assumptions:
     The historical accident rate for heated center wing tank 
(HCWT) airplanes is 1 accident per 60 million hours of flight (before 
implementing corrective actions following TWA 800).
     That SFAR 88 and other corrective actions would prevent 50 
percent of future fuel tank explosions.
     That Boeing and Airbus airplanes have an equal risk of an 
explosion.
     That a HCWT, depending upon the airplane model and its 
mode of operation, is explosive 12 to 24 percent of the time.
     That the rate of accidents directly correlates to 
flammability exposure.
    Based on the comments received, we have changed the historical 
accident rate estimate to 1 accident per 100 million hours. This change 
does not affect our conclusion that the historical accident rate for 
HCWT airplanes supports the need for this rule. As for the other 
estimates and conclusions, we have not changed these in the final rule.
a. Historical (pre-TWA 800) Accident Rate
    Airbus, the Air Transport Association (ATA), Alaska Airlines 
(Alaska), the Association of Asia Pacific Airlines (AAPA), the 
Association of European Airlines (AEA), Boeing, Cathay Pacific Airways 
(Cathay), Delta Air Lines (Delta) and FedEx stated that the historical 
accident rate of 1 accident every 60 million fleet operating hours was 
too high. Most of these commenters recommended a rate of 1 accident per 
140 million hours. Their proposed rate is based on the number of 
accidents and the total fleet hours for heated center wing tank (HCWT) 
airplanes through 2005 (3 accidents over 430 million hours). Several of 
these commenters also noted that this rate is closer to the 
conservative estimate in the MITRE Corporation's assessment of the 
FAA's accident prediction/avoidance model (1 accident every 160 million 
hours).\9\
---------------------------------------------------------------------------

    \9\ The Mitre assessment of the FAA accident prediction 
methodology is included as Appendix H of the Initial Regulatory 
Evaluation and is available in the docket for this rulemaking 
(Document Number FAA-2005-22997-3).
---------------------------------------------------------------------------

    Boeing proposed a rate of 1 accident every 100 million hours. 
Boeing's analysis also started with the number of accidents and the 
total fleet hours for HCWT airplanes through 2005. However, Boeing 
recognized that some of the improvement since 2001 may be attributable 
to the FAA/industry focus on ignition prevention and concluded that the 
rate of 1 accident every 100 million hours more accurately represents 
the pre-TWA 800 rate.
    FedEx stated that, from a historical basis, 140 million hours would 
be a correct mean time between accidents. However, FedEx noted that a 
more conservative estimate closer to 100 million hours would still be 
acceptable.
    In a related comment, ATA questioned our use of flight hours as the 
measure of exposure to risk. ATA noted that two of the historical 
accidents did not occur in flight. Therefore, flight hours may 
understate exposure and overstate risk. ATA concluded that these 
accidents support the use of block hours or some other measure that 
accounts for time on the ground (and would lower the accident rate by 
about 16 percent).
    We agree that the accident rate used in the NPRM was too high and 
needs adjustment. While the rate of 1 accident every 140 million hours 
is correct if you only use the total fleet hours for HCWT airplanes 
through 2005, it fails to consider the beneficial effects of FAA/
industry action following the TWA 800 accident. Since that accident, we 
have issued many ADs to address specific findings of unsafe conditions 
that could produce fuel tank ignition sources. In addition, the Fuel 
Tank Safety Rule, of which SFAR 88 was a part, was issued in 2001 to 
establish a systematic process for identifying and eliminating ignition

[[Page 42449]]

sources. Many of the improvements resulting from these actions have 
been implemented in the transport airplane fleet, and the improved 
safety record since TWA 800 is largely attributable to them. While the 
commenters acknowledge that these actions have been effective at 
preventing future accidents, most of them failed to reduce their 
proposed historical rate accordingly to address these benefits. In 
contrast, Boeing's recommended rate considers the benefits of these 
actions (which we calculate covers about 170 million hours).
    We believe that an accident rate of 1 per 100 million hours is an 
accurate calculation of the historical accident rate before 
implementation of post-TWA 800 ignition prevention actions. Therefore, 
we used this rate in developing this final rule and its supporting 
documents. However, this change does not affect our conclusion that the 
historical accident rate for HCWT airplanes supports the need for this 
rule. We continue to believe that the risk of an accident is too high.
    Several commenters referred to the rate in the MITRE Corporation's 
report (1 accident every 160 million hours). This rate includes 
operations of airplanes without HCWT. Recommendations resulting from 
MITRE's review included a suggestion that only fleet hours from 
airplanes with HCWT be used in the accident prediction model. We agreed 
with this recommendation and have adjusted the accident rate 
accordingly.
    Finally, we do not agree with ATA's conclusion that the use of 
flight hours to predict future accidents results in an overstated risk. 
Both the past accident rate and the future predicted number of 
accidents were based upon the number of flight hours of airplanes with 
high flammability fuel tanks, and in both cases the number of flight 
hours does not include ground time. The ratio of flight time to ground 
time is unlikely to change significantly in the future because the 
average flight length and the amount of time spent on the ground before 
and after each flight are unlikely to change significantly. Therefore, 
whether past and future accident rates are stated in terms of flight 
time only or flight time plus ground time, the projected future 
accident rates would predict the same number of accidents over any 
given time period.
b. SFAR 88 Effectiveness Rate
    In the NPRM and its supporting documents, we estimated that SFAR 88 
would prevent 50 percent of future fuel tank explosions (although we 
also conducted a sensitivity analysis using effectiveness rates of 25 
and 75 percent). ATA stated that the 50 percent effectiveness rate was 
without basis or explanation and recommended a rate of 90 percent. 
Airbus recommended an effectiveness rate in the range of 75 to 90 
percent. If these higher rates are used, ATA and Airbus noted the 
safety benefits of the proposed rule are insufficient to justify the 
costs, and they requested that we withdraw the NPRM.
    Predicting the effectiveness of ignition prevention actions is 
challenging, since many ignition sources are the result of human error, 
which cannot be precisely predicted or quantitatively evaluated. 
Despite extensive efforts by the FAA and industry to prevent ignition 
sources, we continue to learn of new ignition sources. Some of these 
ignition sources are attributable to failures on the part of 
engineering organizations to identify potential ignition sources and 
provide design changes to prevent them. Others are attributable to 
actions by production, maintenance, and other operational personnel, 
who inadvertently compromise wiring and equipment producing ignition 
sources. Regardless of the causes, we believe that ignition prevention 
actions, while necessary, are insufficient to eliminate ignition 
sources.
    Based on the recently discovered ignition sources discussed 
earlier, we continue to believe that an assumed effectiveness rate of 
50 percent is reasonable and appropriate. In its study on SFAR 88 
effectiveness, Sandia National Laboratories concluded that our estimate 
of 50 percent was reasonable, and the value of 75 percent effectiveness 
assumed in the initial Aviation Rulemaking Advisory Committee (ARAC) 
report was overly optimistic. While the report of the ARAC Fuel Tank 
Inerting Harmonization Working Group \10\ initially assumed an 
effectiveness of 75 percent, the report was later amended to use a 
range of effectiveness between 25 to 75 percent because of the 
uncertainty in predicting the effectiveness.
---------------------------------------------------------------------------

    \10\ Document Number FAA-22997-6 in the docket for this 
rulemaking.
---------------------------------------------------------------------------

    Finally, since ATA did not submit any data to substantiate that a 
higher effectiveness rate is more reasonable, we believe the post-SFAR 
88 service experience supports the use of a range of effectiveness 
between 25 to 75 percent and a median value of 50 percent.
c. Boeing and Airbus Airplanes Have an Equal Risk of an Explosion
    We concluded that all airplanes with HCWT had similar levels of 
fuel tank flammability and the associated increase in the likelihood of 
a fuel tank explosion. We based the SFAR 88 effectiveness estimates on 
the HCWT fleet as a whole. We did not differentiate among airplane 
models based upon design differences that could affect the likelihood 
of an ignition source forming.
    AEA, Airbus, Frontier Airlines (Frontier), the Air Safety Group UK, 
Singapore Airlines (Singapore), BAE Systems (BAE), TDG Aerospace (TDG) 
disagreed with this proposal and argued that the risk of an explosion 
is lower for Airbus airplanes. These commenters noted that fuel tank 
designs for those airplanes that experienced a fuel tank explosion are 
at least a decade older than Airbus' designs. Airbus argued that its 
airplanes use newer technology and design philosophies that have 
incorporated the lessons learned from prior designs. BAE and two 
individuals suggested that we address fuel tank flammability by issuing 
ADs to address specific design shortfalls in the two airplane types 
that have experienced fuel tank explosions (i.e., the Boeing 737 and 
747 series airplanes).
    While we did note differences between the designs and technologies 
used by Boeing and Airbus, we concluded that the risk of an explosion 
was equal for Boeing and Airbus airplanes based on similarities in 
their fuel tank designs and service history. We found that both 
manufacturers have similar problematic fuel tank design features. For 
example, air conditioning equipment is located below the center wing 
tank in both manufacturers' designs (and HCWT have flammability 
exposure well above that of a conventional unheated aluminum wing 
tank). Likewise both manufacturers locate fuel gauging systems with 
capacitance measuring probes inside the fuel tank, and associated 
wiring to the probes enters the fuel tank from outside. These wires are 
co-routed with high-energy wiring to other airplane systems that have 
sufficient energy to cause an ignition source inside the fuel tanks. 
Finally, high-energy electrical fuel pumps are located within the fuel 
tanks and are fuel-cooled and manufactured by the same component 
suppliers. Arcing of the pump could cause a spark inside the fuel tank 
or could create a hole at the pump connector, causing a fuel leak and 
an uncontrolled fire outside of the tank.
    As for the service history and design reviews of Airbus airplanes, 
we found numerous situations that indicate a risk of an explosion 
similar to those aboard Boeing airplanes, including:
     The electrical bonding straps used on Airbus airplanes 
have been reported

[[Page 42450]]

to degrade due to corrosion; the bonding jumpers used by Boeing are 
made of a different material that does not corrode.
     All fuel pumps on Boeing airplanes are being modified to 
incorporate ground fault power interrupters, whereas only pumps that 
can arc directly into the fuel tank ullage are being modified to 
incorporate ground fault power interrupters on Airbus airplanes.
     The safety assessments conducted by both manufacturers 
resulted in very similar numbers of ignition sources that required 
modifications to their airplanes.
     After the SFAR 88 assessments were completed, we learned 
that fuel quantity indicating probes within the fuel tanks of Airbus 
A320 airplanes could be an ignition source due to sparks that could be 
created following a lightning strike. This resulted in the issuance of 
AD 2006-06-14.
     After the SFAR 88 assessments were completed, we learned 
that the improper installation of a screw inside the fuel pumps of 
Airbus A320 airplanes could result in the screw loosening and falling 
into the pump electrical windings. This could create a spark and ignite 
vapors in the pump that could exit the fuel pump housing into the fuel 
tank through the hole created when the screw fell out of the housing. 
This resulted in the issuance of AD 2006-12-02.
    The recent discovery of the ignition sources in Airbus A320 
airplanes is evidence that unforeseen failures will occur in the future 
that can result in ignition sources on Airbus airplanes. The Airbus 
fleet has significantly fewer flight hours than Boeing airplanes and, 
as the Airbus airplanes age, we expect to see more unforeseen failures. 
Therefore, based on design similarities and service history, we see no 
reason to differentiate between Airbus and Boeing airplanes. This rule 
requires all affected manufacturers to determine the fuel tank 
flammability exposure of their airplanes by assessing them against 
performance-based requirements that specify a flammability exposure 
that we have determined provides an acceptable level of safety. 
Additional action is only required for those airplanes that do not meet 
the required level of fuel tank flammability safety.
d. ARAC Flammability Exposure Data
    Airbus and AEA both commented that the ARAC flammability exposure 
data cited in the NPRM are incorrect and need to be reduced based on 
updated data developed by both Boeing and Airbus. They said this 
reduction is important since the lower data reduce the level of safety 
improvement that can be achieved by this rule from the FAA's intended 
``order of magnitude'' (factor of 10) to a safety improvement in the 
range of only a factor of 7.7 to 2.7, depending on the model used. 
Airbus also objected to our conclusion that a HCWT, depending upon the 
airplane model and its mode of operation, is explosive 12 to 24 percent 
of the time. Airbus requested that this be corrected to reflect the 
latest industry estimates for Airbus products (i.e., 8 to 12 percent) 
and 16 to 18 percent for other manufacturers.
    We acknowledge that the flammability exposure data cited in the 
NPRM may not reflect current values. However, Boeing and Airbus 
submitted those data to us as part of the SFAR 88 reviews. While we 
agree with Airbus that more recent information has indicated lower 
flammability for HCWTs, we do not agree that the more recent values 
should be used since the manufacturers have not submitted a validated 
analysis using the revised flammability assessment techniques (as 
defined in Sec.  25.981) to support its figures. Changes to the method 
for calculating fuel tank flammability, such as airplane ground times 
used in the Monte Carlo analysis required by Appendix N may result in 
additional variations in flammability calculations. Since flammability 
reduction was first considered by the aviation industry, the 
flammability values quoted by airplane manufacturers have varied 
considerably. These variations were the result of the method used to 
calculate the flammability of the fuel tanks and more accurate fuel 
tank temperature data based upon flight tests. For example, the first 
ARAC determined values ranged from 10 to 50 percent for generic 
airplanes equipped with HCWT. After the conclusion of this activity, 
Airbus was quoted in Air Safety Week as stating the A310 HCWT having a 
flammability exposure of 4 percent. In 2001, as part of the SFAR 88 
compliance, Airbus submitted flammability values to the European 
Aviation Safety Agency (EASA) and to us that ranged between 12 and 23 
percent.
    We recognize that as methods for measuring fuel tank flammability 
are refined, it is likely that calculated flammability exposure will 
also change. These refinements also apply to the conventional unheated 
aluminum wing tanks that ARAC used as the baseline for determining an 
acceptable exposure. We now know that the exposure of these tanks is 
considerably lower than originally estimated by ARAC. However, none of 
this new information changes the findings of ARAC that HCWTs have 
significantly higher risk of fuel tank explosions, or that the 
reduction in flammability exposure would be on the order of a factor of 
10. Therefore, we do not believe that these refinements change the 
overall conclusion that certain fuel tanks that are affected by this 
rule have significantly higher flammability exposure than conventional 
unheated aluminum wing tanks. No change has been made to the final rule 
as a result of these comments.
e. Accidents Directly Correlate to Flammability Exposure
    Airbus did not agree with the assumption that the rate of accidents 
directly correlates to flammability exposure. Airbus contended that the 
risk of ignition source development must also be considered when 
evaluating the benefits of flammability reduction.
    We agree with Airbus that the overall risk of a fuel tank explosion 
includes both the potential for an ignition source and the likelihood 
that the fuel tank will be flammable when an ignition source occurs. 
There may be differences in the likelihood of an ignition source 
occurring between different airplane types, but these differences would 
be very difficult to quantify. We have no statistically significant, 
validated data that could be used to establish rates of development of 
ignition sources for different airplane types. As discussed in the 
Sandia report, there is a wide variation in the predicted rate of 
ignition sources developing in fuel tanks and there is no industry 
agreement on the rate that should be used for individual airplane 
designs. In addition, recent service history shows there have been a 
number of ignition sources that have developed following the TWA 800 
accident in both Airbus and Boeing airplane models.
    Given this lack of data and consensus on ignition source risks, we 
continue to believe that correlating accident rates with flammability 
exposure is the most appropriate analytical approach.
2. Additional Research Needed
    Airbus, AAPA, AEA, EASA, Iberia Maintenance and Engineering 
(Iberia), Singapore and Virgin Atlantic Airways (Virgin) stated that 
this rulemaking is premature because the risks of additional fuel tank 
explosions are not adequately defined. These commenters argued that 
additional research is necessary to better understand flammability, 
SFAR 88 effectiveness and the risks of additional explosions. In a 
related comment, the International Federation Victims of Aviation 
Accident (IFVAA) stated that additional research should be performed to 
identify

[[Page 42451]]

technology that would completely eliminate, not just reduce, fuel tank 
flammability.
    We think it would be a mistake to delay this rule to conduct 
additional research. Service history and the recent occurrences of 
ignition sources described earlier demonstrate that the risk of future 
explosions remains significant. In addition, we believe that additional 
research would not provide any useful information that would change our 
finding that flammability reduction, in combination with the SFAR 88 
measures, is needed to prevent such explosions. As for IFVAA's comment, 
we consider existing flammability reduction means highly effective and 
sufficient to reduce the risk of fuel tank explosions to an acceptable 
level. While further research might identify even better solutions, the 
resulting delay would deprive the public of the benefits of these 
currently available safety improvements.
3. Consistent Safety Level With Other Systems
    Airbus commented that SFAR 88 improvements, together with the 
current rate of occurrence, put fuel tank safety on the order of one 
accident for every billion flight hours (i.e. 10-9 accidents 
per flight hour) which is consistent with safety objectives of other 
critical airplane systems.\11\ Airbus argued that this rule requires 
fuel tanks to go to a higher level of safety than other critical 
systems and that this is inconsistent with the overall risk.
---------------------------------------------------------------------------

    \11\ This is the quantitative probability measure (one in one 
billion) of an event that is ``extremely improbable'' as that term 
is used in Sec.  25.1309 and other part 25 airworthiness standards. 
See AC 25.1309.
---------------------------------------------------------------------------

    Application of existing safety standards to prevent ignition 
sources that are similar to those applied to other systems has not 
resulted in an acceptable level of safety, and we have determined that 
limiting fuel tank flammability is also needed. Fuel tank explosions 
are unacceptably occurring at a rate greater than 10-9 per 
flight hour and the recent events described above show that 
unanticipated failures continue to result in ignition sources within 
airplane fuel tanks. To protect the flying public, we have developed a 
``fail safe'' policy for fuel tank safety that includes both ignition 
prevention and flammability reduction to reduce fuel tank explosion 
risk to an acceptable level.
4. Human Errors
    AEA stated that human errors are not new and should not be used to 
justify this rule. AEA pointed out that TC holders are obliged to 
consider human error during airplane design to mitigate errors. In 
addition, continuing airworthiness instructions (e.g., maintenance 
manuals) highlight safety considerations where necessary. AEA also 
contended that, in the 17 accidents cited by the FAA in the NPRM, there 
is no evidence that any were caused by the introduction of an ignition 
source through human error. Finally, AEA noted that human errors will 
always be a factor in aviation safety, particularly when introducing 
added complexity such as an inerting system.
    We agree with AEA that human errors are not a new phenomenon and 
that the introduction of new systems on airplanes can have unintended 
consequences resulting from human error. We also believe the safety 
benefits of FRM or IMM is warranted. Service history shows the current 
regulations do not provide an adequate mitigation of human errors for 
fuel tank systems. Ignition sources continue to occur even though 
designers have conducted analyses that concluded ignition sources would 
not occur. Earlier in this document, we discussed numerous ignition 
sources that have recently developed in airplanes that had previously 
been shown by safety assessments to have features that would prevent 
ignition sources from developing. These ignition sources were caused by 
errors in defining assumptions in safety assessments, as well as in the 
design, manufacture and maintenance of these airplanes. These events 
show that an additional layer of protection (in the form of FRM or IMM) 
is needed to prevent future fuel tank explosions.
5. Explosion Risk Analysis
    American Trans Air commented that the assumptions made in the 
explosion risk analysis were erroneous and not within the range of 
reasonable values. American Trans Air recommended that a completely new 
analysis of the fuel tank explosion risk be undertaken. This new 
analysis should utilize widely accepted assumptions, including taking 
into account:
     The history of particular type designs.
     The actual ignition risk potential (i.e., potential 
ignition sources not in the ullage are either exempted, or 
substantially discounted in the analysis).
     Actual ignition energies, applying these energies to the 
potential ignition sources.
     The definitions and assumptions of fuel-air vapor mixtures 
that have been further derived and applied on an individual type design 
basis.
    We agree with the commenter that the assumed fuel air vapor mixture 
should be based upon the individual fuel tank design, and we included 
variations in the pressure and temperature of the fuel when developing 
the fuel tank flammability model. This factor is already accounted for 
in the Monte Carlo method defined in Appendix N. As for the other 
assumptions offered by American Trans Air, they cannot be used in an 
analysis, because there is a wide variation in the possible values.
6. Special Certification Review Process vs. Rulemaking
    American Trans Air commented that if an analysis identifies type 
designs still found to have unacceptable risk after all SFAR 88 
alterations have been executed, an appropriate response to address the 
remaining at-risk type designs may be the use of the special 
certification review process. American Trans Air noted that there 
appears to be wide variability in the risk between type designs, and 
concluded that generalized rulemaking is inappropriate at this time.
    We do not agree that we should address each type design with 
unacceptable flammability risk by special certification review and then 
by an appropriate AD. Through careful study, we have determined that 
the flammability risk on many airplanes is too high. To address this 
risk, we have created an objective design standard by which all 
airplanes can be measured. If airplanes currently meet this design 
standard, no action will be required. The TC holder for those airplanes 
that do not meet it will have to make only those changes that bring 
that airplane model into compliance. We have determined that the 
uncertainty involved in the elimination of ignition sources requires 
reduced flammability to acceptably reduced tank explosion risk, and the 
most effective and efficient way to address this issue is through the 
rulemaking process.
7. Flammability Reduction Means (FRM) Effectiveness
    In the NPRM, we said lowering the flammability exposure of the 
affected fuel tanks in the existing fleet and limiting the permissible 
level of flammability on new production airplanes would result in an 
overall reduction in the flammability potential of these airplanes of 
approximately 95 percent. Airbus and AEA commented that we overstated 
the potential benefits of flammability reduction measures by a factor 
between 4 and 7. They said we used a factor of 20 (95 percent) for the

[[Page 42452]]

reduction in flammability exposure achieved by reducing the 
flammability of HCWT to 3 percent or less. They said the subsequent 
reduction in flammability will be in the order of a factor of three to 
five and not a factor of 20. Therefore, the number of accidents 
prevented would consequentially be less than projected by the FAA. 
Airbus also said the FAA appears not to have considered the 
effectiveness of the FRM itself, which it said is in the order of 67 to 
87 percent by latest industry estimates. Therefore, Airbus suggests 
that the Initial Regulatory Evaluation (IRE) is incomplete and should 
be revised to include this key parameter.
    The 95 percent value used in the NPRM was not based on the ratio of 
fuel tank fleet average flammability exposure before and after 
implementing the requirements of this rule. It was derived by 
qualitatively evaluating the effectiveness of an FRM in preventing fuel 
tank explosions that would not be prevented by ignition prevention 
measures.
    When an FRM is installed on a fuel tank, it must meet both the 3 
percent fleet average flammability exposure and also the 3 percent warm 
day (specific risk) flammability exposure requirements.\12\ For the 
warm day requirement, the flammability exposure must be below 3 percent 
during ground and takeoff/climb conditions for those days above 80 
degrees F when the FRM is operational. These are the conditions when 
fuel tanks tend to have the highest flammability exposure and when the 
accidents discussed earlier occurred.
---------------------------------------------------------------------------

    \12\ The overall time the fuel tank is flammable cannot exceed 3 
percent of the Flammability Exposure Evaluation Time (FEET), which 
is the total time, including both ground and flight time, considered 
in the flammability assessment defined in proposed Appendix N. As a 
portion of this 3 percent, if flammability reduction means (FRM) are 
used, each of the following time periods cannot exceed 1.8 percent 
of the FEET: (1) When any FRM is operational but the fuel tank is 
not inert and the tank is flammable; and (2) when any FRM is 
inoperative and the tank is flammable.
---------------------------------------------------------------------------

    The combination of the warm day requirement and the fleet average 
flammability requirement results in an FRM with overall flammability 
reduction benefits that are significantly higher than those estimated 
by the commenters. Since the NPRM was issued, we have reviewed and 
approved FRM designs and have found the performance exceeds the 
certification limits. When the FRM is operating, the fuel tanks are 
rarely flammable. So, the major risk of fuel tank flammability occurs 
when the system is inoperative and this time is limited to a maximum of 
1.8 percent of the Flammability Exposure Evaluation Time (FEET). 
Historically, designers provide a safety margin in the design so that 
the design limits are never exceeded, so we would expect the 
flammability to be below this level.
    Another consideration in using a 95 percent effectiveness measure 
is the safety improvement noted during warm days. Without any FRM, a 
HCWT is flammable about 50 percent of the time during climb. Meeting 
both the 3 percent warm day requirement and the 3 percent reliability 
requirement results in a flammability exposure of the tank of less than 
half of one percent during climb. For an airplane with an initial warm 
day flammability of 50 percent, this is a 99 percent reduction in the 
flammability during climb. We, therefore, used the 95 percent 
effectiveness for flammability reduction in the risk model for the 
final regulatory evaluation.

C. Applicability

1. Airplanes With Fewer Than 30 Seats
    The proposed DAH requirements would apply (with some exclusions) to 
transport category turbine-powered airplanes approved for a passenger 
capacity of 30 or more persons or a maximum payload capacity of 7,500 
pounds or more. The UK Air Safety Group disagreed with the proposed 
rule's limited applicability because the design of fuel tank systems is 
similar for both large and small airplanes. Therefore, it argued that 
the potential explosion hazard is equal. The commenter also noted that 
EASA's CS-25 regulation for Fuel Tank Ignition Prevention does not make 
any distinction based on the number of passenger seats.
    We did not include smaller part 25 airplanes in the DAH 
requirements of this final rule because those airplanes generally do 
not have high flammability tanks. While some parts of their fuel tank 
system designs are similar to those of larger airplanes, we do not 
agree that the overall architecture and the risk of a fuel tank 
explosion are equal. Data submitted by manufacturers of smaller part 25 
airplanes as part of the SFAR 88 analysis show that their airplanes 
typically do not have fuel tanks located within the fuselage contour, 
and would not be considered high flammability fuel tanks. In most 
cases, cool fuel from the wing tanks is drawn into the center wing box, 
so the overall flammability is low. In addition, these tanks are not 
normally emptied, reducing the amount of ullage.
    Based on these facts, the benefits of including these smaller 
airplanes in all of the requirements of this rule are minimal and do 
not warrant the cost. However, we do agree that the part 25 
requirements applicable to new type designs should be the same for all 
transport category airplanes, regardless of size. The cost to design 
and produce a new airplane to meet the flammability requirements is 
significantly less than that for existing airplanes since the designers 
can optimize the performance of the FRM or IMM and integrate it into 
the airplane design to minimize costs. Therefore, Sec.  25.981 of this 
rule applies to all transport category airplanes regardless of size.
2. Part 91 and 125 Operators
    The NPRM proposed that operators under parts 91, 121, 125, and 129 
incorporate FRM or IMM and keep it operational on their affected 
airplanes. The AEA and Airbus asked that parts 91 and 125 operations be 
excluded and cited corporate use airplanes as an example of operations 
where the cost would far exceed the benefit. According to AEA and 
Airbus, the cost/benefit analysis for these airplanes, when operated 
under part 91 or part 125, would produce results similar to those for 
all-cargo airplanes (which are excluded from the retrofit requirements 
of this rule).
    We recognize a distinction between part 91 and part 125 operations, 
in that part 91 does not allow commercial operations for compensation 
or hire, while part 125 does allow such operations, as long as the 
operator does not ``hold out'' to the public that they are available 
for such operations (in which case they would be required to operate as 
an air carrier). For example, many business jets are operated under 
part 91 if the operator does not receive compensation for transporting 
passengers (e.g., a corporate jet transporting the corporation's 
employees). On the other hand, charter companies frequently operate 
under part 125 to transport sports teams and other groups for 
compensation.
    While we recognize that private owners and operators may choose to 
assume the risk of possible fuel tank explosions, we see no reason why 
persons flying on commercial charter flights should be exposed to a 
greater risk of a fuel tank explosion than passengers flying on 
airplanes operated under parts 121 and 129. Commercial charter 
passengers are in no better position to recognize and accept the risk 
of a fuel tank explosion than are air carrier passengers. Additionally, 
the risk and likelihood of a fuel tank explosion are potentially 
commensurate with that of the same airplane model operated

[[Page 42453]]

under parts 121 and 129. Therefore, the final rule has been revised to 
exclude part 91 operations, but does not exclude part 125 operations. 
However, because of the significant safety benefits of this rule, we 
encourage part 91 operators to install FRM on their airplanes, and not 
to remove it if it is already installed.
3. All-Cargo Airplanes
    In response to our request for comments on the proposed exclusion 
of all-cargo airplanes from this rulemaking, we received numerous 
comments both supporting and opposing the exclusion. Airbus, the Cargo 
Airline Association (CAA), FedEx, ATA, ABX Air (ABX), United Parcel 
Service (UPS), and National Air Carrier Association (NACA) agreed that 
all-cargo airplanes should be excluded from this rulemaking. The CAA 
argued that the risks are lower for cargo carriers due to several 
factors:
    a. Cargo operations are predominately night operations with lower 
outside ambient temperatures (making fuel tanks less likely to be 
flammable).
    b. Cargo operators do not typically run air conditioning packs 
prior to takeoff as many passenger operators do.
    c. The CAA members typically operate one to two round trips each 
day, which is a lower utilization rate than most passenger airplanes.
    The CAA stated that costs to various airline industry segments 
should be considered when proposing any new regulation. The CAA 
supported establishing a safety baseline which allows different 
operations to meet the baseline in different ways. Based on the factors 
articulated above, the CAA maintained the cost/benefit analysis does 
not justify its application to cargo airplanes.
    FedEx commented that there is a finite amount of safety dollars and 
it is important to use them effectively. As the cost/benefit analysis 
does not justify inclusion of all-cargo airplanes, FedEx claimed it is 
not permissible to include them under FAA rulemaking authority. ATA 
stated that the proposed rule should not apply to all-cargo airplanes, 
other than the design rules proposed to prevent modifications that 
could increase the flammability exposure of a fuel tank. ABX agreed 
with ATA, and noted that the ignition prevention measures of SFAR 88 
provide an acceptable level of safety for these airplanes. Finally, 
Airbus and UPS based their support for our proposal to exclude cargo 
airplanes on the reasons stated in the NPRM.
    On the other hand, the National Transportation Safety Board (NTSB), 
the Independent Pilots Association (IPA), the Air Line Pilots 
Association (ALPA), the EASA, the Coalition of Airline Pilots 
Association (CAPA), Singapore and the National Air Traffic Controllers 
Association (NATCA) do not agree that all-cargo airplanes should be 
excluded from this rulemaking. While the NTSB, IPA and NATCA 
acknowledged that cargo airplanes typically carry fewer people, they 
pointed out that these airplanes regularly use airports in densely 
populated areas where an accident could have a catastrophic effect for 
people on the ground. The NTSB and IPA also cited a recent DC-8 cargo 
fire accident where an inerting system might have prevented or 
substantially reduced the magnitude of the fire, and a C-5A accident at 
Dover Air Force Base where the presence of an inerting system may have 
been the reason many lives were saved.
    The IPA also stated that there should be one level of safety for 
all part 25 airplanes, and noted that all-cargo airplanes are typically 
older (which makes them more susceptible to ignition sources within the 
tank). In addition, ADs are being issued on even the newer models to 
restrict operations for flammability/ignition concerns.
    ALPA commented that all-cargo airplanes should not be excluded from 
critical safety improvements simply because there are fewer fatalities 
in a typical crash. ALPA recommended that we apply a firm deadline for 
the manufacturers to complete a flammability analysis on all-cargo 
airplanes compared to the passenger versions of the same airplane 
model.
    EASA did not agree with introducing a new distinction among part 25 
products. In EASA's view, the justification for excluding all-cargo 
airplanes has yet to be substantiated. CAPA thought the logic of 
excluding all-cargo airplanes could be extended to each individual 
operator or to all airplanes with differing passenger capacities. For 
example, CAPA questioned whether, if operator ``A'' had many more 
Boeing 737 airplanes than operator ``B'', would we require Operator 
``A'' to use FRM while Operator ``B'' would not have to. CAPA stated 
that this same type of flawed logic is being applied to all-cargo 
airplanes. In its opinion, the value of pilot lives should not depend 
on what is in the back of the airplane. Finally, NATCA commented that 
confidence in flying would be diminished if there were a cargo airplane 
accident, and we should not set a precedent that sets a different 
safety standard based on the intended operation of the airplane.
    Boeing stated that its safety philosophy is to not differentiate 
between passenger and cargo airplanes in managing fleet-wide airplane 
risk and therefore, did not exclude airplanes designed solely for cargo 
operations in their proposed revision to Sec.  25.981(b).
    After reviewing these comments, we have decided that we will not 
require existing all-cargo airplanes to meet the retrofit requirements 
in this final rule. We did not receive any data on the costs, benefits 
or risks for all-cargo airplanes in response to our request in the 
NPRM, and we do not have any new data to justify requiring retrofit of 
FRM or IMM on the current fleet of all-cargo airplanes. We will 
continue to gather additional data regarding these factors and may 
initiate further rulemaking action if the flammability of these 
airplanes is found to be excessive.
    However, we will require compliance with the requirements of this 
final rule for (i) future designs; (ii) the conversion of any passenger 
airplane with an FRM or IMM to all-cargo use; and (iii) future 
production of all-cargo airplanes. We agree with NATCA and other 
commenters with respect to removing the exclusion from Sec.  25.981 of 
airplanes designed solely for all-cargo operations. The airworthiness 
standards of part 25 do not impose different requirements depending on 
the intended use of the airplane. 49 U.S.C. 44701 requires that we 
adopt such minimum airworthiness standards as are necessary, and 
historically we have recognized that those minimum standards should be 
the same for all transport category airplanes, regardless of their 
intended use. There are practical reasons for this approach, since the 
intended use can change quickly based on business considerations 
unrelated to safety. Therefore, we agree that the proposed new design 
standards in part 25 should not distinguish between all-cargo and 
passenger airplanes.
    The rationale for including a production cut-in for all-cargo 
airplanes is based upon the long-term goal of fleet-wide reduction in 
flammability exposure to eliminate the likelihood of fuel tank 
explosions. In addition to the immediate effects of an accident, we 
believe a fuel tank explosion on an all-cargo airplane could have a 
significant impact on the aviation industry due to public sensitivity 
to terrorist actions. The cost of installing FRM in new production 
airplanes is less than the cost of to retrofit airplanes, because the 
installation can be efficiently integrated into the production process. 
In most cases, this integration will be done for the passenger version 
of the same airplane, so additional engineering work will be minimal. 
The benefits of production cut-in are also higher than

[[Page 42454]]

for retrofit since the new airplane has a longer life and reduced 
flammability will provide safety benefits for the life of the airplane.
    As for conversion airplanes, when older airplanes can no longer be 
operated competitively in passenger service, it is common for them to 
be converted to all-cargo service. Since many passenger airplanes will 
have FRM or IMM already installed as a result of this rule, operators 
may be inclined to deactivate or remove the FRM or IMM to reduce 
operational costs, if these airplanes are converted to all-cargo 
airplanes in the future. We do not believe it would be in the public 
interest to allow previously installed systems to be deactivated 
because the capital cost to install the systems would already have been 
incurred, and the safety benefits of retaining the system would 
outweigh any cost savings that might result from deactivating them. 
Accordingly, we have revised the operational rules to prohibit 
deactivation or removal of FRM or IMM under this scenario.
    The regulatory evaluation for this final rule has been revised to 
address these factors and concludes that imposing these requirements on 
all-cargo airplanes is cost effective for new designs and newly 
produced all-cargo airplanes. Prohibiting deactivation of FRM or IMM on 
converted airplanes is also cost effective.
4. Specific Airplane Models
    Proposed Sec.  25.1815(j) listed specific airplane models that 
would be excluded from the requirements of proposed Sec.  25.1815 (now 
Sec.  26.33). These are airplane models that, because of their advanced 
age and small numbers, would likely make compliance economically 
impractical. In the NPRM, we asked for comments on other airplane 
models that may present unique compliance challenges and should be 
excluded from the requirements of this rule. In response to this 
request, we received several comments requesting that additional 
specific airplane models be excluded from this rule. Given the number 
of models identified, we have decided it makes more sense to 
``grandfather'' all models manufactured before a certain date. Based on 
these comments, we have changed the applicability of the design 
approval holder requirements in proposed Sec.  25.1815(a) (now Sec.  
26.33(a)) from those airplanes type certificated after January 1, 1958 
to those airplanes produced on or after January 1, 1992.
a. Out-of-Production/Low Service Life Remaining Models
    Boeing and Airbus recommended that the rule only apply to airplane 
models and auxiliary tanks currently in production, or recently out-of-
production, that have significant numbers in service and will continue 
in service well beyond the date when 100 percent compliance is 
achieved. Based on this standard, Boeing submitted a list of airplane 
models and auxiliary tanks to add to the excluded models in proposed 
Sec.  25.1815(j), including the DC-8, DC-9, DC-10, MD-80, MD-90, MD-11, 
Boeing 707, 720, 727, 737-100/-200, 747-100/-200/-300 and associated 
derivatives, and 737-300/-400/-500 (auxiliary tanks only). Airbus 
requested that the Airbus A300/A310 series airplanes be added to the 
list based on this standard.
    We acknowledge that there is no reason to require design approval 
holders (DAHs) to develop design changes for airplanes that will be 
retired before FRM or IMM installation is required by this rule. 
Conducting the flammability assessments and developing design 
modifications for those airplanes would require significant engineering 
resources. More importantly, these airplanes would not benefit from the 
development of FRM or IMM, since they would be retired or converted to 
cargo operations before the installation of these systems is required. 
Therefore, we have limited the applicability of the DAH requirements in 
the final rule (proposed Sec.  25.1815(a), now Sec.  26.33(a)) to 
airplanes produced on or after January 1, 1992.
    The youngest of the airplanes produced before then would be more 
than 25 years old by the time operators would be required to modify 
them. We agree with the commenters that the vast majority of these 
airplanes would either be retired or converted to cargo service before 
they reach that age. This is consistent with current practice. This 
limitation has the effect of excluding the Boeing 707, 727, 737-100/200 
and 747-100/200/300; the McDonnell Douglas DC-8, DC-9, DC-10, and KC-
10/KDC-10; and the Lockheed L-1011. Airplanes of the other models that 
Boeing, Airbus and ATA requested be excluded have been produced on or 
after January 1, 1992. For airplanes produced on or after January 1, 
1992, the remaining life and likelihood of their continued operation in 
passenger service is sufficient to require compliance with the 
requirements of this rule.
    To clearly differentiate between airplanes produced before and 
after this date, we changed proposed Sec.  25.1815(a) (now Sec.  
26.33(a)) to refer to the date when ``the State of Manufacture issued 
the original certificate of airworthiness or export airworthiness 
approval.'' This information is readily available to the TC holders who 
applied for these approvals. We also added a provision to proposed 
Sec.  25.1815(d) (now Sec.  26.33(d)) to require the service 
information describing FRM or IMM to identify the airplanes that must 
be modified under this rule. This will make it readily apparent to 
operators which of their airplanes are subject to the retrofit 
requirements.
    For airplanes with high flammability tanks produced before 1992, 
instead of requiring operators to retrofit these airplanes, we have 
added a provision in the operational rules prohibiting passenger 
operations of these airplanes after the date by which an operator's 
airplanes that are subject to the retrofit requirement must be 
retrofitted.\13\ This enables operators to convert these airplanes to 
cargo service rather than to retrofit them. If operators of these 
airplanes choose to operate them in passenger service past this date, 
they could contract with the DAH or a STC vendor to develop an FRM or 
IMM to meet the safety requirements of this rule. Without this 
provision, the exclusion of airplanes produced before 1992 could have 
the unintended consequence of encouraging operators to continue to 
operate these airplanes with high flammability tanks in passenger 
service, since the retrofit and operating costs of FRM or IMM would not 
have to be incurred.
---------------------------------------------------------------------------

    \13\ As discussed later, we are also adding a provision that 
allows operators under parts 121 and 129 to extend the compliance 
date by one year based on use of ground conditioned air. Operators 
using this extension will be able to operate these pre-1992 
airplanes in passenger service until they are required to have all 
of their post-1991 airplanes retrofitted.
---------------------------------------------------------------------------

    These changes to the DAH and operational rules have the effect of 
making the applicability of these requirements different. The DAH 
requirements now only apply to airplanes produced on or after January 
1, 1992, but the operational rules still apply to all airplanes meeting 
the applicability criteria proposed in the NPRM.\14\ Therefore, we have 
revised the applicability provisions of the operational rule sections 
to incorporate these criteria, rather than referencing the 
applicability of the DAH rules.
---------------------------------------------------------------------------

    \14\ With certain listed exceptions, transport category turbine-
powered airplanes type certificated after January 1, 1958, with a 
maximum passenger capacity of 30 or more or a maximum payload 
capacity of 7,500 pounds or more.
---------------------------------------------------------------------------

    As for Boeing's request to exempt certain auxiliary fuel tanks, as 
discussed

[[Page 42455]]

later in more detail, we have retained the requirement to conduct 
flammability assessments and impact assessments for auxiliary fuel 
tanks. However, we have delayed any action to require retrofit of IMM 
or FRM for auxiliary fuel tanks installed under STCs and field 
approvals until additional information can be gathered. We agree with 
Boeing that any auxiliary fuel tank installed in pre-1992 airplane 
models should also be excluded from the need to conduct flammability 
assessments, since we have determined we would not take action against 
any tank in these airplane models due to their advanced age.
b. Limited U.S. Inventory Models
    Airbus requested that airplanes having a limited U.S. inventory be 
excluded from this rule, because the operators of these airplanes would 
shoulder a disproportionate impact of non-recurring engineering 
expenses needed to design and develop FRM systems. Under this standard, 
Airbus asked that the A330-200 (only 11 N-registered airplanes) and the 
A340 (no N-registered airplanes) be added to proposed Sec.  25.1818(j). 
We cannot agree with the Airbus suggested approach. We have no way to 
predict future market conditions in the United States for the A330-200 
and A340 model airplanes. Airbus continues to sell these models and 
lessors continue to offer them for lease. Based on market conditions, 
U.S. operators may add these models to their fleets in larger numbers 
and we see no reason why persons flying on these airplanes should be 
exposed to a greater risk of a fuel tank explosion. Therefore, we are 
not excluding these airplane models from the requirements of this final 
rule.
c. Airbus A321
    Airbus and ATA suggested the A321 should be excluded because this 
model does not have fuel pumps in the center wing tank, reducing the 
risk of a fuel tank explosion. The lack of fuel pumps does not 
adequately mitigate the risk of an explosion. There are numerous 
potential ignition sources inside fuel tanks that can result from 
failure of various components, including the fuel quantity indication 
system, motor driven valves, fuel level sensors, and electrical bonds. 
In addition, heating of the fuel tank walls by external heat sources 
introduces a concern that the hot surface could ignite the vapors in 
the tank. The justification provided for excluding this model (because 
the center tank does not have motor driven pumps located in the tank) 
does not address the overall fuel tank safety issue and would only have 
merit if fuel pump failures were the only potential ignition sources. 
Therefore, we are not excluding this airplane model from the 
requirements of this final rule.
d. Airplanes With Low Flammability Tanks
    The proposed retrofit limit for an acceptable fleet-wide average 
flammability exposure was 7 percent. We determined that fuel tanks 
having a flammability exposure greater than 7 percent are high 
flammability tanks that present a greater risk for fuel tank explosion. 
American Trans Air commented that, we stated in the NPRM that some 
airplanes have center tanks with a fleet average flammability exposure 
that does not exceed 7 percent, including ``the Lockheed L-1011, and 
Boeing MD-11, DC10, MD80, and Boeing 727, and Fokker F28 MK100.'' 
American Trans Air stated that this implies that we have information in 
our possession indicating that these airplane models already meet the 
proposed flammability limits, and asked that we add these models to the 
list of excluded airplanes in proposed Sec.  25.1815(j) (now Sec.  
26.33).\15\
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    \15\ As we discussed above, we have limited the applicability of 
the DAH requirements in Sec.  26.33 to airplane models produced on 
or after January 1, 1992. This date excludes the Boeing Model 727, 
DC-10 and the Lockheed L-1011. The other airplane models mentioned 
by the commenter have airplanes produced after 1991 and would be 
covered by this rule.
---------------------------------------------------------------------------

    The statement quoted by American Trans Air from the NPRM was based 
on previous flammability assessments provided to us for SFAR 88 
compliance. These assessments were based upon simplified assessment 
methods. For airplanes produced after January 1, 1992, we have retained 
the requirement to conduct flammability assessments on these airplanes 
to ensure that the earlier assessments are correct and that design 
changes for these tanks are not necessary. Once the assessment has been 
made, a manufacturer or operator may not need to make any change to the 
airplane. This is because the flammability risk assessment may disclose 
a level of risk below the threshold required for modification. As 
discussed earlier, we are allowing a qualitative assessment for 
conventional unheated aluminum wing tanks, which will substantially 
reduce the burden for completing the flammability assessments.
5. Wing Tanks
a. General
    Proposed Sec.  25.981 does not apply the same flammability standard 
to all fuel tanks, and requires lower flammability limits for ``fuel 
tanks that are normally emptied and located within the fuselage 
contour.'' The NTSB expressed concern that wing fuel tanks have 
exploded, and noted that its safety recommendations were not limited 
to:
    (1) Certain types of fuel tanks,
    (2) Tanks with specific types of exposure, or
    (3) Tanks with explosive risks that vary or lessen over time.
    The NTSB stated that we should take action to prevent all tanks 
from having flammable fuel-air mixtures in the ullage. The NATCA 
agreed, and stated that, to achieve an acceptable level of safety, the 
requirements of Sec.  25.981 that apply to new airplanes should 
establish the same flammability standard for all fuel tanks regardless 
of location. The NATCA supported this suggestion by referencing the 
ARAC accident summaries that showed 8 out of 17 fuel tank explosions 
have involved wing tanks. The ALPA also expressed concern that certain 
wing designs and system installations may result in internal heating of 
the wing structure and ultimately the wing fuel tanks. The ALPA stated 
that we must insist that those specific installations fall under the 
requirements of this rule and that no unsafe flammability exposure 
exist in those wing tanks.
    In contrast, Embraer, Bombardier Aerospace (Bombardier), and 
American Trans Air opposed incorporation of new flammability standards 
for conventional wing tanks. Embraer stated the benefits would be 
negligible and would not justify the costs. Embraer maintained that 
service history provides ample evidence that conventionally designed 
wing tanks inherently provide sufficient protection from fuel tank 
ignition when conventional fuels are used and that the current 
requirements are adequate. American Trans Air commented that many twin 
engine airplane type designs utilize a common fuel system operational 
concept that results in low exposure to high energy ignition sources in 
the main wing tanks. This exposure is further reduced in airplanes 
operated in extended-range twin-engine operations (ETOPS) service, due 
to the increased fuel reserves required in these operations.
    The service history of conventional unheated aluminum wing tanks 
that contain Jet A fuel indicates that there would be little safety 
benefit by further limiting the flammability of these tanks. While 
NATCA and the NTSB expressed concern because accidents have occurred in 
wing fuel tanks, they did not differentiate service experience based on 
fuel type used (JP-4 versus Jet

[[Page 42456]]

A). Our review of the nine \16\ wing tank ignition events shows that 5 
of the 9 airplanes were using JP-4 fuel and this type fuel is no longer 
used except on an emergency basis in the U.S. Three of the remaining 
four events were caused by external heating of the wing by engine 
fires, and the remaining event occurred on the ground during 
maintenance. To date, there have been no fuel tank explosions in 
conventional unheated aluminum wing tanks fueled with Jet A fuel that 
have resulted in any fatalities. The flammability characteristics of 
JP-4 fuel results in the fuel tanks being flammable a significant 
portion of the time when an airplane is in flight. This is not the case 
for wing tanks containing Jet A fuel. Therefore, a conventional 
unheated aluminum wing tank (that quickly cools in an airplane model 
approved for Jet A fuel) would not require FRM or IMM.
---------------------------------------------------------------------------

    \16\ As discussed previously, on May 6, 2006, a ninth wing tank 
ignition event occurred.
---------------------------------------------------------------------------

    As proposed, Sec.  25.981(b) maintained the intended flammability 
standards for wing tanks that were introduced in 2001, as part of 
Amendment 25-102 to part 25.\17\ The proposed text clarified the 
existing term ``means to minimize the development of flammable vapors'' 
by including references to a conventional unheated aluminum wing tank, 
or 3 percent average flammability. Therefore, no new flammability 
standards are introduced for conventional wing tanks. Fuel tanks 
manufactured from materials other than aluminum, or that have unique 
features that would not allow cooling of the fuel tank (such as a small 
surface area exposed to the air stream) or that are heated (such as by 
having warm fuel transferred from another tank) may need FRM to comply 
with the previously issued requirements.
---------------------------------------------------------------------------

    \17\ As discussed in the NPRM, Amendment 25-102 revised Sec.  
25.981 to require that fuel tank flammability exposure be 
``minimized.'' As explained in the preamble to that final rule, the 
objective of this requirement is to reduce the flammability exposure 
to that of an unheated aluminum wing tank.
---------------------------------------------------------------------------

b. Use of Composite Materials
    Airbus pointed to the industry trend towards the use of composite 
materials, which tend to have a lower heat transfer coefficient than 
aluminum. These materials act as insulators, slowing down any heating 
or cooling effects. Therefore, new TC designs using composite 
structures will have a natural flammability exposure greater than an 
equivalent conventional unheated aluminum wing tank, and designers will 
be forced to implement FRM. The NATCA noted that, with increased use of 
composites in wing designs, the assumption that wing tanks cool 
adequately may be incorrect.
    We agree that composite materials may act as an insulator that will 
not allow fuel tank cooling, resulting in increased flammability. 
Limiting fuel tank flammability using FRM may be needed to meet the 
flammability exposure of a ``conventional unheated aluminum wing tank'' 
that is required by Sec.  25.981. Airbus's suggestion that it is 
impractical for the rule to mandate the use of inerting for wing fuel 
tanks on airplanes with composite fuel tanks is not supported by recent 
events. While this rule is performance based and means other than 
inerting could be used, inerting has been found to be one means that is 
both technically feasible and economically viable. For example, the 
Boeing 787 will have wing fuel tanks constructed of composites, and FRM 
using nitrogen has been incorporated into the design to reduce the fuel 
tank flammability below that of a conventional aluminum wing tank.
6. Auxiliary Fuel Tanks
a. Definition
    In the NPRM, we described auxiliary fuel tanks as tanks that are 
installed to permit airplanes to fly for longer periods of time by 
increasing the amount of available fuel. The proposed rule defined an 
auxiliary fuel tank as one that is normally emptied and has been 
installed pursuant to an STC or field approval to make additional fuel 
available. We also stated that auxiliary fuel tanks are ``aftermarket'' 
installations not contemplated by the original manufacturer of the 
airplane.
    Airbus and AEA suggested the definition of auxiliary fuel tank 
should be clarified. They recommended that we use the generally 
accepted definition that is in AC 25.981-2. Boeing also requested that 
the definition of an auxiliary fuel tank be revised to more generally 
state that it is a fuel tank added to an airplane to increase range 
instead of referencing it as one installed pursuant to an STC or field 
approval. Boeing noted that an airplane might be delivered with an 
Original Equipment Manufacturer designed, manufactured and type 
certified auxiliary fuel tank.
    Changes to the regulatory text in proposed subpart I (now part 26) 
resulted in eliminating the need for this definition in the final rule. 
Therefore, we have deleted the definition of auxiliary fuel tank from 
proposed Sec.  25.1803(a) (now Sec.  26.31(a)) and will maintain the 
definition in AC 25.981-2.
b. Existing Auxiliary Tanks
    Boeing, Airbus, AEA, and ATA commented that older auxiliary fuel 
tanks should be exempt from the requirements of this rule since the 
benefits would be small compared to the cost of the retrofits. Boeing 
stated by the year 2016, most of the airplanes with auxiliary tanks 
installed during production would be over 30 years old. Future service 
life is generally thought to be minimal for these older airplanes. 
Boeing also commented, based upon feedback received from some 
operators, that these operators would deactivate their auxiliary fuel 
tanks rather than install FRM or IMM. The ATA added that the favorable 
service history (no operational accidents caused by auxiliary tank 
overpressures or explosions), operating environment (minimal exposure 
to flammable conditions), and proximity to retirement for many of these 
tanks makes it unnecessary to include auxiliary tanks in the 
applicability of this rule. Finally, Embraer commented that only 
auxiliary fuel tanks located close to heat sources and lacking free 
stream cooling require the special attention that the rule proposes.
    As discussed previously, we changed the language in proposed Sec.  
25.1815 (now Sec.  26.33), which applies to TC holders, to limit its 
applicability to airplanes produced on or after January 1, 1992, and 
this would include any auxiliary fuel tanks installed by the original 
TC holder. Since Sec.  26.35 (formerly Sec.  25.1817) applies only to 
design changes to airplanes subject to Sec.  26.33, this change from 
the NPRM has the effect of excluding most of the older auxiliary tank 
designs installed by STC or field approval, which were approved for 
installation on airplanes no longer subject to this rule.
    For those auxiliary tanks approved under STCs or field approvals 
(if any) that are still covered under the rule, we believe that most of 
these tanks transfer fuel by pressurizing the tank with cabin air. The 
increased pressure results in reduced flammability that could be 
considered an FRM if the minimum flammability performance requirements 
are met. However, we have limited data on the number of these tanks 
currently in operation and their age. We currently do not have adequate 
information on the flammability exposure or the number and the type of 
auxiliary fuel tanks installed under STCs or field approvals to 
determine whether to subject them to the requirements of this final 
rule. Based upon these limited data, we cannot predict the number of 
high flammability auxiliary fuel tanks that

[[Page 42457]]

will be in service in 2016 or the number of airplanes with auxiliary 
fuel tanks installed by STC or field approvals that could still be 
operational for some period of time past the year 2016.
    While no conclusive evidence has been presented, the commenters 
have raised issues worthy of further study. To prevent delaying the 
safety benefits of compliance with this rule, we have elected to defer 
the portion of this rulemaking that would have required development and 
installation of an FRM or IMM for auxiliary fuel tanks installed by STC 
or field approvals for further study. We have removed these proposed 
requirements from both the DAH and operational rules.
    To assess the possible safety benefits and costs more accurately, 
we are requesting further comments regarding information needed to 
determine if future action should be taken to address auxiliary fuel 
tanks installed by STC or field approvals. The rule retains the 
requirements for STC holders to conduct a flammability assessment of 
auxiliary fuel tank designs, to conduct an impact assessment of the 
auxiliary tank on any FRM or IMM, and to develop the modifications for 
any adverse impact that is found. These requirements are still 
necessary both to assess the need for further rulemaking and to prevent 
increasing the flammability exposure of tanks into which the auxiliary 
tanks feed fuel. This could potentially defeat the purpose of requiring 
reduced flammability for these tanks. To limit the scope and cost of 
the requirement to perform impact assessments, this requirement only 
applies to auxiliary tanks approved for installation on Boeing and 
Airbus airplanes that we currently are aware will be required to have 
FRM or IMM installed.
c. Future Installation of Auxiliary Tanks
    While we are foregoing action to require retrofit of existing 
auxiliary fuel tanks, we recognize that this decision could allow 
installation of currently approved auxiliary fuel tanks indefinitely, 
even if their flammability exposure exceeds those allowed under this 
rule. Therefore, we have added a new paragraph to the operational rule 
sections \18\ in this final rule to prohibit installation of any 
auxiliary tank after the retrofit compliance date (nine years after the 
effective date) unless we have certified that the tank complies with 
Sec.  25.981, as amended by this rule.
---------------------------------------------------------------------------

    \18\ Sec. Sec.  121.1117(n), 125.509(n), and 129.117(n).
---------------------------------------------------------------------------

d. Request for Comments
    As discussed previously, we have concluded that additional 
information is needed before we can determine whether it would be cost 
effective to apply the requirements of this final rule to auxiliary 
fuel tanks installed under STCs or field approvals. The FAA, therefore, 
requests additional comments addressing the following specific 
questions:
    1. Which airplanes produced on or after January 1, 1992, with 30 
passengers or more or a payload of 7500 pounds, have auxiliary fuel 
tanks installed by STC or field approval?
    2. What are the U.S. registration tail numbers of the airplanes 
with the tanks installed?
    3. How many of these tanks are installed in airplanes used in all-
cargo operations?
    4. What is the STC holder's name and what are the STC numbers for 
these tanks?
    5. How many of these tanks are installed under the Form 337 field 
approval process?
    6. Are the tanks operational or deactivated?
    7. How many engineering hours would be required to develop an FRM 
or IMM for these tanks?
    8. How much would the parts cost for an FRM or IMM for these tanks?
    9. What would the labor costs be for installing an FRM or IMM in 
these tanks?
    10. How many days would it take to install an FRM or IMM in the 
affected airplane?
    11. If the FAA required operators to install FRM or IMM, would 
those operators modify those tanks accordingly, or would they comply by 
simply deactivating those tanks? Please be model-specific for both 
passenger and all-cargo airplanes, if possible.
    12. What would be the economic consequences to the operator of 
deactivating an auxiliary fuel tank?
    Comments should be submitted to Docket No. FAA-2005-22997 by 
January 20, 2009. Comments may be submitted to the docket using any of 
the means listed in the Addresses section later in the document.
7. Existing Horizontal Stabilizer Fuel Tanks
    In the NPRM, we stated that horizontal stabilizer fuel tanks are 
fuel tanks that may be required to be retrofitted with FRM or IMM. We 
understood that these tanks may not cool rapidly, since a large portion 
of the fuel tank surface is located within the fuselage contour. Airbus 
stated that they do not believe the rule should apply to horizontal 
stabilizer fuel tanks, because these types of fuel tanks are low 
flammability and, if these tanks are treated as high flammability, the 
rule would impose significant additional costs to install FRM or IMM 
for these tanks. Therefore, Airbus concluded that we should either 
review these additional engineering complications and associated costs 
(particularly with respect to retrofit) or apply the same requirements 
to these tanks as those proposed for wing tanks not in the fuselage 
contour.
    The retrofit requirement of this rule only applies to fuel tanks 
that have an average flammability exposure above 7 percent. To the 
extent the risk analysis indicates a particular fuel tank actually is a 
low risk tank, no further requirements would apply. Some horizontal 
stabilizers, including those made by Airbus, are manufactured from 
composite material that acts as an insulator. These tanks may also be 
used to maintain airplane center of gravity, so warmer fuel may be 
transferred into them during flight. These features may result in 
flammability exposure that exceeds the 7 percent limit that is used to 
establish whether retrofit of an FRM or IMM is required. Tanks 
constructed of composites may also exceed the flammability exposure 
established for new designs in Sec.  25.981(b).
    The analysis required by this rule will establish the flammability 
exposure and determine the need for an FRM or IMM in horizontal 
stabilizer fuel tanks. If fuel tanks located within the horizontal 
stabilizer are not high flammability tanks, then no FRM or IMM would be 
needed and no additional cost would be incurred for retrofit. However, 
if an FRM or IMM is required because the tank is determined to be high 
flammability, it should be possible, using standard design methods, to 
address the technical issues. For example, the pressure drop mentioned 
by Airbus can be addressed by using a properly sized and designed FRM 
so that adequate nitrogen can be supplied to any affected tank. This 
can be done using available technology and with costs that are 
consistent with those for other tanks considered in the regulatory 
evaluation. Airbus provided no technical justification for its 
assertion to the contrary.
8. Foreign Persons/Air Carriers Operating U.S. Registered Airplanes
    Airbus, EASA, and the UK Civil Aviation Authority (UKCAA) requested 
a change to the wording of proposed Sec.  129.117(a). This change would 
clarify that the applicability of this rule is

[[Page 42458]]

limited to foreign persons and foreign air carriers operating U.S. 
registered transport category, turbine powered airplanes for which 
development of an IMM, FRM or Flammability Impact Mitigation Means 
(FIMM) is required under proposed Sec. Sec.  25.1815, 25.1817 or 
25.1819 (now Sec. Sec.  26.33, 26.35, and 26.37). Their understanding 
is that the paragraph is not intended to apply to airplanes registered 
outside of the United States.
    As provided in Sec. Sec.  129.1(b) and 129.101(a), the commenters 
are correct that Sec.  129.117 would not apply to aircraft registered 
outside the United States. To clarify our intent, we have revised Sec.  
129.117(a) to include the words ``U.S. registered.''
9. Airplanes Operated Under Sec.  121.153
    In the proposed rule, the FAA requested comments on whether 
categories of airplane operations other than all-cargo operations 
should be excluded. In response to our request, AEA and Airbus noted 
that Sec.  121.153 permits the operation, by U.S. airlines, of 
airplanes registered in another International Civil Aviation 
Organization (ICAO) member states under specified circumstances. They 
said that, while history shows that the use of the Sec.  121.153 
provisions is relatively rare, it can provide important flexibility 
when unusual circumstances dictate the urgent need of replacement 
airplanes for U.S. carriers. Given the small effect of excluding 
airplanes leased under the provisions of Sec.  121.153 from any 
requirements of the proposed rule, the commenters recommend that they 
be excluded from applicability provisions of the proposed rule. 
Otherwise, they said, if compliance with the proposed retrofit 
requirements are applied as proposed, Sec.  121.153 would preclude this 
practice for airplanes that have not been retrofitted with FRM. These 
commenters argued that this result would present a burden to both U.S. 
operators (who would lose the flexibility provided by Sec.  121.153) 
and non-U.S. operators (for whom the value of their unmodified 
airplanes would be reduced).
    Section 121.153(c) does not relate to a ``category of operation,'' 
such as all-cargo operations. Rather, it permits certificate holders to 
operate foreign registered airplanes for any type of operation, as long 
as the airplanes meet all applicable regulations. Allowing the 
operation of foreign registered airplanes that do not comply with this 
rule would be contrary to the intent of both Sec.  121.153(c) and this 
rulemaking. It would also subject a certificate holder's passengers to 
differing levels of safety based on the registry of the airplane. This 
is not acceptable and we did not make the change proposed by the 
commenters in the final rule. However, as discussed later in more 
detail, we are working with foreign authorities to establish harmonized 
flammability reduction standards. If we achieve that objective, the 
``burdens'' suggested by the commenters would disappear.
10. International Aspects of Production Requirements
    The AEA and Airbus disagreed with the proposed requirement to 
incorporate FRM or IMM into all new production airplanes. They stated 
that existing procedures for exporting airplanes from the United States 
allow the importing country to accept specific non-compliances on the 
export certificate of airworthiness. The AEA also asked for 
clarification of the discussion of FAA authority over airplanes 
produced outside the United States. Likewise, Embraer asked that the 
requirement to incorporate FRM or IMM into all new production airplanes 
be dropped from the proposal. Embraer pointed out that foreign 
regulatory authorities do not currently have certification standards 
for FRM or IMM, so Embraer is unclear how airplanes with such systems 
would be approved by the importing country. The ATA questioned the FAA 
contention (by context) that the proposed rulemaking has no 
international (ICAO) implications. It asked for the proposal to be 
reviewed by relevant international law experts for compatibility with 
the principles of sovereignty and authority in ICAO International 
Standards and Recommended Practices, Annex 8 to the Convention on 
International Civil Aviation, Airworthiness of Aircraft.
    As discussed in the NPRM, we intend for the proposed new production 
requirements to apply to any manufacturer over which the FAA has 
jurisdiction under ICAO Annex 8. For this reason, we used the same 
language as Annex 8 to define the applicability of those requirements. 
Under that annex (and under this rule), we have jurisdiction over 
organizations to which we issue production approvals, including 
production certificates. This may include organizations that accomplish 
final assembly outside the United States. While no affected U.S. 
production certificate holders currently accomplish final assembly 
outside the United States, it is possible that they might in the 
future. For example, if Boeing were to perform final assembly of a 
future version of the Boeing 737 in another country, those airplanes 
would still be subject to the production cut-in requirements of this 
final rule as long as Boeing produces them under Boeing's U.S. 
production certificate.
    Regarding the comment that current procedures allow the importing 
country to accept specific non-compliances on the export certificate of 
airworthiness, the commenters are referring to the waiver provisions of 
Sec.  21.327(e)(4). The non-compliances referenced in that section 
relate to the requirements for issuance of an export airworthiness 
approval.\19\ The production cut-in requirement of this rule is 
unrelated to those requirements. Rather, it requires that affected 
airplanes produced under U.S. production approvals must conform to an 
approved type design that meets the fuel tank flammability requirements 
of this rule. Therefore, while a foreign authority may be able to waive 
the requirements for issuing airworthiness approvals, it does not have 
the authority under ICAO Annex 8 to override our requirements, imposed 
as the State of Manufacture, for our production approval holders.
---------------------------------------------------------------------------

    \19\ For example, Sec.  21.327(e)(4) references Sec.  21.329, 
which in turn references Sec.  21.183 for the requirements for a 
standard U.S. airworthiness certificate. For new airplanes, Sec.  
21.183 requires that the product conform to its approved type design 
and is in condition for safe operation.
---------------------------------------------------------------------------

    Finally, in addition to meeting the requirements of this rule, any 
airplane produced for export would also have to meet all other 
requirements applicable to the production certificate holder (such as 
the requirement to maintain its quality control system in accordance 
with its FAA approval). These requirements cannot be waived under the 
provisions of Sec.  21.327(e)(4). Therefore, we are not aware of any 
basis for a foreign authority to object to our requirement for 
production cut-in. Of course, once the airplane is placed into 
operation by a foreign operator, the operator would have to comply with 
the requirements of its authority for operation and maintenance of the 
airplane, which may or may not include requirements relating to fuel 
tank flammability. As discussed later in more detail, we are currently 
working with foreign authorities to harmonize our requirements with 
theirs.

D. Requirements for Manufacturers and Holders of Type Certificates, 
Supplemental Type Certificates and Field Approvals

1. General Comments About Design Approval Holder (DAH) Requirements
    We received a number of general comments responding to the concept 
of DAH requirements rather than to the DAH requirements in this 
specific

[[Page 42459]]

rulemaking. We responded to these types of comments in the comment 
disposition document accompanying our policy statement titled 
``Safety--A Shared Responsibility--New Direction for Addressing 
Airworthiness Issues for Transport Airplanes.'' Both were published in 
the Federal Register on July 12, 2005 (70 FR 40168 AND 70 FR 40166, 
respectively). We received similar comments on our NPRM on Enhanced 
Airworthiness Program for Airplane Systems (70 FR 58508, October 6, 
2005, RIN 2120-AI31). As a result, we will not respond to such comments 
again here.
2. Flammability Exposure Requirements for New Airplane Designs
    As proposed, the rule requires those airplanes incorporating FRM to 
limit the fleet average flammability exposure to 3 percent, and to 
limit warm day exposure to 3 percent, for all normally emptied fuel 
tanks located, in whole or in part, in the fuselage. All other fuel 
tanks can either meet the 3 percent average flammability exposure 
limitation or have a flammability exposure that is not higher than the 
exposure in a conventional unheated aluminum wing tank that is cooled 
by exposure to ambient temperatures during flight.
a. General Comments About Applicability to New Production Airplanes
    The NACA and its member airlines fully support the requirement for 
incorporation of either an FRM or IMM to provide fuel tank inerting for 
all new production airplanes, including those that already have an 
approved TC or STC. Airbus, AEA, AAPA, and EASA also commented that 
installation of FRM during an airplane manufacturing process may be 
appropriate. The EASA expressed its support for production cut-in and 
plans to amend its rules to a harmonized approach that requires 
production incorporation.
    As we stated in the NPRM, ``The safety objective of these proposed 
rules is to have the required modifications installed and operational 
at the earliest opportunity.'' \20\ For U.S.-manufactured airplanes, we 
proposed to meet this objective by requiring affected production 
approval holders to incorporate these changes by the compliance date 
for developing FRM or IMM service information. Recognizing that we do 
not have similar authority over affected foreign manufacturers, we did 
not propose a similar requirement for them. However, as noted by the 
commenters, our safety objective still applies to those airplanes, and 
it is equally feasible for FRM or IMM to be incorporated on new 
foreign-manufactured airplanes after the necessary design changes are 
developed. Further, as stated by EASA, it has agreed to harmonize 
requirements for new production airplanes. Including FRM or IMM in 
production is more efficient and less costly than retrofitting these 
airplanes, which is also required under the NPRM.
---------------------------------------------------------------------------

    \20\ 70 FR at 70940.
---------------------------------------------------------------------------

    Based on these factors, we had assumed that FRM or IMM would be 
incorporated on all airplanes produced by both domestic and foreign 
manufacturers after designs were developed within two years after the 
effective date of this final rule. Given the reluctance of foreign 
manufacturers to commit to developing these design changes within the 
prescribed period (as discussed later), we now recognize that an 
operational requirement is needed to effectuate our intent. 
Accordingly, operators may not operate affected airplanes produced 
after September 20, 2010 unless they are equipped with FRM or IMM. 
Because we had intended that all airplanes delivered after these design 
changes had been developed would include these safety improvements, 
this requirement is a logical outgrowth of the NPRM.
b. Flammability Analysis Using the Monte Carlo Method
    For all fuel tanks, an analysis must be performed to determine 
whether the fuel tank, as originally designed, meets the fleet average 
flammability exposure limits discussed above. To determine the 
flammability exposure of fuel tanks, the ARAC used a specific 
methodology incorporating a Monte Carlo analysis.\21\ As proposed, any 
analysis of a fuel tank must be performed in accordance with this 
methodology (as detailed in proposed appendix L, now appendix N, and in 
the draft FAA document, Fuel Tank Flammability Assessment Method User's 
Manual).\22\ We considered approving alternative methodologies in lieu 
of Appendix N, but we found that no other alternative considered all 
factors that influence fuel tank flammability exposure (which is the 
safety objective of this rule).
---------------------------------------------------------------------------

    \21\ This methodology determines the fuel tank flammability 
exposure for numerous simulated airplane flights during which 
various parameters such as ambient temperature, flight length, fuel 
flash point are randomly selected. The results of these simulations 
are averaged together to determine the fleet average fuel tank 
flammability exposure.
    \22\ As indicated in the proposed Appendix L (now Appendix N), 
we are incorporating the User's Manual by reference into the final 
rule. This was incorporated by reference in the final rule by 
creating a new Sec.  25.5.
---------------------------------------------------------------------------

    The ATA proposed upgrading the Monte Carlo method or developing a 
similar method that would be used to evaluate airplane risk of a fuel 
tank explosion. The method proposed by ATA would include not only fuel 
tank flammability, but also the risk of ignition sources developing in 
a fuel tank based upon the specific airplane design.
    The Monte Carlo method is intended to be used to determine fuel 
tank flammability alone, not the overall likelihood of a fuel tank 
explosion. While the ATA's suggestion is intriguing, we do not believe 
there is presently a method of accurately predicting the risk of an 
ignition source developing in a fuel tank. With this final rule, we are 
implementing a balanced approach to prevent fuel tank explosions: By 
addressing both ignition prevention (as defined in the requirements of 
Sec.  25.981(a) and SFAR 88) and flammability reduction (as defined in 
this rule). Compliance with both standards ensures that fuel tank 
explosion risk is acceptable.
    The EASA also expressed concerns about the proposed methodology 
since it is complex and allows variations in fuel tank flammability to 
be introduced by variations in the input parameters used in the 
analysis. Although EASA welcomed the improvements to the Monte Carlo 
method proposed in the NPRM that set the majority of the input 
parameters, EASA expressed concern that the method does not adequately 
address heat transfer and the assumptions retained do not allow proper 
quantification of the exposure.
    We share the concern expressed by EASA that, unless properly 
controlled, variation in the DAH input parameters used in the 
flammability assessment could result in significant differences between 
various DAHs. Fuel tank thermal modeling, including heat transfer, is 
the one major variable parameter provided by the user. Appendix 
N25.3(e) requires that substantiating data for the fuel tank thermal 
model, along with other input parameters, be submitted with the 
analysis. Therefore, we believe that Appendix N does adequately address 
heat transfer and provides a method that allows for proper 
quantification of flammability exposure.
    Finally, Parker Hannifin Corporation noted an error in the Monte 
Carlo computer code that mistakenly added the time prior to flight and 
utilized the flight time constants rather than ground time constants in 
certain calculations. This error could produce two counter-

[[Page 42460]]

acting effects. In some circumstances, it could produce higher 
flammability exposure when the tank-full time constant is used longer 
than actually required. In other circumstances, it tends to reduce the 
flammability exposure by using the tank empty-time constant earlier 
than actually warranted. Overall this has the net effect of slightly 
underestimating the actual fuel tank flammability exposure so 
assessments using the revised computer code would produce slightly 
higher flammability values. We addressed this error in the final rule 
and the computer code is now correct.
c. Definition of ``Normally Emptied Tank''
    As defined in proposed Sec.  25.1803(d) (now Sec.  26.31(b)), 
``normally emptied tank'' refers to a fuel tank that is emptied of fuel 
during the course of a flight and, therefore, can contain a substantial 
vapor space during a significant portion of the airplane operating 
time. Boeing requested that the definition for ``normally emptied'' be 
removed. Boeing based this request on the fact that heat input to the 
tank and the heat rejection rate (i.e., the rate of heat transfer from 
the tank) play more of a factor in a tank's flammability than whether 
it is normally emptied.
    While we acknowledge that the heat input to the fuel tank and heat 
rejection from the tank are major factors in fuel tank flammability, 
the reason we are concerned about tanks that are normally emptied is 
not related to their flammability. As stated in the preamble to the 
NPRM, normally emptied fuel tanks can contain a substantial fuel vapor 
space that could expose potential ignition sources to the fuel vapor 
for an extended period of time. Fuel in tanks that are not normally 
emptied covers potential ignition sources more often than fuel in 
normally emptied tanks. This prevents ignition sources from igniting 
fuel vapors in the tank. Therefore, normally emptied fuel tanks have a 
higher likelihood of exposing flammable vapor to ignition sources than 
tanks that are not normally emptied. This rule specifically 
differentiates between fuel tanks that are normally emptied and other 
fuel tanks by requiring reduced fuel tank flammability because of the 
increased risk of an explosion in normally emptied tanks.
d. Fixed Numerical Standard
    For new airplane designs, we requested comments on whether the 
reference to a conventional unheated aluminum wing tank or a fixed 
numerical standard for the requirements of Sec.  25.981(b) would be 
more workable and effective. The safety objective of a ``conventional 
unheated aluminum wing tank'' is consistent with the ARAC 
recommendation and Sec.  25.981(c) (amendment 102). However, it does 
not provide a numerical standard to apply in future type certification 
programs. In certain cases, the compliance demonstration would be 
simplified if a fixed numerical standard were provided in the 
regulation, because there would be no analysis needed to establish the 
flammability exposure of a conventional unheated aluminum wing tank 
that is the alternative flammability exposure. We believe this approach 
has implementation advantages and should achieve the safety level 
intended by the ARAC recommendation and the current approach in Sec.  
25.981(c) (amendment 102).
    Transport Canada, Boeing, Airbus, and ATA agreed that including a 
fixed numerical standard was preferred. Several of them suggested that 
we needed to provide further justification for the selection of a 3 
percent fixed value and proposed different numerical values. These 
commenters did not agree with the inclusion of a variable standard of 
equivalence to a conventional unheated aluminum wing tank.
    Airbus stated that a numerical value within the level recommended 
by ARAC (i.e., 7 percent) would be more practical and potentially safer 
than a flammability equivalency to a hypothetical wing fuel tank. While 
the 3 percent limit should be considered an acceptable goal if FRM is 
used, Airbus suggested that for fuel tanks that have a base 
flammability exposure less than 7 percent, there should not be a 
requirement to use FRM. The existing minimization of heat sources, as 
required by EASA, should be adequate. Airbus concluded that 
establishing a standard of 7 percent for fuel tank flammability 
exposure would ensure that FRM would provide a significant benefit (at 
least a 50 percent reduction in flammability) and remove the potential 
to actually reduce the overall safety as a result of increased ignition 
risk potential due to hazards associated with adding new FRM or IMM to 
the airplanes.
    These commenters did not provide any compelling reasons to change 
the proposed 3 percent average flammability exposure or to eliminate 
the provision for showing equivalence to a conventional unheated 
aluminum wing tank. The reason for including the fixed 3 percent 
flammability exposure is to simplify the compliance demonstration. The 
reason for allowing for equivalence to a conventional unheated aluminum 
wing tank is to give flexibility to designers who are willing to 
perform the required evaluations. The proposal from Airbus and other 
commenters to increase the flammability exposure value to 7 percent 
would allow a significant increase in fuel tank flammability over that 
permitted by Sec.  25.981. The fleet of airplanes that ARAC determined 
had achieved an acceptable level of safety was made up of airplanes 
with conventional unheated aluminum wing tanks with flammability 
exposures that varied from very low levels of around 1.5 percent for 
outboard wing fuel tanks to the highest values below 6 percent for some 
larger inboard wing tanks. These numerical values would all be lower if 
calculated today, consistent with the lower values now calculated by 
manufacturers for HCWTs.
    Therefore, in this final rule, we adopted a flammability standard 
that includes showing a fuel tank is equivalent to a conventional 
unheated aluminum wing tank or 3 percent, whichever is greater. For 
purposes of this final rule, a conventional unheated aluminum wing tank 
is a conventional aluminum structure, integral tank of a subsonic 
transport airplane wing, with minimal heating from airplane systems or 
other fuel tanks and cooled by ambient airflow during flight. Heat 
sources that have the potential for significantly increasing the 
flammability exposure of a fuel tank would preclude the tank from being 
considered ``unheated.'' Examples of such heat sources that may have 
this effect are heat exchangers, adjacent heated fuel tanks, transfer 
of fuel from a warmer tank, and adjacent air conditioning equipment. 
Thermal anti-ice systems and thermal anti-ice blankets typically do not 
significantly increase flammability of fuel tanks.
e. Tanks Located Within the Fuselage Contour
    Boeing disagreed with the distinction in proposed Sec.  25.981 
between tanks located within the fuselage contour that are normally 
emptied and other tanks. Boeing suggested that main tanks and tanks not 
partially within the fuselage do not represent all the tanks with low 
flammability exposure and acceptable safety records. Boeing stated that 
on the other hand it is possible to design a main or wing tank with 
exceptional heat sources and/or minimal cooling. It is also possible to 
design a normally emptied tank that is partially within the contour of 
the fuselage which is low flammability (3 percent or less).
    Bombardier did not understand the justification for introducing a 
maximum

[[Page 42461]]

3 percent fuel tank flammability exposure for wing tanks with a portion 
of the tank located within the fuselage. Bombardier stated that there 
is an inconsistency in requiring wing tanks to have flammability 
exposure of between 2 percent and 5 percent, while requiring fuselage 
tanks to be below 3 percent. Bombardier concluded that keeping all 
tanks below a 7 percent flammability exposure level should be 
considered acceptable, and recommended that tanks with less than 7 
percent flammability exposure not be required to have FRM.
    The distinction in flammability exposures in the rule between tanks 
located within the fuselage contour that are normally emptied and other 
tanks was made because the former generally have an increased risk of 
explosion. The location within the fuselage typically results in little 
or no cooling of the tank and, in some cases, actually heats the tank. 
Tanks that are normally emptied operate much of the time empty. 
Therefore, components that could be potential ignition sources are 
exposed to the tank ullage. We agree with Boeing on the possibility 
that fuel tanks located in the wing can be high flammability if the 
tank is heated or does not cool due to tank design features. However, 
the rule limits fuel tank flammability in these tanks to 3 percent or 
equivalent to a conventional unheated aluminum wing tank, addressing 
that risk.
    For fuel tanks located outside the fuselage contour, Sec.  25.981, 
as amended by this final rule, retains the flammability limits 3 
percent or equivalent to a conventional unheated aluminum wing tank. 
Only if any portion of the fuel tank is located within the fuselage 
contour, and if the tank is normally emptied, is it required to meet 
the 3 percent average and 3 percent warm day requirement. If an 
applicant chooses to locate a portion of a main fuel tank inside the 
fuselage, the rule requires that the fuel tank meet the same standard 
as a main fuel tank located solely outside of the fuselage contour 
(i.e., 3 percent or equivalent to a conventional unheated aluminum wing 
tank wing).
    Since existing airplane types with main fuel tanks that go from the 
wing into the fuselage are not normally emptied, FRM or IMM is required 
for these tanks only if the tank flammability exposure exceeds 7 
percent (proposed Sec.  25.1815 (now Sec.  26.33)). For future designs 
using similar architecture, these types of designs would need to show 
that the main tank that extends into the fuselage meets the standard of 
equivalent to a conventional unheated aluminum wing tank or 3 percent.
f. Compliance Demonstration
    Boeing, Airbus, and BAE requested that applicants be allowed to use 
design review to determine that an aluminum fuel tank is equivalent to 
the low flammability standard fuel tank as defined by ARAC. This would 
be in lieu of a detailed Monte Carlo based flammability analysis. The 
BAE stated that performing a cumbersome and expensive Monte Carlo 
analysis for metallic wing tanks of conventional design is unnecessary 
and adds no value. For other types of tanks, or wing tanks with a 
substantial heat input, BAE believes the use of alternative analytical 
methods may be appropriate and suggested a qualitative assessment of 
the design and the installation should be adequate to determine whether 
a given tank has a low flammability exposure. Finally, BAE recommended 
a simple set of objective criteria be allowed for establishing fuel 
tank flammability in these tanks.
    Boeing requested that we:
     Revise proposed Sec.  25.981(b) to allow a simplified 
flammability analysis for fuel tanks shown by design review to be a 
Conventional Unheated Aluminum Wing Tank.
     Delete proposed Sec.  25.981(b)(1) and (b)(2), which 
reference Appendixes N and M for the flammability analysis methodology 
and flammability exposure criteria, respectively.
     Revise the definition of conventional unheated aluminum 
wing tanks to consider allowing some minimal heat sources (i.e., 
hydraulic systems) and significant cooling which results in low 
flammability exposure and a satisfactory level of safety.
    We agree with the commenters' assertion that a simplified 
qualitative flammability analysis for conventional unheated aluminum 
wing tanks is appropriate and have modified Appendix N to permit this. 
Our intent is to limit the quantitative analysis for aluminum wing 
tanks with unique or unconventional designs that are heated or designed 
such that minimal cooling occurs. For example, a quantitative 
flammability analysis would be necessary for a wing tank that has a 
relatively small surface area, thereby minimizing surface cooling 
effects, a composite tank or a tank that has equipment inducing heat 
into the fuel tank greater than a small amount.
    We have also added guidance to AC 25.981-2 that describes how to 
conduct a qualitative analysis to establish equivalency to a 
conventional unheated aluminum wing tank. This guidance provides 
examples of allowable heat sources and cooling characteristics for a 
fuel tank to be considered a ``conventional unheated aluminum wing 
tank,'' so that the safety standard established by the ARAC definition 
for a conventional unheated aluminum wing tank is maintained. For 
compliance with Sec.  25.981(d), the guidance also includes a 
discussion of how Critical Design Configuration Control Limitations 
(CDCCL) would need to be developed to define any critical features of 
the fuel tank design needed to limit the flammability to that of a 
conventional unheated aluminum wing tank.
    As for Boeing's specific changes to Sec.  25.981, we do not agree 
that Sec.  25.981(b)(1) and (b)(2) should be deleted because Appendix N 
provides necessary definitions and methods for establishing Fleet 
Average Flammability Exposure and Appendix M establishes performance 
standards for FRM. These appendices, and the references to them in 
Sec.  25.981(b)(1) and (b)(2), are necessary to achieve the safety 
objectives of this rulemaking. We have not adopted Boeing's suggestion 
to modify the definition of ``Equivalent Conventional Unheated Aluminum 
Wing.'' However, we do agree with the comment to allow some minimal 
heating of tanks such as that from a hydraulic heat exchanger that does 
minimal heating. We have revised the term ``Conventional Unheated 
Aluminum Wing'' used in Sec.  25.981 to ``Conventional Unheated 
Aluminum Wing Tank'' to clarify that the flammability of the fuel tank 
is the standard. Since some minimal degree of heating typically occurs 
in many of these tanks, this change recognizes that such minimal 
heating is permissible.
g. Heat Sources Located in or Near Fuel Tanks
    Transport Canada and the UK Air Safety Group suggested we prohibit 
the placement of heat sources within or near fuel tanks. Transport 
Canada questioned why we would allow such an undesirable design 
practice to continue. The UK Air Safety Group contended the NPRM failed 
to address the contribution of high fuel tank temperature to fuel tank 
explosions. The commenter noted that the Boeing 737 and 747 have air 
conditioning units that raise the fuel tanks' temperature well above 
the outside ambient temperature because these units are located beneath 
the center fuel tanks.
    We agree with the commenters' underlying concern about controlling 
fuel tank temperature. While locating heat sources in or near fuel 
tanks increases the tanks' flammability, specifically prohibiting this 
design

[[Page 42462]]

practice may not be the most efficient and effective way to address the 
problem. This rule is performance-based and is seeking innovative 
design solutions which could permit locating heat sources near or in 
fuel tanks. For example, designers may wish to develop an FRM based 
upon managing the fuel tank temperature by transferring heat between 
tanks. These designs may provide flammability exposures well below that 
of a tank that complied with the proposal made by the commenters. Risk 
is directly proportionate to the flammability exposure of a tank. 
Therefore, we have developed a flammability performance standard that 
is independent of the design details of a tank installation.
h. Effects of Systems Failures on Flammability
    The CAPA requested that we ensure the effects of any system 
failures that might increase the fuel tank flammability above the 
acceptable limit be considered and properly evaluated prior to issuing 
the final rule.
    The flammability analysis required by Sec.  25.981 includes a 
requirement to show that flammability exposure does not exceed minimum 
levels. It also requires that the overall flammability exposure 
analysis includes consideration of system failures when demonstrating 
that the FRM meets the reliability requirements of this rule. In 
addition, the analysis required by Sec.  25.981(d) that determines the 
CDCCL and airworthiness limitations includes consideration of possible 
critical design features that must be maintained and may not be altered 
to assure the flammability limits are achieved. We have provided 
additional guidance and clarification in AC 25.981-2 regarding 
reliability assessments and establishing CDCCL and airworthiness 
limitations for FRM and IMM. Accordingly, we believe the commenter's 
concerns are already addressed by the proposed language, and no change 
was made to the final rule.
i. Move Flammability Exposure Method to Advisory Circular
    The EASA, Transport Canada, Boeing, and Bombardier commented that 
the Monte Carlo method should not be defined in the rule as the method 
for determining fuel tank flammability. Instead, it would be more 
appropriately included in advisory material.
    We do not agree with these commenters. The Monte Carlo method is 
specified in the rule to ensure standardization of the methodology for 
determining fuel tank flammability across all airplane models so a 
uniform level of safety is achieved. Advisory circulars (ACs) provide 
guidance for methods, procedures, or practices that are acceptable to 
us for complying with regulations. ACs are only one means of 
demonstrating compliance, and we cannot require their use. Specifying 
Monte Carlo analysis in an AC could result in numerous methodologies 
and input parameters being used to determine flammability exposure, and 
we believe that this could result in differing flammability exposures 
in the fleet that may allow some fuel tanks to have greater 
flammability than intended by the rule. To ensure that all DAHs reach 
comparable conclusions from their assessments, it is necessary to 
require that they use the same methodology. This can only be 
accomplished through the rulemaking process.
    However, to accommodate minor revisions that would not appreciably 
affect analytical results, we have included a provision in Appendix 
N25.1(c) permitting use of alternative methods if approved by the FAA. 
This is similar to the flexibility provided in Sec.  25.853 for 
alternative test methods to those defined in Appendix F of part 25.
3. Flammability Exposure Requirements for Current Airplane Designs
    Proposed Sec.  25.1821 (now Sec.  26.39) contains the fuel tank 
flammability safety requirements for newly produced airplanes. 
Paragraph (b) sets forth the criteria that, when met by any fuel tank, 
requires that fuel tank to have an FRM or IMM meeting the new 
requirements of Sec.  25.981. Paragraph (c) contains the requirements 
for all other fuel tanks that exceed a Fleet Average Flammability 
Exposure of 7 percent.
a. Same Standards for New and Current Airplane Designs
    Boeing asked that we revise proposed Sec.  25.1821(b) to state 
``any fuel tank not shown by design review to be a Conventional 
Unheated Aluminum Wing Tank, must meet the requirements of Sec.  25.981 
in effect on [effective date of final rule].'' In conjunction with this 
change, paragraph (c) would be deleted. Boeing stated that new 
production airplanes should meet the same requirements as new airplane 
designs, since the criteria for tanks at risk should be a function of 
heating and cooling, not whether the fuel tank is normally emptied and 
located partially within the fuselage.
    We do not agree with Boeing. As discussed earlier, tanks that are 
normally emptied and located at least partially within the fuselage are 
generally more susceptible to explosion because of both increased 
ullage and operating at higher temperatures. We have determined that 
the 7 percent flammability exposure limit recommended by ARAC is an 
adequate standard to determine which fuel tanks in newly produced 
airplanes need an FRM or IMM. If the fleet average flammability 
exposure is above 7 percent for fuel tanks normally emptied and located 
within the fuselage contour, these fuel tanks will be required to be 
flammable no more than 3 percent on average and 3 percent for warm day 
operations. We expect that the vast majority of large transport 
category airplanes will have a fleet average flammability exposure 
above 7 percent for these specific fuel tanks and will be required to 
comply with Sec.  25.981 for production airplanes affected by the DAH 
requirement.
    Other tanks on newly produced airplanes also may not exceed the 7 
percent flammability exposure limit, but the final rule would allow 
reduction to that level by various methods of FRM described in AC 
25.981-2 that would not necessarily require the added complexity and 
cost of a nitrogen inerting based FRM. We believe this requirement is 
sufficient to provide an acceptable level of safety for current 
production airplanes because these tanks have significantly lower risk 
of fuel tank explosions, as demonstrated by their service history. 
Therefore, we do not believe the safety improvements from redesign of 
these tanks to meet the new requirements of Sec.  25.981 are sufficient 
to justify the resulting costs.
b. 7 Percent Exposure Flammability Questioned
    In the NPRM, we stated that fuel tanks that have a flammability 
exposure higher than 7 percent are unduly dangerous. American Trans Air 
commented that this statement is arbitrary, based on flawed analysis, 
and cannot be supported. Bombardier expressed its opinion that the NPRM 
and its supporting data did not adequately substantiate the declared 7 
percent exposure. Although Bombardier considered that achieving 7 
percent exposure is feasible with reasonable design precautions, 
Bombardier stated that this is not an acceptable reason for creating a 
standard. Bombardier also quoted information shared among the airline 
industry and authorities that heated tanks may vary between 8 percent 
to as high as 40 percent in flammability exposure.
    Boeing did not agree with the proposed flammability requirements 
for newly produced airplanes, because fuel tanks other than those 
located within

[[Page 42463]]

the fuselage contour that are normally emptied would be allowed to have 
flammability of up to 7 percent. Boeing commented that this 
flammability is more than twice that of what is allowed for similar 
tanks in new designs. Boeing noted that the first ARAC determination 
that 7 percent flammability exposure is acceptable was based on the 
original coarse ARAC flammability analysis which determined that 
unheated tanks had a flammability level of approximately 5 percent. Two 
percent was added for potential variation resulting in the 7 percent 
proposal. Boeing pointed out that the Monte Carlo analysis has been 
significantly refined since the first ARAC report, and the estimated 
flammability exposure of 5 percent (7 percent with potential variation) 
has been reduced to be in the range of 3 percent (4 percent with 
potential variation) or less for the same fuel tanks.
    We have determined that the 7 percent or less fleet average 
flammability exposure recommended by ARAC is an adequate value that can 
be used to identify those airplane models that need to be retrofitted 
with an FRM or IMM. The fuel tank flammability limits established for 
newly produced airplanes (subject to the production cut-in 
requirements) are the same as those for retrofit of the existing fleet 
(proposed Sec.  25.1815 (now Sec.  26.33)). We determined this 
flammability exposure achieves the desired safety benefits, since 
currently produced airplanes generally have conventional unheated 
aluminum wing tanks, the tanks ARAC determined to have adequate safety 
level, with flammability exposures below 7 percent.
    We agree with Boeing that newly produced airplanes should not be 
allowed to have fuel tank flammability that is twice that of new 
designs, and this is not what we intended. The intent of this rule is 
to apply its safety improvements to the fuel tanks that have been shown 
to have an increased risk of explosion, not to require modifications to 
conventional unheated aluminum wing tanks, or other fuel tanks that 
have significantly lower flammability. Data we have available for 
currently produced airplanes indicate the flammability of tanks located 
outside the fuselage contour have flammability below 7 percent and 
further reduction in flammability exposure as recommended by Boeing 
would add significant cost to the rule, since a number of fuel tanks 
would be required to have an FRM or IMM to meet the suggested 
flammability values of 3 to 4 percent.
    Recognizing that, based on the applicability criteria of proposed 
Sec.  25.1821(a) (now Sec.  26.39), this section only applies to 
current production Boeing models. We have revised paragraph (a) to 
specifically identify those models. As discussed previously, we have 
also added a requirement to the operational rules that operators must 
meet these requirements for any airplane subject to this rule that is 
produced more than two years after the effective date.
4. Continued Airworthiness and Safety Improvements
a. 7 Percent Standard Should Apply to All Tanks
    Boeing requested that Sec.  25.1815(c)(1) be modified to state 
that, for fuel tanks with flammability exposure exceeding 7 percent 
that require an FRM, ``a means must be provided to reduce the fuel tank 
flammability exposure to meet the criteria of Appendix M of this 
part.'' In addition, Boeing recommended that we delete Sec.  
25.1815(c)(1)(i) and (ii). Boeing stated that any fuel tank that has 
significant heat loads, regardless of the location on the airplane, 
should meet the requirements of Appendix M if an FRM is selected as the 
design modification.
    We do not concur with Boeing's comment that the flammability 
requirements of Appendix M should apply to any fuel tank that exceeds 7 
percent average flammability. As discussed previously, the reason we 
are adopting more stringent requirements for fuel tanks that are 
normally emptied and located within the fuselage contour is that those 
tanks both have higher flammability exposure and are more likely to 
have ullage exposed to ignition sources. For other fuel tanks where the 
fleet average flammability exposure exceeds 7 percent, the requirements 
of Appendix M apply with the exception that the flammability 
requirements of M25.1(a) and (b) are replaced by the requirement that 
fleet average flammability exposure must not exceed 7 percent. We 
believe this is acceptable for these tanks on existing airplanes. Since 
most of these tanks are not ``normally emptied,'' the risk that 
flammable vapors will be exposed to ignition sources is generally much 
lower.
b. Compliance Planning
    Airbus requested that the compliance planning requirements 
contained in Sec.  25.1815 be removed because they are unnecessary. 
Airbus believes the only important compliance date is the final date 
for DAHs to submit the data and documents necessary to support operator 
compliance. Airbus commented that the compliance plan requirements in 
Sec. Sec.  25.1815(g), (h) and (i) add constraints on the manufacturer 
with no safety benefit. Airbus stated these documents should not be 
subject to a requirement with respect to the DAH documentation delivery 
date. However, if the delivery dates for these documents are mandated, 
Airbus requested that they be expressed in the format of a duration 
tied to the date of approval of the previous submittal.
    Boeing recommended we remove the Sec.  25.1815(g)(3) requirement to 
identify deviations to methods of compliance identified in FAA advisory 
material, because the proposed means of compliance should not be 
compared to other means. Instead, they should be evaluated on their own 
merits.
    While we understand the commenters' concerns, these documents will 
provide assurance that the required flammability exposure analyses and, 
if applicable, proposed design changes, are being addressed in a timely 
fashion. As stated in the NPRM, the resolution of fuel tank safety 
issues needs to be handled in a ``uniform and expeditious'' manner. 
Providing compliance times based on the dates of our previous approvals 
would result in various compliance times, depending upon whether DAHs' 
submissions are acceptable. It would have the undesirable effect of 
providing more time for those manufacturers submitting deficient 
documents.
    Compliance planning will promote communication between the affected 
manufacturer and us. It will also provide sufficient time to discuss 
any concerns with respect to how the affected manufacturer proposes to 
analyze fleet average flammability exposure or certify design changes. 
Compliance planning will also help to ensure that the affected 
manufacturer is able to meet the required compliance times of the rule 
for accomplishing the submittal of the flammability exposure analysis, 
design changes, and service instructions, if applicable (proposed Sec.  
25.1815 (now Sec.  26.33) and proposed Sec.  25.1817 (now Sec.  
26.35)). We intend to closely monitor compliance status and take 
appropriate action, if necessary.
    However, we do acknowledge that some provisions of proposed Sec.  
25.1815(g), (h) and (i) could be removed without adversely affecting 
our ability to facilitate TC holder compliance. Specifically, proposed 
paragraph (g)(3) would require TC holders to identify intended means of 
compliance that differ from those described in FAA advisory materials.

[[Page 42464]]

While this is still a desirable element of any compliance plan, we now 
believe that an explicit requirement is unnecessary and it is not 
included in the final rule. As with normal type certification planning, 
we expect that TC holders will identify differences and fully discuss 
them with the FAA Oversight Office early in the compliance period to 
ensure that these differences will ultimately not jeopardize full and 
timely compliance. Because we believe that timely review and approval 
is beneficial and will save both DAH and FAA resources, the advisory 
material will recommend that if the DAH proposes a compliance means 
differing from that described in the advisory material, the DAH should 
provide a detailed explanation of how it will demonstrate compliance 
with this section. The FAA Oversight Office will evaluate these 
differences on their merits, and not by comparison with FAA advisory 
material.
    Similarly, proposed Sec.  25.1815(i) contains provisions that would 
have authorized the FAA Oversight Office to identify deficiencies in a 
compliance plan, or the TC holder's implementation of the plan, and 
require specified corrective actions to remedy those deficiencies. 
While we anticipate that this process will still occur in the event of 
potential non-compliance, we have concluded that it is unnecessary to 
adopt explicit requirements to correct deficiencies and have removed 
them from the final rule. Ultimately, TC holders are responsible for 
submitting compliant FRM or IMM by the date specified. This section 
retains the requirements to submit a compliance plan and to implement 
the approved plan. If the FAA Oversight Office determines that the TC 
holder is at risk of not submitting compliant FRM or IMM by the 
compliance date because of deficiencies in either the compliance plan 
or the TC holder's implementation of the plan, the FAA Oversight Office 
will document the deficiencies and request TC holder corrective action. 
Failure to implement proper corrective action under these 
circumstances, while not constituting a separate violation, will be 
considered in determining appropriate enforcement action if the TC 
holder ultimately fails to meet the requirements of this section.
    Finally, we realized that the rule text could more clearly state 
our intent to allow DAHs flexibility to modify their approved plan if 
necessary. Accordingly, we changed proposed Sec.  25.1815 (now Sec.  
26.33(i)) to read: ``Each affected type certificate holder must 
implement the compliance plans, or later revisions, * * *''
c. Changes to Type Certificates Affecting Flammability
    Proposed Sec.  25.1817 (now Sec.  26.35) addressed changes to TCs 
that could affect fuel tank flammability. This section proposed to 
require that a flammability exposure analysis be accomplished in 
accordance with Appendix N for all affected fuel tanks installed under 
an STC, amended TC, or field approval within 12 months after the 
effective date of the final rule. An impact assessment that identifies 
any features of the design change that compromise any CDCCL applicable 
to any airplane with high flammability tanks for which CDCCL are 
required must also be submitted to the FAA Oversight Office. This 
section also proposed a requirement to develop service instructions to 
correct designs that compromise airworthiness limitations, defined by 
the TC holder under proposed Sec.  25.1815 (now Sec.  26.33), within 48 
months after the final rule's effective date.
    Airbus proposed we restrict the application of any proposed changes 
to Sec.  25.981 to new TCs and significant design changes (i.e., new 
fuel tanks). For minor design changes such as relocating a fuel level 
sensor or a small increase in tank capacity, the TC holder should only 
be required to show no degradation in the flammability under the 
criteria proposed by Sec.  25.1815. Airbus stated that the cross-
reference between what is in the preamble and Sec.  25.1815, and what 
is required by Sec.  25.1817, is misleading.
    We agree with Airbus, and have revised proposed Sec.  25.1817 (now 
Sec.  26.35) to require compliance with the new Sec.  25.981 only for 
new fuel tanks. Other design changes that increase capacity of existing 
fuel tanks must comply with Sec.  26.33. Design changes that affect the 
flammability exposure of existing tanks equipped with FRM or IMM must 
comply with CDCCLs for those tanks. This will ensure that these design 
changes do not degrade the level of safety required by this rule.
d. Combine Sec. Sec.  25.1815 and 25.1817
    Boeing requested that we combine proposed Sec. Sec.  25.1815 and 
25.1817 into one section. We do not agree with this suggestion, since 
it would not achieve the goals of this rulemaking. As proposed, 
Sec. Sec.  25.1815 (now Sec.  26.33) and 25.1817 (now Sec.  26.35) 
would apply to different entities. Section 25.1815 (now Sec.  26.33) 
would apply to TC holders of transport category airplanes, and Sec.  
25.1817 (now Sec.  26.35) to auxiliary tank STC holders and future 
applicants for design changes. The STC holders have distinctly 
different compliance dates because information such as CDCCL developed 
by the DAHs under proposed Sec.  25.1815 (now Sec.  26.33) is needed 
before the STC holders can comply with proposed Sec.  25.1817 (now 
Sec.  26.35). Separate sections provide a clear statement of the 
requirements for each situation so affected persons can more easily 
understand what is needed to comply with the rules applicable to them. 
Therefore, the final rule retains the language as proposed with no 
change.
e. Pending Type Certification Projects
    Proposed Sec.  25.1819 contains the requirements for pending TC 
projects. As proposed, this section contains different requirements for 
those transport category airplanes based on whether the application was 
made before or on/after June 6, 2001 (the effective date of Amendment 
25-102). Boeing requested that this section be deleted because it saw 
no reason to differentiate among designs based on the date of 
application.
    We partially agree with Boeing and have revised this section. In 
the final rule, any pending certification projects that have not 
received type certification by the effective date of this rule will be 
required to meet the requirements of Sec.  25.981, as amended by this 
rule. Since there are no longer any ongoing TC projects where the 
application was received prior to June 6, 2001, there is no reason for 
this distinction and we have removed proposed Sec.  25.1819(c). 
However, we have received applications for type certification projects 
after June 6, 2001, that are still pending (e.g., the Boeing 787 and 
Airbus A350), and we have determined that a specific requirement in 
Sec.  25.1819 is needed to address these projects. We do not believe 
this section should be completely deleted, as requested, because these 
projects (and future design changes to these airplanes), would not 
otherwise be required to comply with Sec.  25.981, as amended by this 
final rule. The change to the rule will maintain the requirement that 
pending projects meet the same flammability standards as required for 
new type certificates and that applicants develop CDCCL as proposed in 
the NPRM.
f. Type Certificates Applied for on or After June 6, 2001
    Proposed Sec.  25.1819(d) (now Sec.  26.37(b)) requires that if an 
application for type certification was made on or after June 6, 2001, 
the requirements of Sec.  25.981 of this rule apply. Section 25.981 
requires, in part, that the fleet average flammability exposure of a 
fuel

[[Page 42465]]

tank not exceed 3 percent or that of a conventional unheated aluminum 
wing tank.
    Airbus objected to the setting of a 3 percent flammability limit 
for all fuel tanks for a pending type certification, if the application 
was made on or after June 6, 2001. Airbus agreed that a 3 percent 
flammability limit could be considered as an acceptable goal when FRM 
is used. However, for fuel tanks that have a base flammability exposure 
less than 7 percent, there should not be a requirement to impose FRM, 
and the existing minimization of heat sources should be considered 
adequate. If initial flammability is between 3 and 7 percent, the 
safety benefit to reduce it to 3 percent through the use of FRM is not 
justified, when considering the introduction of new failure conditions, 
and operational and ownership costs of an FRM.
    Airbus apparently misunderstood the effect of the proposed 
requirements of Sec.  25.1819 (now Sec.  26.37) for TCs for which 
application was made on or after June 6, 2001. The following is 
provided to clarify the requirements of the rule and address the 
concern expressed by Airbus. The flammability requirements for an 
airplane for which application was made on or after June 6, 2001, would 
include Sec.  25.981 at Amendment 25-102 for all tanks except normally 
emptied tanks located within the fuselage contour. As stated earlier in 
this preamble, the rule text has been changed to clarify that the 
flammability exposure is equivalent to a conventional unheated aluminum 
wing tank or 3 percent, at the applicant's option. This flammability 
exposure is unchanged from Amendment 25-102, which would not have 
permitted a flammability exposure of 7 percent. This rule adds a new 
requirement for fuel tanks located within the fuselage contour that are 
normally emptied. Normally emptied tanks located within the fuselage 
must meet the 3 percent average and the 3 percent warm day flammability 
limits defined in Appendix M, which is the same flammability 
requirement being applied to these types of fuel tanks on existing 
airplanes.
g. Design Change to Add a Normally Emptied or Auxiliary Fuel Tank
    As proposed, Sec.  25.1819(e) would require that any future design 
change to a TC for which the application is pending when this rule is 
adopted and that--
     Adds an auxiliary fuel tank, or
     Adds a fuel tank designed to be normally emptied, or
     Increases fuel tank capacity, or
     May increase the flammability exposure of an existing fuel 
tank must meet the requirements of Sec.  25.981, as amended by this 
rule. Boeing asked that this paragraph be deleted because it is 
specifically for ``pending'' type certification projects and, by 
definition, there is no existing type certificate to change. If the 
intent of proposed Sec.  25.1819 (now Sec.  26.37) is to define 
requirements for projects in work at the time of the final rule, then 
Boeing suggested there is no need for this section. Any change after 
the new production compliance date would have to meet the new 
production requirements (Sec.  25.1821).
    Proposed Sec.  25.1819(e) specifically targets potential future 
changes to certain long-term, pending type certification programs. 
Under proposed Sec.  25.1819(c), these programs would not be required 
to comply with Sec.  25.981, as amended by this rule. Our intent was 
that, although the original TC would not have to comply with the 
current requirements, any later changes would have to comply. Since we 
issued the NPRM, all of these projects have been certified, so there 
are no pending projects for which this paragraph is needed. Therefore, 
we have removed it from the final rule.

E. Flammability Exposure Requirements for Airplane Operators

    The proposed operating rules would prohibit the operation of 
certain transport category airplanes operated under parts 91, 121, 125, 
and 129 beyond specified compliance dates, unless the operator of those 
airplanes has incorporated approved IMM, FRM or FIMM modifications and 
associated airworthiness limitations for the affected fuel tanks. The 
proposed rules would not apply to airplanes used only in all-cargo or 
part 135 operations. Finally, the proposed operating rules would also 
create new subparts that pertain to the support of continued 
airworthiness and safety improvements.
1. General Comments About Applicability to Existing Airplanes
    Airbus, AEA and AAPA believe the retrofit requirement is not cost 
effective. Our analysis showed that the benefit/cost ratio of the 
production cut-in and retrofit requirements are similar. This was our 
rationale for adopting the combined approach of production cut-in and 
retrofit. However, these commenters believe the 7 percent discount rate 
used in our cost/benefit analysis is too high and is responsible for 
the determination that cost/benefit ratios are similar between the 
production cut-in and retrofit. We infer from their comments that they 
believe that 3 percent is a more realistic number and supports their 
contention that retrofit is not justified. The commenters note that an 
EASA analysis concluded that the retrofit was not justified. A major 
concern was that the bulk of the retrofit costs (present value terms) 
will be incurred in about 1/3 of the time (7 years) required for the 
forward fit costs (22 years). They believe that the cash outlay to 
retrofit in such a short time, coupled with the small safety benefit, 
is not justified when compared with the cost/benefit of the production 
cut-in. They also stated that the high cost of the retrofit over such a 
short period would place financial stress on an industry that is 
already financially constrained. In contrast, the cost of production 
incorporation of FRM in new airplanes will be borne by airlines that 
are prepared to accept the cost of new airplanes with the FRM included 
in the ``sticker price.''
    Except as discussed previously regarding the exclusion of part 91 
operations, we continue to believe that a retrofit requirement is 
justified. As discussed in the NPRM and earlier in this preamble, the 
risk of fuel tank explosions on the current fleet of airplanes with 
high flammability tanks is still significant because, despite our 
efforts to eliminate ignition sources, they continue to occur. At the 
same time, we have made a number of changes to the proposed 
requirements to reduce their cost and improve their cost-effectiveness. 
As discussed later in this preamble, the final regulatory evaluation 
(FRE) has been revised to include the benefits of preventing lost 
revenue to the industry as a whole if another fuel tank explosion were 
to occur. When these benefits are included, variations in the discount 
rate do not alter the conclusion that this rule is reasonably cost-
effective.
    The compliance time for the retrofit requirement allows for 
incorporation of design modifications over a seven-year period. 
Operators can spread the costs over this time period. We have also 
included a provision in the operational rules (discussed later) that 
allows operators an extension of up to one year after the 50 percent 
and 100 percent retrofit deadlines for full fleet incorporation of the 
design modifications if the operator includes requirements in their 
operations specifications to use ground conditioned air when available. 
For 50 percent of an operator's fleet, this would allow retrofit to be 
completed by September 21, 2015 rather than September 19, 2014. 
Similarly, for 100 percent of an operator's fleet, this would allow 
retrofit to be completed by

[[Page 42466]]

September 19, 2018 rather than September 19, 2017. This provision 
provides a reduction in the costs to operators because it allows an 
additional year to install an FRM or IMM. We also adjusted the 
applicability of the rule so that older airplanes that were produced 
prior to 1992, which will be nearing the end of their useful life in 
passenger service, will not be subject to the phase-in-requirement of 
the rule. The DAH-supported design modifications will only be required 
on airplanes with significant remaining useful life in passenger 
service so the benefits of the rule are optimized.
    As for the comments on the standard discount rate, the rate that is 
mandated by the Office of Management and Budget when conducting 
regulatory evaluations is 7 percent. The Initial Regulatory Evaluation 
included a sensitivity study where variations in the discount rate 
(using 3 and 7 percent) were considered. Variations in the discount 
rate affect both the cost and the benefits of the rulemaking. Thus, 
using a discount rate of 3 percent (as they recommend) increases the 
benefits of the rulemaking, because the value of averted future 
accidents would also have a higher present value.
2. Authority to Operate With an Inoperative FRM, IMM or FIMM
    In the NPRM, we requested public comment on the proposal to allow 
the current Flight Operations Evaluation Board (FOEB) process to 
establish the Master Minimum Equipment List (MMEL) interval for the FRM 
or IMM rather than requiring a specific maximum fixed time interval 
that the FRM can be inoperative. Airbus, Boeing, ATA, AEA and British 
Airways supported the rule as proposed and generally agreed the FOEB is 
the appropriate vehicle to establish the approved MMEL interval for 
inoperative FRM. In contrast, Smith's Aero commented that FRM must be 
considered a flight critical system, without MMEL relief for the 
performance of the system to meet the overall intended safety level 
stated by the FAA in the NPRM. Finally, Frontier asked how long an 
airplane could be operated with an inoperative FRM system.
    As stated in the NPRM, the intent of the rule is to provide an 
additional layer of protection from having a fuel tank explosion if an 
ignition source occurs inside a fuel tank. While the FRM system is 
needed to maintain the safety of a fleet of airplanes, it is not 
considered flight critical for every flight, since the ignition 
prevention means required by Sec.  25.981 requires robust fail-safe 
features that provide an adequate level of safety during short periods 
of time when the FRM is inoperative under the MMEL (no greater than 1.8 
percent of the operating time). We agree with the commenters that ``FRM 
designers'' should make the design goals for the MMEL relief intervals 
available and notify the FOEB of their recommendation. The allowable 
MMEL interval is design dependent and cannot be defined by us until a 
design is presented and the interval is justified by the system 
reliability analysis and the FOEB.
    Frontier also asked whether en route weather conditions would be a 
factor with the MEL. At this time, en route weather conditions are not 
part of the consideration for operation under the operator's MEL. This 
is one of the considerations in the Monte Carlo assessment, so 
operation under an operator's MEL during warm days would not be an 
additional consideration for the MMEL.
3. Availability of Spare Parts
    Frontier asked if we had given proper consideration to the fact 
that there will most likely be an initial spare parts shortage. The 
compliance time for fleet-wide retrofit of FRM or IMM is nine years 
after the effective date of this final rule, with 50 percent compliance 
required within 6 years. Therefore, the manufacturers of components 
should have the capability to produce needed spares and no shortage of 
parts is anticipated. We have not included a consideration of parts 
shortages when establishing the MMEL interval.
4. Requirement That Center Fuel Tank Be Inert Before First Flight of 
the Day
    Frontier requested information on whether the final rule would 
require that the center fuel tank be inert before the first flight of 
the day and, if so, if the Auxiliary Power Unit is inoperative, could 
the inerting system then be inoperative until after main engine start. 
The final rule does not directly address the operational details of the 
FRM. These will be determined based on the DAH's design and any 
operating limitations that may be necessary to meet the performance 
standards of this final rule.

F. Appendix M--FRM Specifications

    Appendix M to part 25 contains detailed specifications for all FRMs 
if they are used to meet the flammability exposure limitations. These 
specifications are designed to ensure the performance and reliability 
of FRMs. We received several comments on Appendix M and have made 
changes to the rule based on some of them.
1. Fleet Average Flammability Exposure Level
    Paragraph M25.1(a) requires that the Fleet Average Flammability 
Exposure of each fuel tank may not exceed 3 percent of the Flammability 
Exposure Evaluation Time. As discussed previously, as a portion of this 
3 percent, if flammability reduction means (FRM) are used, each of the 
following time periods cannot exceed 1.8 percent of the FEET: (1) When 
any FRM is operational but the fuel tank is not inert and the tank is 
flammable; and (2) when any FRM is inoperative and the tank is 
flammable. Boeing requested a change to this paragraph to clarify that, 
for both the operational and inoperative requirements, only time 
periods when the fuel tank is in a flammable state are counted toward 
each 1.8 percent flammability exposure limit.
    We agree that the method of determining these times needs 
clarification and we have revised paragraph M25.1(a) as requested by 
Boeing.
2. Inclusion of Ground and Takeoff/Climb Phases of Flight
    Paragraph M25.1(b) requires that ground, takeoff and climb phases 
of flight be included in the fuel tank fleet average flammability 
exposure analysis. Boeing asked that paragraph M25.1(b) be reworded to 
exclude a specific reference to the takeoff flight phase. Boeing's 
justification was that there is no benefit in conducting a separate 
flammability analysis for the takeoff phase of flight since it is a 
very short duration. Boeing recommended the takeoff phase be included 
with the climb phase of flight. Boeing also suggested the rule clarify 
that the transition from ground to climb phase for this analysis occurs 
at weight off wheels.
    We agree with Boeing and have revised paragraph M25.1(b) in the 
final rule to remove consideration of the takeoff phase of flight as a 
separate requirement. These two phases are now required to be 
considered in combination using the term ``takeoff/climb'' phase. In 
addition, we added a sentence to paragraph M25.1(b)(2) stating that the 
transition from ground to takeoff/climb phase for this analysis occurs 
at weight off wheels.
3. Clarification of Sea Level Ground Ambient Temperature
    Paragraph M25.1(b)(1) requires that the fuel tank fleet average 
flammability

[[Page 42467]]

exposure analysis, as defined in Appendix N, ``must use the subset of 
flights starting with a sea level ground ambient temperature of 
80[deg]F. (standard day plus 21[deg]F. atmosphere) or more, from the 
flammability exposure analysis done for overall performance.'' An 
individual commenter requested that we define the term ``more'' in this 
statement. We agree that this requirement needs clarification and, in 
the final rule, paragraph M25.1(b)(1), we replaced the word ``more'' 
with the word ``above.'' We also replaced the word ``starting'' with 
``that begin.''
4. Deletion of Proposed Paragraph M25.2 (Showing Compliance)
    Paragraph M25.2 establishes the means for showing compliance with 
fuel tank flammability requirements. Boeing requested the contents of 
paragraph M25.2 be moved to Advisory Circular 25.981-2A as it defines a 
method of compliance and, as such, should be located in an AC.
    As discussed previously, ACs provide guidance for methods, 
procedures, or practices that are acceptable to us for complying with 
regulations. ACs are only one means of demonstrating compliance, and we 
cannot require their use. The compliance means in paragraph M25.2 is 
regulatory in nature to ensure that applicants are providing the data 
necessary to validate the parameters used in their calculations for 
fuel tank fleet average flammability exposure (as required by paragraph 
M25.1), and to substantiate that their system meets these requirements 
during normal airplane operations for any combination of airplane 
configuration (as required by paragraph M25.2(b)). We have made no 
change as a result of this comment.
5. Deletion of ``Fuel Type'' From List of Requirements in Proposed 
Paragraph M25.2(b)
    Boeing also requested that paragraph M25.2(b) be revised to remove 
``fuel type'' from the list of requirements and add ``or other relevant 
airplane system configuration'' to it. Boeing stated the items listed 
in paragraph M25.2(b) affect the performance of a FRM system that is 
supplied by engine bleed air, and fuel type does not affect bleed 
system pressure. We agree with Boeing and have revised this paragraph 
in the final rule.
6. Latent Failures
    Paragraph M25.3(a) requires that reliability indications be 
provided to identify latent failures of the FRM. These indications are 
needed to ensure appropriate actions can be taken to maintain the FRM's 
reliability. An individual commenter asked that we define what is meant 
by ``reliability indications'' in paragraph M25.3.
    In this context, reliability indications are normally computer 
messages or lights that identify whether components are functioning 
properly. Reliability indications are likely to be needed for the FRM 
to meet the reliability requirements in the rule. The type of 
indications needed will depend on the design and the outcome of the 
reliability analysis. If a nitrogen inerting FRM were to be developed 
with no indication of system failures, the system would have 
significant exposure to long-term operation with latent failures. 
Maintenance indications would likely be needed so that the minimum 
reliability of the system could meet the rule.
    Boeing requested that paragraph M25.3 be deleted or modified to 
remove the term ``latent.'' This would be consistent with the special 
conditions issued for the Boeing 737 and 747 flammability reduction 
systems. In addition, the term ``latent'' would not be applicable if an 
indication is provided. An individual commenter agreed, stating that 
latent failures are not detectable and, hence, cannot be indicated. 
Embraer commented that both paragraphs M25.3(a) and (b) should be 
deleted because a literal interpretation would require any latent 
failure to be detected and indicated. This contradicts the NPRM's 
preamble, which states that the designer is allowed to make a trade-off 
between system failure probability and failure detection/ annunciation 
to show compliance with the system performance requirements. In 
addition, Embraer maintained that paragraph M25.3(a) is already 
addressed and should not be repeated here because the requirement for 
failure detection is inherent in the flammability exposure requirement 
and in the 1.8 percent limit on system failure contribution to 
flammability exposure.
    On a related topic, Airbus and Embraer commented that the proposed 
rule is too restrictive and mandates an excessive amount of indication 
and monitoring. Airbus indicated that the proposed text appears to 
assume the adoption of an active system to reduce flammability and this 
may not necessarily be appropriate if a passive system were to be used. 
Some means of verifying that the passive means is fully functional 
could be required, but it may be inherent in the design and therefore, 
no specific action would be required except to ensure that other 
airplane modifications do not adversely affect the fuel tank 
flammability.
    The FAA agrees with these commenters and has modified paragraph 
M25.3(a) in the final rule.
    This change makes it clear that the intent of the rule is to 
require only those indications needed to assure any FRM meets the 
minimum reliability requirements of the rule. The preamble to the NPRM 
provided a detailed explanation of the intent of these requirements. 
The need for indications is determined from the system reliability 
assessment that requires a minimum reliability for any FRM. The type of 
indications that may be needed to meet the reliability requirements 
depends upon the details of the design and the outcome of the system 
reliability analysis. Various design methods may be used to make sure 
an FRM meets the reliability and performance requirements in this rule. 
For example, if an FRM based upon nitrogen inerting is developed and no 
indication of system failures is provided, the system would have 
significant exposure to long-term operation with latent failures. 
Maintenance indications would likely be needed so that the minimum 
reliability of the system could meet the rule. Other designs may use 
active or passive cooling means for flammability reduction. For these 
systems, the level of indication required would depend upon the 
reliability of the cooling system components.
    The need for FRM indications and the frequency of checking system 
performance (maintenance intervals) must be determined based on the 
results of the FRM fuel tank fleet average flammability exposure 
analysis. The determination of a proper maintenance interval and 
procedure will follow completion of the certification testing and the 
reliability analysis used to establish the system complies with the 
performance requirements.
7. Identification of Airworthiness Limitations
    Paragraph M25.4(a) requires that if FRM is used to comply with 
paragraph M25.1, airworthiness limitations must be identified for all 
maintenance or inspection tasks required to identify failures of 
components within the FRM that are needed to meet paragraph M25.1. 
Boeing requested that paragraph M25.4(a) be modified to require only 
airworthiness limitations be identified for ``significant'' maintenance 
or inspection tasks. Boeing stated that it is overly restrictive to 
require that all maintenance tasks be identified as airworthiness 
limitations. It argued that applicants should be granted the 
flexibility to identify significant tasks as

[[Page 42468]]

airworthiness limitations and other non-significant tasks as 
maintenance significant items.
    We agree with Boeing that we should not require that all 
maintenance tasks for FRM be identified as airworthiness limitations. 
Airworthiness limitations for the FRM system are only required for 
those FRM components that, in the event of failure, would affect the 
ability of the fuel tank to meet the Fleet Average Flammability 
Exposure specified in paragraph M25.1. We regard any task that is 
necessary to meet this objective as ``significant.'' We recognize that 
manufacturers are also required to provide other maintenance 
information for the FRM as part of the instructions for continued 
airworthiness required by Sec.  25.1529.
8. Catastrophic Failure Modes
    EASA noted that Appendix M significantly differs from the 
harmonized special conditions it used for certifying FRM on some 
specific airplane models. EASA asked that we explicitly state that 
catastrophic results must not occur from any single failure or 
combination of failures not shown to be extremely improbable (for the 
FRM system) as required in the noted special conditions. We agree that 
possible catastrophic failure modes of the FRM must be shown to meet 
the requested standard. However, we do not agree that EASA's change is 
needed since the regulatory intent is already addressed by other 
regulations that apply to FRM. For example, the general requirements of 
Sec.  25.901 that apply to all Subpart E regulations apply to an FRM 
certificated to meet Sec.  25.981 and Appendix M. Therefore, we did not 
make any change to Appendix M based on EASA's comment.
9. Reliability Reporting
    Paragraph M25.5 requires the applicant to demonstrate an effective 
means to ensure collection of FRM reliability data and to provide a 
report to the FAA. We requested comments on the proposal to require 
DAHs to submit a quarterly report on FRM reliability for 5 years. We 
consider these reports necessary to determine whether the predicted 
reliability for these systems is accurate, and to enable us to initiate 
necessary corrective actions if they are not. We intend for DAHs to 
gather the needed data from operators using existing reporting systems 
that are currently used for airplane maintenance, reliability, and 
warranty claims. The operators would provide this information through 
existing or new business arrangements between the DAHs and the 
operators.
    The AEA and ATA questioned this reliability reporting process. They 
stated the current reporting systems may not be equipped to accommodate 
this new data requirement without additional burden and cost. Airbus 
also stated the reporting requirement is unclear and without sufficient 
detail to enable them to fully comment. The AEA and Airbus also contend 
that the reporting requirement places operators in a position of having 
an obligation to report this information to the DAHs where such an 
obligation did not previously exist. They suggested that we not rely on 
technicalities and recognize the new obligation being imposed on the 
operators. Finally, Transport Canada commented that the rule appears to 
require extensive data collecting and reporting and requested more 
details be provided regarding what this data will be used for.
    The purpose of collecting reliability data is to ensure that 
failures of the system are reviewed and corrected. In this manner, 
system reliability is enhanced and FRM malfunctions will become very 
infrequent. The reporting requirement will also provide data necessary 
to validate that the reliability of the FRM achieved in service meets 
the values used in the fleet average flammability exposure and 
reliability analyses so that the actual flammability reduction in 
service airplanes will achieve the safety goals of this rulemaking.
    The reliability reporting requirements in paragraph M25.5 would not 
add an additional burden or cost to the operators. We also continue to 
believe that this rule does not directly impose reporting requirements 
on operators. These reporting requirements are placed upon the DAH, not 
the operator. The NPRM and proposed AC 25.981-2B provided a description 
of the level of complexity that was intended in the quarterly reporting 
requirements. Furthermore, they do not specify that a new reporting 
system be created. The current reporting system could be used to gather 
the data and it could then be provided to the DAHs through normal 
business agreements. The DAH is required to make arrangements to 
collect sufficient data and provide a report to us. Reporting would be 
necessary only for a representative sampling of airplanes, as 
determined by the manufacturer in its compliance plan. Airlines 
routinely collect and store reliability data from airplane systems for 
a variety of reasons, such as engine and airplane system reliability 
data collected for Extended Twin Operations, warranty claims and 
maintenance planning, and in many cases they report these data to DAHs.
    Therefore, DAHs should be able to readily obtain these data through 
normal business practices. As a practical matter, DAHs will be 
monitoring the performance of these systems, just as they monitor other 
systems, both for warranty and liability reasons. Operators will be 
providing this information to DAHs as normal business practice to 
obtain DAH support in correcting any problems that occur. Our 
expectation is that the DAHs' compliance plans will simply state that 
DAHs will compile this information into periodic reports (which they 
would normally do for their own use anyway) and provide them to the 
FAA. No change has been made to the final rule as a result of these 
comments.
    Bombardier requested that paragraph M25.5(b) be revised to allow 
non-U.S. manufacturers to submit their reports to their national 
authorities rather than the FAA. While we acknowledge that submitting a 
report to a foreign manufacturer's national authority might simplify 
the paperwork exchange, at this time other authorities have not agreed 
to harmonize with this rule. Therefore, there are no corresponding 
regulations that would require the submittal of reliability reports to 
these authorities or to ensure that we will see these reports. We have 
revised the requirement to allow for FAA approval of alternative 
reporting procedures, which would include reporting to other 
authorities with harmonized requirements. The rule also provides that, 
after the first five years of reporting, if the demonstrated 
reliability of the FRM meets and will continue to meet the reliability 
requirements in paragraph M25.1 (not to exceed 1.8 percent of the 
FEET), other reliability tracking methods could be proposed to us for 
approval, or possibly reporting could be eliminated.
    Boeing requested that M25.5(b) be revised to allow the applicant to 
suggest alternative methods of reporting and submit the report to us on 
a yearly basis instead of a quarterly basis. It asserted that a one-
year reporting requirement will allow for more statistically 
significant data to be collected for new systems. We agree that a 
quarterly requirement may be unduly burdensome, but we believe that a 
yearly requirement is too long to enable us to initiate timely 
corrective action to address reliability problems. Therefore, we have 
modified paragraph M25.5(b) in the final rule to extend the reporting 
to once every 6 months for the first five years after service 
introduction of the FRM. This reporting period should

[[Page 42469]]

allow adequate time to gather data to establish the performance of the 
FRM and for any needed corrective actions to be taken if the 
performance of the FRM falls below minimum levels.
    Boeing also requested changes be made to allow applicants that have 
established reporting methods to suggest these as alternative methods 
of meeting the reporting requirements. We believe the current wording 
allows the DAH the latitude to develop a reporting system and request 
FAA approval based upon their business arrangements with operators so 
long as the reporting system provides sufficient data to the FAA to 
determine the reliability of the FRM. Allowing the use of alternative 
reporting methods could lead to disparate reports among manufacturers, 
making FAA oversight difficult.

G. Appendix N--Fuel Tank Flammability Exposure and Reliability Analysis

1. General
    Appendix N to part 25 provides the requirements for conducting the 
analyses for fleet average fuel tank flammability exposure required to 
meet Sec.  25.981(b) and Appendix M and to comply with part 26 
requirements. Appendix N contains the method for calculating overall 
and warm day fuel tank flammability exposure values needed to show that 
the affected airplane's tanks comply with the proposed limitations on 
flammability exposure.
2. Definitions
    Paragraph N25.2 provides specific definitions associated with 
flammability and analysis terminology used in Appendix N. We received 
comments requesting clarification on five of these definitions:
    a. Ullage: Boeing suggested this definition should ensure that all 
of the ullage space is considered (not just the fuel volume), and we 
agree. In the final rule, this definition has been revised to clarify 
that the total ullage space must be considered.
    b. Flammability Exposure Evaluation Time (FEET): An individual 
commenter wanted to understand when the evaluation time begins and ends 
for airplanes using ground conditioned air with the auxiliary power 
unit (APU)/ground power unit (GPU) operating or electrical power that 
is connected to the airplane. The evaluation time would begin as soon 
as the airplane is prepared for flight, regardless of whether an APU or 
electrical ground power is used. The time would end as soon as the 
airplane has landed and passengers and crew have disembarked and 
payload has been unloaded. In passenger operations where numerous 
flights may occur each day, this definition would result in all the 
time between flights also being part of the FEET. The only exception 
would be the time at the end of the last flight of the day to the point 
in the next morning when the airplane is being readied for flight. This 
is consistent with the definition for FEET given in paragraph N25.2(b).
    c. Bulk Average Fuel Temperature: An individual commenter suggested 
the definition include the means for determining ``bulk average fuel 
temperature.'' As we stated in the preamble to the NPRM, the 
determination of whether the ullage in the fuel tank is flammable is 
based on the temperature of the fuel in the tank or compartment of 
interest. This is derived from a fuel tank thermal model, the 
atmospheric pressure in the tank, and the properties of the fuel. The 
thermal model is comprised of temperature data acquired from various 
locations within the fuel tank. In order to express the fuel 
temperature of the tank as a whole in the fuel tank fleet flammability 
exposure analysis, a weighted average by volume should be calculated at 
each point in time since the temperature may vary across the tank or 
compartments of the tank depending upon the volume of that area. We 
will provide additional guidance on how to determine Bulk Average Fuel 
Temperature in AC 25.981-2A.
    d. Flash Point: An individual commenter asked what the term 
``heated sample'' meant in this definition. The standardized methods 
for determining flash point are ASTM D 56 and ASTM 3828. Both methods 
place a sample of fuel in a closed cup and heat it at a constant rate. 
A small flame is introduced into the cup, and the lowest temperature at 
which ignition is observed is referred to as the flash point. The 
heated sample is the fuel that is placed in the closed cup when 
conducting this test.
    e. Inerting: An individual commenter requested that fuel removal 
from the ullage mixture be included as an acceptable inerting method. 
We do not agree with this request. The definition of inerting is based 
upon oxygen concentration, not fuel content of the ullage. The Monte 
Carlo method uses the bulk fuel temperature to determine fuel tank 
flammability, and does not consider transport effects or tank 
ventilation. However, if an applicant wishes to consider methods for 
removing fuel from the ullage mixture, it could request a finding of 
equivalent safety under the provisions of Sec.  21.21. To be 
equivalent, such a method would have to be shown to provide at least 
the same level of safety as an FRM meeting the performance requirements 
of Appendix M.
3. Input Parameters
    Paragraph N25.3(c) provides the parameters that are specific to a 
particular airplane model under evaluation that must be provided as 
inputs to the Monte Carlo analysis. Boeing had two comments on these 
parameters.
    First, Boeing requested we add a new parameter to paragraph 
N25.3(c) for airplane utilization. This parameter would require the 
applicant to provide data supporting the number of flights per day and 
the number of hours per flight from existing fleet data. Boeing stated 
that this information is necessary to determine when to apply the 
diurnal effect that is required by paragraph N25.4(c) based upon the 
number of flights per day. The number of hours per flight will also 
provide validation of the mean hours per flight generated by the Monte 
Carlo analysis.
    We agree with Boeing's comment and the final rule includes a new 
paragraph N25.3(c)(7) for airplane utilization that addresses this 
comment. Boeing's second comment was a request that the statement ``or 
for the section of the tank having the highest flammability exposure'' 
be removed from paragraph N25.3(c)(5). As proposed, paragraph 
N25.3(c)(5) requires that, for any fuel tank that is subdivided by 
baffles or compartments, the bulk average fuel temperature inputs must 
be provided either for each section of the tank or for the section of 
the tank having the highest flammability exposure. Boeing stated that 
every region in a fuel tank should be considered in order to establish 
the total flammability exposure of the tank. If the bulk temperature 
input only consisted of a section of the fuel tank having the highest 
flammability exposure, Boeing argued that the total flammability of the 
tank would not be accurately accounted for because the analysis would 
not consider regions that were less flammable.
    Any fuel tank that is compartmentalized or subdivided into sections 
by baffles is ``flammable'' under the definition for Appendix N 
(N25.2(c)) when the bulk average fuel temperature within any section of 
the tank that is not inert is within the flammable range for the fuel 
type being used. We agree with Boeing that the clause ``or for the 
section for the tank having the highest flammability exposure'' in 
paragraph N25(c)(3) causes confusion, and we

[[Page 42470]]

have revised paragraph N25.3(c)(5) as requested.
    We are providing guidance in AC 25.981-2 on the need to conduct the 
flammability analysis for each bay or compartment and then sum the time 
any portion of the tank is flammable in the flammability analysis.
4. Verification of ``Flash Point Temperature''
    An individual commenter requested verification of the flash point 
temperature (120 [deg]F) that is used in Table 1 of Appendix N. We have 
defined in Table 1 of Appendix N a ``mean fuel flash point 
temperature'' based upon worldwide survey data that was collected from 
1998 through 1999. The Monte Carlo analysis varies the flash point 
based upon the distribution of possible flash point temperatures for 
the fuel, similar to what would be expected for a fleet of airplanes 
where fuels from various refineries and locations are used.

H. Critical Design Configuration Control Limitations (CDCCLs)

    Past experience has shown that critical features of airplane 
designs have inadvertently been changed when maintenance actions or 
alterations to airplanes have been made. For example, critical wiring 
that was intended to be separated from other wiring to prevent possible 
unsafe conditions has been modified so new or rerouted wiring was co-
routed with the critical wires. These instances revealed the need for 
airplane designers to identify safety critical features, in this case 
wiring separations, and for these features to be marked so that 
maintenance personnel are aware of the critical features.
    We proposed adding fuel tank flammability related design features 
to the existing fuel tank ignition source CDCCL requirements in Sec.  
25.981(d) (formerly paragraph (b)). This section requires CDCCL, 
inspections, or other procedures as necessary, to prevent increasing 
the flammability exposure of tanks above that permitted by the amended 
Sec.  25.981(b) and to prevent degradation of the performance and 
reliability of any means provided for compliance with paragraphs 
25.981(a), (b) or (c). We also proposed adding fuel tank flammability 
to the existing requirements to place visible means of identifying 
critical features of the design in areas of the airplane where 
foreseeable maintenance actions, repairs or alterations could 
compromise the CDCCL. Similar provisions were proposed in Sec.  
25.1815(e) for existing type certificates.
1. Remove Requirement
    Boeing, Embraer and Bombardier requested that we remove the 
requirement to establish CDCCLs to prevent the increase of flammability 
in the fuel tanks and to prevent degradation of the performance and 
reliability of the FRM. They stated that it is not practical or 
effective to try to control flammability through the use of CDCCLs. 
Instead, they argued that the certification process should be used to 
establish the design's flammability exposure. Bombardier also pointed 
out that the type certification data sheet is the appropriate means to 
capture limitations (e.g., fuel type, fuel temperature) that would 
affect flammability.
    The intent of the CDCCL requirement is to define the critical 
features of the design that could be unintentionally altered in a way 
that could cause a reduction in fuel tank safety. In the case of IMM or 
FRM, maintenance or alterations to the airplane could significantly 
affect fuel tank flammability and the performance of these systems. 
Since the heating or cooling rate of a fuel tank could be a critical 
feature, placing a heat exchanger or other heat source in or near the 
tank or changing the cooling rate by transferring warm fuel to the tank 
are examples of changes that could result in a significant increase in 
fuel tank flammability.
    The commenters did not provide any substantiating information as to 
why they believe it is not practical or effective to use CDCCLs to 
control fuel tank flammability. Our experience with applying the CDCCL 
concept to fuel tank ignition sources has shown it to be both practical 
and effective. Locating this information on the TC data sheet, as 
suggested by Bombardier, would not provide the information to 
individuals, such as maintenance personnel, who could be responsible 
for inadvertently changing the system. Accordingly, we do not believe 
this suggestion would be effective. In contrast, as airworthiness 
limitations, CDCCLs are clearly defined as maintenance requirements 
that are routinely complied with by maintenance personnel and that are 
enforceable under the operational rules (e.g., Sec.  91.403(c)). The 
intent of applying the CDCCL concept to FRM and IMM is to provide a 
common location within the maintenance instructions where information 
on fuel tank safety related critical features are located. Therefore, 
we have retained the requirement in Sec.  25.981(d) to identify CDCCLs 
for FRM and IMM.
    On a related issue, paragraph (h) of each of the proposed 
operational rules would have required operators to comply with the 
CDCCLs. In the NPRM, we inadvertently omitted reference to Sec.  25.981 
as one of the sources of requirements for these CDCCLs. Therefore, we 
have added these references to the final rule. This change is simply 
clarifying, since operators are required to comply with airworthiness 
limitations under existing regulations.
2. Clarification on Responsibility for Later Modifications
    As proposed, Sec.  25.1817(d) (now Sec.  26.35(d)) would require 
that modifications made to an airplane comply with any CDCCL applicable 
to that airplane. The AEA questioned whether this paragraph would 
require the TC holder or STC applicant applying for a design change to 
achieve a flammability exposure level equal to or better than that 
existing on the unmodified airplanes, or if the TC holder or STC 
applicant will be held to the flammability exposure limits specified in 
the rule.
    The proposed requirement for TC holders to develop CDCCL is 
contained in proposed Sec.  25.1815(e) (now Sec.  26.33(d)). It would 
require CDCCL ``to prevent increasing the flammability exposure of the 
tanks above that permitted under this section and to prevent 
degradation of the performance of any means provided under paragraph 
(c)(1) or (c)(2) \23\ of this section.'' The AEA has identified an 
ambiguity and potential conflict in this quoted provision. 
Specifically, if a TC holder develops FRM whose performance exceeds 
that required by proposed Sec.  25.1815(c)(1), it is not clear whether 
the CDCCL would have to maintain the flammability exposure provided by 
the FRM or whether the rule would allow an increase in flammability 
exposure up to that permitted (i.e., 3 percent or equivalent to a 
conventional unheated aluminum wing tank, along with the ``warm day'' 
requirement).
---------------------------------------------------------------------------

    \23\ Paragraphs (c)(1) and (c)(2) provide for FRM and IMM, 
respectively.
---------------------------------------------------------------------------

    To eliminate this ambiguity, we have deleted the reference to 
paragraph (c)(1) in the quoted provision. This revision has the effect 
of requiring CDCCL for FRM that allow increasing flammability up to 
that permitted by the rule, but retains the requirement that 
degradation of performance of IMM is not permitted. Since IMM may be 
installed on high flammability tanks, degradation of IMM could have 
serious safety consequences and would not be consistent with the intent 
of the rule.

[[Page 42471]]

    We note that TC holders may be inclined to develop overly stringent 
CDCCL for FRM that could potentially make it impossible for holders of 
auxiliary fuel tank STCs to meet them. This would force operators to 
deactivate these tanks. This over-stringency would not be consistent 
with this rule's intent, which is to minimize the burden on operators, 
consistent with achieving the safety objectives of this rule. This 
issue is discussed in more detail in AC 25.981-2B.
    Proposed Sec.  25.981(d) contained the same ambiguity by requiring 
CDCCL to prevent degradation of performance and reliability of any 
means provided according to paragraph (b) of that section (FRM). We 
have made a similar change to paragraph (d) to allow degradation of FRM 
as long as the airplane still meets the standard required by paragraph 
(b).
3. Limit CDCCLs to Fuel Tanks That Require FRM or IMM
    Boeing requested that proposed Sec.  25.1815(e) (now Sec.  
26.33(e)) be modified to only require CDCCLs that are necessary to 
prevent the increase of fuel tank flammability for fuel tanks that 
require an FRM or IMM. Boeing stated that development of CDCCLs for 
other fuel tanks is not practical, nor is there history to show that 
changes to the fuel tanks of airplanes in service significantly 
increase flammability in the tanks. Boeing also requested that the 
requirement to make critical features of the design visibly 
identifiable only apply to areas where it is practical to do so.
    For existing designs subject to proposed Sec.  25.1815(e) (now 
Sec.  26.33(e)), we agree with Boeing, and have limited the 
applicability of the requirement to develop CDCCL to those tanks for 
which FRM or IMM are required. We recognize that there are many 
existing modifications that may affect the flammability exposure of 
existing fuel tanks. We agree with Boeing that, for main tanks and 
other tanks not incorporating FRM or IMM, it is impractical to impose 
CDCCLs on these tanks that may result in significant compliance 
problems for affected operators. For tanks equipped with FRM or IMM, 
however, we believe CDCCLs are necessary to prevent degradation of 
these systems below acceptable levels of performance.
    We also agree with Boeing that, in many instances, it may not 
always be practical to mark critical features relating to controlling 
fuel tank flammability and the proposed rule should be modified to 
allow the applicant to justify why markings are not needed. We have 
modified the next to last sentence in Sec.  26.33(e) accordingly.
    This change will allow acceptance of designs without markings when 
the applicant can show that such markings would be impracticable. We 
intend for applicants to identify any CDCCL that are required and to 
provide justification for why the marking would be impracticable. Like 
all CDCCLs, these would still be documented as airworthiness 
limitations in the instructions for continued airworthiness.
4. STC Holders May Not Have Data to Comply
    The AEA and Airbus challenged our statement in the NPRM that 
operators have access to information that may be needed by STC and 
field approval holders to perform flammability and impact assessments. 
The commenters noted that such information is highly proprietary and is 
rarely provided to operators. AEA added that contractual agreements to 
obtain TC holder information are difficult, if not impossible, to 
obtain.
    For many years, the FAA and other regulatory authorities (including 
EASA) have routinely required manufacturers to make available 
information that they consider proprietary when we determine providing 
this information is necessary for aviation safety. For example, most 
ADs reference information that would otherwise be proprietary in the 
form of service bulletins, which manufacturers are required to make 
available to operators. Similarly, Sec.  21.50 requires manufacturers 
to make available instructions for continued airworthiness, which 
manufacturers would also typically consider proprietary.
    In existing Sec.  25.981(b), we required DAHs to define and make 
available CDCCL to prevent the unintended creation of ignition sources 
as a result of maintenance or airplane modifications. In proposed Sec.  
25.981(e), we required the identification of critical features of a 
design that cannot be altered without consideration of the effects on 
safety. As discussed previously in this section, the final rule 
includes a new requirement for CDCCLs affecting fuel tank flammability.
    Some of the data that STC and field approval holders may need are 
already normally provided to operators in the airplane flight manual, 
including fuel management information and airplane climb rates. For 
other necessary data, such as fuel tank thermal characteristics, we 
believe that the market will promote business agreements where TC 
holders will make their data available to customers willing to pay for 
the data. Airbus or other TC holders may make a business decision not 
to support their customers and provide these data. In these cases, it 
may be necessary for the operator or STC applicant to acquire the data 
from other sources. Another option is for applicants to provide a Monte 
Carlo analysis based on conservative inputs for parameters where no 
data are available. For example, an applicant could provide thermal 
characteristics data that are conservative so that detailed testing and 
confirmation of data from flight testing of an airplane would not be 
required. Finally, if these approaches are not practical, the 
information needed to conduct the Monte Carlo analysis could be 
obtained from in-service airplanes.\24\
---------------------------------------------------------------------------

    \24\ Most of the STCs that could be affected by this rulemaking 
are auxiliary fuel tanks that use pressurized air to transfer fuel. 
In these cases, the inputs needed for the Monte Carlo assessment are 
simplified because the fuel tank pressure is controlled to provide 
fuel transfer, and the temperature changes of the fuel tank are 
limited because the fuel tank is located in the cargo compartment.
---------------------------------------------------------------------------

I. Methods of Mitigating the Likelihood of a Fuel Tank Explosion

1. Alternatives to Inerting
    In the IRE, we selected the use of onboard nitrogen inerting to 
assess the costs of reducing fuel tank flammability. By doing this, 
several commenters thought we were mandating fuel tank inerting as the 
only acceptable means of compliance. ATA and Bombardier commented that 
the proposal is not a performance-based rule, since it ``effectively 
prescribes the use of fuel tank inerting.'' ATA also stated that they 
were not aware of any existing or emerging FRM or IMM that would meet 
the proposed performance-based requirements other than inerting. 
Frontier Airlines questioned why we focused on FRM and IMM as methods 
of compliance when the FAA concluded that other solutions were better 
and more practical.
    This rule does not mandate fuel tank inerting as the only 
acceptable means of compliance. Rather, it establishes performance-
based requirements that allow applicants to choose the FRM or IMM that 
best suits their particular airplane design, so long as it meets the 
performance requirements of this final rule. While the Initial 
Regulatory Evaluation is based upon the use of inerting, this 
technology was chosen because it is considered the most cost-

[[Page 42472]]

effective based upon extensive review by industry experts on the ARAC.
    Technology now provides a variety of commercially feasible methods 
to accomplish the vital safety objectives addressed by this rule. 
Advisory Circular 25.981-2 discusses a number of technologies other 
than fuel tank inerting that can be used for demonstrating compliance. 
For example, many auxiliary tank manufacturers are considering 
pressurizing the fuel tanks to reduce flammability, and many military 
airplanes use IMM consisting of polyurethane foam. One recent applicant 
has proposed FRM incorporating pressurization of the fuel tanks and a 
fuel recirculation system that circulates fuel to the outboard wing to 
cool the fuel. Therefore, we believe that other technologies are 
available.
    ATA commented that we should consider convening an industry study 
group to re-examine the potential of higher flash point fuel as a 
possible alternative method for reducing flammability and overall 
airplane level risk. ATA noted that refineries may now be capable of 
producing higher flash point fuels in the near term in sufficient 
quantity for commercial aviation use. In addition, Boeing advised ATA 
that a 10 [deg]F elevation in the flash point standard for Jet A could 
effect a reduction in flammability exposure rates approximately 
equivalent to the proposed FRM. While ATA acknowledged the likelihood 
is not high that this approach would provide a more cost-effective 
solution than FRM, particularly in the long term, it deserves 
reconsideration. The UK Air Safety Group, through one of its members, 
agreed with ATA and suggested the use of higher flash point fuels (such 
as JP-5) should be investigated as a possible solution.
    While we welcome the potential for using various forms of FRM, we 
do not believe delaying implementation of the rule is in the public's 
interest. The FAA and industry participated in ARAC activities that 
provided economic analysis of existing technologies, including inerting 
and mandatory use of higher flash point fuels. At that time, inerting 
was found to be a more cost-effective means of showing compliance with 
the performance-based FRM rule. In contrast, as shown in the ARAC 
report,\25\ using higher flash point fuels was not the most practical 
means of achieving the desired safety level because of the higher cost 
of these fuels.
---------------------------------------------------------------------------

    \25\ Document Number FAA-22997-7 in the docket for this 
rulemaking.
---------------------------------------------------------------------------

    If technology and refining capabilities have advanced to the point 
where higher flash point fuels are available in quantity at a 
competitive cost, the industry may use that means to show compliance, 
and this means is discussed in the proposed AC 25.981-2. Flammability 
assessments with a specified minimum fuel flash point, in conjunction 
with airplane flight manual limitations requiring use of such fuel, 
could be used as a means of compliance with this rule. Since the rule 
is performance-based and does not mandate any particular solution, 
industry may find innovative ways to show compliance to standards.
2. Inerting Systems Could Create Ignition Sources
    Transport Canada expressed concern that adding inerting systems to 
fuel tanks may create ignition sources and result in additional heating 
of in-fuselage tanks. It argued the solution may inadvertently increase 
flammability exposure. Transport Canada recommended the FRM be designed 
to ensure its reliable operation and minimal maintenance. The UK Air 
Safety Group, through one of its members, also expressed this concern. 
The commenter suggested that inerting systems could actually compromise 
the fuel tank system, that insulation could impede inspections of 
equipment and structure, and that ventilation could cause performance 
penalties.
    We acknowledge the commenters' concerns that installing FRM could 
introduce negative safety consequences. However, these potential 
consequences do not outweigh the safety benefits of flammability 
reduction. As with all safety equipment, the FRM must comply with the 
existing applicable airworthiness standards that are intended to 
prevent system failures from having a negative safety impact. In 
addition, we have introduced new requirements in this rule to address 
the possible negative safety impact of using an onboard nitrogen 
inerting system. Compliance with these combined requirements should 
produce systems that are reliable, maintainable, and meet the 
flammability requirements of this rule.
3. Instruments to Monitor Inerting Systems
    ATEXA recommended that when a nitrogen dilution system is used, the 
airplane should be equipped with instruments to verify that the system 
is functioning as expected. These instruments should record data 
continuously so the pilot can control the oxygen concentration in the 
tanks within prescribed limits on the ground, before take-off, and at 
landing. This data should also be recorded in the flight data recorder 
so that, should another accident happen, the cause/origin could be 
identified.
    As we stated before, this rule is performance based and allows 
designers the ability to be innovative. The need for indications and 
controls is design dependent, and the blanket requirement recommended 
by ATEXA could be overly stringent. DAHs may choose to provide flight 
crew indications of FRM status, or they may propose an automated FRM 
with built-in test to verify proper operation. It would be 
inappropriate for the rule to mandate specific design features.
    As for the suggestion to record data, adding additional parameters 
to the FDR would be cost-prohibitive. Furthermore, we do not consider 
this necessary because the functioning of any FRM or IMM would likely 
not have any direct bearing on determining the cause of an accident. 
The flammability exposure of the fuel tank is not actually an indicator 
that a tank has exploded and the determination that a fuel tank 
explosion caused an accident could be made using physical evidence.
    In a related comment, the Shaw Aerospace team (Shaw) commented that 
failure monitoring of system operation is inadequate. As proposed, the 
system relies totally on the built-in test to detect when the tanks are 
not inert due to a failure rather than direct measurement of the fuel 
tank oxygen concentration to determine if the tank is flammable. Shaw 
cited factors such as oxygen evolution from the fuel as the airplane 
climbs and local areas of high oxygen in the tanks because of lack of 
adequate nitrogen distribution as sources of flammability that will not 
be detected by monitoring the performance of the FRM, rather than 
measuring the oxygen concentration in the tank. Shaw stated that if the 
oxygen concentration in the fuel tank ullage is not monitored and 
periodically sampled, it would be difficult to prove the effectiveness 
of the system.
    From the Shaw team's comments, we infer that Shaw believes the 
monitoring requirements should be modified to require ullage sampling 
to ensure that the tank remains non-flammable. We do not agree that a 
change to the proposed regulation is needed. Compliance methods are 
discussed in AC 25.981-2. Applicants may choose to measure fuel tank 
oxygen concentration directly or infer the concentration through system 
performance capability and monitoring. Appendix M25.2 requires that 
localized higher concentrations of oxygen that

[[Page 42473]]

might result from inadequate distribution of nitrogen, as well as the 
possible effects of oxygen evolution from the fuel, be addressed in the 
compliance demonstration.
4. Risk of Nitrogen Asphyxiation
    If fuel tank inerting is used to reduce the flammability exposure 
of a fuel tank, several commenters noted that the introduction of 
nitrogen enriched air within the fuel tank, and possibly in 
compartments adjacent to the tank, could create additional risk because 
of the lack of oxygen in these areas. They believe the risk to 
maintenance personnel from nitrogen asphyxiation may exceed any safety 
benefit that fuel tank inerting may provide. To support their position, 
these commenters cited the Fuel Tank Inerting Harmonization Working 
Group's (FTIHWG) 2002 Final Report (24-81 lives could be lost between 
2005-2020 due to asphyxiation while servicing transport airplanes) and 
other industrial accident data showing that oxygen depleted atmospheres 
account for significant loss of life. The commenters are concerned that 
we have failed to consider this potential loss of life that will result 
from this rule.
    We acknowledge that special precautions are needed for worker entry 
into confined spaces where fuel vapors or nitrogen enriched air may be 
present. The standard practice of U.S. industry today is to comply with 
existing Occupational Safety and Health Administration (OSHA) 
requirements. These requirements have resulted in ventilating fuel 
tanks with air and measuring the oxygen concentration before entry into 
a fuel tank. In addition, persons entering a fuel tank must wear 
respirators as well as oxygen monitors to alert them should the oxygen 
concentration be insufficient.
    The introduction of nitrogen into a fuel tank does not change the 
existing requirements for personnel to enter a fuel tank. No new 
training or changes to fuel tank entry procedures should be needed as a 
result of this rule. Since there are already specific OSHA requirements 
for fuel tanks that would prevent any fatalities, any loss of life 
would be due to non-compliance with OSHA regulations, not this 
rulemaking. Despite these existing OSHA requirements and the 
protections they afford, we have added new requirements for markings to 
notify workers at all access points and areas of the airplane where 
lack of oxygen could be a hazard. For these reasons, we have not 
included costs for loss of life due to asphyxiation in the final 
regulatory evaluation for this rulemaking.
    We are also not persuaded by the commenters' reference to the 
FTIHWG 2002 Final Report. The predicted number of fatalities in that 
report is based upon application of data from every possible cause of 
nitrogen asphyxiation that is included in data collected between 1980 
and 1989 by the U.S. National Institute of Occupational Safety and 
Health. The data quotes a total number of fatalities for all causes, 
including cases such as bottled nitrogen being hooked up to oxygen 
systems at a nursing home. This bulletin is not based upon data that 
can easily be applied to the aviation industry and does not provide any 
data that could be used to predict a rate of fatalities for the 
specific circumstances relating to airplane fuel tank safety. In 
addition, we do not think it is appropriate to extrapolate the data 
from the bulletin without taking into account existing OSHA 
requirements used in the aviation industry or that the placards 
required by this rule will heighten awareness to the risks associated 
with entering fuel tanks.
5. Warning Placards
    This rule attempts to reduce the risk of nitrogen asphyxiation by 
requiring markings on the access doors and panels to the fuel tanks 
with FRMs, and to any other enclosed areas that could contain hazardous 
atmosphere. These markings will warn maintenance personnel of the 
possible presence of a potentially hazardous atmosphere. Bombardier 
commented that the use of placards and the exact wording proposed is 
too prescriptive. Bombardier recommended the rule require a general 
warning, with guidance defining methods of compliance placed in the 
corresponding AC 25.981-2.
    The requirement for placards is based upon methods used throughout 
aviation and other industries where safety warnings are needed to 
protect workers from possible harm. Locating the requirements in the 
regulation rather than in advisory material provides appropriate level 
of regulatory review of this safety critical information and will 
result in standardizing the means of warning maintenance personnel. 
Applicants may apply for a finding of equivalent safety should they 
wish to propose an alternative means of achieving the level of safety 
provided by the placard requirement in the rule.
6. Definition of ``Inert''
    A fuel tank is considered inert when the bulk average oxygen 
concentration within each compartment of the tank is 12 percent or less 
from sea level up to 10,000 feet altitude, then linearly increasing 
from 12 percent at 10,000 feet to 14.5 percent at 40,000 feet altitude, 
and extrapolated linearly above that altitude.
    Several commenters, including Airbus, AAPA, AEA and Blaze Tech, 
questioned whether an allowable oxygen concentration of 12 percent 
would inert a fuel tank. They pointed to comments in an FAA research 
document stating that ``(f)urther experiments to examine the trend of 
peak pressure rise as a function of both altitude and oxygen 
concentration are needed.'' The commenters stated that this is an 
indication that the 12 percent oxygen concentration limit would not 
prevent the ignition of fuel vapors from rupturing an airplane fuel 
tank and that further work is necessary before accepting the 12 percent 
value. American Trans Air and ATEXA noted that the chemical process 
industry, as quoted by the French National Institute for Research and 
Security (INRS, 2004), uses a safety factor of 0.5 for industrial 
volumes on non-homogenous fuels, and operators must strive to maintain 
a maximum oxygen content of 5 percent for inerting purposes. Based on 
this, American Trans Air and ATEXA stated that the 12 percent limit 
would not be safe.
    In 1997, we initiated research activity to determine a maximum 
oxygen concentration level at which civilian transport category 
airplane fuel tanks would be inert from ignition sources resulting from 
airplane system failures and malfunctions. Our testing determined that 
a maximum value of 12 percent was adequate at sea level. The 12 percent 
value was initially based on the limited energy sources associated with 
an electrical arc or thermal sparks that could be generated by airplane 
system failures and lightning on typical transport airplanes and was 
not intended to include events such as explosives or hostile fire.\26\ 
As a result of this research, we learned that the quantity of nitrogen 
needed to inert commercial airplane fuel tanks was less than previously 
believed. An effective FRM can now be smaller and less complex than 
earlier systems that were designed to meet the more stringent military 
standards intended to prevent ignition from high energy battle damage.
---------------------------------------------------------------------------

    \26\ These test results are available on our Web site: http://www.fire.tc.faa.gov/pdf/tn02-79.pdf as FAA Technical Note ``Limiting 
Oxygen Concentrations Required to Inert Jet Fuel Vapors Existing at 
Reduced Fuel Tank Pressures,'' report number DOT/FAA/AR-TN02/79.
---------------------------------------------------------------------------

    The 12 percent value is further substantiated by the results of 
live fire testing conducted by China Lake Naval Weapons Center that 
showed a 12 percent oxygen concentration prevents

[[Page 42474]]

ignition, even when high energy incendiary rounds were used that had 
ignition energies well in excess of any source anticipated to occur on 
a commercial airplane. These data show that 12 percent oxygen 
concentration for commercial airplanes achieves a comparable level of 
protection against catastrophic fuel tank explosions as the traditional 
9 percent value used by the military for combat airplanes. The 
suggestion that the oxygen concentration should be limited to 5 percent 
is impractical for commercial airplanes since a significantly larger 
flammability reduction system would be needed and, based upon these 
test results, there would be no appreciable improvement in airplane 
safety.
    Finally, the quoted FAA comment that additional testing is needed 
was taken out of context. The recommendation for additional testing 
referred to conditions when the oxygen concentration was between 1 to 
1.5 percent greater than the limit of 12 percent. Testing at these 
higher oxygen concentration values was not extensive since the focus of 
the testing was to establish the limiting oxygen concentration where 
ignition was not possible. Our report's suggestion that additional 
experiments are needed was not an indication that the 12 percent limit 
was inadequate--quite the opposite. In fact, the next sentence of the 
report confirms the importance of the study's validation of the 12 
percent limit: ``The results contained in this report should be useful 
in the design, sizing, and optimization of future airplanes inerting 
systems and add to the overall knowledge base of jet fuel flammability 
characteristics.'' \27\
---------------------------------------------------------------------------

    \27\ Document FAA-22997-14, Executive Summary.
---------------------------------------------------------------------------

7. Use of Carbon Dioxide
    An individual commenter stated that inerting a fuel tank with 
carbon dioxide may introduce new concerns because of the solubility of 
this gas in fuel and the possible effects on fuel system operation. 
This commenter also wanted to know what the acceptable level of oxygen 
would be to consider the fuel tank ullage inert when this gas was used.
    We acknowledge the use of carbon dioxide for inerting may require 
special considerations for fuel feed system performance. The subject of 
inerting with carbon dioxide is addressed in AC 25.981-2 and we have 
revised it to highlight these concerns. As for the commenter's specific 
question about oxygen concentration in the fuel tank, the acceptable 
level of oxygen is the same as if nitrogen is used.
8. Environmental Impact of FRM
    The UK Air Safety Group, Phyre Tech and one individual questioned 
the environmental impact of using FRM to displace air and fuel vapor 
from the fuel tanks into the surrounding environment. These commenters 
expressed concern about increased hydrocarbon emissions into the 
atmosphere.
    The IRE did not include an environmental assessment or analysis 
because we determined the environmental impact of a FRM or IMM to be 
negligible. Their installation will not affect the amount of fuel 
vapors and hydrocarbon emissions that are discharged from fuel tanks 
during refueling. Currently, fuel tank designs vent fuel vapors and 
hydrocarbon emissions into the atmosphere when air is exhausted from 
the fuel tanks during refueling and flight. Data from recent flight 
tests of a Boeing 737 equipped with a nitrogen-based FRM showed that 
installation of FRM and related design changes actually reduce the 
amount of hydrocarbons vented from the tanks during flight.\28\ In 
those test flights, the data indicated that pressure differences from 
one wing tip to the other wing tip, where the two airplane fuel tank 
vent outlets are located, resulted in cross flow of air through the 
fuel tanks including the center wing tank for the original vent 
configuration. This occurred often in flight and periodically on the 
ground when any crosswinds were present. As a result, fuel vapors were 
exhausted from the fuel tanks into the atmosphere. Any air that entered 
the fuel tank diluted the nitrogen concentration in the tank such that 
the fuel tank vent outlets needed to be modified to prevent cross flow 
of air through the vent system. Modification of the vent system 
resulted in reduced hydrocarbon discharge to the atmosphere.
---------------------------------------------------------------------------

    \28\ Data from flight testing on the Boeing 737 (DOT/FAA/AR-01/
63, ``Ground and Flight Testing of a Boeing 737 Center Wing Fuel 
Tank Inerted With Nitrogen-Enriched Air,'' dated August 2001).
---------------------------------------------------------------------------

9. Current FRMs Fail To Meet Requirements
    Transport Canada noted that an FRM must meet not only the 
requirements in this rule, but also the relevant other sections within 
part 25, in particular Sec.  25.1309. Transport Canada stated that 
current FRM designs would not meet Sec.  25.1309 because of a lack of 
system redundancy, a lack of appropriate system performance monitoring 
and indication, and the allowance of MMEL relief.
    We do not agree that existing FRM systems do not meet all the 
relevant sections of part 25, including Sec.  25.1309. We approved the 
FRM systems for the Boeing 747-400 and 737NG series airplanes in August 
2005, and December 2006, respectively, as showing compliance with all 
the applicable part 25 regulations. This approval was validated by EASA 
shortly thereafter. While the commenter is correct that these systems 
lack redundancy, and limited dispatch with the systems inoperative is 
allowed under the MMEL, these systems are supplementary safety systems 
that are intended to work in combination with the ignition prevention 
features required by Sec.  25.981 to prevent future fuel tank 
explosions.
10. FRM Based on Immature Technology
    Airbus had numerous objections regarding our description of the 
prototype hybrid onboard inert gas generation system (OBIGGS) that was 
tested on an Airbus A320 in 2003. Airbus objected to the OBIGGS being 
called a ``prototype.'' Instead, Airbus would characterize the OBIGGS 
as ``laboratory demonstration equipment.'' Airbus (and AEA) commented 
that the OBIGGS was not in an advanced state of development and would 
require extensive development before it reached a level of maturity 
suitable for certification and operation. Airbus also stated that we 
have not identified to Airbus an existing regulation that would require 
Airbus to develop an FRM, and Airbus is not committed to any such 
development program. British Airways also expressed concerns that the 
proposed systems have not been fully tested or developed and operators 
may find themselves required to install a system that is not yet fully 
certified.
    We acknowledge that the development and certification of a 
production and retrofit FRM would require significant engineering and 
development. While the FRM equipment (i.e., FAA-developed prototype 
OBIGGS) installed and flown on an Airbus airplane had not been 
certified, an FRM system similar in concept was designed, tested, and 
certified on Boeing 737 and 747 series airplanes within two years of 
the Airbus demonstration flights. This certification demonstrates that 
the technology is mature, and that our proposed two-year compliance is 
reasonable and achievable. The harmonized certification requirements 
for the Boeing 737 and 747 FRM, which were nearly identical to those 
proposed in the NPRM, were published as Special Conditions in 2005 for 
public comment.

[[Page 42475]]

This provided the public, including Airbus, with detailed information 
needed to develop an FRM. In addition, much of the hardware and 
components needed for an FRM have been developed by aerospace 
manufacturers and this developmental work should reduce the time needed 
for Airbus to develop a system.
    During development of the NPRM, Airbus provided us with a cost 
analysis for an FRM that included the cost of engineering, components 
and operation of the system. We trust that the cost information was 
based upon initial engineering assessments of FRM and contact with 
component vendors. We concur with Airbus that, prior to this final 
rule, there was no regulation that would require a flammability 
reduction means to be developed and installed. However, since the NPRM 
was published, two Boeing 737 and two Boeing 747 airplanes have been 
delivered with operational FRM based upon nitrogen inerting technology. 
These systems have performed very well and provide an indication that 
the technology is mature for application to commercial aviation. In 
addition, in its March 5, 2007, letter, Airbus confirmed information it 
shared with FAA in November 2006, that Airbus is proceeding with the 
development of an FRM (Docket No. 22997-149).

J. Compliance Dates

    The Families of TWA Flight 800 Association, Inc., as well as 
several members of the public, commented that the compliance times are 
too long and should be shortened. While we understand the commenters' 
frustration with the proposed compliance times, the schedules chosen 
are based on the industry's ability to respond to this rule. Each DAH, 
operator, and after-market modifier will have to follow a series of 
steps to make appropriate assessments and develop designs and 
installation plans. Designing FRM for each affected airplane model will 
require engineering resources; allowing less than 24 months for 
developing the design changes is not practical and could result in 
unintended reduction in airplane safety because of increased likelihood 
of design errors. Accelerating the retrofit schedule could 
significantly increase the cost of the program due to the need to 
introduce FRM into operators' fleets during lengthy out-of-sequence 
maintenance visits. We believe that the schedules chosen correctly 
balance the risk of a fuel tank explosion during the compliance period 
with the industry implementation capability.
1. Part 26 Design Approval Holder Compliance Dates
a. Submitting the Flammability Exposure Analysis
    Boeing requested that proposed Sec.  25.1815(b)(1) (now Sec.  
26.33(b)(1)) be revised to remove the compliance time (i.e., 150 days 
after the effective date of the rule) for TC holders to submit the 
flammability exposure analysis for affected airplane fuel tanks. Boeing 
stated that a large amount of test data is required to develop the 
analysis and, as such, a compliance time of 150 days would be 
inadequate. They believe this requirement is primarily for program 
planning purposes and that the compliance time in Table 1 of proposed 
Sec.  25.1815(d) is appropriate for that purpose.
    Embraer and Bombardier similarly commented that the 150-day 
compliance time for submitting the flammability analysis is inadequate. 
The basis for their comment was that validation of fuel tank thermal 
models will require developing new flammability tools and flight 
testing, which will require additional time. Embraer proposed a 24-
month compliance time, and Bombardier proposed a 12-month compliance 
time.
    We believe the proposed compliance time is adequate. It will ensure 
that the flammability exposure analyses are completed for every 
affected fuel tank in a timeframe we consider acceptable because of the 
reduced amount of work required for conventional unheated aluminum wing 
tanks. These analyses will determine if FRM is required for a given 
fuel tank, and the timeliness of completing the analysis is needed to 
meet the design and implementation schedule. As discussed earlier, we 
have revised proposed Sec.  25.1815(b)(2) (now Sec.  26.33(b)(2)(i)) of 
the final rule to allow TC holders to avoid performing the flammability 
analysis for particular tanks by stating in their compliance plans that 
they will treat the tank as high flammability and develop FRM or IMM, 
as required. In addition, no flammability analysis will likely be 
required to determine the flammability of the center wing tanks of 
Boeing and Airbus models, since we have determined from their comments 
that these models exceed the 7 percent limit. We have also 
significantly reduced the complexity of fuel tank thermal analyses that 
will be required by the industry because we modified the analysis 
requirements to allow a qualitative flammability assessment for 
conventional unheated aluminum wing tanks. No flight testing would be 
needed to gather data for conventional unheated aluminum wing tanks.
    For the remaining tanks for which a flammability assessment is 
needed, the DAHs have been aware of the need to address fuel tank 
flammability and have conducted testing of airplanes to develop fuel 
tank thermal models. Therefore, additional time should not be needed to 
develop fuel tank thermal modeling for the majority of fuel tanks in 
the fleet. We believe 150 days is sufficient to complete the required 
analyses, and have made no change to the compliance time in the final 
rule.
b. Submitting a Compliance Plan for Developing Design Changes and 
Service Instructions
    Under proposed Sec.  25.1815(h), each holder of an existing TC 
would need to submit to the FAA Oversight Office a compliance plan for 
developing design changes and service instructions within 210 days of 
the effective date of the rule, which equals 60 days after the 
compliance date for submitting the flammability analysis. Embraer and 
Bombardier claimed developing a compliance plan within 60 days of 
submitting the flammability analysis was impractical. They based their 
objections on the fact that Boeing and Airbus, who are specifically 
cited in the NPRM, were already preparing for compliance prior to 
publication of the NPRM. They claimed that those DAHs not cited in the 
NPRM are not doing advanced preparation and will need extra time.
    While Airbus acknowledged that 210 days is a reasonable timeframe, 
Airbus was concerned about how this timeframe would accommodate delays 
caused by our review. For example, if the TC holder delivers a 
flammability analysis which indicates a value under 7 percent, and, 
after review, the FAA identifies failings resulting in a value above 7 
percent, the TC holder would then have significantly less time to draw 
up any potential compliance plan. Airbus stated that, in such cases, it 
could be unreasonable for us to require the TC holder to comply within 
210 days. Therefore, Airbus suggested that we consider removing the 
fixed time period of 210 days and allow 60 days after the FAA and TC 
holder have agreed that the correct result is greater than 7 percent. 
It noted the requirements on operators of such airplanes should also be 
adjusted by a similar time.
    We do not agree with this suggestion. Airbus provided comments to 
the NPRM that its airplane models have HCWT with flammability that 
ranges between 9 and 16 percent. Boeing has

[[Page 42476]]

previously provided a statement to the FAA in response to SFAR 88 
evaluations that all of its airplane models with HCWT are above the 7 
percent value that determines when an FRM or IMM is needed. Based upon 
this information we have determined that all Boeing and Airbus models 
specifically listed in proposed Sec.  25.1815 (now Sec.  26.33) have 
center wing fuel tanks that will require an FRM or IMM. Since the 
analysis needed to determine whether the affected tanks would require 
an FRM or IMM is already completed, Airbus and Boeing can begin 
developing compliance plans for design changes immediately after 
publication of this final rule. Similarly, if Embraer and Bombardier 
believe their tanks may be high flammability, they should also begin 
developing compliance plans for design changes immediately after 
publication of this final rule.
c. Service Instruction Submittal Dates
    Airbus and Boeing recommended that the compliance dates for each 
airplane model shown in Sec.  25.1815(d), Table 1, be replaced by a 
specific time period for all airplanes in the table. Boeing suggested 
the same two-year compliance period be applied to all affected models 
to allow adequate time to complete design development, validation and 
certification of flammability reduction systems, and development and 
validation of service bulletins. Boeing stated that this two-year 
period would provide the required timing for airline coordination and 
parts procurement flow time needed to support the beginning of the 
retrofit period. Airbus suggested 36 months is required to develop the 
system design and that an additional 6 months should be provided to 
allow for an in-service evaluation of the FRM so that any problems with 
the design could be identified and corrected before implementation into 
the fleet by the operating rules. Embraer requested a compliance time 
of 48 months to develop the design change. Cathay similarly commented 
that, while Boeing is making advanced preparations, Airbus is not. 
Cathay also requested that the compliance time be extended to support a 
more ``realistic'' FRM development schedule. Cathay also commented that 
the FAA states ``the proposed compliance date is based on the premise 
that the NPRM was to be issued in 2005.'' The new compliance dates need 
to be revised to reflect delays in issuing the final rule. Bombardier 
felt that 24 months for the design changes should only commence once 
the authorities have accepted the design change plan.
    We agree with the commenters that a fixed time for all airplane 
models should be established. We have determined that a 24-month 
compliance time for DAH development of the IMM or FRM is adequate for 
each of the DAHs to complete the task. Since we have determined from 
the comments that the Airbus and Boeing models listed in Table 1 in the 
NPRM require FRM or IMM, no flammability analysis is needed before 
design development begins. The full 24-month time can, therefore, be 
used by Airbus and Boeing to develop the design and service 
instructions for our approval.
    In addition, Airbus and Boeing have had significant notification of 
this rulemaking. In February 17, 2004, we made a public announcement of 
our plans to develop and publish a proposal to require both retrofit 
and production incorporation of FRM or IMM. The NPRM was issued in 
November, 2005, and the rulemaking processing time has provided 
extensive time to develop designs as well as work with suppliers to 
discuss cost and schedule issues. Special conditions for the Boeing 737 
and 747 were published by the FAA and EASA that provided performance 
standards for FRM in 2005. Many of the components in nitrogen based FRM 
systems are similar or identical to components used in military 
applications or pneumatic systems on commercial airplanes. The air 
separation modules used in these systems are based on technology 
currently used extensively in other industries. Therefore, we believe 
Airbus's request to increase the development and certification time 
from 24 months to 42 months, and Embraer's request for 48 months, are 
excessive, and we are confident that 24 months provides adequate time 
for design and service instruction development. Extending this 
compliance time would delay the operators' installation of these 
important safety improvements. Therefore, we have not revised the final 
rule as requested.
2. Operator Fleet Retrofit Compliance Dates
    In proposed Sec. Sec.  91.1509, 121.1117, 125.509 and 129.117, we 
included a Table 1 that contained the interim and final compliance 
dates for operators to complete the installations of IMM, FRM or FIMM 
required by those sections. Table 1 proposed unique compliance dates 
for those affected Boeing and Airbus models with high flammability fuel 
tanks. These dates were selected based upon the availability of service 
instructions and the risk associated with each airplane model.
a. Removal of Unique Compliance Dates for Affected Airplane Models
    Boeing stated that, assuming the FAA concludes that retrofit is 
justified, the compliance time should be 7 years from the date that 
service instructions are available for all airplane models. Boeing 
maintained there is no justification for requiring unique compliance 
times tied to airplane models and recommended deleting Table 1.
    We agree and have removed Table 1 from the final rule. This table 
has been replaced with a standardized compliance date for all affected 
airplanes. As explained below, the new compliance time for all models 
is 9 years from the effective date of this rule. We did not link the 
operators' compliance time to our approval of the service instructions 
because the length of time it will take us to approve the submission 
will depend upon the quality of the submission. While the compliance 
planning provisions are intended to ensure that the submissions are 
approvable, whether they have that effect is within the control of the 
DAHs.
b. Increase Compliance Times From 7 to 10 Years
    The ATA asked that the compliance times be increased from 7 to 10 
years after manufacturers develop the necessary design changes. ATA 
argued that the accident rate is such that there is little risk of 
catastrophic in-flight fuel tank explosion during that period. A 10-
year compliance time would allow all operators to incorporate the FRM 
in heavy maintenance visits instead of only 85 percent of them.
    We partially agree with ATA. As discussed previously, we are 
providing a compliance time of 24 months for all affected manufacturers 
to develop necessary design changes. We have adjusted the compliance 
times in the operational rules to allow 6 years after the effective 
date for compliance by 50 percent of an operator's fleet, and 9 years 
for full implementation, i.e., we are retaining the compliance time of 
7 years after the design changes are developed. The compliance period 
of 7 years for operators to incorporate the design modifications into 
each fleet was selected to allow the vast majority of the FRM or IMM to 
be incorporated during airplane heavy checks and to achieve the safety 
level expected by the public.
    Nevertheless, as ATA noted, 15 percent of the airplanes may need to 
incorporate FRM at a time other than during a heavy check. To address 
this concern and reduce the costs of this rule, we have revised the 
operational requirements of parts 121 and 129 to

[[Page 42477]]

allow a one-year extension for retrofit if the operator elects to use 
ground conditioned air for all airplanes with high flammability tanks 
(i.e., Boeing and Airbus models) for ``actual gate times'' exceeding 30 
minutes when ground air is available at the gate and operational and 
the ambient temperature exceeds 60 degrees F. This approach responds to 
requests for more time to retrofit while providing compensating risk 
reduction by use of ground conditioned air, which reduces flammability 
for airplanes on the ground. We are not including this extension 
provision in part 125, because these airplanes are typically not parked 
at gates where ground conditioned air is available. Also, these 
operators typically only operate one or very few airplanes subject to 
this rule, so they will not encounter the difficulties that ATA 
identified in scheduling large fleets of airplanes for modifications.
    For purposes of this provision, ``actual gate time'' is time when 
the airplane is parked at a gate for servicing and passenger egress and 
ingress. If scheduled gate time is 30 minutes or less, but departure is 
delayed so that airplane is parked for more than 30 minutes, use of 
ground air is required for any period longer than 30 minutes. This 
ensures that heating of tanks (and resulting increased flammability) is 
limited. ``Available'' means installed at the gate. ``Operational'' 
means working, so that an operator is not in violation simply because 
ground conditioned air is out of service for maintenance. Ambient 
temperature is the official temperature at the airport as provided by 
the U.S. National Weather Service or worldwide METAR \29\ weather 
report system. This provision requires revision of operator's 
operations specifications and relevant manuals to ensure that the 
commitment to use of ground air is fully implemented and enforceable. 
In the near future we will be issuing guidance on compliance with the 
conditions for this extension.
---------------------------------------------------------------------------

    \29\ METAR (from the French, ``message d'observation 
m[eacute]t[eacute]orologique r[eacute]guli[egrave]re pour 
l'aviation,'') is a format for reporting weather information. METAR 
means ``aviation routine weather report'' and is predominantly used 
by pilots in fulfillment of a part of a pre-flight weather briefing, 
and by meteorologists, who use aggregated METAR information to 
assist in weather forecasting.
    METAR reports usually come from airports. Typically, reports are 
generated once an hour; however, if conditions change significantly, 
they may be updated in special reports called SPECI's. Some reports 
are encoded by an Automated Surface Observing System located at 
airports, military bases and other sites. Some locations still use 
augmented observations, which are recorded by digital sensors and 
encoded via software, but are reviewed by certified weather 
observers or forecasters prior to being transmitted. Observations 
may also be taken by trained observers or forecasters who manually 
observe and encode their observations prior to their being 
transmitted. Source: Wikipedia, August 2007.
---------------------------------------------------------------------------

c. Interim Compliance Dates
    We proposed interim compliance dates for operators to incorporate 
any FRM or IMM into 50 percent of their affected high flammability 
airplanes within their fleet. Boeing requested we revise Sec. Sec.  
91.1509(d)(1), 121.1117(d)(1), 125.509(d)(1), and 129.117(d)(1) to 
state:
    ``IMM, FRM or FIMM, if required by Sec. Sec.  25.1815, 25.1817, or 
25.1819 of this chapter, that are approved by the FAA Oversight Office, 
are installed in at least 50 percent of the operator's fleet within 4 
years from the date service instructions are available. This does not 
apply for certificate holders with only one airplane in the fleet.''
    Boeing stated that newly delivered airplanes should be included in 
the operator's ``fleet'' for purposes of Table 1. Boeing also commented 
that Table 1 should not be split by individual airplane model, but 
should include all airplanes in a given operator's current fleet. The 
recommended revision to 50 percent of the operator's fleet should also 
specify if this is 50 percent of their fleet operating on the 
compliance date, 50 percent of their fleet that is operating at the 
beginning of the compliance period, or 50 percent of their fleet that 
will be operating at the end of the compliance period.
    We agree that additional clarification is needed on the definition 
of ``50 percent of fleet.'' We intended that the 50 percent figure be 
based on all airplanes that are required to be modified under this rule 
and that are being operated by an operator 6 years after the effective 
date of this rule. Any airplanes transferred or purchased with high 
flammability fuel tanks, would be included in the operator's ``fleet.'' 
Since newly delivered airplanes are not required to be modified, they 
are not included as part of the 50 percent of the fleet to meet this 
requirement.

K. Cost/Benefit Analysis

    As noted in the Regulatory Evaluation Summary, specific comments on 
the quantitative costs and benefits estimates are more completely 
discussed in the FRE. In this section, we only address general economic 
issues that were addressed by the comments.
1. Security Benefits
    In the NPRM, we noted that the potential benefits from preventing 
terrorist-initiated accidents were excluded from consideration in both 
the ARAC reports and the IRE. While the proposed FRM requirements were 
not primarily intended to address terrorist-initiated explosions, we 
invited public comment on possible additional security benefits that 
inerting fuel tanks may provide. In response to this request, we 
received several comments, including the following:
     The NTSB and several individuals supported including 
benefits from prevented consequences of terrorist action in the FRE and 
suggested we should complete a cost/benefit analysis of inerting all 
fuel tanks to address terrorist threats. The NTSB noted that, although 
not intended for missile defense or entirely effective as such, 
flammability reduction systems could mitigate the results of shrapnel 
entering fuel tanks during a terrorist act. Therefore, the NTSB 
recommended that the cost-benefit analysis for the final rule should 
include estimates of potential missile attacks on airplanes. In 
addition, these commenters also supported including possible benefits 
from preventing terrorist actions caused by bombs exploding in the 
airplane.
     CAPA stated that the United States is at a heightened risk 
of terrorist attacks. CAPA noted the aviation industry affects nearly 9 
percent of the U.S. Gross Domestic Product, and suggested that 
terrorists will undoubtedly seek ways to attack the aviation 
infrastructure. CAPA recommended that we should complete a cost benefit 
analysis of inerting all fuel tanks and make recommendations to the 
Department of Homeland Security and aviation industry.
     NATCA commented that there would be an adverse effect on 
the public's confidence in flying if another fuel tank explosion 
occurred.
     Airbus and AEA stated that, in theory, there may be some 
benefit to improving security by installing FRM on airplanes. However, 
they noted that we have no basis for estimating the amount of that 
benefit and they do not believe it to be substantial.
     ATA and FedEx objected to the FAA's including the Avianca 
727 accident in its justification of this rule. They stated that this 
accident, which resulted from a small bomb placed above the center wing 
fuel tank on the previous flight, would not have been prevented by the 
requirements of this rule.
    Based upon the comments received and our review of historical 
evidence, we have not quantified any potential benefits from an FRM 
system preventing a fuel tank explosion caused by a terrorist missile 
or an on-board bomb.
    We have also not quantified the potential benefits from a fuel tank 
explosion being misinterpreted as a terrorist-caused event because such 
an

[[Page 42478]]

outcome is too speculative to include in the main body of the analysis. 
However, we have provided a quantified estimate of the possible 
benefits from preventing this misinterpretation in Appendix A of the 
FRE.
    However, some of the public will cancel or curtail their air travel 
after they discover that the in-flight accident was caused by an 
airplane electrical or mechanical malfunction. An in-flight explosion 
is a catastrophic accident. There is a long history that air travel 
declines for two to three months after a major catastrophic accident. 
We use a study by Wong and Yen, ``Impact of Flight Accidents on 
Passenger Traffic Volume of the Airlines in Taiwan'', in the Journal of 
Eastern Asia Society for Transportation Studies, vol. 5, October 2003, 
to provide an estimate of the potential demand losses from a fuel tank 
explosion.
2. Likelihood of Future Explosions in Flight
    The IRE assumed that all future accidents caused by fuel tank 
explosions will occur in flight. This assumption was based upon an 
evaluation of the flammability exposure times for various flight phases 
that showed the majority of the time fuel tanks are flammable is during 
flight. The method used by us in the IRE to estimate the likelihood of 
future explosions occurring in flight or on the ground was based upon 
an earlier version of the Monte Carlo model, ``Fuel Tank Flammability 
Assessment Method User's Manual, DOT/FAA/AR-05/8.'' This earlier model 
used ground times of 30, 60 and 90 minutes for short, medium, and long-
range airplanes. Using this model, we determined 90 percent of the 
flammability exposure time occurred during flight. We then simplified 
the IRE by assuming all future accidents would occur in flight.
    Our review of recent fleet data collected from in-service airplanes 
indicates that ground times are longer than used in the earlier version 
of the Monte Carlo model. This results in a higher percentage of the 
flammability exposure time being when an airplane is on the ground. In 
addition, the historical accident rate of one accident out of three 
occurring in flight is based upon a limited number of events and is not 
a valid sample size for establishing the future accident rate. Since 
ignition sources may occur at any time during ground or flight 
operations, the ARAC fuel tank study concluded that the likelihood of 
future fuel tank explosions correlates to the flammability exposure of 
a fuel tank. We agree with this conclusion.
    MyTravel Airlines, AEA, Alaska Airlines, ATA, and Airbus stated 
that, the probabilities of an in-flight explosion and an on-the-ground 
explosion is the simple extrapolation of the three events; that is, 
there is a 33.33 percent probability of an in-flight explosion and a 
66.67 percent probability of an on-the-ground explosion. Boeing 
commented that its engineering analysis indicated an 80 percent 
probability of an in-flight explosion and a 20 percent probability of 
an on-the-ground explosion and supported its recommendation with a 
recent flammability assessment using a revised Monte Carlo model. 
Boeing also recommended that a sensitivity analysis be included in the 
regulatory evaluation varying the number of in-flight events by values 
of 33 percent or 50 percent. In the GRA, Incorporated appendix to the 
ATA comment, they noted that using plausible assumptions in FAA's 
model, a better estimate of the percentage of time that a tank is 
flammable would be 78 percent in the air.
    We believe that the appropriate method to evaluate the future risk 
is through a flammability assessment rather than observations of an 
infrequently occurring event. As a result, we agree with the Boeing 
analysis and disagree with the ATA and Airbus analyses and revise our 
risk analysis so that there is an 80 percent probability that an 
explosion will occur in flight and a 20 percent probability that it 
will occur on the ground.
    Finally, we do not agree with Boeing's recommendation to include in 
the FRE an assessment of the sensitivity of varying the ground versus 
flight accidents between 30 and 50 percent. The IRE already included 
variations in many factors that affect the predicted cost and benefits 
and adding another sensitivity factor would not provide useful data for 
determining the need for this rule.
3. Costs to Society of Future Accidents
    Several commenters said the cost of future accidents used in the 
IRE did not include all the costs to society. They said the IRE 
excluded the costs of investigating the accident, cleanup at the 
accident scene, replacement and retraining of flight crew, and any 
design change needed to correct failures of parts or systems on the 
airplane. They added that an accident would also cause a loss of 
confidence in the aviation industry leading to the public reducing 
their airline travel. They requested these additional costs be included 
in the final rule.
    We agree with some of these comments and, as previously discussed, 
we include quantitative estimates of the potential benefits from the 
loss of confidence in aviation transport. We disagree that we did not 
include accident investigation and clean-up costs because the IRE 
contained a specific $8 million cost for the accident investigation. 
Although it may occur that design changes will need to be made, these 
changes would be done via rulemaking or AD and the costs for those 
specific changes would be estimated when proposed.
4. Value of a Prevented Fatality
    AEA and ATA stated that the value of a prevented fatality should be 
3 million dollars. AEA stated there is no basis for using a higher 
value.
    Different government entities use different estimates of the value 
of a prevented fatality. For example, the Environmental Protection 
Agency uses a value of $7 million and the Department of Transportation 
has historically used a value of $3 million (which we used in the IRE). 
There are several different values that have been reported in economic 
literature and there is no one value on which there is universal or 
near-universal agreement. The Office of Management and Budget allows 
agencies to evaluate their cost-benefit analyses using alternative 
values for a prevented fatality in order to evaluate how sensitive the 
analytic results are to the assumed values. Therefore, we believe that 
varying the value to show the range of reasonable effects is 
appropriate and we have included values of $3 million, $5.5 million, 
and $8 million to provide a better understanding of the sensitivity of 
the evaluation to changes in this baseline assumption.
5. Cost Savings if Transient Suppression Units (TSUs) Are Not Required
    The NTSB determined that the probable cause of the TWA Flight 800 
explosion was ignition of the flammable fuel/air mixture in the center 
wing fuel tank. Although the ignition source could not be determined 
with certainty, the NTSB determined that the most likely source was a 
short circuit outside of the center wing tank that allowed excessive 
voltage to enter the tank through electrical wiring associated with the 
fuel quantity indication system (FQIS). We issued ADs mandating 
separation of the FQIS wiring that enters the fuel tank from high power 
wires and circuits on the classic Boeing 737 and 747 airplanes after 
the TWA 800 accident, and this resulted in installation of TSUs as an

[[Page 42479]]

alternative method of compliance with the ADs.
    In the NPRM for this rulemaking, we requested public comment on the 
possible cost savings that would occur if airlines were not required to 
install transient suppression units (TSUs) on the fuel quantity gauging 
systems of the high flammability fuel tanks that would need FRM to 
comply with this rule. We received the following responses:
     Several commenters stated that we need to clarify the 
requirements for design changes resulting from SFAR 88, since they 
believed no additional changes to incorporate TSU would be needed for 
their fleet.
     According to ATA, the cost avoidances would be minor, 
compared to the impact of the ignition-prevention ADs and pending SFAR 
88 maintenance upgrades.
     AEA stated that TSUs will not be removed, so there is no 
cost savings. If the TSUs were removed, additional costs would be 
incurred for certification, service bulletins, manpower, and hangar 
space.
     Airbus and My Travel Airways commented that they 
anticipate no significant savings since only a fraction of the fleet is 
designed with a need for these devices, and the cost of these devices 
is small, compared to the cost of flammability reduction systems.
     Transport Canada commented that ignition prevention should 
not be traded off against flammability reduction. Both should be 
required.
     Qantas stated that, if these devices could be removed from 
its existing fleet, it would realize a significant cost savings in 
operations and maintenance. Qantas also said that the cost of these 
devices is minimal compared to the installation of an FRM, but if the 
FQIS requires replacement of the fuel gauging system to make the 
devices effective, it would be similar in cost to an FRM. However, 
Qantas noted that an FRM may produce a weight penalty such that a FQIS 
replacement would still be preferred.
    Prior to this rule, the findings from the analysis required by SFAR 
88 showed that most transport category airplanes with high flammability 
fuel tanks needed TSUs to prevent electrical energy from airplane 
wiring from entering the fuel tanks in the event of a latent failure in 
combination with a single failure. Since this rule requires FRM or IMM 
to mitigate an unsafe condition by converting these fuel tanks into low 
flammability fuel tanks, TSUs will no longer be needed. Therefore, we 
believe it is appropriate to include this as a cost avoidance of this 
rule. However, based on the comments that installing these TSUs will 
impose a minimal cost, we did not estimate a cost offset for those 
airplanes that would have been required to have TSUs installed but are 
no longer required to do so under this rule.
6. Corrections About Boeing Statements
    Boeing stated that the IRE has several statements that should be 
corrected in the final version. First, Boeing will not provide 
engineering analyses via service bulletins or provide initial aid to 
large airlines and independent third party repair stations. Boeing 
asked that these statements be deleted. Boeing also indicated that it 
will follow the regulatory requirements for providing service 
information. Finally, Boeing pointed out that the IRE improperly 
references STCs where it should be referencing amended TCs.
    We agree with Boeing and have revised these issues in the FRE 
accordingly.
7. 757 Size Category
    Boeing noted that the Model 757 was classified as a small airplane 
in the IRE and suggested that it be included in the medium category. 
Boeing based this on the fact that the Model 757's fuel tank volume and 
airplane performance is similar to that of other airplanes categorized 
as medium-sized by ARAC.
    We agree and have included the Boeing 757 in the medium category 
and have adjusted the weight and cost estimates accordingly.
8. Number of Future Older In-Service Airplanes Overestimated
    Alaska Airlines commented that the IRE overestimated the number of 
older in-service airplanes in future years, which artificially 
increases the benefits of the FRM retrofit requirements. Alaska 
Airlines asserted that industry projects a higher proportion of newer 
airplanes versus older airplanes for the projected benefit period.
    The fleet mix in the IRE was based upon our fleet forecast. 
Therefore, the number of newer airplanes reflected the official FAA 
fleet projections. In the FRE, we have updated the fleet mix data using 
the most recent FAA Aerospace Forecasts Fiscal Years 2006-2017. This 
forecast projects higher retirement rates than those forecasted in the 
FAA Aerospace Forecasts Fiscal Years 2004-2015, which we used in the 
IRE.
9. Revisions to the FRM Kit Costs
    ATA, AEA, AAPA, Federal Express, Airbus, and Boeing suggest that we 
revise the price of the FRM components because the original ARAC 
estimates had not been fully developed and tested and, subsequent to 
this additional development, the FRM kit costs are higher.
    Boeing has provided new kit costs for its various models, which are 
revised from its previous component costs. We agree with Boeing and use 
them in the FRE for production airplanes.
    However, United/Shaw Aero Devices/Air Liquide have recently 
developed an FTI system to retrofit in airplanes and they have reported 
kit costs. As they have a patent for the system and operational 
prototypes, we use the United/Shaw Aero Devices/Air Liquide 
retrofitting kit costs in this analysis.
10. Revisions to the Labor Time To Retrofit FRM Components
    Several commenters reported that the labor hours to retrofit an 
airplane used in the IRE were too low. In its discussions with the 
airlines, Boeing provided an estimated number of labor hours to 
retrofit its kits by model. The ATA reviewed these estimated hours and 
commented that its expected labor hours were approximated 25 percent to 
40 percent higher than the preliminary numbers provided by Boeing. 
Qantas reported that the retrofitting labor hours are 50 percent 
greater than those in the service bulletins.
    However, the United/Shaw Aero Devices/Air Liquide retrofitting kit 
is different from the retrofitting kit on which the ATA based its 
reported hours. As a result, just as we use the United/Shaw Aero 
Devices/Air Liquide retrofitting kit costs, we also use their labor 
hour estimates to install their system.
    However, the labor hours to retrofit these kits will decline over 
time due to mechanics becoming more familiar with the installation 
procedures. T.P. Wright found that an 80 percent learning efficiency 
has been a common occurrence in airplane production. We assume that 
this 80 percent learning efficiency also applies to retrofitting 
operations.
11. Retrofitting Costs per Airplane
    Cathay Pacific and the AAPA commented that the per airplane 
retrofitting costs reported by EASA for an Airbus airplane would be 
between $600,000 to about $1 million (converting Euros into Dollars). 
Airbus provided similar comments.
    In combining the United/Shaw Aero Devices/Air Liquide kit costs and 
their labor hours costs, we calculate that the per airplane 
retrofitting costs will initially be $110,000 to $250,000. Over time, 
these costs will decline by $10,000 to $17,000 per airplane.

[[Page 42480]]

12. Percentage of Retrofits Completed During a Heavy Check
    Airbus commented that the average time between heavy checks is 10 
to 12 years. Thus, 85 percent of the retrofits could not be completed 
within the proposed 8 year time-frame.
    We disagree. Our experience has been that the vast majority of 
airplanes in commercial passenger service in the United States have 
some form of a heavy check no later than every 8 years.
    The AEA commented that 60 percent of the retrofits would be 
completed during a heavy check while ATA commented that 85 percent 
would be completed during a heavy check. In the IRE, we had used 85 
percent.
    We agree with the ATA comment and use the 85 percent value in the 
FRE. Operators who choose to take advantage of the extension allowed by 
use of ground conditioned air will be able to complete the retrofits of 
an even higher percentage of their fleet during heavy checks.
13. Number of Additional Days of Out-of-Service Time To Complete a 
Retrofit
    The ATA commented that retrofitting FRM during a heavy check would 
add two days of out-of-service time, AEA commented that it would add 
two to three days, while Airbus commented that the airlines had told 
EASA that it would add one day.
    In the IRE, we had used two days. We agree with ATA and use two 
days in the FRE for the out-of-service time if the retrofit is 
performed during a heavy check.
    Airbus commented that retrofitting FRM during a medium check would 
add 5 days while it would add seven days if completed during a special 
maintenance visit. In the IRE, we had used four days out-of-service for 
a retrofit performed during a special maintenance visit based on the 
ARAC report. Airbus provided no justification for its disagreement with 
the ARAC conclusion. As we received no comments other than the Airbus 
comment on this topic, we disagree with Airbus and use four days out-
of-service for a special maintenance visit.
14. Economic Losses From an Out-of-Service Day
    Airbus and the ATA commented that the losses to an airline from an 
out-of-service day should be based on the airplane on ground economic 
loss or the loss in net operating revenue, not a pro-rated monthly 
lease rate as used in the IRE.
    We disagree. While it is true that the loss to air carrier A is 
greater than the prorated monthly lease rate, most potential air 
travelers will use alternative air carrier B if air carrier A takes an 
airplane out of service for a short time. Consequently, alternative air 
carrier B receives an economic benefit that is not captured by only 
focusing on the air carrier airplane that is out of service. The FAA's 
responsibility is to cost the potential loss to the aviation system, 
not individual air carriers at specific points in time. This is 
particularly apparent when alternative air carrier B will need to 
remove an airplane from service and air carrier B's air travelers will 
use air carrier A that will receive an economic benefit that is not 
captured by focusing solely on the loss to air carrier B at that 
specific point in time.
    Airbus commented that the FRM cost for its products is 
underestimated by a factor of two to three. Based upon review of all 
comments, including those based upon a certificated FRM provided by 
Boeing, we believe the FAA cost estimates should be revised by a factor 
of 1.6 and we have adjusted the regulatory evaluation accordingly. We 
applied the revised retrofitted airplane costs for the certificated FRM 
systems to all similarly-sized airplane models because we determined 
that the fuel tank inerting systems will be similar for both 
manufacturers.
15. Updated FRM Weight Data
    Boeing provided updated weight data for the flammability reduction 
systems that have been or are being developed for its airplane models. 
Boeing stated that the final weights for the Boeing 747-400 and 737-NG 
systems are known since the designs have been certified. Boeing 
estimated the weight for the Boeing 777 system. As for the Boeing 757 
and 767 systems, preliminary designs indicate these systems will be 
similar and Boeing estimated the weights based upon comparison to the 
other models. Boeing also provided updated estimates for average annual 
flight hours for Boeing airplanes.
    We have revised the weight and annual flight hour data in the FRE 
for production airplanes based on Boeing's updated information. We also 
used this updated data for similarly sized Airbus airplane models.
    United/Shaw Aero Devices/Air Liquide reported that their 
retrofitting kits weigh less than the Boeing kits. We used United/Shaw 
Aero Devices/Air Liquide kit weights for the retrofitted airplanes.
16. Updated Fuel Consumption Data
    Boeing also provided revised annual fuel consumption due to the FRM 
weight and increased bleed flow and ram drag. A GRA, Incorporated 
report that surveyed several air carriers provided current air carrier 
fuel consumption per pound of additional weight.
    For the annual fuel consumption due to the FRM weight, we have used 
the GRA values from the air carriers because we believe the air 
carriers will be more accurate in reflecting their actual usage over a 
variety of flight mission lengths and conditions than the Boeing 
engineers would be. We used the Boeing estimates of the additional fuel 
consumption for increased bleed air flow and ram drag in the FRE. We 
used these rates for both production and retrofitted airplanes because 
United/Shaw Aero Devices/Air Liquide did not provide independent 
estimated rates for their kits.
17. Updated Fuel Cost Data
    Several commenters reported that the $1 per gallon aviation fuel 
cost used in the IRE no longer reflected the economic reality. For a 
cost per gallon, Frontier suggested $2.11, ATA suggested $1.50, Qantas 
suggested $2.00, and Airbus suggested $1.50.
    We agree that the per gallon price of aviation fuel has increased. 
Based on our FAA Aerospace Forecasts Fiscal Years 2008-2025, we 
determined that the average future price per gallon will be $2.01. 
Although this fuel price is based on the most recently published FAA 
forecast, we recognize that, given the current record high oil prices, 
this estimate may underestimate the long term aviation fuel cost.
18. Cost of Inspections
    Air Safety Group, UK commented that the NPRM does not include any 
costs associated with the impact of FRM inspections on flight delays 
and cancellations. The commenter recommended that the cost/benefit 
analysis be revised to take a more realistic account of these 
additional operational costs. Boeing's comments included revised 
estimates of these costs.
    With respect to flight delays and cancellations due to these 
inspections, the DAH requirements allow placing a nonfunctional FRM or 
IMM on the MEL provided the overall system performance meets the 
minimum criteria. We agree with the revised costs from Boeing on the 
costs of delays and cancellations in the FRE and used them for both 
production and retrofitted airplanes.

[[Page 42481]]

19. Inspection and Maintenance Labor Hours
    Boeing commented that the annual labor hours for inerting system 
inspection and maintenance time should be revised to 6 hours for Boeing 
passenger and all-cargo airplanes. Boeing cited design features and 
related fault indication systems that will eliminate the need for 
scheduled maintenance performance checks on the inerting systems. 
Boeing also reported that unscheduled delays will only occur for 
failures that require locking the NGS Shutoff Valve closed.
    We agree with Boeing's estimates for both production and 
retrofitted airplanes and use them in the FRE.
20. Daily Check
    ATA commented that its estimates for inerting system operational 
and maintenance costs are much higher than those used by the FAA. ATA 
stated that 15 maintenance minutes per airplane per day will be 
required and this was not accounted for by the FAA.
    We infer from ATA's comment that ATA believes that our estimated 
maintenance costs should be revised to include a 15 minute daily check 
of the FRM. The inerting system certified by the FAA (and validated by 
EASA) for the Boeing Model 737NG and 747-400 airplanes did not include 
a daily check. Specific features of the design, in conjunction with 
indication systems, removed the need for a daily check. We anticipate 
that Airbus's design will be similar in that the electronic centralized 
airplane monitor will be utilized for FRM status. This would impose no 
greater burden on operators than the FRM systems that have been 
certified to date. As a result, we have not included costs associated 
to a 15 minute daily check of the FRM in the FRE.
21. Spare Parts Costs
    Boeing asked that the inerting system spare parts costs be revised 
based on its updated costs from suppliers. Boeing estimated that the 
air separator/filter capacity and life is directly related to the 
environment in which the airplane is operated. Boeing added that its 
filter installation includes monitoring for excessive pressure drop 
that is used to determine when the filter needs to be replaced. 
Finally, Boeing noted that its expected filter maintenance interval is 
greater than one year for average environmental conditions.
    We agree with the cost information provided by Boeing and used the 
new cost for the filter element replacement in the FRE. While we 
acknowledge the filters will be replaced when the pressure across the 
filter is excessive, Boeing did not provide an expected average filter 
replacement interval. In general, air separator/filters are expected to 
last between 1 and 3 years, depending upon the conditions under which 
the airplane is flown. An annual filter element replacement is a worst 
case situation. As a result, in the FRE, we use an average filter 
element replacement interval of every 2 years.
22. Air Separation Module (ASM) Replacement
    Boeing asked the FAA to revise the cost of ASMs that would need to 
be purchased for replacing modules when they reach their design life. 
The IRE contained estimates ranging from $5,275 to $28,814. Boeing 
stated the revised costs range from $30,520 to $151,000. As United/Shaw 
Aero Devices/Air Liquide did not provide an estimate for this cost 
component, we applied the Boeing estimate to retrofitted airplanes.
    Boeing also requested that the ASM replacement costs be evaluated 
based upon data provided in a table for average annual utilization by 
Boeing airplane model. Boeing believed this data is more realistic of 
model specific fleet utilization. While the IRE assumed an average 
utilization rate of 3,000 flight hours, Boeing's current data for 
different models range from 3,000 to 4,250 flight hours for passenger 
carrying airplanes and 1,000 to 4,250 for all-cargo airplanes. Finally, 
Boeing stated that the design life goal for the ASM remains 27,000 
hours. FedEx commented that a manufacturer had told them that the ASMs 
will need to be replaced every few years.
    We agree with Boeing that the design goal of an ASM replacement 
every 27,000 flight hours will be reached and we use that interval for 
the ASM replacement frequencies in this Regulatory Evaluation.

L. Miscellaneous

1. Harmonization
    Several commenters (Boeing, Transport Canada, Alitalia, AAPA, 
Virgin, Cathay) expressed the need for harmonization of FAA 
requirements with those of other national aviation authorities. These 
commenters noted that harmonization with the other major regulatory 
agencies would benefit the industry and encourage a broader dialogue. 
We agree that harmonization of the fuel tank flammability safety 
requirements is usually desirable. Prior to and throughout the 
development of this rule, we used several avenues to involve other 
foreign regulatory authorities and industry, including:
     Aviation Rulemaking Advisory Committee (ARAC) working 
groups comprised of representatives of foreign regulatory authorities 
and industry and other interested parties were used to review issues 
and provide recommendations for developing and harmonizing this rule. 
EASA, Transport Canada and the Brazilian CTA participated in these 
working groups, which conducted extensive studies of fuel tank safety. 
These studies included a review of the fleet history as well as 
evaluating the various options for improving airplane safety through 
flammability reduction. One working group was created to review fuel 
tank flammability and methods to reduce flammability in the tanks. This 
then led to the creation of a second working group that exclusively 
reviewed fuel tank inerting. The recommendations from these working 
groups became part of the basis for this proposed rule. The 
recommendations from the two fuel tank safety ARAC studies guided our 
rulemaking proposal and this final rule.
     We also participated in an industry and regulatory 
authority group assembled by EASA to review fuel tank flammability 
safety and produce an EASA Regulatory Impact Assessment (RIA). This RIA 
is available on EASA's Web site at (www.easa.eu.int/doc/Events/fueltanksafety_24062005/easa_fueltanksafety_24062005_qa_summary.pdf).
    EASA's RIA recommended production incorporation of FRM on newly 
produced airplanes that have high flammability tanks and EASA has 
indicated that it plans to propose an amendment to their regulations 
applying to new transport airplane designs in CS-25. We anticipate 
harmonization of these requirements. However, EASA has not yet 
determined that FRM retrofit should be required.\30\ We believe the 
fleet operation projections show that the risk of an explosion 
occurring on existing airplanes and newly produced airplanes is 
similar. This safety issue needs to be addressed, despite the lack of 
harmonization, and we have included a FRM retrofit requirement in this 
final rule.
---------------------------------------------------------------------------

    \30\ EASA has commissioned a study to reconsider the 
desirability of a retrofit requirement.
---------------------------------------------------------------------------

    While we remain committed to the goal of harmonization, our primary 
objective in this rulemaking is to improve aviation safety. When we 
determine that the need exists for a certain regulation, and the other 
regulatory agencies find that a more stringent or lenient requirement 
is appropriate, we review their findings

[[Page 42482]]

and will revise our regulation if our regulatory goals are met, an 
equivalent level of safety is achieved, and any additional burden 
imposed on the industry is justified. This is the approach we have 
taken in drafting this rule.
2. Part 25 Safety Targets
    AEA commented that part 25 is missing safety targets and 
recommended the final rule include a specific target for both ignition 
and flammability reduction. This target could be achieved by ignition 
source prevention in combination with flammability reduction. AEA 
proposed the target be the same as for any other catastrophic event in 
transport category airplanes: 10-9 per flight hour.
    We do not agree with AEA's proposal to include a safety target in 
part 25. As discussed previously, because ignition sources are caused 
by human error and other unpredictable factors, it is impossible to 
assign an accurate probability value to them. Therefore, Sec.  25.981 
is based on a balanced approach for preventing fuel tank explosions. 
This section provides both ignition prevention plus an additional 
safety improvement by controlling fuel tank flammability exposure to an 
acceptable level. Today's rule adds requirements for fuel tanks located 
in the fuselage contour and extend the mitigation into the fleet of 
existing airplanes.

IV. Rulemaking Analyses and Notices

Paperwork Reduction Act

    As required by the Paperwork Reduction Act of 1995 (44 U.S.C. 
3507(d)), the FAA submitted a copy of the new (or amended) information 
collection requirement(s) in this final rule to the Office of 
Management and Budget for its review. OMB approved the collection of 
this information and assigned OMB Control Number 2120-0710.
    This rule supports the information needs of the FAA in approving 
design approval holder and operator compliance with the rule. The 
likely respondents to this proposed information requirement are the 
design approval holders such as Boeing, Airbus and several auxiliary 
fuel tank manufacturers as well as operators. The rule requires the 
certificate holders to submit a report to the FAA twice each year for a 
period up to 5 years. Operators who choose to use ground air 
conditioning would be required to provide a one time statement of their 
intent to use this option. The burden would consist of the work 
necessary for:
     DAH to develop flammability analysis reports and the 
service instructions for installation of IMM or FRM.
     DAH to develop changes and incorporate a maintenance plan 
into the existing maintenance programs.
     DAH to provide bi-annual reliability reports for FRM for 
the first 5 years of operation.
     Operators to provide notification to the FAA of their 
intent to use ground air conditioning.
     Operators to record the results of the installation and 
maintenance activities.
    The largest paperwork burden will be a one-time effort (spread over 
3 years) associated with the Design approval holders (TC and STC 
holders) to develop design changes. Operators will also need to update 
their maintenance programs, including maintenance manuals, to include 
the design changes. The basis for these estimates is the industry 
Aviation Rulemaking Advisory Committee report, which provided hours for 
each of the 3 major areas of paperwork. Based on an aerospace engineer 
total compensation rate of $110 an hour, the total burden will be as 
follows:

------------------------------------------------------------------------
                                                            Total cost
  Documents required to show compliance        Hours       (in millions
           with the final rule                               of $2007)
------------------------------------------------------------------------
Application to FAA for Amended TC or STC         405,000          44.550
Documents (Specifications, ICDs, etc.)..          30,900           3.399
Revisions to Manuals (Flight Manuals,             29,500           3.245
 Operations, and Maintenance) for FRM
 Systems................................
                                         -------------------------------
    Total...............................         465,400          51.194
------------------------------------------------------------------------

    As these recordkeeping costs will be spread out evenly over the 
three years, the yearly burden will be $17.065 million and involve 
155,133 hours.
    After this initial 3-year period, this rulemaking would result in 
an annual recordkeeping and reporting burden of 4,000 hours. This 
burden is based on five (5) design approval holders submitting 40 total 
reports per year requiring an average of 100 hours to complete each 
report. All records that will be generated to verify the installation, 
to record any fuel tank system inerting failures, and to record any 
maintenance would use forms currently required by the FAA.
    The FAA computed the annual recordkeeping (Total Pages) burden by 
analyzing the necessary paperwork requirements needed to satisfy each 
process of the rule.
    An agency may not collect or sponsor the collection of information, 
nor may it impose an information collection requirement unless it 
displays a currently valid Office of Management and Budget (OMB) 
control number.

International Compatibility

    In keeping with U.S. obligations under the Convention on 
International Civil Aviation, it is FAA policy to comply with 
International Civil Aviation Organization (ICAO) Standards and 
Recommended Practices to the maximum extent practicable. The FAA has 
determined that there are no ICAO Standards and Recommended Practices 
that correspond to these proposed regulations.

Regulatory Evaluation Summary

Regulatory Evaluation, Regulatory Flexibility Determination, 
International Trade Assessment, and Unfunded Mandates Assessment

    Changes to Federal regulations must undergo several economic 
analyses. First, Executive Order 12866 directs that each Federal agency 
shall propose or adopt a regulation only upon a reasoned determination 
that the benefits of the intended regulation justify its costs. Second, 
the Regulatory Flexibility Act of 1980 (Pub. L. 96-354) requires 
agencies to analyze the economic impact of regulatory changes on small 
entities. Third, the Trade Agreements Act (Pub. L. 96-39) prohibits 
agencies from setting standards that create unnecessary obstacles to 
the foreign commerce of the United States. In developing U.S. 
standards, this Trade

[[Page 42483]]

Act requires agencies to consider international standards and, where 
appropriate, that they be the basis of U.S. standards. Fourth, the 
Unfunded Mandates Reform Act of 1995 (Pub. L. 104-4) requires agencies 
to prepare a written assessment of the costs, benefits, and other 
effects of proposed or final rules that include a Federal mandate 
likely to result in the expenditure by State, local, or tribal 
governments, in the aggregate, or by the private sector, of $100 
million or more annually (adjusted for inflation with base year of 
1995). This portion of the preamble summarizes the FAA's analysis of 
the economic impacts of this final rule. We suggest readers seeking 
greater detail read the full regulatory evaluation, a copy of which we 
have placed in the docket for this rulemaking.
    In conducting these analyses, the FAA has determined that this 
final rule: (1) Has benefits that justify its costs, (2) is an 
economically ``significant regulatory action'' as defined in section 
3(f) of Executive Order 12866, (3) is ``significant'' as defined in 
DOT's Regulatory Policies and Procedures; (4) will have a significant 
economic impact on a substantial number of small entities; (5) will not 
create unnecessary obstacles to the foreign commerce of the United 
States; and (6) will impose an unfunded mandate on state, local, or 
tribal governments, or on the private sector by exceeding the 
previously identified threshold. These analyses are summarized as 
follows.
Aviation Industry Affected
    The rule affects Boeing, Airbus, and operators of certain Boeing 
and Airbus airplanes that have heated center wing tanks (HCWTs).\31\
---------------------------------------------------------------------------

    \31\ The following airplane models are not included as HCWT 
airplanes: B-717; B-727; certain B-767 and B-777 models, A-321, A-
330-200 and A380. In addition, the B-787 is not included because it 
needs FRM to comply with its existing Part 25 certification 
requirements.
---------------------------------------------------------------------------

Disposition of Comments
    There were many comments on the Initial Regulatory Evaluation (IRE) 
associated with FRM. We accepted many of these comments. However, the 
volume and the technical nature of these comments require a more 
detailed response than is possible in this summary. As a result, the 
complete disposition of the economic comments and their effects on the 
economic analysis are contained in the complete Final Regulatory 
Evaluation, which is filed separately.
Period of Analysis and Affected Airplanes
    The period of analysis begins in 2008 and concludes in 2042. We 
used a 10-year time period (2008-2017) to calculate the equipment 
installation costs for airplanes affected by the final rule. The end of 
the analysis period of 2042 captures the full operative lives of the 
2009-2017 production airplanes.
    The airplanes affected by the final rule include passenger 
airplanes with HCWTs manufactured prior to the 2009 production cut-in 
date. These airplanes will need to be retrofitted with FRM by 2017. In 
addition, these affected airplanes also include all production 
passenger and cargo airplanes with HCWTs that will be manufactured 
between 2009 and 2017 (except the B-787 and A380 that will be 
manufactured with FRM. Cargo airplanes manufactured before 2009 and 
cargo airplanes that have been or will be converted from passenger 
airplanes (conversion cargo airplanes) are not included unless FRM was 
installed while the airplane was used in passenger service.
    Airplanes have an average 25-year life expectancy. Thus, the 2009 
production airplanes will be retired in 2033 and the last of the 
production airplanes in this analysis (those produced in 2017) will be 
out of service by 2042. Similarly, all of the pre-2009 existing 
airplanes requiring retrofitting will be retired by 2033 (the 2008 
production airplanes will be the last year of production airplanes will 
not have FRM installed as original equipment). Thus, the maintenance 
and fuel costs will begin in 2009 and continue to 2042 for production 
airplanes and will begin in 2010 and continue to 2033 for retrofitted 
airplanes.
    During the analysis period the final rule will affect an estimated 
5,110 airplanes, 5,022 retrofitted and production passenger airplanes 
(2,732 retrofitted and 2,290 production) and 88 production cargo 
airplanes (see Table 1). These airplanes will fly 370 million hours, 
364 million for passenger airplanes and 6 million for production cargo. 
Of the 364 million passenger airplane flight hours, 303 million will be 
flown by airplanes with FRM and 61 million will be flown by airplanes 
without FRM. The airplanes without FRM will be those manufactured prior 
to 2009 until they are retired or retrofitted between 2008 and 2017.

  Table 1.--Summary of the Total Numbers of Airplanes and Flight Hours
                          Affected by the Rule
------------------------------------------------------------------------
                                                           Flight hours
            Airplane category                Airplanes      (millions)
------------------------------------------------------------------------
PASSENGER PRODUCTION....................           2,290             199
RETROFITTED WITH FRM....................           2,732             105
NO FRM..................................  ..............              61
                                         -------------------------------
    TOTAL PASSENGER.....................           5,022             364
CARGO PRODUCTION........................              88               6
                                         -------------------------------
    TOTAL...............................           5,110             370
------------------------------------------------------------------------

Risk of a HCWT Explosion
    If there were no final rule and no SFAR 88, engineering analysis 
indicates that there would be 1 explosion for every 100 million HCWT 
airplane flight hours. Air carrier passenger airplanes would incur 3.64 
explosions of which production airplanes would incur 1.99 explosions 
and retrofitted airplanes would incur 1.65 explosions. Of the 
retrofitted airplanes, 1.04 would occur to airplanes with FRM and 0.61 
would occur to airplanes without FRM. Production cargo airplanes would 
incur 0.06 explosions. As, obviously, fractions of accidents do not 
occur, we describe the cumulative probability of the number of 
accidents in fractions of an accident for analytic purposes. For 
example, engineering analysis would project that the first accident 
would occur in 2012, the second one in 2019, the third one in 2026, and 
the final 0.64 of an accident in 2035. However, care

[[Page 42484]]

should be taken in assuming that these rare events will necessarily 
occur in the forecasted year. As an illustration, in a 1,000 Monte 
Carlo simulation trials, 3 accidents occurred 233 times out of the 1000 
trials. For those 3-accident cases, two accidents happened in the same 
year 25 times.
Number of HCWT Explosions Potentially Affected by the Rule
    Our Monte Carlo analysis indicates that we cannot statistically 
reject the hypothesis that SFAR 88 is 50 percent effective in 
preventing these accidents. This analysis, in combination with the 
service history since the implementation of SFAR 88, indicates that a 
50 percent SFAR 88 effectiveness rate is appropriate, but we conducted 
a sensitivity analysis using two other possible SFAR 88 effectiveness 
rates of 25 percent and 75 percent in the Final Regulatory Evaluation. 
Using a 50 percent SFAR 88 effectiveness rate, in the absence of this 
final rule, we calculate that there would be 1.82 HCWT air carrier 
passenger airplane explosions occurring to the HCWT airplanes during 
the time period of the analysis. As it will take time to install FRM, 
77 percent of the flight hours will be flown by airplanes with FRM 
while 23 percent of the flight hours will be flown by airplanes without 
FRM. Thus, 1.52 air carrier passenger airplane HCWT explosions will be 
prevented by the rule and 0.3 HCWT explosions could occur to airplanes 
without FRM.
Percentage of In-Flight Explosions
    Our engineering analysis determined that eighty percent of the 
accidents would occur in flight and twenty percent would occur on the 
ground.
Benefits
    There are two types of benefits from preventing an airplane 
explosion. Direct safety benefits arise from preventing the resulting 
fatalities and property losses. Secondly, demand benefits arise from 
preventing the aviation demand losses resulting from the reduction in 
demand to fly, which will be a consequence of a loss of public 
confidence in commercial aviation safety following an airplane 
explosion. Further, the explosion that results from an electrical 
charge is indistinguishable (until the accident is investigated) from 
an explosion caused by a terrorist bomb. This uncertainty about the 
explosion cause may result in costly governmental and industry 
reactions to a perceived terrorist plot. However, the benefits 
preventing such a potential reaction is too speculative to provide a 
definitive quantitative benefit estimate, although we have quantified a 
possible estimate in Appendix A of the Regulatory Evaluation.
Quantified Demand Benefits
    As discussed in the economic literature, there is a direct, 
immediate, but temporary decrease in air travel in the aftermath of a 
catastrophic air carrier passenger airplane explosion. We estimate the 
loss to the aviation industry to be $292 million from such an accident.
Quantified Direct Benefits
Direct Benefits From Preventing a HCWT Explosion--Assumptions and 
Values
     Final rule is published on January 1, 2008.
     Discount rate is 7 percent.
     Passenger airplanes would be retrofitted between 2010 and 
2017.
     No airplane scheduled to be retired before 2018 will be 
retrofitted.
     Passenger airplanes have a 25-year service life.
     With no SFAR 88 and no FRM rule, a heated center wing tank 
(HCWT) airplane will have a fuel tank explosion every 100 million 
flight hours.
     Special Federal Air Regulation (SFAR) 88 will prevent half 
of the future explosions.
     Boeing and Airbus HCWT airplanes have equal explosion 
risks.
     80 percent of the accidents will be catastrophic in-flight 
accidents; with an average of 142 fatalities for a passenger airplane 
and 2 fatalities for a cargo airplane.
     20 percent of the accidents will occur on-the-ground with 
an average of 14 fatalities for a passenger airplane and no fatalities 
for a cargo airplane.
     The airplane is destroyed in an HCWT explosion.
     The value of a prevented fatality is $5.5 million.
Direct Benefits From Preventing a HCWT Explosion--Results
     The average undiscounted direct benefits from preventing 
an air carrier passenger airplane in-flight HCWT explosion will be $841 
million, with a range of $628 million to $2.2 billion.
     The average undiscounted direct benefits from preventing 
an air carrier passenger airplane on-the-ground HCWT explosion will be 
$115 million, with a range of $77 million to $320 million.
     The average undiscounted direct benefits from preventing 
an air carrier passenger airplane HCWT explosion weighted by an 80 
percent probability of an in-flight accident and a 20 percent 
probability of an on-the-ground accident will be $696 million.
     The average undiscounted direct benefits from preventing 
an air carrier cargo airplane HCWT explosion will be $77 million.
Total Benefits
    Of great concern to the FAA is that a practical solution now exists 
for a real threat of an aviation catastrophe. Even though these are low 
probability accidents, they are high consequence accidents. For 
example, if a single in-flight catastrophic accident with 190 occupants 
(235 seats) is prevented by 2012, the present value of the benefits 
will be greater than the present value of the costs. Using a $5.5 
million value for a prevented fatality, the benefits from preventing an 
in-flight explosion range of $625 million to $750 million for a B-737 
or an A-320 family airplane to $1.0 billion to $2.15 billion for all 
other affected airplanes. The mean of the estimated benefits from 
preventing an in-flight explosion (weighted by the number of flight 
hours for each type of affected airplane model) are $840 million.
    Thus, the undiscounted total weighted average benefit from 
preventing an in-flight explosion is $1.130 billion. Adjusting this 
value for the 20 percent of the accidents that will occur on the ground 
produces an undiscounted average benefit of about $1 billion.
    We calculated that the present value of the weighted average 
benefits from preventing the 1.5 accidents would be $657 million.
Compliance Cost Assumptions and Values
    The compliance costs are based on installing a fuel tank inerting 
(FTI) system because that is the only FRM system that has been 
developed. If a future FRM system is developed that competes with FTI 
then we have likely overestimated the compliance costs.
     Fully burdened aviation engineer labor rate is $110 an 
hour.
     Fully burdened aviation mechanic labor rate is $80 an 
hour.
     One-time engineering costs to develop STCs or modified TCs 
are between $2.2 million to $5.7 million a model.
     Retrofitting kits cost from $77,000 (B-737 and A-320 
Family), $120,000-$164,000 (B-757, B-767, and A-300/310), to $165,000-
$192,000 (all other airplanes).
     Initial retrofitting labor costs in 2010 will range from 
$24,000 to $70,000.

[[Page 42485]]

     There is a retrofitting labor learning curve of 30 percent 
such that the retrofitting labor hours (and costs) will be 
approximately 70 percent of the 2010 labor hours in 2013 and 49 percent 
of the 2010 labor hours by 2017.
     Retrofitting kit and labor costs in 2010 will range from 
$100,000 for the B-737 and A-320 Family and $148,000 to $203,000 (for 
all other airplanes).
     Out-of-Service Losses (Associated with a retrofit during a 
routine ``D'' check) are $10,000 to $28,000.
     Out-of-Service Losses (Associated with a retrofit during a 
special maintenance session) are $30,000 to $84,000.
     The same reduction in hours out-of-service for labor hours 
will apply to the number of out-of-service hours.
     Retrofitting kits weigh 84 pounds (for the B-737 and the 
A-320 family), 117 pounds to 150 pounds (for the B-757, B-767, and A-
300/310), and 182 pounds to 215 pounds for the B-747, B-777, and A-330/
340).
     Retrofitted airplane increased annual fuel burn from 
weight, bleed air intake, and ram drag is 2,000-2,500 gallons (B-737) 
to 4,000 gallons (A-320 Family) to 4,400 to 6,500 gallons (everything 
else).
     Production airplane FTI kit costs are $92,000 (B-737 and 
A-320) to $186,000-$205,000 (for all other airplanes).
     Production airplane labor installation costs are $6,500-
$8,000.
     Production kit and labor costs in 2009 will be $100,000 
for the B-737 and A-320 Family) and $195,000 to $212,500 (for all other 
airplanes).
     Production airplane FTI weight is 105 pounds (B-737 and A-
30 Family) to 250-300 pounds (for all other airplanes).
     Production airplane increased annual fuel burn from 
weight, bleed air intake, and ram drag is 2,900 gallons (B-737) to 
4,600 gallons (A-320 Family) to 6,300 to 7,100 gallons (everything 
else).
     Cost of aviation fuel is $2.01 per gallon.
     Additional scheduled and unscheduled maintenance, delays, 
and water separator/filter replacement costs are $3,250 to $5,150.
     Annual operating costs are between $10,000 (B-737) to 
$15,000 (A-320 Family) to $17,500-$20,000 (for all other airplanes).
     Air separation module (ASM) replaced every 27,000 flight 
hours.
     ASM replacement cost is $45,000 (B-737 and A-320 Family) 
to $135,000-$153,000 (for all other airplanes).
    Weighted average compliance costs (excluding the engineering costs) 
are:
    Retrofitted Passenger Airplanes: $213,000 ($135,000 for retrofit 
and $78,000 for operational). Range: $144,000 to $395,000.
    Production Passenger Airplanes: $177,000 ($68,000 for installation 
and $109,000 for operational). Range: $156,000 to 410,000.
Total Compliance Costs
    As shown in Table 2, the present value of the total compliance 
costs is $1.012 billion, of which $975 million will be incurred by air 
carrier passenger airplane operators, and $37 million will be incurred 
by air carrier production cargo airplanes.
    Of the air carrier passenger airplane present value costs of $975 
million, operators of retrofitted airplanes will incur $436 million (43 
percent) while operators of production airplanes will incur $539 
million (57 percent).

                      Table 2.--Compliance Costs by Type of Operation and Type of Airplane
                                          [In millions of 2007 dollars]
----------------------------------------------------------------------------------------------------------------
                                                                                    Total costs
                                                                 -----------------------------------------------
                            Operator                                               Present value   Present value
                                                                   Undiscounted        (7%)            (3%)
----------------------------------------------------------------------------------------------------------------
AIR CARRIER PASSENGER:
    RETROFITTED.................................................            $839            $436            $623
    PRODUCTION..................................................           1,237             539             825
    AUXILIARY FUEL TANKS........................................              <1              <1              <1
                                                                 -----------------------------------------------
        TOTAL...................................................           2,076             975           1,448
AIR CARRIER CARGO:
    PRODUCTION..................................................             100              37              63
        TOTAL...................................................             100              37              63
                                                                 -----------------------------------------------
        GRAND TOTAL.............................................           2,176           1,012           1,511
----------------------------------------------------------------------------------------------------------------

    As shown in Table 3, 54 percent of the present value costs (at 7 
percent) for retrofitted air carrier passenger airplanes are from the 
engineering and one-time equipment installation costs while these costs 
are 47 percent for production airplanes. Similarly, 46 percent of the 
present value costs for retrofitted airplanes are due to additional 
fuel, operational, and ASM (air separation module) costs while these 
costs are 53 percent for production airplanes.

                         Table 3.--Compliance Costs for Air Carrier Passenger Airplanes
                                          [In millions of 2007 dollars]
----------------------------------------------------------------------------------------------------------------
                                                                                    Total costs
                                                                 -----------------------------------------------
                          Cost category                                            Present value   Present value
                                                                   Undiscounted        (7%)            (3%)
----------------------------------------------------------------------------------------------------------------
RETROFITTED:
    ENGINEERING.................................................             $19             $16             $18
    INSTALLATION................................................             346             220             283
    INVENTORY...................................................               9               6               7
    FUEL........................................................             215              93             149
    OPERATIONAL.................................................             113              49              77

[[Page 42486]]

 
    ASM REPLACEMENT.............................................             137              52              89
                                                                 -----------------------------------------------
        TOTAL...................................................             839             436             623
PRODUCTION:
    ENGINEERING.................................................             107             100             103
    INSTALLATION................................................             230             152             191
    INVENTORY...................................................               7               4               5
    FUEL........................................................             459             149             272
    OPERATIONAL.................................................             197              63             116
    ASM REPLACEMENT.............................................             237              71             138
                                                                 -----------------------------------------------
        TOTAL...................................................           1,237             539             825
                                                                 -----------------------------------------------
        GRAND TOTAL.............................................           2,076             975           1,448
----------------------------------------------------------------------------------------------------------------

Benefit Cost Analysis
    As previously described, these are low probability, high 
consequence accidents. If a single in-flight catastrophic accident with 
190 occupants (a 235 seat airplane) were to be prevented by 2012, the 
present value of the benefits will be greater than the present value of 
the costs. Further, as shown in the Regulatory Evaluation in Appendix 
IV-7, there is a 26 percent probability that the final rule present 
value benefits will be greater than its present value costs.
    As shown in Table 4, using the weighted average benefits at a 7 
percent discount rate, the net benefit losses for the final rule would 
be $355 million, of which production passenger airplanes would account 
for $151 million, retrofitted passenger airplanes would account for 
$167 million and production cargo airplanes would account for $37 
million.

                             Table 4.--Present Value of the Rule Benefits and Costs
                                          [In millions of 2007 dollars]
----------------------------------------------------------------------------------------------------------------
                                                                                Present value (7%)
                        Type of operation                        -----------------------------------------------
                                                                     Benefits          Costs       Net benefits
----------------------------------------------------------------------------------------------------------------
PASSENGER:
    RETROFITTED.................................................            $271            $438          ($167)
    PRODUCTION..................................................             386             537           (151)
                                                                 -----------------------------------------------
        TOTAL...................................................             657             975           (318)
    PRODUCTION CARGO............................................              <1              37            (37)
                                                                 -----------------------------------------------
        GRAND TOTAL.............................................             657           1,012           (355)
----------------------------------------------------------------------------------------------------------------

Sensitivity Analysis of the Rule Costs and Benefits
    Table 5 provides a sensitivity analysis for the final rule that, 
using the weighted by flight hours average benefit value, varies the 
discount rate (7 and 3 percent), the value of preventing a statistical 
fatality ($3 million, $5.5 million, and $8 million), and the SFAR 88 
effectiveness rate (25, 50, and 75 percent). As is shown, the 
quantified benefits are greater than the costs when the SFAR 88 
effectiveness rate is 25 percent for: (1) An $8 million value of a 
prevented fatality and; (2) a $5.5 million value of a prevented 
fatality using a 3 percent discount rate. Net benefits numbers in 
parentheses are negative.

   Table 5.--Present Values of the Benefits and Costs for all Affected Airplanes by Discount Rate, Value of a
                               Prevented Fatality, and SFAR 88 Effectiveness Rate
                                          [In millions of 2007 dollars]
----------------------------------------------------------------------------------------------------------------
                                                      SFAR 88                     Present values
          Discount rate              Value of      effectiveness -----------------------------------------------
                                     fatality        (percent)       Benefits          Costs       Net benefits
----------------------------------------------------------------------------------------------------------------
7%..............................            $5.5              50            $657          $1,012          ($355)
7%..............................               3              50             469           1,012           (543)
7%..............................               8              50             828           1,012           (184)
7%..............................             5.5              25             989           1,012            (23)
7%..............................               3              25             704           1,012           (308)

[[Page 42487]]

 
7%..............................               8              25           1,242           1,012             230
7%..............................             5.5              75             330           1,012           (682)
7%..............................               3              75             235           1,012           (777)
7%..............................               8              75             414           1,012           (598)
----------------------------------------------------------------------------------------------------------------
3%..............................             5.5              50           1,141           1,509           (368)
3%..............................               3              50             842           1,509           (667)
3%..............................               8              50           1,434           1,509            (75)
3%..............................             5.5              25           1,658           1,509             149
3%..............................               3              25           1,263           1,509           (246)
3%..............................               8              25           2,151           1,509             642
3%..............................             5.5              75             517           1,509           (992)
3%..............................               3              75             421           1,509         (1,088)
3%..............................               8              75             717           1,509           (792)
----------------------------------------------------------------------------------------------------------------

Differences Between the Initial Regulatory Evaluation (IRE) and Final 
Regulatory Evaluation (FRE) Assumptions and Unit Values
    In the IRE, we had estimated that the present value of the proposed 
rule's direct benefits would be $495 million and that the present value 
of the proposed rule's costs would be $808 million. Table 6 provides a 
summary of the important differences in the assumptions and the unit 
values between those in the IRE and those used in this FRE. The 
significant benefits increases are due to the quantification of the 
demand benefits and the use of $5.5 million for the value of a 
prevented fatality. In the final rule the benefits and costs were both 
substantially increased by the inclusion of Boeing production airplanes 
(except the B-787). In the NPRM analysis we assumed Boeing would 
voluntarily comply for its production airplanes; we did not assume this 
for the final rule analysis. The benefits and costs were both decreased 
by the shorter period of analysis. The significant cost increases are 
due to the increases in the production FTI kit costs, their annual 
additional fuel consumption due to the FTI weights and the bleed air 
and ram drag effects, the increased price of aviation fuel, and the air 
separation module (ASM) replacement costs (there will be 1 ASM 
replacement for most retrofitted airplanes and 2 ASM replacements for 
most production airplanes).

                    Table 6.--Differences in the Assumptions/Values in the IRE and in the FRE
----------------------------------------------------------------------------------------------------------------
           Assumptions/values                        FRE                                 IRE
----------------------------------------------------------------------------------------------------------------
Time Period of Analysis................  2009-2042.................  2006-2055.
Accident Rate..........................  1 Every 100 Million HCWT    1 Every 60 Million HCWT Flight Hours.
                                          Flight Hours.
Number of Flight Hours.................  370 Million Total.........  460 Million.
                                         364 Million Passenger.....
                                         6 Million Production
                                          Cargo..
Number of Accidents....................  3.7 Total.................  7.67.
                                         3.64 Passenger............
                                         0.06 Cargo................
Percentage of In-Flight Accidents......  80%.......................  100%.
Base Year for Dollars..................  2007......................  2004.
Reduction in Air Travel Demand.........  $292 Million (annual real   Qualitatively large.
                                          growth rate of 3%).
Value of a Prevented Fatality..........  $5.5 Million..............  $3 Million.
Average Number of In-Flight Fatalities.  142.......................  142.
Average Number of On-the-Ground          14........................  8.
 Fatalities.
Average Accident Value for an In-Flight  $841 Million..............  $505 Million.
 Explosion (Passenger Airplane).
Average Accident Value for an On-the-    $115 Million..............  Not Estimated.
 Ground Explosion (Passenger Airplane).
Weighted Average Accident Value          $696 Million..............  $505 Million.
 (Passenger Airplane).
Weighted Average Accident Value          $77 Million...............  $75 Million.
 (Production Cargo Airplane).
Hourly Labor Rates.....................  Engineer $110.............  Engineer $115.
                                         Mechanic $80..............  Mechanic $75.
Total Number of Retrofits..............  Passenger 2,732...........  Passenger 3,328.
                                         Boeing 1,780..............  Boeing 2,327.
                                         Airbus 952................  Airbus 1,001.
Retrofitting Kit Costs.................  Small $77,000.............  Small $105,000.
                                         Medium $120,000-$164,000..  Medium $135,000.
                                         Large $175,000-$192,000...  Large $179,000.
Retrofitting Labor Costs (Scheduled      $24,000-$28,000...........  $30,000-$35,000.
 Maintenance).

[[Page 42488]]

 
Number of Out-of-Service Days            2.........................  2.
 (Scheduled Maintenance).
Out-of-Service Costs (Scheduled          Small $10,000.............  Small $9,000.
 Maintenance).
                                         Medium $22,000............  Medium $14,000.
                                         Large $28,000.............  Large $13,000.
Retrofitting Costs (Scheduled            Small $110,000............  Small $135,000.
 Maintenance).
                                         Medium $165,000-$215,000..  Medium $170,000.
                                         Large $214,000-$229,000...  Large $214,000.
Retrofitting Labor Costs (Dedicated      $62,000-$70,000...........  $40,000-$45,000.
 Visit).
Number of Out-of-Service Days            6.........................  4.
 (Dedicated Visit).
Out-of-Service Costs (Dedicated Visit).  Small $30,000.............  Small $19,000.
                                         Medium $66,000............  Medium $56,000.
                                         Large $84,000.............  Large $53,000.
Retrofitting Costs (Dedicated Visit)...  Small $137,000............  Small $163,000.
                                         Medium $211,000-$264,000..  Medium $234,000.
                                         Large $289,000-$311,000...  Large $276,000.
Fuel Cost per Gallon...................  $2.01.....................  $1.00.
Retrofitting FTI Weight................  Small 84 lbs..............  Small 95 lbs.
                                         Medium 117-150 lbs........  Medium 148 lbs.
                                         Large 182-215 lbs.........  Large 218 lbs.
Annual Retrofitted Passenger Airplane    Small 2,500-4,000 Gals....  Small 1,500-3,900.
 Fuel Consumption (Weight, Bleed Air,
 and Ram Drag).
                                         Medium 3,000-4,125 Gals...  Medium 2,900.
                                         Large 4,500-6,550 Gals....  Large 4,800.
Annual Retrofitted Passenger Airplane    Small $5,250-$8,000.......  Small $1,500-$3,900.
 Fuel Cost.
                                         Medium $6,000-$8,300......  Medium $2,900.
                                         Large $9,000-$13,150......  Large $4,800.
Total Number of Production Passenger     Total 2,290 (2009-2017)...  Total 3,274 (2008-2030).
 Airplanes.
                                         Boeing 1,268..............  Boeing 0.
                                         Airbus 1,022..............  Airbus 2,650.
Total Number of Production (No           Total 88 (2009-2017)......  Total 624 (2008-2030).
 Conversion) Cargo Airplanes.
                                         Boeing 66.................  Boeing 0.
                                         Airbus 22.................  Airbus 624 (includes Conversion).
Production Kit Costs...................  Small $92,000.............  Small $83,000.
                                         Medium $186,000...........  Medium $107,000.
                                         Large $205,000............  Large $137,000.
Production Labor Costs.................  $6,500-$8.000.............  $7,000-$8.000.
Unit Production Costs..................  Small $98,000.............  Small $90,000.
                                         Medium $194,000...........  Medium $115,000.
                                         Large $213,000............  Large $145,000.
Production FTI Weight..................  Small 105 lbs.............  Small 95 lbs.
                                         Medium 280 lbs............  Medium 148 lbs.
                                         Large 300 lbs.............  Large 218 lbs.
Annual Production Passenger Airplane     Small 2,300-4,625 Gals....  Small 1,500-3,900.
 Fuel Consumption (Weight, Bleed Air,
 and Ram Drag).
                                         Medium 5,600-6,725 Gals...  Medium 2,900.
                                         Large 6,850-8,600 Gals....  Large 4,800.
Annual Production Passenger Airplane     Small $3,850-$7,625.......  Small $1,500-$3,900.
 Fuel Cost.
                                         Medium $9,250-$11,100.....  Medium $2,900.
                                         Large $11,300-$14,300.....  Large $4,800.
Maintenance............................  $3,250-$5,150.............  $5,900-$7,500.
ASM Replacement Cost (Every 9 Years)...  Small $30,500-$45,000.....  Small $5,275.
                                         Medium $135,000...........  Medium $18,761.
                                         Large $153,000............  Large $28,814.
----------------------------------------------------------------------------------------------------------------

Costs and Benefits of Alternatives to the Final Rule
    As shown in Table 7, we evaluated the baseline costs and weighted 
average benefits for the 8 alternatives to the final rule using a value 
of $5.5 million for a prevented fatality, a 7 percent discount rate, 
and a 50 percent SFAR 88 effectiveness rate. These expected benefits 
are based on a rare event mean probability. The date when an avoided 
accident occurs has a significant impact on the expected benefits.

ALTERNATIVE 1. Cover only air carrier passenger airplanes
ALTERNATIVE 2. Exclude auxiliary fuel tanks
ALTERNATIVE 3. Cover only air carrier retrofitted passenger airplanes
ALTERNATIVE 4. Cover only air carrier production passenger airplanes
ALTERNATIVE 5. Cover only air carrier production passenger and cargo 
airplanes
ALTERNATIVE 6. Final rule plus part 91 airplanes
ALTERNATIVE 7. Final rule plus conversion cargo airplanes
ALTERNATIVE 8. Final rule plus conversion and retrofitted cargo 
airplanes

[[Page 42489]]



  Table 7.--Benefits and Cost Summaries for 8 Alternatives to the Final
  Rule Using a $5.5 Million Value for a Prevented Fatality, a 7 Percent
       Discount Rate, and a 50 Percent SFAR 88 Effectiveness Rate
                      [In millions of 2007 dollars]
------------------------------------------------------------------------
                                      Present value (7%)
              Option              --------------------------     Net
                                     Benefits      Costs       benefits
------------------------------------------------------------------------
FINAL RULE.......................         $657       $1,012       ($355)
ALTERNATIVES:
    1. Cover Only Part 121                 657          975        (318)
     Passenger Airplanes
     (excludes Part 121 cargo and
     Part 91)....................
    2. Cover Only Part 121                 657          975        (318)
     Passenger Airplanes but No
     Auxiliary Tanks.............
    3. Cover Only Part 121                 271          438        (167)
     Retrofitted Passenger
     Airplanes (excludes All
     Production Passenger, all
     Cargo, and Part 91
     Airplanes)..................
    4. Cover Only Part 121                 386          537        (151)
     Production Passenger
     Airplanes...................
    5. Cover Only Part 121                 386          574        (188)
     Production Passenger and
     Cargo Airplanes.............
    6. Final Rule Plus Part 91             657        1,026        (369)
     Airplanes...................
    7. Final Rule Plus Conversion          657        1,109        (452)
     Cargo Airplanes.............
    8. Final Rule Plus Conversion          657        1,229        (572)
     and Retrofitted Cargo
     Airplanes...................
------------------------------------------------------------------------

    Another way to analyze these alternatives is to evaluate them on an 
incremental cost per life saved; i.e., a cost-effectiveness analysis. 
For this rule, the effectiveness metric is the number of expected 
prevented fuel tank explosions, which is then converted into the 
present value of the number of fatalities prevented. The mid-point of 
the time-frame in which an accident would happen is 2022 for production 
airplanes and 2019 for retrofitted airplanes. For all other airplanes, 
the mid-point would be about 50 years from today, or 2060. In Table 8, 
the first column lists the specific types of airplanes that could have 
FRM installed. The second column reports the number of fuel tank 
explosions that FRM would prevent using an SFAR 88 effectiveness rate 
of 50 percent. The third column provides the present value of the total 
costs to install FRM on those airplanes minus the present value of the 
destroyed airplane and minus the demand benefits weighted by the number 
of flight hours. The passenger airplane hull value is $50, which gives 
present values of $19 million for production airplanes and $24 million 
for retrofitted airplanes. The present value of the demand benefits 
would be $100 million for retrofitted airplanes and $151 million for 
production airplanes. The fourth column takes the number of prevented 
explosions and divides it into the costs to calculate the present value 
of the cost to prevent one explosion. The fifth column provides the 
number of fatalities that would be prevented if FRM were installed on 
the airplane assuming that 80 percent of the explosions would be in-
flight and 20 percent would be on the ground. These numbers are then 
adjusted by the discount rate to reflect the present value of the 
fatalities for production and retrofitted passenger airplanes. The 
final column supplies the average present value of the cost for that 
option to prevent one fatality. As shown in Table 8, the two most cost-
effective options would be to install FRM on production passenger 
airplanes and on existing passenger airplanes. The final rule contains 
all of the options except conversion cargo airplanes and retrofitted 
cargo airplanes.

 Table 8.--Incremental Cost Effectiveness Analysis of the Individual Alternatives Using a Present Value Analysis
                   With a 7 Percent Discount Rate and a 50 Percent SFAR 88 Effectiveness Rate
                                    [Total costs in millions of 2007 dollars]
----------------------------------------------------------------------------------------------------------------
                                                       PV           PV                              PV
                                      Number of  -------------------------- Average No. ------------------------
              Options                 explosions  Costs--hull    Cost to         of
                                      prevented    and demand  prevent one   fatalities     Cost to prevent 1
                                                      loss       accident                  statistical fatality
----------------------------------------------------------------------------------------------------------------
Production Passenger Airplanes.....         1.00         $367         $367           46                   $8.000
Production Cargo Airplanes.........       0.0385           37          961         .055               17,473.000
Production Part 91 Airplanes.......      0.00082            2        2,439         .249                9,785.000
Retrofitted Passenger Airplanes....         0.52          314          604           56                   11.000
Conversion Cargo Airplanes.........        0.095           83          874         .055               15,891.000
Retrofitted Cargo Airplanes........        0.064          110        1,719         .055               31,255.000
Retrofitted Part 91 Airplanes......       0.0194           12        6,186         .249               24,843.000
Final Rule.........................       1.5585          741          475           49                   10.000
----------------------------------------------------------------------------------------------------------------

Conclusion
    When modeling discrete rare events such as fuel tank explosions, it 
is important to understand and evaluate the distribution around the 
mean value rather than to rely only on a single point estimated value. 
This variability analysis indicates there is a substantial (23 percent) 
probability that the quantified benefits will be greater than the 
costs.
    The Federal Aviation Administration believes that the correct 
public policy choice is to eliminate the substantial probability of a 
high consequence fuel tank explosion accident by proceeding with the 
final rule.
Regulatory Flexibility Analysis
Introduction and Purpose of This Analysis
    The Regulatory Flexibility Act of 1980 (Pub. L. 96-354) (RFA) 
establishes ``as a principle of regulatory issuance that agencies shall 
endeavor, consistent with the objectives of the rule and of

[[Page 42490]]

applicable statutes, to fit regulatory and informational requirements 
to the scale of the businesses, organizations, and governmental 
jurisdictions subject to regulation. To achieve this principle, 
agencies are required to solicit and consider flexible regulatory 
proposals and to explain the rationale for their actions to assure that 
such proposals are given serious consideration.'' The RFA covers a 
wide-range of small entities, including small businesses, not-for-
profit organizations, and small governmental jurisdictions.
    Agencies must perform a review to determine whether a rule will 
have a significant economic impact on a substantial number of small 
entities. If the agency determines that it will, the agency must 
prepare a regulatory flexibility analysis as described in the RFA.
    We believe that this final rule will have a significant economic 
impact on a substantial number of small entities. The purpose of this 
analysis is to provide the reasoning underlying the FAA determination. 
The FAA has determined that:

--There will not be a significant impact on a substantial number of 
manufacturers.
--There will be a significant impact on a substantial number of small 
operators.

    To make this determination in this final rule, we perform a 
Regulatory Flexibility Analysis (RFA). Under Section 63(b) of the RFA, 
the analysis must address:

--Description of reasons the agency is considering the action.
--Statement of the legal basis and objectives for the rule.
--Significant issues raised during public comment.
--Description of the recordkeeping and other compliance requirements of 
the rule.
--All federal rules that may duplicate, overlap, or conflict with the 
rule.
--Description and an estimated number of small entities.
--Economic impact.
--Describe the alternatives considered.
Description of Reasons the Agency Is Considering the Action
    Fuel tank explosions have been a threat with serious aviation 
safety implications for many years. The explosion of TWA Flight 800 (a 
Boeing 747) off Long Island, New York in 1996 occurred in-flight with 
the loss of all 230 on board. Two other explosions on airplanes 
operated by Philippine Airlines and Thai Airlines occurred on the 
ground (resulting in nine fatalities). While the accident 
investigations of the TWA, Philippine Airlines, and Thai Airlines 
accidents failed to identify the ignition source that caused the 
explosion, the investigations found several similarities
    The requirements contained in this final rule will reduce the 
likelihood of fuel tank fires, and mitigate the effects of a fire if 
one occurs.
Statement of the Legal Basis and Objectives for the Rule
    The FAA's authority to issue rules regarding aviation safety is 
found in Title 49 of the United States Code. Subtitle I, Section 106 
describes the authority of the FAA Administrator. Subtitle VII, 
Aviation Programs, describes in more detail the scope of the agency's 
authority.
    This rulemaking is promulgated under the authority described in 
Subtitle VII, Part A, Subpart III, Section 44701, ``General 
requirements.'' Under that section, the FAA is charged with promoting 
safe flight of civil aircraft in air commerce by prescribing minimum 
standards required in the interest of safety for the design and 
performance of aircraft; regulations and minimum standards in the 
interest of aviation safety for inspecting, servicing, and overhauling 
aircraft; and regulations for other practices, methods, and procedures 
the Administrator finds necessary for safety in air commerce. This 
regulation is within the scope of that authority because it prescribes:
     New safety standards for the design of transport category 
airplanes, and
     New requirements necessary for safety for the design, 
production, operation and maintenance of those airplanes, and for other 
practices, methods, and procedures related to those airplanes.
    Accordingly, this final rule amends Title 14 of the Code of Federal 
Regulations and address deficiencies in current regulations regarding 
airplane designs of the current and future fleet. The rule will require 
transport category airplanes to minimize flammability of fuel tanks.
Significant Issues Raised During Public Comment
    Individuals and companies commented that they will incur costs as a 
result of the requirements contained in the rule. The National Air 
Carrier Association (NACA) supports FRM being applied to production 
passenger airplanes. They oppose applying FRM to existing passenger 
airplanes and to any cargo airplanes. Their primary concerns were that 
the cost of retrofitting passenger airplanes was too high for the 
potential benefits and they believe that cargo airplanes were not at 
risk. They did not provide specific cost estimates. The Regional 
Airline Association (RAA) opposes any FRM requirement, although only 
one of their member airlines has airplanes that will be affected by the 
final rule.
Description of the Recordkeeping and Other Compliance Requirements of 
the Rule
    We expect no more than minimal new reporting and recordkeeping 
compliant requirements to result from this rule. The rule will require 
additional entries in existing required maintenance records to account 
for either the additional maintenance requirements or the installation 
of nitrogen-inerting systems and the addition of insulation between 
heat-generating equipment and fuel tanks.
All Federal Rules That May Duplicate, Overlap, or Conflict With the 
Rule
    SFAR 88 was enacted to ensure no ignition sources exist in the fuel 
tanks. After that rule was promulgated and the manufacturers' safety 
analyses were submitted to the regulatory authorities, we continued to 
find ignition sources that had not been revealed in the safety 
analyses. Thus, SFAR 88 cannot eliminate all future ignition sources. 
This rule is designed to work in conjunction with SFAR 88 to prevent 
future HCWT explosions. We are unaware that the rule will overlap, 
duplicate or conflict with any other existing Federal Rules.
Description and an Estimated Number of Small Entities
    The FAA uses the size standards from the Small Business 
Administration for Air Transportation and Aircraft Manufacturing 
specifying companies having less than 1,500 employees as small 
entities. Boeing is the sole U.S. manufacturer affected by this final 
rule. As Boeing has more than 1,500 employees and is not considered a 
small entity, there will not be a significant impact on a substantial 
number of manufacturers.
    We identified a total of 15 U.S. operators who will be affected by 
this final rule and qualify as small businesses because they have fewer 
than 1,500 employees. These 15 entities operate a total of 214 
airplanes. Once the firms were classified as small entities, we 
gathered information on their annual revenues.
    We obtained the small entities' fleets using data from FAA Flight 
Standards and BACK Associates Fleet Database. The number of employees 
and revenues

[[Page 42491]]

were obtained from the U.S. Department of Transportation Form 41 
filings, BTS Office of Airline Information, Hoovers Online, and Thomas 
Gale Business and Company Resource Center.
Economic Impact
    To assess the cost impact to small business part 121 airlines, we 
estimated the present value retrofit cost for the affected aircraft in 
the small entities fleet. Table 8 summarizes the cost to retrofit per 
airplane and the associated model types.

                Table 8.--Retrofit Cost by Airplane Model
------------------------------------------------------------------------
                                                               Present
                           Model                              value cost
------------------------------------------------------------------------
Retrofit Cost Per Model:
    B-737-Classic..........................................     $137,000
    B-737-NG...............................................      121,000
    B-757..................................................      211,000
    B-767..................................................      264,000
    B747-100/100/300.......................................      289,000
    B-747-400..............................................      289,000
    B-777..................................................      311,000
    A-320 Family...........................................      137,000
    A-330..................................................      311,000
------------------------------------------------------------------------

    We estimated each operator's compliance cost by multiplying the 
average retrofit cost per airplane by the total number of each type of 
airplane the operator currently has. Then we measured the economic 
impact on small entities by dividing the firms' total estimated present 
value compliance cost by its annual revenue. We believe that if the 
retrofit cost exceeds 2% of a firm's annual revenue, then there is a 
significant economic impact. As shown in the following table, the 
present value of the retrofitting costs is estimated to be greater than 
two percent of annual revenues for three small operators. Thus, as the 
rule will have a significant economic impact on three small operators 
we determined this final rule will have a significant impact on a 
substantial number of small entities.

   Table 9.--Total Retrofitting Costs and Their Percentage of Annual Revenues for the Affected Small Operators
----------------------------------------------------------------------------------------------------------------
                                                         Number of                                    Cost as a
          Airplane model               Small entity       affected       Cost       Annual revenue    percent of
                                         operator         aircraft                                     revenue
----------------------------------------------------------------------------------------------------------------
BOEING 737-700...................  ALOHA AIRLINES.....            2     $242,000  .................  ...........
BOEING 737-700...................  ALOHA AIRLINES.....            5      605,000  .................  ...........
BOEING 737-700...................  ALOHA AIRLINES.....            1      121,000  .................  ...........
                                                                    --------------------------------------------
    Total........................  ...................  ...........      968,000       $300,601,582         0.32
                                                                    ============================================
BOEING 737-300...................  ATA AIRLINES.......            3      411,000  .................  ...........
BOEING 737-800...................  ATA AIRLINES.......           11    1,331,000  .................  ...........
BOEING 737-800...................  ATA AIRLINES.......            1      121,000  .................  ...........
BOEING 757-200...................  ATA AIRLINES.......            4    1,055,000  .................  ...........
BOEING 757-200...................  ATA AIRLINES.......            2      422,000  .................  ...........
BOEING 757-300...................  ATA AIRLINES.......            4      844,000  .................  ...........
                                                                    --------------------------------------------
    Total........................  ...................  ...........    4,184,000        330,177,135         1.27
                                                                    ============================================
BOEING 757-200...................  EOS AIRLINES.......            3      633,000          1,084,907       58.350
AIRBUS A318-100..................  FRONTIER AIRLINES              8    1,096,000  .................  ...........
                                    [CO-USA].
AIRBUS A319-100..................  FRONTIER AIRLINES             39    5,343,000  .................  ...........
                                    [CO-USA].
AIRBUS A319-100..................  FRONTIER AIRLINES             10    1,370,000  .................  ...........
                                    [CO-USA].
                                                                    --------------------------------------------
    Total........................  ...................  ...........    7,809,000      1,130,837,682         0.69
                                                                    ============================================
BOEING 767-300...................  HAWAIIAN AIRLINES..            4    1,056,000  .................  ...........
BOEING 767-300...................  HAWAIIAN AIRLINES..            8    2,112,000  .................  ...........
BOEING 767-300...................  HAWAIIAN AIRLINES..            3      792,000  .................  ...........
BOEING 767-300...................  HAWAIIAN AIRLINES..            3      792,000  .................  ...........
                                                                    --------------------------------------------
    Total........................  ...................  ...........    4,752,000        881,599,398         0.54
                                                                    ============================================
BOEING 767-200...................  MAXJET AIRWAYS.....            1      264,000  .................  ...........
BOEING 767-200...................  MAXJET AIRWAYS.....            1      264,000  .................  ...........
BOEING 767-200...................  MAXJET AIRWAYS.....            1      264,000  .................  ...........
                                                                    --------------------------------------------
    Total........................  ...................  ...........      792,000          2,422,199        32.70
                                                                    ============================================
BOEING 737-400...................  MIAMI AIR                      2      274,000  .................  ...........
                                    INTERNATIONAL.
BOEING 737-800...................  MIAMI AIR                      3      363,000  .................  ...........
                                    INTERNATIONAL.
BOEING 737-800...................  MIAMI AIR                      1      121,000  .................  ...........
                                    INTERNATIONAL.
BOEING 737-800...................  MIAMI AIR                      1      121,000  .................  ...........
                                    INTERNATIONAL.
BOEING 737-800...................  MIAMI AIR                      2      121,000  .................  ...........
                                    INTERNATIONAL.
                                                                    --------------------------------------------
    Total........................  ...................  ...........    1,000,000         73,403,477         1.36
                                                                    ============================================
BOEING 757-200...................  PRIMARIS AIRLINES..            1      211,000         19,403,658         1.09
BOEING 737-300...................  RYAN INTERNATIONAL             1      137,000  .................  ...........
                                    AIRLINES.
BOEING 737-400...................  RYAN INTERNATIONAL             1      137,000  .................  ...........
                                    AIRLINES.
BOEING 737-800...................  RYAN INTERNATIONAL             2      242,000  .................  ...........
                                    AIRLINES.
BOEING 737-800...................  RYAN INTERNATIONAL             1      121,000  .................  ...........
                                    AIRLINES.

[[Page 42492]]

 
BOEING 737-800...................  RYAN INTERNATIONAL             1      121,000  .................  ...........
                                    AIRLINES.
BOEING 757-200...................  RYAN INTERNATIONAL             1      211,000  .................  ...........
                                    AIRLINES.
BOEING 757-200...................  RYAN INTERNATIONAL             1      211,000  .................  ...........
                                    AIRLINES.
BOEING 757-200...................  RYAN INTERNATIONAL             2      422,000  .................  ...........
                                    AIRLINES.
                                                                    --------------------------------------------
    Total........................  ...................  ...........    1,602,000        101,560,750         1.58
                                                                    ============================================
AIRBUS A319-100..................  SPIRIT AIRLINES               30    4,100,000  .................  ...........
                                    [USA].
AIRBUS A321-100..................  SPIRIT AIRLINES                6      822,000  .................  ...........
                                    [USA].
                                                                    --------------------------------------------
    Total........................  ...................  ...........    4,922,000        540,426,363         0.91
                                                                    ============================================
BOEING 737-800...................  SUN COUNTRY                    2      242,000  .................  ...........
                                    AIRLINES.
BOEING 737-800...................  SUN COUNTRY                    6      726,000  .................  ...........
                                    AIRLINES.
BOEING 737-800...................  SUN COUNTRY                    2      242,000  .................  ...........
                                    AIRLINES.
BOEING 737-800...................  SUN COUNTRY                    3      363,000  .................  ...........
                                    AIRLINES.
                                                                    --------------------------------------------
    Total........................  ...................  ...........    1,573,000        225,789,595         0.70
                                                                    ============================================
AIRBUS A320-100..................  USA 3000 AIRLINES..            1      137,000  .................  ...........
AIRBUS A320-100..................  USA 3000 AIRLINES..            1      137,000  .................  ...........
AIRBUS A320-100..................  USA 3000 AIRLINES..            9    1,233,000  .................  ...........
                                                                    --------------------------------------------
    Total........................  ...................  ...........    1,507,000        132,077,603         1.14
                                                                    ============================================
B-737-429........................  CASINO EXPRESS.....            1      137,000  .................  ...........
B-737-46B........................  CASINO EXPRESS.....            1      137,000  .................  ...........
B-737-4S3........................  CASINO EXPRESS.....            1      137,000  .................  ...........
B-737-8Q8........................  CASINO EXPRESS.....            2      242,000  .................  ...........
B-737-8Q8........................  CASINO EXPRESS.....            1      121,000  .................  ...........
B-737-86N........................  CASINO EXPRESS.....            1      121,000  .................  ...........
                                                                    --------------------------------------------
    Total........................  ...................  ...........      895,000         34,178,453         2.62
                                                                    ============================================
B-737-3Y0........................  PACE AIRLINES......            1      137,000  .................  ...........
B-757-256........................  PACE AIRLINES......            1      137,000  .................  ...........
B-757-236........................  PACE AIRLINES......            1      137,000  .................  ...........
                                                                    --------------------------------------------
    Total........................  ...................  ...........      411,000         40,411,353         1.02
----------------------------------------------------------------------------------------------------------------

Describe the Alternatives Considered
    As described in the Analysis of Alternatives section, we evaluated 
the following 8 alternatives to the final rule.

ALTERNATIVE 1. Cover only air carrier passenger airplanes
ALTERNATIVE 2. Exclude auxiliary fuel tanks
ALTERNATIVE 3. Cover only air carrier retrofitted passenger airplanes
ALTERNATIVE 4. Cover only air carrier production passenger airplanes
ALTERNATIVE 5. Cover only air carrier production passenger and cargo 
airplanes
ALTERNATIVE 6. Final rule plus part 91 airplanes
ALTERNATIVE 7. Final rule plus conversion cargo airplanes
ALTERNATIVE 8. Final rule plus conversion and retrofitted cargo 
airplanes

    Our conclusion was that the final rule provided the best balance of 
cost and benefits for the United States society. Whether an airplane is 
flown by a small entity or by a large entity, the risk is largely the 
same. Consequently, we determined that the final rule should apply to 
all passenger airplanes and to production cargo airplanes.
Regulatory Flexibility Analysis Summary
    As the rule will have a significant economic impact on three small 
operators, we determined this final rule will have a significant impact 
on a substantial number of small entities.
International Trade Analysis
    The Trade Agreements Act of 1979 (Pub. L. 96-39), as amended by the 
Uruguay Round Agreements Act (Pub. L. 103-465), prohibits Federal 
agencies from establishing any standards or engaging in related 
activities that create unnecessary obstacles to the foreign commerce of 
the United States. Pursuant to these Acts, the establishment of 
standards are not considered unnecessary obstacles to the foreign 
commerce of the United States, when the standards have a legitimate 
domestic objective, such as the protection of safety, and when the 
standards do not operate in a manner that excludes imports that meet 
this objective. The statute also requires consideration of 
international standards and, where appropriate, that they be the basis 
for U.S. standards. The FAA notes the purpose of this rule is to ensure 
the safety of the American public. We have assessed the effects of this 
rule to ensure that it does not exclude imports that meet this 
objective. As a result, this rule is not considered as creating 
unnecessary obstacles to foreign commerce.
Unfunded Mandates Act
    Title II of the Unfunded Mandates Reform Act of 1995 (Pub. L. 104-
4)

[[Page 42493]]

requires each Federal agency to prepare a written statement assessing 
the effects of any Federal mandate in a proposed or final agency rule 
that may result in an expenditure of $100 million or more (adjusted 
annually for inflation with the base year 1995) in any one year by 
State, local, and tribal governments, in the aggregate, or by the 
private sector; such a mandate is deemed to be a ``significant 
regulatory action.'' The FAA currently uses an inflation-adjusted value 
of $136.1 million in lieu of $100 million.
    There will be 3 years (2015, 2016, and 2017) in which the 
undiscounted costs will be greater than $136.1 million. Consequently, 
in Table 7 of the regulatory evaluation summary, we evaluated the costs 
and benefits of 8 alternatives to the final rule.

Executive Order 13132, Federalism

    The FAA has analyzed this rule under the principles and criteria of 
Executive Order 13132, Federalism. We determined that this action will 
not have a substantial direct effect on the States, on the relationship 
between the national Government and the States, or on the distribution 
of power and responsibilities among the various levels of government, 
and therefore will not have federalism implications.

Regulations Affecting Intrastate Aviation in Alaska

    Section 1205 of the FAA Reauthorization Act of 1996 (110 Stat. 
3213) requires the Administrator, when modifying regulations in title 
14 of the CFR in manner affecting intrastate aviation in Alaska, to 
consider the extent to which Alaska is not served by transportation 
modes other than aviation, and to establish such regulatory 
distinctions, as he or she considers appropriate. Because this rule 
applies to the certification of future designs of transport category 
airplanes and their subsequent operation, it could affect intrastate 
aviation in Alaska. Nevertheless, the FAA has determined that it is 
inappropriate to relieve intrastate aviation interests in Alaska from 
the requirements of today's rule because of the safety objective served 
by this rule.

Environmental Analysis

    FAA Order 1050.1E identifies FAA actions that are categorically 
excluded from preparation of an environmental assessment or 
environmental impact statement under the National Environmental Policy 
Act in the absence of extraordinary circumstances. The FAA has 
determined this rulemaking action qualifies for the categorical 
exclusion identified in paragraph 312f and involves no extraordinary 
circumstances.

Regulations that Significantly Affect Energy Supply, Distribution, or 
Use

    The FAA has analyzed this rule under Executive Order 13211, Actions 
Concerning Regulations that Significantly Affect Energy Supply, 
Distribution, or Use (May 18, 2001). We have determined that it is not 
a ``significant energy action'' under the executive order because the 
rule is not likely to have a significant adverse effect on the supply, 
distribution, or use of energy.

Submission of Comments

Request for Comments

    Comments should be submitted to Docket No. FAA-2005-22997 by 
January 20, 2009. Comments may be submitted to the docket using any of 
the means listed in the Addresses section below.
    We will file in the docket all comments we receive, as well as a 
report summarizing each substantive public contact with FAA personnel 
concerning this rulemaking. The docket is available for public 
inspection before and after the comment closing date.
    Privacy Act: We will post all comments we receive, without change, 
to http://www.regulations.gov, including any personal information you 
provide. Using the search function of our docket Web site, anyone can 
find and read the comments received into any of our dockets, including 
the name of the individual sending the comment (or signing the comment 
for an association, business, labor union, etc.). You may review DOT's 
complete Privacy Act Statement in the Federal Register published on 
April 11, 2000 (65 FR 19477-78) or you may visit http://DocketsInfo.dot.gov.

Proprietary or Confidential Business Information

    Do not file in the docket information that you consider to be 
proprietary or confidential business information. Send or deliver this 
information directly to the person identified in the FOR FURTHER 
INFORMATION CONTACT section of this document. You must mark the 
information that you consider proprietary or confidential. If you send 
the information on a disk or CD ROM, mark the outside of the disk or CD 
ROM and also identify electronically within the disk or CD ROM the 
specific information that is proprietary or confidential.
    Under 14 CFR 11.35(b), when we are aware of proprietary information 
filed with a comment, we do not place it in the docket. We hold it in a 
separate file to which the public does not have access, and we place a 
note in the docket that we have received it. If we receive a request to 
examine or copy this information, we treat it as any other request 
under the Freedom of Information Act (5 U.S.C. 552). We process such a 
request under the DOT procedures found in 49 CFR part 7.

ADDRESSES: You may send comments identified by Docket Number FAA-2004-
22997 using any of the following methods:
     Federal eRulemaking Portal: Go to http://www.regulations.gov and follow the online instructions for sending your 
comments electronically.
     Mail: Send comments to Docket Operations, M-30, U.S. 
Department of Transportation, 1200 New Jersey Avenue, SE., West 
Building Ground Floor, Room W12-140, Washington, DC 20590-0001.
     Fax: Fax comments to the Docket Operations at 202-493-
2251.
     Hand Delivery or Courier: Bring comments to Docket 
Operations in Room W12-140 of the West Building Ground Floor at 1200 
New Jersey Avenue, SE., Washington, DC, between 9 a.m. and 5 p.m., 
Monday through Friday, except Federal holidays.
    Docket: To read background documents or comments received, go to 
http://www.regulations.gov at any time or to Room W12-140 of the West 
Building Ground Floor at 1200 New Jersey Avenue, SE., Washington, DC, 
between 9 a.m. and 5 p.m., Monday through Friday, except Federal 
holidays.

Availability of Rulemaking Documents

    You can get an electronic copy using the Internet by:
    (1) Searching the Federal eRulemaking Portal (http://www.regulations.gov);
    (2) Visiting the FAA's Regulations and Policies Web page at http://www.faa.gov/regulations_policies/; or
    (3) Accessing the Government Printing Office's web page at http://www.gpoaccess.gov/fr/index.html.
    You can also get a copy by submitting a request to the Federal 
Aviation Administration, Office of Rulemaking, ARM-1, 800 Independence 
Avenue, SW., Washington, DC 20591, or by calling (202) 267-9680. Make 
sure to identify the docket number, or amendment number of this 
rulemaking.

Small Business Regulatory Enforcement Fairness Act

    The Small Business Regulatory Enforcement Fairness Act (SFREFA) of 
1996 requires FAA to comply with

[[Page 42494]]

small entity requests for information or advice about compliance with 
statutes and regulations within its jurisdiction. If you are a small 
entity and you have a question regarding this document, you may contact 
its local FAA official, or the person listed under FOR FURTHER 
INFORMATION CONTACT. You can find out more about SBREFA on the Internet 
at http://www.faa.gov/regulations_policies/rulemaking/sbre_act/.

List of Subjects

14 CFR part 25

    Aircraft, Aviation safety, Incorporation by reference, Reporting 
and recordkeeping requirements.

14 CFR part 26

    Aircraft, Aviation safety, Continued airworthiness.

14 CFR part 121

    Air carriers, Aircraft, Aviation safety, Reporting and 
recordkeeping requirements, Safety, Transportation.

14 CFR part 125

    Aircraft, Aviation safety, Reporting and recordkeeping 
requirements.

14 CFR part 129

    Air carriers, Aircraft, Aviation safety, Reporting and 
recordkeeping requirements, Security measures.

V. The Amendment

0
In consideration of the foregoing, the Federal Aviation Administration 
amends Chapter 1 of Title 14, Code of Federal Regulations (CFR) parts 
25, 26, 121, 125, and 129, as follows:

PART 25--AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY AIRPLANES

0
1. The authority citation for part 25 continues to read as follows:

    Authority: 49 U.S.C. 106(g), 40113, 44701, 44702 and 44704.


0
2. Part 25 is amended by adding a new Sec.  25.5 to read as follows:


Sec.  25.5  Incorporations by reference.

    (a) The materials listed in this section are incorporated by 
reference in the corresponding sections noted. These incorporations by 
reference were approved by the Director of the Federal Register in 
accordance with 5 U.S.C. 552(a) and 1 CFR part 51. These materials are 
incorporated as they exist on the date of the approval, and notice of 
any change in these materials will be published in the Federal 
Register. The materials are available for purchase at the corresponding 
addresses noted below, and all are available for inspection at the 
National Archives and Records Administration (NARA), and at FAA, 
Transport Airplane Directorate, Aircraft Certification Service, 1601 
Lind Avenue, SW., Renton, Washington 98057-3356. For information on the 
availability of this material at NARA, call 202-741-6030, or go to: 
http://www.archives.gov/federal_register/code_of_federal_regulations/ibr_locations.html.
    (b) The following materials are available for purchase from the 
following address: The National Technical Information Services (NTIS), 
Springfield, Virginia 22166.
    (1) Fuel Tank Flammability Assessment Method User's Manual, dated 
May 2008, document number DOT/FAA/AR-05/8, IBR approved for Sec.  
25.981 and Appendix N. It can also be obtained at the following Web 
site: http://www.fire.tc.faa.gov/systems/fueltank/FTFAM.stm.
    (2) [Reserved]

0
3. Amend Sec.  25.981 by revising paragraphs (b) and (c) and adding a 
new paragraph (d) to read as follows:


Sec.  25.981  Fuel tank explosion prevention.

* * * * *
    (b) Except as provided in paragraphs (b)(2) and (c) of this 
section, no fuel tank Fleet Average Flammability Exposure on an 
airplane may exceed three percent of the Flammability Exposure 
Evaluation Time (FEET) as defined in Appendix N of this part, or that 
of a fuel tank within the wing of the airplane model being evaluated, 
whichever is greater. If the wing is not a conventional unheated 
aluminum wing, the analysis must be based on an assumed Equivalent 
Conventional Unheated Aluminum Wing Tank.
    (1) Fleet Average Flammability Exposure is determined in accordance 
with Appendix N of this part. The assessment must be done in accordance 
with the methods and procedures set forth in the Fuel Tank Flammability 
Assessment Method User's Manual, dated May 2008, document number DOT/
FAA/AR-05/8 (incorporated by reference, see Sec.  25.5).
    (2) Any fuel tank other than a main fuel tank on an airplane must 
meet the flammability exposure criteria of Appendix M to this part if 
any portion of the tank is located within the fuselage contour.
    (3) As used in this paragraph,
    (i) Equivalent Conventional Unheated Aluminum Wing Tank is an 
integral tank in an unheated semi-monocoque aluminum wing of a subsonic 
airplane that is equivalent in aerodynamic performance, structural 
capability, fuel tank capacity and tank configuration to the designed 
wing.
    (ii) Fleet Average Flammability Exposure is defined in Appendix N 
to this part and means the percentage of time each fuel tank ullage is 
flammable for a fleet of an airplane type operating over the range of 
flight lengths.
    (iii) Main Fuel Tank means a fuel tank that feeds fuel directly 
into one or more engines and holds required fuel reserves continually 
throughout each flight.
    (c) Paragraph (b) of this section does not apply to a fuel tank if 
means are provided to mitigate the effects of an ignition of fuel 
vapors within that fuel tank such that no damage caused by an ignition 
will prevent continued safe flight and landing.
    (d) Critical design configuration control limitations (CDCCL), 
inspections, or other procedures must be established, as necessary, to 
prevent development of ignition sources within the fuel tank system 
pursuant to paragraph (a) of this section, to prevent increasing the 
flammability exposure of the tanks above that permitted under paragraph 
(b) of this section, and to prevent degradation of the performance and 
reliability of any means provided according to paragraphs (a) or (c) of 
this section. These CDCCL, inspections, and procedures must be included 
in the Airworthiness Limitations section of the instructions for 
continued airworthiness required by Sec.  25.1529. Visible means of 
identifying critical features of the design must be placed in areas of 
the airplane where foreseeable maintenance actions, repairs, or 
alterations may compromise the critical design configuration control 
limitations (e.g., color-coding of wire to identify separation 
limitation). These visible means must also be identified as CDCCL.

0
4. Part 25 is amended by adding a new APPENDIX M to read as follows:

APPENDIX M TO PART 25--FUEL TANK SYSTEM FLAMMABILITY REDUCTION MEANS

    M25.1 Fuel tank flammability exposure requirements.
    (a) The Fleet Average Flammability Exposure of each fuel tank, 
as determined in accordance with Appendix N of this part, may not 
exceed 3 percent of the Flammability Exposure Evaluation Time 
(FEET), as defined in Appendix N of this part. As a portion of this 
3 percent, if flammability reduction means (FRM) are used, each of 
the following time periods may not exceed 1.8 percent of the FEET:
    (1) When any FRM is operational but the fuel tank is not inert 
and the tank is flammable; and
    (2) When any FRM is inoperative and the tank is flammable.
    (b) The Fleet Average Flammability Exposure, as defined in 
Appendix N of this

[[Page 42495]]

part, of each fuel tank may not exceed 3 percent of the portion of 
the FEET occurring during either ground or takeoff/climb phases of 
flight during warm days. The analysis must consider the following 
conditions.
    (1) The analysis must use the subset of those flights that begin 
with a sea level ground ambient temperature of 80[deg] F (standard 
day plus 21[deg] F atmosphere) or above, from the flammability 
exposure analysis done for overall performance.
    (2) For the ground and takeoff/climb phases of flight, the 
average flammability exposure must be calculated by dividing the 
time during the specific flight phase the fuel tank is flammable by 
the total time of the specific flight phase.
    (3) Compliance with this paragraph may be shown using only those 
flights for which the airplane is dispatched with the flammability 
reduction means operational.
    M25.2 Showing compliance.
    (a) The applicant must provide data from analysis, ground 
testing, and flight testing, or any combination of these, that:
    (1) Validate the parameters used in the analysis required by 
paragraph M25.1 of this appendix;
    (2) Substantiate that the FRM is effective at limiting 
flammability exposure in all compartments of each tank for which the 
FRM is used to show compliance with paragraph M25.1 of this 
appendix; and
    (3) Describe the circumstances under which the FRM would not be 
operated during each phase of flight.
    (b) The applicant must validate that the FRM meets the 
requirements of paragraph M25.1 of this appendix with any airplane 
or engine configuration affecting the performance of the FRM for 
which approval is sought.
    M25.3 Reliability indications and maintenance access.
    (a) Reliability indications must be provided to identify 
failures of the FRM that would otherwise be latent and whose 
identification is necessary to ensure the fuel tank with an FRM 
meets the fleet average flammability exposure requirements listed in 
paragraph M25.1 of this appendix, including when the FRM is 
inoperative.
    (b) Sufficient accessibility to FRM reliability indications must 
be provided for maintenance personnel or the flightcrew.
    (c) The access doors and panels to the fuel tanks with FRMs 
(including any tanks that communicate with a tank via a vent 
system), and to any other confined spaces or enclosed areas that 
could contain hazardous atmosphere under normal conditions or 
failure conditions, must be permanently stenciled, marked, or 
placarded to warn maintenance personnel of the possible presence of 
a potentially hazardous atmosphere.
    M25.4 Airworthiness limitations and procedures.
    (a) If FRM is used to comply with paragraph M25.1 of this 
appendix, Airworthiness Limitations must be identified for all 
maintenance or inspection tasks required to identify failures of 
components within the FRM that are needed to meet paragraph M25.1 of 
this appendix.
    (b) Maintenance procedures must be developed to identify any 
hazards to be considered during maintenance of the FRM. These 
procedures must be included in the instructions for continued 
airworthiness (ICA).
    M25.5 Reliability reporting.
    The effects of airplane component failures on FRM reliability 
must be assessed on an on-going basis. The applicant/holder must do 
the following:
    (a) Demonstrate effective means to ensure collection of FRM 
reliability data. The means must provide data affecting FRM 
reliability, such as component failures.
    (b) Unless alternative reporting procedures are approved by the 
FAA Oversight Office, as defined in part 26 of this subchapter, 
provide a report to the FAA every six months for the first five 
years after service introduction. After that period, continued 
reporting every six months may be replaced with other reliability 
tracking methods found acceptable to the FAA or eliminated if it is 
established that the reliability of the FRM meets, and will continue 
to meet, the exposure requirements of paragraph M25.1 of this 
appendix.
    (c) Develop service instructions or revise the applicable 
airplane manual, according to a schedule approved by the FAA 
Oversight Office, as defined in part 26 of this subchapter, to 
correct any failures of the FRM that occur in service that could 
increase any fuel tank's Fleet Average Flammability Exposure to more 
than that required by paragraph M25.1 of this appendix.


0
5. Part 25 is amended by adding a new APPENDIX N to read as follows:

APPENDIX N TO PART 25--FUEL TANK FLAMMABILITY EXPOSURE AND RELIABILITY 
ANALYSIS

    N25.1 General.
    (a) This appendix specifies the requirements for conducting fuel 
tank fleet average flammability exposure analyses required to meet 
Sec.  25.981(b) and Appendix M of this part. For fuel tanks 
installed in aluminum wings, a qualitative assessment is sufficient 
if it substantiates that the tank is a conventional unheated wing 
tank.
    (b) This appendix defines parameters affecting fuel tank 
flammability that must be used in performing the analysis. These 
include parameters that affect all airplanes within the fleet, such 
as a statistical distribution of ambient temperature, fuel flash 
point, flight lengths, and airplane descent rate. Demonstration of 
compliance also requires application of factors specific to the 
airplane model being evaluated. Factors that need to be included are 
maximum range, cruise mach number, typical altitude where the 
airplane begins initial cruise phase of flight, fuel temperature 
during both ground and flight times, and the performance of a 
flammability reduction means (FRM) if installed.
    (c) The following definitions, input variables, and data tables 
must be used in the program to determine fleet average flammability 
exposure for a specific airplane model.
    N25.2 Definitions.
    (a) Bulk Average Fuel Temperature means the average fuel 
temperature within the fuel tank or different sections of the tank 
if the tank is subdivided by baffles or compartments.
    (b) Flammability Exposure Evaluation Time (FEET). The time from 
the start of preparing the airplane for flight, through the flight 
and landing, until all payload is unloaded, and all passengers and 
crew have disembarked. In the Monte Carlo program, the flight time 
is randomly selected from the Flight Length Distribution (Table 2), 
the pre-flight times are provided as a function of the flight time, 
and the post-flight time is a constant 30 minutes.
    (c) Flammable. With respect to a fluid or gas, flammable means 
susceptible to igniting readily or to exploding (14 CFR Part 1, 
Definitions). A non-flammable ullage is one where the fuel-air vapor 
is too lean or too rich to burn or is inert as defined below. For 
the purposes of this appendix, a fuel tank that is not inert is 
considered flammable when the bulk average fuel temperature within 
the tank is within the flammable range for the fuel type being used. 
For any fuel tank that is subdivided into sections by baffles or 
compartments, the tank is considered flammable when the bulk average 
fuel temperature within any section of the tank, that is not inert, 
is within the flammable range for the fuel type being used.
    (d) Flash Point. The flash point of a flammable fluid means the 
lowest temperature at which the application of a flame to a heated 
sample causes the vapor to ignite momentarily, or ``flash.'' Table 1 
of this appendix provides the flash point for the standard fuel to 
be used in the analysis.
    (e) Fleet average flammability exposure is the percentage of the 
flammability exposure evaluation time (FEET) each fuel tank ullage 
is flammable for a fleet of an airplane type operating over the 
range of flight lengths in a world-wide range of environmental 
conditions and fuel properties as defined in this appendix.
    (f) Gaussian Distribution is another name for the normal 
distribution, a symmetrical frequency distribution having a precise 
mathematical formula relating the mean and standard deviation of the 
samples. Gaussian distributions yield bell-shaped frequency curves 
having a preponderance of values around the mean with progressively 
fewer observations as the curve extends outward.
    (g) Hazardous atmosphere. An atmosphere that may expose 
maintenance personnel, passengers or flight crew to the risk of 
death, incapacitation, impairment of ability to self-rescue (that 
is, escape unaided from a confined space), injury, or acute illness.
    (h) Inert. For the purpose of this appendix, the tank is 
considered inert when the bulk average oxygen concentration within 
each compartment of the tank is 12 percent or less from sea level up 
to 10,000 feet altitude, then linearly increasing from 12 percent at 
10,000 feet to 14.5 percent at 40,000 feet altitude, and 
extrapolated linearly above that altitude.
    (i) Inerting. A process where a noncombustible gas is introduced 
into the ullage of a fuel tank so that the ullage becomes non-
flammable.
    (j) Monte Carlo Analysis. The analytical method that is 
specified in this appendix as the compliance means for assessing the 
fleet average flammability exposure time for a fuel tank.

[[Page 42496]]

    (k) Oxygen evolution occurs when oxygen dissolved in the fuel is 
released into the ullage as the pressure and temperature in the fuel 
tank are reduced.
    (l) Standard deviation is a statistical measure of the 
dispersion or variation in a distribution, equal to the square root 
of the arithmetic mean of the squares of the deviations from the 
arithmetic means.
    (m) Transport Effects. For purposes of this appendix, transport 
effects are the change in fuel vapor concentration in a fuel tank 
caused by low fuel conditions and fuel condensation and 
vaporization.
    (n) Ullage. The volume within the fuel tank not occupied by 
liquid fuel.
    N25.3 Fuel tank flammability exposure analysis.
    (a) A flammability exposure analysis must be conducted for the 
fuel tank under evaluation to determine fleet average flammability 
exposure for the airplane and fuel types under evaluation. For fuel 
tanks that are subdivided by baffles or compartments, an analysis 
must be performed either for each section of the tank, or for the 
section of the tank having the highest flammability exposure. 
Consideration of transport effects is not allowed in the analysis. 
The analysis must be done in accordance with the methods and 
procedures set forth in the Fuel Tank Flammability Assessment Method 
User's Manual, dated May 2008, document number DOT/FAA/AR-05/8 
(incorporated by reference, see Sec.  25.5). The parameters 
specified in sections N25.3(b) and (c) of this appendix must be used 
in the fuel tank flammability exposure ``Monte Carlo'' analysis.
    (b) The following parameters are defined in the Monte Carlo 
analysis and provided in paragraph N25.4 of this appendix:
    (1) Cruise Ambient Temperature, as defined in this appendix.
    (2) Ground Ambient Temperature, as defined in this appendix.
    (3) Fuel Flash Point, as defined in this appendix.
    (4) Flight Length Distribution, as defined in Table 2 of this 
appendix.
    (5) Airplane Climb and Descent Profiles, as defined in the Fuel 
Tank Flammability Assessment Method User's Manual, dated May 2008, 
document number DOT/FAA/AR-05/8 (incorporated by reference in Sec.  
25.5).
    (c) Parameters that are specific to the particular airplane 
model under evaluation that must be provided as inputs to the Monte 
Carlo analysis are:
    (1) Airplane cruise altitude.
    (2) Fuel tank quantities. If fuel quantity affects fuel tank 
flammability, inputs to the Monte Carlo analysis must be provided 
that represent the actual fuel quantity within the fuel tank or 
compartment of the fuel tank throughout each of the flights being 
evaluated. Input values for this data must be obtained from ground 
and flight test data or the approved FAA fuel management procedures.
    (3) Airplane cruise mach number.
    (4) Airplane maximum range.
    (5) Fuel tank thermal characteristics. If fuel temperature 
affects fuel tank flammability, inputs to the Monte Carlo analysis 
must be provided that represent the actual bulk average fuel 
temperature within the fuel tank at each point in time throughout 
each of the flights being evaluated. For fuel tanks that are 
subdivided by baffles or compartments, bulk average fuel temperature 
inputs must be provided for each section of the tank. Input values 
for these data must be obtained from ground and flight test data or 
a thermal model of the tank that has been validated by ground and 
flight test data.
    (6) Maximum airplane operating temperature limit, as defined by 
any limitations in the airplane flight manual.
    (7) Airplane Utilization. The applicant must provide data 
supporting the number of flights per day and the number of hours per 
flight for the specific airplane model under evaluation. If there is 
no existing airplane fleet data to support the airplane being 
evaluated, the applicant must provide substantiation that the number 
of flights per day and the number of hours per flight for that 
airplane model is consistent with the existing fleet data they 
propose to use.
    (d) Fuel Tank FRM Model. If FRM is used, an FAA approved Monte 
Carlo program must be used to show compliance with the flammability 
requirements of Sec.  25.981 and Appendix M of this part. The 
program must determine the time periods during each flight phase 
when the fuel tank or compartment with the FRM would be flammable. 
The following factors must be considered in establishing these time 
periods:
    (1) Any time periods throughout the flammability exposure 
evaluation time and under the full range of expected operating 
conditions, when the FRM is operating properly but fails to maintain 
a non-flammable fuel tank because of the effects of the fuel tank 
vent system or other causes,
    (2) If dispatch with the system inoperative under the Master 
Minimum Equipment List (MMEL) is requested, the time period assumed 
in the reliability analysis (60 flight hours must be used for a 10-
day MMEL dispatch limit unless an alternative period has been 
approved by the Administrator),
    (3) Frequency and duration of time periods of FRM inoperability, 
substantiated by test or analysis acceptable to the FAA, caused by 
latent or known failures, including airplane system shut-downs and 
failures that could cause the FRM to shut down or become 
inoperative.
    (4) Effects of failures of the FRM that could increase the 
flammability exposure of the fuel tank.
    (5) If an FRM is used that is affected by oxygen concentrations 
in the fuel tank, the time periods when oxygen evolution from the 
fuel results in the fuel tank or compartment exceeding the inert 
level. The applicant must include any times when oxygen evolution 
from the fuel in the tank or compartment under evaluation would 
result in a flammable fuel tank. The oxygen evolution rate that must 
be used is defined in the Fuel Tank Flammability Assessment Method 
User's Manual, dated May 2008, document number DOT/FAA/AR-05/8 
(incorporated by reference in Sec.  25.5).
    (6) If an inerting system FRM is used, the effects of any air 
that may enter the fuel tank following the last flight of the day 
due to changes in ambient temperature, as defined in Table 4, during 
a 12-hour overnight period.
    (e) The applicant must submit to the FAA Oversight Office for 
approval the fuel tank flammability analysis, including the 
airplane-specific parameters identified under paragraph N25.3(c) of 
this appendix and any deviations from the parameters identified in 
paragraph N25.3(b) of this appendix that affect flammability 
exposure, substantiating data, and any airworthiness limitations and 
other conditions assumed in the analysis.
    N25.4 Variables and data tables.
    The following data must be used when conducting a flammability 
exposure analysis to determine the fleet average flammability 
exposure. Variables used to calculate fleet flammability exposure 
must include atmospheric ambient temperatures, flight length, 
flammability exposure evaluation time, fuel flash point, thermal 
characteristics of the fuel tank, overnight temperature drop, and 
oxygen evolution from the fuel into the ullage.
    (a) Atmospheric Ambient Temperatures and Fuel Properties.
    (1) In order to predict flammability exposure during a given 
flight, the variation of ground ambient temperatures, cruise ambient 
temperatures, and a method to compute the transition from ground to 
cruise and back again must be used. The variation of the ground and 
cruise ambient temperatures and the flash point of the fuel is 
defined by a Gaussian curve, given by the 50 percent value and a 
1-standard deviation value.
    (2) Ambient Temperature: Under the program, the ground and 
cruise ambient temperatures are linked by a set of assumptions on 
the atmosphere. The temperature varies with altitude following the 
International Standard Atmosphere (ISA) rate of change from the 
ground ambient temperature until the cruise temperature for the 
flight is reached. Above this altitude, the ambient temperature is 
fixed at the cruise ambient temperature. This results in a variation 
in the upper atmospheric temperature. For cold days, an inversion is 
applied up to 10,000 feet, and then the ISA rate of change is used.
    (3) Fuel properties:
    (i) For Jet A fuel, the variation of flash point of the fuel is 
defined by a Gaussian curve, given by the 50 percent value and a 
1-standard deviation, as shown in Table 1 of this 
appendix.
    (ii) The flammability envelope of the fuel that must be used for 
the flammability exposure analysis is a function of the flash point 
of the fuel selected by the Monte Carlo for a given flight. The 
flammability envelope for the fuel is defined by the upper 
flammability limit (UFL) and lower flammability limit (LFL) as 
follows:
    (A) LFL at sea level = flash point temperature of the fuel at 
sea level minus 10 [deg] F. LFL decreases from sea level value with 
increasing altitude at a rate of 1 [deg]F per 808 feet.
    (B) UFL at sea level = flash point temperature of the fuel at 
sea level plus 63.5 [deg] F. UFL decreases from the sea level value 
with increasing altitude at a rate of 1 [deg]F per 512 feet.

[[Page 42497]]

    (4) For each flight analyzed, a separate random number must be 
generated for each of the three parameters (ground ambient 
temperature, cruise ambient temperature, and fuel flash point) using 
the Gaussian distribution defined in Table 1 of this appendix.

Table 1.--Gaussian Distribution for Ground Ambient Temperature, Cruise Ambient Temperature, and Fuel Flash Point
----------------------------------------------------------------------------------------------------------------
                                                                            Temperature in deg F
                                                           -----------------------------------------------------
                         Parameter                           Ground ambient    Cruise ambient   Fuel flash point
                                                               temperature       temperature          (FP)
----------------------------------------------------------------------------------------------------------------
Mean Temp.................................................             59.95               -70               120
Neg 1 std dev.............................................             20.14                 8                 8
Pos 1 std dev.............................................             17.28                 8                 8
----------------------------------------------------------------------------------------------------------------

    (b) The Flight Length Distribution defined in Table 2 must be 
used in the Monte Carlo analysis.

                                      Table 2.--Flight Length Distribution
----------------------------------------------------------------------------------------------------------------
Flight length (NM)                           Airplane maximum range--nautical miles (NM)
----------------------------------------------------------------------------------------------------------------
  From       To       1000      2000      3000      4000      5000     6000     7000     8000     9000    10000
----------------------------------------------------------------------------------------------------------------
          ........                      Distribution of flight lengths (percentage of total)
----------------------------------------------------------------------------------------------------------------
      0       200      11.7       7.5       6.2       5.5       4.7      4.0      3.4      3.0      2.6      2.3
    200       400      27.3      19.9      17.0      15.2      13.2     11.4      9.7      8.5      7.5      6.7
    400       600      46.3      40.0      35.7      32.6      28.5     24.9     21.2     18.7     16.4     14.8
    600       800      10.3      11.6      11.0      10.2       9.1      8.0      6.9      6.1      5.4      4.8
    800      1000       4.4       8.5       8.6       8.2       7.4      6.6      5.7      5.0      4.5      4.0
   1000      1200       0.0       4.8       5.3       5.3       4.8      4.3      3.8      3.3      3.0      2.7
   1200      1400       0.0       3.6       4.4       4.5       4.2      3.8      3.3      3.0      2.7      2.4
   1400      1600       0.0       2.2       3.3       3.5       3.3      3.1      2.7      2.4      2.2      2.0
   1600      1800       0.0       1.2       2.3       2.6       2.5      2.4      2.1      1.9      1.7      1.6
   1800      2000       0.0       0.7       2.2       2.6       2.6      2.5      2.2      2.0      1.8      1.7
   2000      2200       0.0       0.0       1.6       2.1       2.2      2.1      1.9      1.7      1.6      1.4
   2200      2400       0.0       0.0       1.1       1.6       1.7      1.7      1.6      1.4      1.3      1.2
   2400      2600       0.0       0.0       0.7       1.2       1.4      1.4      1.3      1.2      1.1      1.0
   2600      2800       0.0       0.0       0.4       0.9       1.0      1.1      1.0      0.9      0.9      0.8
   2800      3000       0.0       0.0       0.2       0.6       0.7      0.8      0.7      0.7      0.6      0.6
   3000      3200       0.0       0.0       0.0       0.6       0.8      0.8      0.8      0.8      0.7      0.7
   3200      3400       0.0       0.0       0.0       0.7       1.1      1.2      1.2      1.1      1.1      1.0
   3400      3600       0.0       0.0       0.0       0.7       1.3      1.6      1.6      1.5      1.5      1.4
   3600      3800       0.0       0.0       0.0       0.9       2.2      2.7      2.8      2.7      2.6      2.5
   3800      4000       0.0       0.0       0.0       0.5       2.0      2.6      2.8      2.8      2.7      2.6
   4000      4200       0.0       0.0       0.0       0.0       2.1      3.0      3.2      3.3      3.2      3.1
   4200      4400       0.0       0.0       0.0       0.0       1.4      2.2      2.5      2.6      2.6      2.5
   4400      4600       0.0       0.0       0.0       0.0       1.0      2.0      2.3      2.5      2.5      2.4
   4600      4800       0.0       0.0       0.0       0.0       0.6      1.5      1.8      2.0      2.0      2.0
   4800      5000       0.0       0.0       0.0       0.0       0.2      1.0      1.4      1.5      1.6      1.5
   5000      5200       0.0       0.0       0.0       0.0       0.0      0.8      1.1      1.3      1.3      1.3
   5200      5400       0.0       0.0       0.0       0.0       0.0      0.8      1.2      1.5      1.6      1.6
   5400      5600       0.0       0.0       0.0       0.0       0.0      0.9      1.7      2.1      2.2      2.3
   5600      5800       0.0       0.0       0.0       0.0       0.0      0.6      1.6      2.2      2.4      2.5
   5800      6000       0.0       0.0       0.0       0.0       0.0      0.2      1.8      2.4      2.8      2.9
   6000      6200       0.0       0.0       0.0       0.0       0.0      0.0      1.7      2.6      3.1      3.3
   6200      6400       0.0       0.0       0.0       0.0       0.0      0.0      1.4      2.4      2.9      3.1
   6400      6600       0.0       0.0       0.0       0.0       0.0      0.0      0.9      1.8      2.2      2.5
   6600      6800       0.0       0.0       0.0       0.0       0.0      0.0      0.5      1.2      1.6      1.9
   6800      7000       0.0       0.0       0.0       0.0       0.0      0.0      0.2      0.8      1.1      1.3
   7000      7200       0.0       0.0       0.0       0.0       0.0      0.0      0.0      0.4      0.7      0.8
   7200      7400       0.0       0.0       0.0       0.0       0.0      0.0      0.0      0.3      0.5      0.7
   7400      7600       0.0       0.0       0.0       0.0       0.0      0.0      0.0      0.2      0.5      0.6
   7600      7800       0.0       0.0       0.0       0.0       0.0      0.0      0.0      0.1      0.5      0.7
   7800      8000       0.0       0.0       0.0       0.0       0.0      0.0      0.0      0.1      0.6      0.8
   8000      8200       0.0       0.0       0.0       0.0       0.0      0.0      0.0      0.0      0.5      0.8
   8200      8400       0.0       0.0       0.0       0.0       0.0      0.0      0.0      0.0      0.5      1.0
   8400      8600       0.0       0.0       0.0       0.0       0.0      0.0      0.0      0.0      0.6      1.3
   8600      8800       0.0       0.0       0.0       0.0       0.0      0.0      0.0      0.0      0.4      1.1
   8800      9000       0.0       0.0       0.0       0.0       0.0      0.0      0.0      0.0      0.2      0.8
   9000      9200       0.0       0.0       0.0       0.0       0.0      0.0      0.0      0.0      0.0      0.5
   9200      9400       0.0       0.0       0.0       0.0       0.0      0.0      0.0      0.0      0.0      0.2

[[Page 42498]]

 
   9400      9600       0.0       0.0       0.0       0.0       0.0      0.0      0.0      0.0      0.0      0.1
   9600      9800       0.0       0.0       0.0       0.0       0.0      0.0      0.0      0.0      0.0      0.1
   9800     10000       0.0       0.0       0.0       0.0       0.0      0.0      0.0      0.0      0.0      0.1
----------------------------------------------------------------------------------------------------------------

    (c) Overnight Temperature Drop. For airplanes on which FRM is 
installed, the overnight temperature drop for this appendix is 
defined using:
    (1) A temperature at the beginning of the overnight period that 
equals the landing temperature of the previous flight that is a 
random value based on a Gaussian distribution; and
    (2) An overnight temperature drop that is a random value based 
on a Gaussian distribution.
    (3) For any flight that will end with an overnight ground period 
(one flight per day out of an average number of flights per day, 
depending on utilization of the particular airplane model being 
evaluated), the landing outside air temperature (OAT) is to be 
chosen as a random value from the following Gaussian curve:

                Table 3.--Landing Outside Air Temperature
------------------------------------------------------------------------
                                                        Landing outside
                      Parameter                         air temperature
                                                             [deg]F
------------------------------------------------------------------------
Mean Temperature.....................................              58.68
negative 1 std dev...................................              20.55
positive 1 std dev...................................              13.21
------------------------------------------------------------------------

    (4) The outside ambient air temperature (OAT) overnight 
temperature drop is to be chosen as a random value from the 
following Gaussian curve:

              Table 4.--Outside Air Temperature (OAT) Drop
------------------------------------------------------------------------
                                                             OAT drop
                        Parameter                           temperature
                                                              [deg]F
------------------------------------------------------------------------
Mean Temp...............................................            12.0
1 std dev...............................................             6.0
------------------------------------------------------------------------

    (d) Number of Simulated Flights Required in Analysis. In order 
for the Monte Carlo analysis to be valid for showing compliance with 
the fleet average and warm day flammability exposure requirements, 
the applicant must run the analysis for a minimum number of flights 
to ensure that the fleet average and warm day flammability exposure 
for the fuel tank under evaluation meets the applicable flammability 
limits defined in Table 5 of this appendix.

                  Table 5.--Flammability Exposure Limit
------------------------------------------------------------------------
                                         Maximum            Maximum
                                     acceptable Monte   acceptable Monte
                                      Carlo average      Carlo average
                                        fuel tank          fuel tank
Minimum number of flights in Monte     flammability       flammability
          Carlo analysis                 exposure           exposure
                                    (percent) to meet  (percent) to meet
                                        3 percent      7 percent part 26
                                       requirements       requirements
------------------------------------------------------------------------
10,000............................               2.91               6.79
100,000...........................               2.98               6.96
1,000,000.........................               3.00               7.00
------------------------------------------------------------------------

PART 26--CONTINUED AIRWORTHINESS AND SAFETY IMPROVEMENTS FOR 
TRANSPORT CATEGORY AIRPLANES

0
6. The authority citation for part 26 continues to read as follows:

    Authority: 49 U.S.C. 106(g), 40113, 44701, 44702 and 44704.


0
7. Revise Sec.  26.5 to read as follows:


Sec.  26.5  Applicability Table.

    Table 1 of this section provides an overview of the applicability 
of this part. It provides guidance in identifying what sections apply 
to various types of entities. The specific applicability of each 
subpart and section is specified in the regulatory text.

                                    Table 1.--Applicability of Part 26 Rules
----------------------------------------------------------------------------------------------------------------
                                                                  Applicable sections
                                      --------------------------------------------------------------------------
                                        Subpart B EAPAS/    Subpart D fuel tank    Subpart E  damage tolerance
        Effective date of rule                 FTS             flammability                    data
                                      --------------------------------------------------------------------------
                                        December 10, 2007   September 19, 2008           January 11, 2008
----------------------------------------------------------------------------------------------------------------
Existing \1\ TC Holders..............               26.11                 26.33  26.43, 26.45, 26.49
Pending \1\ TC Applicants............               26.11                 26.37  26.43, 26.45
Existing \1\ STC Holders.............                 N/A                 26.35  26.47, 26.49
Pending \1\ STC/ATC Applicants.......               26.11                 26.35  26.45, 26.47, 26.49
Future \2\ STC/ATC Applicants........               26.11                 26.35  26.45, 26.47, 26.49
Manufacturers........................                 N/A                 26.39  N/A
----------------------------------------------------------------------------------------------------------------
\1\ As of the effective date of the identified rule.
\2\ Application made after the effective date of the identified rule.


[[Page 42499]]


0
8. Amend part 26 by adding a new subpart D to read as follows:
Subpart D--FUEL TANK FLAMMABILITY

General

Sec.
26.31 Definitions.
26.33 Holders of type certificates: Fuel tank flammability.
26.35 Changes to type certificates affecting fuel tank flammability.
26.37 Pending type certification projects: Fuel tank flammability.
26.39 Newly produced airplanes: Fuel tank flammability.

Subpart D--Fuel Tank Flammability

General


Sec.  26.31  Definitions.

    For purposes of this subpart--
    (a) Fleet Average Flammability Exposure has the meaning defined in 
Appendix N of part 25 of this chapter.
    (b) Normally Emptied means a fuel tank other than a Main Fuel Tank. 
Main Fuel Tank is defined in 14 CFR 25.981(b).


Sec.  26.33  Holders of type certificates: Fuel tank flammability.

    (a) Applicability. This section applies to U.S. type certificated 
transport category, turbine-powered airplanes, other than those 
designed solely for all-cargo operations, for which the State of 
Manufacture issued the original certificate of airworthiness or export 
airworthiness approval on or after January 1, 1992, that, as a result 
of original type certification or later increase in capacity have:
    (1) A maximum type-certificated passenger capacity of 30 or more, 
or
    (2) A maximum payload capacity of 7,500 pounds or more.
    (b) Flammability Exposure Analysis. (1) General. Within 150 days 
after September 19, 2008, holders of type certificates must submit for 
approval to the FAA Oversight Office a flammability exposure analysis 
of all fuel tanks defined in the type design, as well as all design 
variations approved under the type certificate that affect flammability 
exposure. This analysis must be conducted in accordance with Appendix N 
of part 25 of this chapter.
    (2) Exception. This paragraph (b) does not apply to--
    (i) Fuel tanks for which the type certificate holder has notified 
the FAA under paragraph (g) of this section that it will provide design 
changes and service instructions for Flammability Reduction Means or an 
Ignition Mitigation Means (IMM) meeting the requirements of paragraph 
(c) of this section.
    (ii) Fuel tanks substantiated to be conventional unheated aluminum 
wing tanks.
    (c) Design Changes. For fuel tanks with a Fleet Average 
Flammability Exposure exceeding 7 percent, one of the following design 
changes must be made.
    (1) Flammability Reduction Means (FRM). A means must be provided to 
reduce the fuel tank flammability.
    (i) Fuel tanks that are designed to be Normally Emptied must meet 
the flammability exposure criteria of Appendix M of part 25 of this 
chapter if any portion of the tank is located within the fuselage 
contour.
    (ii) For all other fuel tanks, the FRM must meet all of the 
requirements of Appendix M of part 25 of this chapter, except, instead 
of complying with paragraph M25.1 of this appendix, the Fleet Average 
Flammability Exposure may not exceed 7 percent.
    (2) Ignition Mitigation Means (IMM). A means must be provided to 
mitigate the effects of an ignition of fuel vapors within the fuel tank 
such that no damage caused by an ignition will prevent continued safe 
flight and landing.
    (d) Service Instructions. No later than September 20, 2010, holders 
of type certificates required by paragraph (c) of this section to make 
design changes must meet the requirements specified in either paragraph 
(d)(1) or (d)(2) of this section. The required service instructions 
must identify each airplane subject to the applicability provisions of 
paragraph (a) of this section.
    (1) FRM. The type certificate holder must submit for approval by 
the FAA Oversight Office design changes and service instructions for 
installation of fuel tank flammability reduction means (FRM) meeting 
the criteria of paragraph (c) of this section.
    (2) IMM. The type certificate holder must submit for approval by 
the FAA Oversight Office design changes and service instructions for 
installation of fuel tank IMM that comply with 14 CFR 25.981(c) in 
effect on September 19, 2008.
    (e) Instructions for Continued Airworthiness (ICA). No later than 
September 20, 2010, holders of type certificates required by paragraph 
(c) of this section to make design changes must submit for approval by 
the FAA Oversight Office, critical design configuration control 
limitations (CDCCL), inspections, or other procedures to prevent 
increasing the flammability exposure of any tanks equipped with FRM 
above that permitted under paragraph (c)(1) of this section and to 
prevent degradation of the performance of any IMM provided under 
paragraph (c)(2) of this section. These CDCCL, inspections, and 
procedures must be included in the Airworthiness Limitations Section 
(ALS) of the ICA required by 14 CFR 25.1529 or paragraph (f) of this 
section. Unless shown to be impracticable, visible means to identify 
critical features of the design must be placed in areas of the airplane 
where foreseeable maintenance actions, repairs, or alterations may 
compromise the critical design configuration limitations. These visible 
means must also be identified as a CDCCL.
    (f) Airworthiness Limitations. Unless previously accomplished, no 
later than September 20, 2010, holders of type certificates affected by 
this section must establish an ALS of the maintenance manual or ICA for 
each airplane configuration evaluated under paragraph (b)(1) of this 
section and submit it to the FAA Oversight Office for approval. The ALS 
must include a section that contains the CDCCL, inspections, or other 
procedures developed under paragraph (e) of this section.
    (g) Compliance Plan for Flammability Exposure Analysis. Within 90 
days after September 19, 2008, each holder of a type certificate 
required to comply with paragraph (b) of this section must submit to 
the FAA Oversight Office a compliance plan consisting of the following:
    (1) A proposed project schedule for submitting the required 
analysis, or a determination that compliance with paragraph (b) of this 
section is not required because design changes and service instructions 
for FRM or IMM will be developed and made available as required by this 
section.
    (2) A proposed means of compliance with paragraph (b) of this 
section, if applicable.
    (h) Compliance Plan for Design Changes and Service Instructions. 
Within 210 days after September 19, 2008, each holder of a type 
certificate required to comply with paragraph (d) of this section must 
submit to the FAA Oversight Office a compliance plan consisting of the 
following:
    (1) A proposed project schedule, identifying all major milestones, 
for meeting the compliance dates specified in paragraphs (d), (e) and 
(f) of this section.
    (2) A proposed means of compliance with paragraphs (d), (e) and (f) 
of this section.
    (3) A proposal for submitting a draft of all compliance items 
required by paragraphs (d), (e) and (f) of this section for review by 
the FAA Oversight Office

[[Page 42500]]

not less than 60 days before the compliance times specified in those 
paragraphs.
    (4) A proposal for how the approved service information and any 
necessary modification parts will be made available to affected 
persons.
    (i) Each affected type certificate holder must implement the 
compliance plans, or later revisions, as approved under paragraph (g) 
and (h) of this section.


Sec.  26.35  Changes to type certificates affecting fuel tank 
flammability.

    (a) Applicability. This section applies to holders and applicants 
for approvals of the following design changes to any airplane subject 
to 14 CFR 26.33(a):
    (1) Any fuel tank designed to be Normally Emptied if the fuel tank 
installation was approved pursuant to a supplemental type certificate 
or a field approval before September 19, 2008;
    (2) Any fuel tank designed to be Normally Emptied if an application 
for a supplemental type certificate or an amendment to a type 
certificate was made before September 19, 2008 and if the approval was 
not issued before September 19, 2008; and
    (3) If an application for a supplemental type certificate or an 
amendment to a type certificate is made on or September 19, 2008, any 
of the following design changes:
    (i) Installation of a fuel tank designed to be Normally Emptied,
    (ii) Changes to existing fuel tank capacity, or
    (iii) Changes that may increase the flammability exposure of an 
existing fuel tank for which FRM or IMM is required by Sec.  26.33(c).
    (b) Flammability Exposure Analysis-- (1) General. By the times 
specified in paragraphs (b)(1)(i) and (b)(1)(ii) of this section, each 
person subject to this section must submit for approval a flammability 
exposure analysis of the auxiliary fuel tanks or other affected fuel 
tanks, as defined in the type design, to the FAA Oversight Office. This 
analysis must be conducted in accordance with Appendix N of part 25 of 
this chapter.
    (i) Holders of supplemental type certificates and field approvals: 
Within 12 months of September 19, 2008,
    (ii) Applicants for supplemental type certificates and for 
amendments to type certificates: Within 12 months after September 19, 
2008, or before the certificate is issued, whichever occurs later.
    (2) Exception. This paragraph does not apply to--
    (i) Fuel tanks for which the type certificate holder, supplemental 
type certificate holder, or field approval holder has notified the FAA 
under paragraph (f) of this section that it will provide design changes 
and service instructions for an IMM meeting the requirements of Sec.  
25.981(c) in effect September 19, 2008; and
    (ii) Fuel tanks substantiated to be conventional unheated aluminum 
wing tanks.
    (c) Impact Assessment. By the times specified in paragraphs (c)(1) 
and (c)(2) of this section, each person subject to paragraph (a)(1) of 
this section holding an approval for installation of a Normally Emptied 
fuel tank on an airplane model listed in Table 1 of this section, and 
each person subject to paragraph (a)(3)(iii) of this section, must 
submit for approval to the FAA Oversight Office an assessment of the 
fuel tank system, as modified by their design change. The assessment 
must identify any features of the design change that compromise any 
critical design configuration control limitation (CDCCL) applicable to 
any airplane on which the design change is eligible for installation.
    (1) Holders of supplemental type certificates and field approvals: 
Before March 21, 2011.
    (2) Applicants for supplemental type certificates and for 
amendments to type certificates: Before March 21, 2011 or before the 
certificate is issued, whichever occurs later.

                                 Table 1
------------------------------------------------------------------------
 
-------------------------------------------------------------------------
                              Model--Boeing
------------------------------------------------------------------------
747 Series
737 Series
777 Series
767 Series
757 Series
------------------------------------------------------------------------
                              Model--Airbus
------------------------------------------------------------------------
A318, A319, A320, A321 Series
A300, A310 Series
A330, A340 Series
------------------------------------------------------------------------

    (d) Design Changes and Service Instructions. By the times specified 
in paragraph (e) of this section, each person subject to this section 
must meet the requirements of paragraphs (d)(1) or (d)(2) of this 
section, as applicable.
    (1) For holders and applicants subject to paragraph (a)(1) or 
(a)(3)(iii) of this section, if the assessment required by paragraph 
(c) of this section identifies any features of the design change that 
compromise any CDCCL applicable to any airplane on which the design 
change is eligible for installation, the holder or applicant must 
submit for approval by the FAA Oversight Office design changes and 
service instructions for Flammability Impact Mitigation Means (FIMM) 
that would bring the design change into compliance with the CDCCL. Any 
fuel tank modified as required by this paragraph must also be evaluated 
as required by paragraph (b) of this section.
    (2) Applicants subject to paragraph (a)(2), or (a)(3)(i) of this 
section must comply with the requirements of 14 CFR 25.981, in effect 
on September 19, 2008.
    (3) Applicants subject to paragraph (a)(3)(ii) of this section must 
comply with the requirements of 14 CFR 26.33.
    (e) Compliance Times for Design Changes and Service Instructions. 
The following persons subject to this section must comply with the 
requirements of paragraph (d) of this section at the specified times.
    (1) Holders of supplemental type certificates and field approvals: 
Before September 19, 2012.
    (2) Applicants for supplemental type certificates and for 
amendments to type certificates: Before September 19, 2012, or before 
the certificate is issued, whichever occurs later.
    (f) Compliance Planning. By the applicable date specified in Table 
2 of this section, each person subject to paragraph (a)(1) of this 
section must submit for approval by the FAA Oversight Office compliance 
plans for the flammability exposure analysis required by paragraph (b) 
of this section, the impact assessment required by paragraph (c) of 
this section, and the design changes and service instructions required 
by paragraph (d) of this section. Each person's compliance plans must 
include the following:
    (1) A proposed project schedule for submitting the required 
analysis or impact assessment.
    (2) A proposed means of compliance with paragraph (d) of this 
section.
    (3) For the requirements of paragraph (d) of this section, a 
proposal for submitting a draft of all design changes, if any are 
required, and Airworthiness Limitations (including CDCCLs) for review 
by the FAA Oversight Office not less than 60 days before the compliance 
time specified in paragraph (e) of this section.
    (4) For the requirements of paragraph (d) of this section, a 
proposal for how the approved service information and any necessary 
modification parts will be made available to affected persons.

[[Page 42501]]



                                       Table 2.--Compliance Planning Dates
----------------------------------------------------------------------------------------------------------------
                                                                                            Design changes and
                                        Flammability exposure    Impact assessment plan   service  instructions
                                            analysis plan                                          plan
----------------------------------------------------------------------------------------------------------------
STC and Field Approval Holders.......  December 18, 2008......  November 19, 2010......  May 19, 2011.
----------------------------------------------------------------------------------------------------------------

    (g) Each person subject to this section must implement the 
compliance plans, or later revisions, as approved under paragraph (f) 
of this section.


Sec.  26.37  Pending type certification projects: Fuel tank 
flammability.

    (a) Applicability. This section applies to any new type certificate 
for a transport category airplane, if the application was made before 
September 19, 2008, and if the certificate was not issued September 19, 
2008. This section applies only if the airplane would have--
    (1) A maximum type-certificated passenger capacity of 30 or more, 
or
    (2) A maximum payload capacity of 7,500 pounds or more.
    (b) If the application was made on or after June 6, 2001, the 
requirements of 14 CFR 25.981 in effect on September 19, 2008, apply.


Sec.  26.39  Newly produced airplanes: Fuel tank flammability.

    (a) Applicability: This section applies to Boeing model airplanes 
specified in Table 1 of this section, including passenger and cargo 
versions of each model, when application is made for original 
certificates of airworthiness or export airworthiness approvals after 
September 20, 2010.

                                 Table 1
------------------------------------------------------------------------
                              Model--Boeing
-------------------------------------------------------------------------
747 Series
737 Series
777 Series
767 Series
------------------------------------------------------------------------

    (b) Any fuel tank meeting all of the criteria stated in paragraphs 
(b)(1), (b)(2) and (b)(3) of this section must have flammability 
reduction means (FRM) or ignition mitigation means (IMM) that meet the 
requirements of 14 CFR 25.981 in effect on September 19, 2008.
    (1) The fuel tank is Normally Emptied.
    (2) Any portion of the fuel tank is located within the fuselage 
contour.
    (3) The fuel tank exceeds a Fleet Average Flammability Exposure of 
7 percent.
    (c) All other fuel tanks that exceed an Fleet Average Flammability 
Exposure of 7 percent must have an IMM that meets 14 CFR 25.981(d) in 
effect on September 19, 2008, or an FRM that meets all of the 
requirements of Appendix M to this part, except instead of complying 
with paragraph M25.1 of that appendix, the Fleet Average Flammability 
Exposure may not exceed 7 percent.

PART 121--OPERATING REQUIREMENTS: DOMESTIC, FLAG, AND SUPPLEMENTAL 
OPERATIONS

0
9. The authority citation for part 121 continues to read as follows:

    Authority: 49 U.S.C. 106(g), 40113, 40119, 41706, 44101, 44701-
44702, 44705, 44709-44711, 44713, 44716-44717, 44722, 44901, 44903-
44904, 44012, 46105, 46301.


0
10. Amend part 121 by adding a new Sec.  121.1117, to read as follows:


Sec.  121.1117  Flammability reduction means.

    (a) Applicability. Except as provided in paragraph (o) of this 
section, this section applies to transport category, turbine-powered 
airplanes with a type certificate issued after January 1, 1958, that, 
as a result of original type certification or later increase in 
capacity have:
    (1) A maximum type-certificated passenger capacity of 30 or more, 
or
    (2) A maximum payload capacity of 7,500 pounds or more.
    (b) New Production Airplanes. Except in accordance with Sec.  
121.628, no certificate holder may operate an airplane identified in 
Table 1 of this section (including all-cargo airplanes) for which the 
State of Manufacture issued the original certificate of airworthiness 
or export airworthiness approval after September 20, 2010 unless an 
Ignition Mitigation Means (IMM) or Flammability Reduction Means (FRM) 
meeting the requirements of Sec.  26.33 of this chapter is operational.

                                 Table 1
------------------------------------------------------------------------
               Model--Boeing                        Model--Airbus
------------------------------------------------------------------------
747 Series                                  A318, A319, A320, A321
                                             Series
737 Series                                  A330, A340 Series
777 Series
767 Series
------------------------------------------------------------------------

    (c) Auxiliary Fuel Tanks. After the applicable date stated in 
paragraph (e) of this section, no certificate holder may operate any 
airplane subject to Sec.  26.33 of this chapter that has an Auxiliary 
Fuel Tank installed pursuant to a field approval, unless the following 
requirements are met:
    (1) The certificate holder complies with 14 CFR 26.35 by the 
applicable date stated in that section.
    (2) The certificate holder installs Flammability Impact Mitigation 
Means (FIMM), if applicable, that is approved by the FAA Oversight 
Office.
    (3) Except in accordance with Sec.  121.628, the FIMM, if 
applicable, is operational.
    (d) Retrofit. Except as provided in paragraphs (j), (k), and (l) of 
this section, after the dates specified in paragraph (e) of this 
section, no certificate holder may operate an airplane to which this 
section applies unless the requirements of paragraphs (d)(1) and (d)(2) 
of this section are met.
    (1) IMM, FRM or FIMM, if required by Sec. Sec.  26.33, 26.35, or 
26.37 of this chapter, that are approved by the FAA Oversight Office, 
are installed within the compliance times specified in paragraph (e) of 
this section.
    (2) Except in accordance with Sec.  121.628, the IMM, FRM or FIMM, 
as applicable, are operational.
    (e) Compliance Times. Except as provided in paragraphs (k) and (l) 
of this section, the installations required by paragraph (d) of this 
section must be accomplished no later than the applicable dates 
specified in paragraph (e)(1), (e)(2), or (e)(3) of this section.
    (1) Fifty percent of each certificate holder's fleet identified in 
paragraph (d)(1) of this section must be modified no later than 
September 19, 2014.
    (2) One hundred percent of each certificate holder's fleet 
identified in paragraph (d)(1) of this section must be modified no 
later than September 19, 2017.
    (3) For those certificate holders that have only one airplane of a 
model identified in Table 1 of this section, the airplane must be 
modified no later than September 19, 2017.
    (f) Compliance After Installation. Except in accordance with Sec.  
121.628, no certificate holder may--
    (1) Operate an airplane on which IMM or FRM has been installed 
before the dates specified in paragraph (e) of this section unless the 
IMM or FRM is operational, or
    (2) Deactivate or remove an IMM or FRM once installed unless it is 
replaced

[[Page 42502]]

by a means that complies with paragraph (d) of this section.
    (g) Maintenance Program Revisions. No certificate holder may 
operate an airplane for which airworthiness limitations have been 
approved by the FAA Oversight Office in accordance with Sec. Sec.  
26.33, 26.35, or 26.37 of this chapter after the airplane is modified 
in accordance with paragraph (d) of this section unless the maintenance 
program for that airplane is revised to include those applicable 
airworthiness limitations.
    (h) After the maintenance program is revised as required by 
paragraph (g) of this section, before returning an airplane to service 
after any alteration for which airworthiness limitations are required 
by Sec. Sec.  25.981, 26.33, or 26.37 of this chapter, the certificate 
holder must revise the maintenance program for the airplane to include 
those airworthiness limitations.
    (i) The maintenance program changes identified in paragraphs (g) 
and (h) of this section must be submitted to the operator's Principal 
Maintenance Inspector responsible for review and approval prior to 
incorporation.
    (j) The requirements of paragraph (d) of this section do not apply 
to airplanes operated in all-cargo service, but those airplanes are 
subject to paragraph (f) of this section.
    (k) The compliance dates specified in paragraph (e) of this section 
may be extended by one year, provided that--
    (1) No later than December 18, 2008, the certificate holder 
notifies its assigned Flight Standards Office or Principal Inspector 
that it intends to comply with this paragraph;
    (2) No later than March 18, 2009, the certificate holder applies 
for an amendment to its operations specification in accordance with 
Sec.  119.51 of this chapter and revises the manual required by Sec.  
121.133 to include a requirement for the airplane models specified in 
Table 2 of this section to use ground air conditioning systems for 
actual gate times of more than 30 minutes, when available at the gate 
and operational, whenever the ambient temperature exceeds 60 degrees 
Fahrenheit; and
    (3) Thereafter, the certificate holder uses ground air conditioning 
systems as described in paragraph (k)(2) of this section on each 
airplane subject to the extension.

                                 Table 2
------------------------------------------------------------------------
               Model--Boeing                        Model--Airbus
------------------------------------------------------------------------
747 Series                                  A318, A319, A320, A321
                                             Series
737 Series                                  A300, A310 Series
777 Series                                  A330, A340 Series
767 Series
757 Series
------------------------------------------------------------------------

    (l) For any certificate holder for which the operating certificate 
is issued after September 19, 2008, the compliance date specified in 
paragraph (e) of this section may be extended by one year, provided 
that the certificate holder meets the requirements of paragraph (k)(2) 
of this section when its initial operations specifications are issued 
and, thereafter, uses ground air conditioning systems as described in 
paragraph (k)(2) of this section on each airplane subject to the 
extension.
    (m) After the date by which any person is required by this section 
to modify 100 percent of the affected fleet, no certificate holder may 
operate in passenger service any airplane model specified in Table 2 of 
this section unless the airplane has been modified to comply with Sec.  
26.33(c) of this chapter.
    (n) No certificate holder may operate any airplane on which an 
auxiliary fuel tank is installed after September 19, 2017 unless the 
FAA has certified the tank as compliant with Sec.  25.981 of this 
chapter, in effect on September 19, 2008.
    (o) Exclusions. The requirements of this section do not apply to 
the following airplane models:
    (1) Convair CV-240, 340, 440, including turbine powered 
conversions.
    (2) Lockheed L-188 Electra.
    (3) Vickers Armstrong Viscount.
    (4) Douglas DC-3, including turbine powered conversions.
    (5) Bombardier CL-44.
    (6) Mitsubishi YS-11.
    (7) BAC 1-11.
    (8) Concorde.
    (9) deHavilland D.H. 106 Comet 4C.
    (10) VFW--Vereinigte Flugtechnische VFW-614.
    (11) Illyushin Aviation IL 96T.
    (12) Vickers Armstrong Viscount.
    (13) Bristol Aircraft Britannia 305.
    (14) Handley Page Handley Page Herald Type 300.
    (15) Avions Marcel Dassault--Breguet Aviation Mercure 100C.
    (16) Airbus Caravelle.
    (17) Fokker F-27/Fairchild Hiller FH-227.
    (18) Lockheed L-300.

PART 125--CERTIFICATION AND OPERATIONS; AIRPLANES HAVING A SEATING 
CAPACITY OF 20 OR MORE PASSENGERS OR A MAXIMUM PAYLOAD CAPACITY OF 
6,000 POUNDS OR MORE; AND RULES GOVERNING PERSONS ON BOARD SUCH 
AIRCRAFT

0
11. The authority citation for part 125 continues to read as follows:

    Authority: 49 U.S.C. 106(g), 40113, 44701-44702, 44705, 44710-
44711, 44713, 44716-44717, 44722.


0
12. Amend part 125 by adding a new Sec.  125.509 to read as follows:


Sec.  125.509  Flammability reduction means.

    (a) Applicability. Except as provided in paragraph (m) of this 
section, this section applies to transport category, turbine-powered 
airplanes with a type certificate issued after January 1, 1958, that, 
as a result of original type certification or later increase in 
capacity have:
    (1) A maximum type-certificated passenger capacity of 30 or more, 
or
    (2) A maximum payload capacity of 7,500 pounds or more.
    (b) New Production Airplanes. Except in accordance with Sec.  
125.201, no person may operate an airplane identified in Table 1 of 
this section (including all-cargo airplanes) for which the State of 
Manufacture issued the original certificate of airworthiness or export 
airworthiness approval after September 20, 2010 unless an Ignition 
Mitigation Means (IMM) or Flammability Reduction Means (FRM) meeting 
the requirements of Sec.  26.33 of this chapter is operational.

                                 Table 1
------------------------------------------------------------------------
               Model--Boeing                        Model--Airbus
------------------------------------------------------------------------
747 Series                                  A318, A319, A320, A321
                                             Series
737 Series                                  A330, A340 Series
777 Series
767 Series
------------------------------------------------------------------------

    (c) Auxiliary Fuel Tanks. After the applicable date stated in 
paragraph (e) of this section, no person may operate any airplane 
subject to Sec.  26.33 of this chapter that has an Auxiliary Fuel Tank 
installed pursuant to a field approval, unless the following 
requirements are met:
    (1) The person complies with 14 CFR 26.35 by the applicable date 
stated in that section.
    (2) The person installs Flammability Impact Mitigation Means 
(FIMM), if applicable, that is approved by the FAA Oversight Office.

[[Page 42503]]

    (3) Except in accordance with Sec.  125.201, the FIMM, if 
applicable, are operational.
    (d) Retrofit. Except as provided in paragraph (j) of this section, 
after the dates specified in paragraph (e) of this section, no person 
may operate an airplane to which this section applies unless the 
requirements of paragraphs (d)(1) and (d)(2) of this section are met.
    (1) Ignition Mitigation Means (IMM), Flammability Reduction Means 
(FRM), or FIMM, if required by Sec. Sec.  26.33, 26.35, or 26.37 of 
this chapter, that are approved by the FAA Oversight Office, are 
installed within the compliance times specified in paragraph (e) of 
this section.
    (2) Except in accordance with Sec.  125.201 of this part, the IMM, 
FRM or FIMM, as applicable, are operational.
    (e) Compliance Times. The installations required by paragraph (d) 
of this section must be accomplished no later than the applicable dates 
specified in paragraph (e)(1), (e)(2) or (e)(3) of this section.
    (1) Fifty percent of each person's fleet of airplanes subject to 
paragraph (d)(1) of this section must be modified no later than 
September 19, 2014.
    (2) One hundred percent of each person's fleet of airplanes subject 
to paragraph (d)(1) of this section must be modified no later than 
September 19, 2017.
    (3) For those persons that have only one airplane of a model 
identified in Table 1 of this section, the airplane must be modified no 
later than September 19, 2017.
    (f) Compliance after Installation. Except in accordance with Sec.  
125.201, no person may--
    (1) Operate an airplane on which IMM or FRM has been installed 
before the dates specified in paragraph (e) of this section unless the 
IMM or FRM is operational, or
    (2) Deactivate or remove an IMM or FRM once installed unless it is 
replaced by a means that complies with paragraph (d) of this section.
    (g) Inspection Program Revisions. No person may operate an airplane 
for which airworthiness limitations have been approved by the FAA 
Oversight Office in accordance with Sec. Sec.  26.33, 26.35, or 26.37 
of this chapter after the airplane is modified in accordance with 
paragraph (d) of this section unless the inspection program for that 
airplane is revised to include those applicable airworthiness 
limitations.
    (h) After the inspection program is revised as required by 
paragraph (g) of this section, before returning an airplane to service 
after any alteration for which airworthiness limitations are required 
by Sec. Sec.  25.981, 26.33, 26.35, or 26.37 of this chapter, the 
person must revise the inspection program for the airplane to include 
those airworthiness limitations.
    (i) The inspection program changes identified in paragraphs (g) and 
(h) of this section must be submitted to the operator's assigned Flight 
Standards Office responsible for review and approval prior to 
incorporation.
    (j) The requirements of paragraph (d) of this section do not apply 
to airplanes operated in all-cargo service, but those airplanes are 
subject to paragraph (f) of this section.
    (k) After the date by which any person is required by this section 
to modify 100 percent of the affected fleet, no person may operate in 
passenger service any airplane model specified in Table 2 of this 
section unless the airplane has been modified to comply with Sec.  
26.33(c) of this chapter.
    (l) No person may operate any airplane on which an auxiliary fuel 
tank is installed after September 19, 2017 unless the FAA has certified 
the tank as compliant with Sec.  25.981 of this chapter, in effect on 
September 19, 2008.
    (m) Exclusions. The requirements of this section do not apply to 
the following airplane models:
    (1) Convair CV-240, 340, 440, including turbine powered 
conversions.
    (2) Lockheed L-188 Electra.
    (3) Vickers Armstrong Viscount.
    (4) Douglas DC-3, including turbine powered conversions.
    (5) Bombardier CL-44.
    (6) Mitsubishi YS-11.
    (7) BAC 1-11.
    (8) Concorde.
    (9) deHavilland D.H. 106 Comet 4C.
    (10) VFW--Vereinigte Flugtechnische VFW-614.
    (11) Illyushin Aviation IL 96T.
    (12) Vickers Armstrong Viscount.
    (13) Bristol Aircraft Britannia 305.
    (14) Handley Page Handley Page Herald Type 300.
    (15) Avions Marcel Dassault--Breguet Aviation Mercure 100C.
    (16) Airbus Caravelle.
    (17) Fokker F-27/Fairchild Hiller FH-227.
    (18) Lockheed L-300.

PART 129--OPERATIONS: FOREIGN AIR CARRIERS AND FOREIGN OPERATORS OF 
U.S.-REGISTERED AIRCRAFT ENGAGED IN COMMON CARRIAGE

0
13. The authority citation for part 129 continues to read as follows:

    Authority: 49 U.S.C. 1372, 49113, 440119, 44101, 44701-44702, 
447-5, 44709-44711, 44713, 44716-44717, 44722, 44901-44904, 44906, 
44912, 44105, Pub. L. 107-71 sec. 104.


0
14. Amend part 129 by adding a new Sec.  129.117 to read as follows:


Sec.  129.117  Flammability reduction means.

    (a) Applicability. Except as provided in paragraph (o) of this 
section, this section applies to U.S.-registered transport category, 
turbine-powered airplanes with a type certificate issued after January 
1, 1958, that as a result of original type certification or later 
increase in capacity have:
    (1) A maximum type-certificated passenger capacity of 30 or more, 
or
    (2) A maximum payload capacity of 7,500 pounds or more.
    (b) New Production Airplanes. Except in accordance with Sec.  
129.14, no foreign air carrier or foreign person may operate an 
airplane identified in Table 1 of this section (including all-cargo 
airplanes) for which application is made for original certificate of 
airworthiness or export airworthiness approval after September 20, 2010 
unless an Ignition Mitigation Means (IMM) or Flammability Reduction 
Means (FRM) meeting the requirements of Sec.  26.33 of this chapter is 
operational.

                                 Table 1
------------------------------------------------------------------------
               Model--Boeing                        Model--Airbus
------------------------------------------------------------------------
747 Series                                  A318, A319, A320, A321
                                             Series
737 Series                                  A330, A340 Series
777 Series
767 Series
------------------------------------------------------------------------

    (c) Auxiliary Fuel Tanks. After the applicable date stated in 
paragraph (e) of this section, no foreign air carrier or foreign person 
may operate any airplane subject Sec.  26.33 of this chapter that has 
an Auxiliary Fuel Tank installed pursuant to a field approval, unless 
the following requirements are met:
    (1) The foreign air carrier or foreign person complies with 14 CFR 
26.35 by the applicable date stated in that section.
    (2) The foreign air carrier or foreign person installs Flammability 
Impact Mitigation Means (FIMM), if applicable, that are approved by the 
FAA Oversight Office.
    (3) Except in accordance with Sec.  129.14, the FIMM, if 
applicable, are operational.
    (d) Retrofit. After the dates specified in paragraphs (j), (k), and 
(l) of this section, after the dates specified in paragraph (e) of this 
section, no foreign air carrier or foreign person may operate an 
airplane to which this section applies unless the requirements of 
paragraphs (d)(1) and (d)(2) of this section are met.
    (1) IMM, FRM or FIMM, if required by Sec. Sec.  26.33, 26.35, or 
26.37 of this chapter,

[[Page 42504]]

that are approved by the FAA Oversight Office, are installed within the 
compliance times specified in paragraph (e) of this section.
    (2) Except in accordance with Sec.  129.14, the IMM, FRM or FIMM, 
as applicable, are operational.
    (e) Compliance Times. Except as provided in paragraphs (k) and (l) 
of this section, the installations required by paragraph (d) of this 
section must be accomplished no later than the applicable dates 
specified in paragraph (e)(1) or (e)(2) of this section.
    (1) Fifty percent of each foreign air carrier or foreign person's 
fleet identified in paragraph (d)(1) of this section must be modified 
no later than September 19, 2014.
    (2) One hundred percent of each foreign air carrier or foreign 
person's fleet of airplanes subject to paragraph (d)(1) or this section 
must be modified no later than September 19, 2017.
    (3) For those foreign air carriers or foreign persons that have 
only one airplane for a model identified in Table 1, the airplane must 
be modified no later than September 19, 2017.
    (f) Compliance after Installation. Except in accordance with Sec.  
129.14, no person may--
    (1) Operate an airplane on which IMM or FRM has been installed 
before the dates specified in paragraph (e) of this section unless the 
IMM or FRM is operational.
    (2) Deactivate or remove an IMM or FRM once installed unless it is 
replaced by a means that complies with paragraph (d) of this section.
    (g) Maintenance Program Revisions. No foreign air carrier or 
foreign person may operate an airplane for which airworthiness 
limitations have been approved by the FAA Oversight Office in 
accordance with Sec. Sec.  26.33, 26.35, or 26.37 of this chapter after 
the airplane is modified in accordance with paragraph (d) of this 
section unless the maintenance program for that airplane is revised to 
include those applicable airworthiness limitations.
    (h) After the maintenance program is revised as required by 
paragraph (g) of this section, before returning an airplane to service 
after any alteration for which airworthiness limitations are required 
by Sec. Sec.  25.981, 26.33, 26.35, or 26.37 of this chapter, the 
foreign person or foreign air carrier must revise the maintenance 
program for the airplane to include those airworthiness limitations.
    (i) The maintenance program changes identified in paragraphs (g) 
and (h) of this section must be submitted to the operator's assigned 
Flight Standards Office or Principal Inspector for review and approval 
prior to incorporation.
    (j) The requirements of paragraph (d) of this section do not apply 
to airplanes operated in all-cargo service, but those airplanes are 
subject to paragraph (f) of this section.
    (k) The compliance dates specified in paragraph (e) of this section 
may be extended by one year, provided that--
    (1) No later than December 18, 2008, the foreign air carrier or 
foreign person notifies its assigned Flight Standards Office or 
Principal Inspector that it intends to comply with this paragraph;
    (2) No later than March 18, 2009, the foreign air carrier or 
foreign person applies for an amendment to its operations 
specifications in accordance with Sec.  129.11 to include a requirement 
for the airplane models specified in Table 2 of this section to use 
ground air conditioning systems for actual gate times of more than 30 
minutes, when available at the gate and operational, whenever the 
ambient temperature exceeds 60 degrees Fahrenheit; and
    (3) Thereafter, the certificate holder uses ground air conditioning 
systems as described in paragraph (k)(2) of this section on each 
airplane subject to the extension.

                                 Table 2
------------------------------------------------------------------------
               Model--Boeing                        Model--Airbus
------------------------------------------------------------------------
747 Series                                  A318, A319, A320, A321
                                             Series
737 Series                                  A300, A310 Series
777 Series                                  A330, A340 Series
767 Series
757 Series
------------------------------------------------------------------------

    (l) For any foreign air carrier or foreign person for which the 
operating certificate is issued after September 19, 2008, the 
compliance date specified in paragraph (e) of this section may be 
extended by one year, provided that the foreign air carrier or foreign 
person meets the requirements of paragraph (k)(2) of this section when 
its initial operations specifications are issued and, thereafter, uses 
ground air conditioning systems as described in paragraph (k)(2) of 
this section on each airplane subject to the extension.
    (m) After the date by which any person is required by this section 
to modify 100 percent of the affected fleet, no person may operate in 
passenger service any airplane model specified in Table 2 of this 
section unless the airplane has been modified to comply with Sec.  
26.33(c) of this chapter.

                                 Table 3
------------------------------------------------------------------------
               Model--Boeing                        Model--Airbus
------------------------------------------------------------------------
747 Series                                  A318, A319, A320, A321
                                             Series
737 Series                                  A300, A310 Series
777 Series                                  A330, A340 Series
767 Series
757 Series
707/720 Series
------------------------------------------------------------------------

    (n) No foreign air carrier or foreign person may operate any 
airplane on which an auxiliary fuel tank is installed after September 
19, 2017 unless the FAA has certified the tank as compliant with Sec.  
25.981 of this chapter, in effect on September 19, 2008.
    (o) Exclusions. The requirements of this section do not apply to 
the following airplane models:
    (1) Convair CV-240, 340, 440, including turbine powered 
conversions.
    (2) Lockheed L-188 Electra.
    (3) Vickers Armstrong Viscount.
    (4) Douglas DC-3, including turbine powered conversions.
    (5) Bombardier CL-44.
    (6) Mitsubishi YS-11.
    (7) BAC 1-11.
    (8) Concorde.
    (9) deHavilland D.H. 106 Comet 4C.
    (10) VFW--Vereinigte Flugtechnische VFW-614.
    (11) Illyushin Aviation IL 96T.
    (12) Vickers Armstrong Viscount.
    (13) Bristol Aircraft Britannia 305.
    (14) Handley Page Handley Page Herald Type 300.
    (15) Avions Marcel Dassault--Breguet Aviation Mercure 100C.
    (16) Airbus Caravelle.
    (17) Fokker F-27/Fairchild Hiller FH-227.
    (18) Lockheed L-300.

    Issued in Washington, DC, on July 9, 2008.
Robert A. Sturgell,
Acting Administrator.
[FR Doc. E8-16084 Filed 7-16-08; 10:30 am]
BILLING CODE 4910-13-P