[Federal Register Volume 64, Number 209 (Friday, October 29, 1999)]
[Proposed Rules]
[Pages 58644-58664]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 99-28348]



[[Page 58643]]

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Part VI





Department of Transportation





_______________________________________________________________________



Federal Aviation Administration



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14 CFR Part 21, et al.



Transport Airplane Fuel Tank System Design Review, Flammability 
Reduction, and Maintenance and Inspection Requirements; Proposed Rule

  Federal Register / Vol. 64, No. 209 / Friday, October 29, 1999 / 
Proposed Rules  

[[Page 58644]]



DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Parts 21, 25, 91, 121, 125, and 129

[Docket No. FAA-1999; Notice No. 99-18]
RIN 2120-AG62


 Transport Airplane Fuel Tank System Design Review, Flammability 
Reduction, and Maintenance and Inspection Requirements

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Notice of proposed rulemaking (NPRM).

-----------------------------------------------------------------------

SUMMARY: This proposed rulemaking would require design approval holders 
of certain turbine-powered transport category airplanes to submit 
substantiation to the FAA that the design of the fuel tank system of 
previously certificated airplanes precludes the existence of ignition 
sources within the airplane fuel tanks. It would also require the 
affected design approval holders to develop specific fuel tank system 
maintenance and inspection instructions for any items in the fuel tank 
system that are determined to require repetitive inspections or 
maintenance, to assure the safety of the fuel tank system. In addition, 
the proposed rule would require certain operators of those airplanes to 
incorporate FAA-approved fuel tank system maintenance and inspection 
instructions into their current maintenance or inspection program. 
Three amendments to the airworthiness standards for transport category 
airplanes are also proposed. The first would define new requirements, 
based on existing requirements, for demonstrating that ignition sources 
could not be present in fuel tanks when failure conditions are 
considered. The second would require future applicants for type 
certification to identify any safety critical maintenance actions and 
develop limitations to be placed in the instructions for continued 
airworthiness for the fuel tank system. The third would require means 
to minimize development of flammable vapors in fuel tanks, or means to 
prevent catastrophic damage if ignition does occur. These actions are 
the result of information gathered from accident investigations and 
adverse service experience, which has shown that unforeseen failure 
modes and lack of specific maintenance procedures on certain airplane 
fuel tank systems may result in degradation of design safety features 
intended to preclude ignition of vapors within the fuel tank.

DATES: Comments must be received on or before January 27, 2000.

ADDRESSES: Comments on this proposed rulemaking should be mailed or 
delivered, in duplicate, to: U.S. Department of Transportation, 
Dockets, Docket No. FAA-1999-6411, 400 Seventh Street SW., Room Plaza 
401, Washington DC 20590. Comments may also be sent electronically to 
the following Internet address: [email protected]. Comments may be 
filed and/or examined in Room Plaza 401 between 10 a.m. and 5 p.m. 
weekdays, except Federal holidays. In addition, the FAA is maintaining 
an information docket of comments in the Transport Airplane Directorate 
(ANM-100), Federal Aviation Administration, Northwest Mountain Region, 
1601 Lind Avenue SW., Renton, WA 98055-4056. Comments in the 
information docket may be examined between 7:30 a.m. and 4:00 p.m. 
weekdays, except Federal holidays.

FOR FURTHER INFORMATION CONTACT: Michael E. Dostert, FAA, Propulsion/
Mechanical/Crashworthiness Branch (ANM-112), Transport Airplane 
Directorate, Aircraft Certification Service, 1601 Lind Avenue SW., 
Renton, Washington 98055-4056; telephone (425) 227-2132, facsimile 
(425) 227-1320; e-mail: [email protected].

SUPPLEMENTARY INFORMATION:

Comments Invited

    Interested persons are invited to participate in this proposed 
rulemaking by submitting such written data, views, or arguments as they 
may desire. Comments relating to the environmental, energy, federalism, 
or economic impact that might result from adopting the proposals in 
this notice are also invited. Substantive comments should be 
accompanied by cost estimates. Commenters should identify the 
regulatory docket or notice number and submit comments in duplicate to 
the Docket address specified above. All comments received, as well as a 
report summarizing each substantive public contact with FAA personnel 
concerning this rulemaking, will be filed in the docket. All comments 
received on or before the closing date will be considered by the 
Administrator before taking action on this proposed rulemaking. Late 
filed comments will be considered to the extent practicable. The 
proposals contained in this notice may be changed in light of the 
comments received. The Docket is available for public inspection before 
and after the comment closing date. Commenters wishing the FAA to 
acknowledge receipt of their comments submitted in response to this 
notice must include with those comments a pre-addressed, stamped 
postcard on which the following statement is made: ``Comments to Docket 
No. FAA-1999-6411.'' The postcard will be date stamped and mailed to 
the commenter.

Availability of the NPRM

    An electronic copy of this document may be downloaded using a modem 
and suitable communications software from the FAA regulations section 
of the Fedworld electronic bulletin board service (telephone: 703-321-
3339), the Government Printing Office's electronic bulletin board 
service (telephone: 202-512-1661), or the FAA's Aviation Rulemaking 
Advisory Committee Bulletin Board service (telephone: (800) 322-2722 or 
(202) 267-5948).
    Internet users may reach the FAA's web page at http://www.faa.gov/
avr/arm/nprm/nprm.htm or the Government Printing Office's webpage at 
http://www.access.gpo.gov/nara for access to recently published 
rulemaking documents.
    Any person may obtain a copy of this NPRM 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. Communications must identify the notice number or docket 
number of this NPRM.
    Persons interested in being placed on the mailing list for future 
NPRM's should request from the above office a copy of Advisory Circular 
No. 11-2A, Notice of Proposed Rulemaking Distribution System, that 
describes the application procedure.

Background

    On July 17, 1996, a 25-year old Boeing 747-100 series airplane was 
involved in an inflight breakup after takeoff from Kennedy 
International Airport in New York, resulting in 230 fatalities. The 
accident investigation conducted by the National Transportation Safety 
Board (NTSB) indicated that the center wing fuel tank exploded due to 
an unknown ignition source. The NTSB has issued recommendations 
intended to reduce heating of the fuel in the center wing fuel tanks on 
the existing fleet of transport airplanes, reduce or eliminate 
operation with flammable vapors in the fuel tanks of new type 
certificated airplanes, and also to reevaluate the fuel system design 
and maintenance practices on the fleet of transport airplanes. The 
accident investigation

[[Page 58645]]

has now focused on mechanical failure as providing the energy source 
that ignited the fuel vapors inside the tank. This accident has 
prompted the FAA to examine the underlying safety issues surrounding 
fuel tank explosions, the adequacy of the existing regulations, the 
service history of airplanes certificated to these regulations, and 
existing fuel tank system maintenance practices.

Flammability Characteristics

    The flammability characteristics of the various fuels approved for 
use in transport airplanes results in the presence of flammable vapors 
in the vapor space of fuel tanks at various times during the operation 
of the airplane. Vapors from Jet A fuel (the typical commercial 
turbojet engine fuel) at temperatures below approximately 100 deg.F are 
too lean to be flammable at sea level; at higher altitudes the fuel 
vapors become flammable at temperatures above approximately 45 deg.F 
(at 40,000 feet altitude). However, the regulatory authorities and 
aviation industry have always presumed that a flammable fuel air 
mixture exists in the fuel tanks at all times and have adopted the 
philosophy that the best way to ensure airplane fuel tank safety is to 
preclude ignition sources within fuel tanks. This philosophy has been 
based on the application of fail-safe design requirements to the 
airplane fuel tank system to preclude ignition sources from being 
present in fuel tanks when component failures, malfunctions, or 
lightning encounters occur. Possible ignition sources that have been 
considered include electrical arcs, friction sparks, and autoignition. 
(The autoignition temperature is the temperature at which the fuel/air 
mixture will spontaneously ignite due to heat in the absence of an 
ignition source.) Some events that could produce sufficient electrical 
energy to create an arc include lightning, electrostatic charging, 
electromagnetic interference (EMI), or failures in airplane systems or 
wiring that introduce high-power electrical energy into the fuel tank 
system. Friction sparks may be caused by mechanical contact between 
certain rotating components in the fuel tank, such as a steel fuel pump 
impeller rubbing on the pump inlet check valve. Autoignition of fuel 
vapors may be caused by failure of components within the fuel tank, or 
external components or systems that cause components or tank surfaces 
to reach a high enough temperature to ignite the fuel vapors in the 
fuel tank.

Existing Regulations/Certification Methods

    The current 14 CFR part 25 regulations that are intended to require 
designs that preclude the presence of ignition sources within the 
airplane fuel tanks are as follows:
    Section 25.901 is a general requirement that applies to all 
portions of the propulsion installation, which includes the airplane 
fuel tank system. It requires, in part, that the propulsion and fuel 
tank systems be designed to ensure fail-safe operation between normal 
maintenance and inspection intervals, and that the major components be 
electrically bonded to the other parts of the airplane.
    Airplane system fail-safe requirements are provided in 
Secs. 25.901(c) and 25.1309. Section 25.901(c) requires that ``no 
single failure or malfunction or probable combination of failures will 
jeopardize the safe operation of the airplane.'' In general, the FAA's 
policy has been to require applicants to assume the presence of 
foreseeable latent (undetected) failure conditions when demonstrating 
that subsequent single failures will not jeopardize the safe operation 
of the airplane. Certain subsystem designs must also comply with 
Sec. 25.1309, which requires airplane systems and associated systems to 
be ``designed so that the occurrence of any failure condition which 
would prevent the continued safe flight and landing of the airplane is 
extremely improbable, and the occurrence of any other failure 
conditions which would reduce the capability of the airplane or the 
ability of the crew to cope with adverse operating conditions is 
improbable.'' Compliance with Sec. 25.1309 requires an analysis, and 
testing where appropriate, considering possible modes of failure, 
including malfunctions and damage from external sources, the 
probability of multiple failures and undetected failures, the resulting 
effects on the airplane and occupants, considering the stage of flight 
and operating conditions, and the crew warning cues, corrective action 
required, and the capability of detecting faults.
    This provision has the effect of mandating the use of ``fail-safe'' 
design methods which require that the effect of failures and 
combinations of failures be considered in defining a safe design. 
Detailed methods of compliance with Secs. 25.1309(b), (c), and (d) are 
described in Advisory Circular (AC) 25.1309-1A, ``System Design 
Analysis,'' and are intended as a means to evaluate the overall risk, 
on average, of an event occurring within a fleet of aircraft. The 
following guidance involving failures is offered in that AC:
    1. In any system or subsystem, a single failure of any element or 
connection during any one flight must be assumed without consideration 
as to its probability of failing. This single failure must not prevent 
the continued safe flight and landing of the airplane.
    2. Additional failures during any one flight following the first 
single failure must also be considered when the probability of 
occurrence is not shown to be extremely improbable. The probability of 
these combined failures includes the probability of occurrence of the 
first failure.
    As described in the AC, the FAA fail-safe design concept consists 
of the following design principles or techniques intended to ensure a 
safe design. The use of only one of these principles is seldom 
adequate. A combination of two or more design principles is usually 
needed to provide a fail-safe design (i.e., to ensure that catastrophic 
failure conditions are not expected to occur during the life of the 
fleet of a particular airplane model).
     Design integrity and quality, including life limits, to 
ensure intended function and prevent failures.
     Redundancy or backup systems that provide system function 
after the first failure (e.g., two or more engines, two or more 
hydraulic systems, dual flight controls, etc.)
     Isolation of systems and components so that failure of one 
element will not cause failure of the other (sometimes referred to as 
system independence).
     Detection of failures or failure indication.
     Functional verification (the capability for testing or 
checking the component's condition).
     Proven reliability and integrity to ensure that multiple 
component or system failures will not occur in the same flight.
     Damage tolerance that limits the safety impact or effect 
of the failure.
     Designed failure path that controls and directs the 
failure, by design, to limit the safety impact.
     Flightcrew procedures following the failure designed to 
assure continued safe flight by specific crew actions.
     Error tolerant design that considers probable human error 
in the operation, maintenance, and fabrication of the airplane.
     Margins of safety that allow for undefined and 
unforeseeable adverse flight conditions.
    These regulations, when applied to typical airplane fuel tank 
systems, lead to a requirement for prevention of

[[Page 58646]]

ignition sources inside fuel tanks. The approval of the installation of 
mechanical and electrical components inside the fuel tanks was 
typically based on a qualitative system safety analysis and component 
testing which showed: (1) that mechanical components would not create 
sparks or high temperature surfaces in the event of any failure, and 
(2) that electrical devices would not create arcs of sufficient energy 
to ignite a fuel-air mixture in the event of a single failure or 
probable combination of failures.
    Section 25.901(b)(2) requires that the components of the propulsion 
system be ``constructed, arranged, and installed so as to ensure their 
continued safe operation between normal inspection or overhauls.'' 
Compliance with this regulation is typically demonstrated by 
substantiating that the propulsion installation, which includes the 
fuel tank system, will safely perform its intended function between 
inspections and overhauls defined in the maintenance instructions.
    Section 25.901(b)(4) requires electrically bonding the major 
components of the propulsion system to the other parts of the airplane. 
The affected major components of the propulsion system include the fuel 
tank system. Compliance with this requirement for fuel tank systems has 
been demonstrated by showing that all major components in the fuel tank 
are electrically bonded to the airplane structure. This precludes 
accumulation of electrical charge on the components and the possible 
arcing in the fuel tank that could otherwise occur. In most cases, 
electrical bonding is accomplished by installing jumper wires from each 
major fuel tank system component to airplane structure. Advisory 
Circular 25-8, ``Auxiliary Fuel Tank Installations,'' also provides 
guidance for bonding of fuel tank system components and means of 
precluding ignition sources within transport airplane fuel tanks.
    Section 25.954 requires that the fuel tank system be designed and 
arranged to prevent the ignition of fuel vapor within the system due to 
the effects of lightning strikes. Compliance with this regulation is 
typically shown by incorporation of design features such as minimum 
fuel tank skin thickness, location of vent outlets out of likely 
lightning strike areas, and bonding of fuel tank system structure and 
components. Guidance for demonstrating compliance with this regulation 
is provided in AC 20-53A, ``Protection of Aircraft Fuel Systems Against 
Fuel Vapor Ignition Due to Lightning.''
    Section 25.981 requires that the applicant determine the highest 
temperature allowable in fuel tanks that provides a safe margin below 
the lowest expected autoignition temperature of the fuel that is 
approved for use in the fuel tanks. No temperature at any place inside 
any fuel tank where fuel ignition is possible may then exceed that 
maximum allowable temperature. This must be shown under all probable 
operating, failure, and malfunction conditions of any component whose 
operation, failure, or malfunction could increase the temperature 
inside the tank. Guidance for demonstrating compliance with this 
regulation has been provided in AC 25.981-1A, ``Guidelines For 
Substantiating Compliance With the Fuel Tank Temperature 
Requirements.'' The AC provides a listing of failure modes of fuel tank 
system components that should be considered when showing that component 
failures will not create a hot surface that exceeds the maximum 
allowable fuel tank component or tank surface temperature for the fuel 
type for which approval is being requested. Manufacturers have 
demonstrated compliance with this regulation by testing and analysis of 
components to show that design features, such as thermal fuses in fuel 
pump motors, preclude an ignition source in the fuel tank when failures 
such as a seized fuel pump rotor occur.

Airplane Maintenance Manuals and Instructions for Continued 
Airworthiness

    Historically, manufacturers have been required to provide 
maintenance related information for fuel tank systems in the same 
manner as for other systems. Prior to 1970, most manufacturers provided 
manuals containing maintenance information for large transport category 
airplanes, but there were no standards prescribing minimum content, 
distribution, and a timeframe in which the information must be made 
available to the operator. Section 25.1529, as amended by Amendment 25-
21 in 1970, required the applicant for a type certificate (TC) to 
provide airplane maintenance manuals (AMM) to owners of the airplanes. 
This regulation was amended in 1980 to require that the applicant for 
type certification provide Instructions for Continued Airworthiness 
(ICA) prepared in accordance with Appendix H to part 25. In developing 
the ICA, the applicant is required to include certain information such 
as a description of the airplane and its systems, servicing 
information, and maintenance instructions, including the frequency and 
extent of inspections necessary to provide for the continuing 
airworthiness of the airplane (including the fuel tank system). As 
required by Appendix H to part 25, the ICA must also include an FAA-
approved Airworthiness Limitations section enumerating those mandatory 
inspections, inspection intervals, replacement times, and related 
procedures approved under Sec. 25.571, relating to structural damage 
tolerance. Currently the Airworthiness Limitations section of the ICA 
applies only to airplane structure and not to the fuel tank system.
    One method of establishing initial scheduled maintenance and 
inspection tasks is the Maintenance Steering Group (MSG) process, which 
develops a Maintenance Review Board (MRB) document for a particular 
airplane model. Operators may incorporate those provisions, along with 
other maintenance information contained in the ICA, into their 
maintenance or inspection program.
    Section 21.50 requires the holder of a design approval, including 
the TC or supplemental type certificate (STC) for an airplane, aircraft 
engine, or propeller for which application was made after January 28, 
1981, to furnish at least one set of the complete ICA to the owner of 
the product for which the application was made. The ICA for original 
type certificated products must include instructions for the fuel tank 
system. A design approval holder who has modified the fuel tank system 
must furnish a complete set of the ICA for the modification to the 
owner of the product.

Type Certificate Amendments Based on Major Change in Type Design

    Over the years, many design changes have been introduced into fuel 
tank systems that may affect their safety. There are three ways in 
which major design changes can be approved: (1) the TC holder can apply 
for an amendment to the type design; (2) any person, including the TC 
holder, wanting to alter a product by introducing a major change in the 
type design not great enough to require a new application for a TC, may 
apply for an STC; and (3) in some instances a person may also make a 
major alteration to the type design through a field approval. The field 
approval process is a streamlined method for obtaining approval of 
relatively simple modifications to airplanes. An FAA Flight Standards 
Inspector can approve the alteration using Form FAA-337.

[[Page 58647]]

Maintenance and Inspection Program Requirements

    Airplane operators are required to have extensive maintenance or 
inspection programs that include provisions relating to fuel tank 
systems.
    Section 91.409(e), which generally applies to other than commercial 
operations, requires an operator of a large turbojet multiengine 
airplane or a turbopropeller-powered multiengined airplane to select 
one of the following four inspection programs:
    1. A continuous airworthiness inspection program that is part of a 
continuous airworthiness maintenance program currently in use by a 
person holding an air carrier operating certificate, or an operating 
certificate issued under part 119 for operations under parts 121 or 
135, and operating that make and model of airplane under those parts;
    2. An approved airplane inspection program approved under 
Sec. 135.419 and currently in use by a person holding an operating 
certificate and operations specifications issued under part 119 for 
part 135 operations;
    3. A current inspection program recommended by the manufacturer; or
    4. Any other inspection program established by the registered owner 
or operator of that airplane and approved by the Administrator.
    Section 121.367, which is applicable to those air carrier and 
commercial operations covered by part 121, requires operators to have 
an inspection program, as well as a program covering other maintenance, 
preventative maintenance, and alterations.
    Section 125.247, which is generally applicable to operation of 
large airplanes, other than air carrier operations conducted under part 
121, requires operators to inspect their airplanes in accordance with 
an inspection program approved by the Administrator.
    Section 129.14 requires a foreign air carrier and each foreign 
operator of a U.S. registered airplane in common carriage, within or 
outside the U.S., to maintain the airplane in accordance with an FAA-
approved program.
    In general, the operators rely on the TC data sheet, MRB reports, 
ICA's, the Airworthiness Limitations section of the ICA, other 
manufacturers' recommendations, and their own operating experience to 
develop the overall maintenance or inspection program for their 
airplanes.
    The intent of the rules governing the inspection and/or maintenance 
program is to ensure that the inherent level of safety that was 
originally designed into the system is maintained and that the airplane 
is in an airworthy condition.
    Historically, for fuel tank systems these required programs include 
operational checks (e.g., preflight and enroute), functional checks 
following maintenance actions (e.g., component replacement), overhaul 
of certain components to prevent dispatch delays, and general zonal 
visual inspections conducted concurrently with other maintenance 
actions, such as structural inspections. However, specific maintenance 
instructions to detect and correct conditions that degrade fail-safe 
capabilities have not been deemed necessary because it has been assumed 
that the original fail-safe capabilities would not be degraded in 
service.

Design and Service History Review

    The FAA has examined the service history of transport airplanes and 
performed an analysis of the history of fuel tank explosions on these 
airplanes. While there were a significant number of fuel tank fires and 
explosions that occurred during the 1960's and 1970's on several 
airplane types, in most cases the fire or explosion was found to be 
related to design practices, maintenance actions, or improper 
modification of fuel pumps. Some of the events were apparently caused 
by lightning strikes. In most cases, an extensive design review was 
conducted to identify possible ignition sources and actions were taken 
that were intended to prevent similar occurrences. However, recent fuel 
tank system related accidents have occurred in spite of these efforts.
    On May 11, 1990, the center wing fuel tank of a Boeing 737-300 
exploded while the airplane was on the ground at Nimoy Aquino 
International Airport, Manila, Philippines. The airplane was less than 
one year old. In the accident, the fuel-air vapors in the center wing 
tank exploded as the airplane was being pushed back from a terminal 
gate prior to flight. The accident resulted in 8 fatalities and 
injuries to an additional 30 people. Accident investigators considered 
a plausible scenario in which damaged wiring located outside the fuel 
tank may have created a short between 115 volt airplane system wires 
and 28 volt wires to a fuel tank level switch. This, in combination 
with a possibly defective fuel level float switch, was investigated as 
a possible source of ignition. However, a definitive ignition source 
was never confirmed during the accident investigation. This unexplained 
accident occurred on a newer airplane, in contrast to the July 17, 
1996, accident which occurred on an older Boeing 747 airplane that was 
approaching the end of its initial design life. These two accidents 
indicate that the development of an ignition source inside the fuel 
tank may be related to both the design and maintenance of the fuel tank 
systems.

National Transportation Safety Board (NTSB) Recommendations

    Since the July 17, 1996, accident, the FAA, NTSB, and aviation 
industry have been reviewing the design features and service history of 
the Boeing 747 and certain other transport airplane models. Based upon 
its review, the NTSB has issued the following recommendations to the 
FAA intended to reduce the exposure to operation with flammable vapors 
in fuel tanks and address possible degradation of the original type 
certificated fuel tank system designs on transport airplanes.

Reduced Flammability Exposure

    A-96-174: Require the development of and implementation of design 
or operational changes that will preclude the operation of transport-
category airplanes with explosive fuel-air mixtures in the fuel tanks:
Long Term Design Modifications:
    (a) Significant consideration should be given to the development of 
airplane design modification, such as nitrogen-inerting systems and the 
addition of insulation between heat-generating equipment and fuel 
tanks. Appropriate modifications should apply to newly certificated 
airplanes and, where feasible, to existing airplanes.
    A-96-175: Require the development of and implementation of design 
or operational changes that will preclude the operation of transport-
category airplanes with explosive fuel-air mixtures in the fuel tanks:
Near Term Operational
    (b) Pending implementation of design modifications, require 
modifications in operational procedures to reduce the potential for 
explosive fuel-air mixtures in the fuel tanks of transport-category 
aircraft. In the B-747, consideration should be given to refueling the 
center wing fuel tank (CWT) before flight whenever possible from cooler 
ground fuel tanks, proper monitoring and management of the CWT fuel 
temperature, and maintaining an appropriate minimum fuel quantity in 
the CWT.
    A-96-176: Require that the B-747 Flight Handbooks of TWA and other 
operators of B-747s and other aircraft in which fuel tank temperature 
cannot be determined by flightcrews be immediately revised to reflect 
the

[[Page 58648]]

increases in CWT fuel temperatures found by flight tests, including 
operational procedures to reduce the potential for exceeding CWT 
temperature limitations.
    A-96-177: Require modification of the CWT of B-747 airplanes and 
the fuel tanks of other airplanes that are located near heat sources to 
incorporate temperature probes and cockpit fuel tank temperature 
displays to permit determination of the fuel tank temperatures.

Ignition Source Reduction

    A-98-36: Conduct a survey of fuel quantity indication system probes 
and wires in Boeing 747's equipped with systems other than Honeywell 
Series 1-3 probes and compensators and in other model airplanes that 
are used in Title 14 Code of Federal Regulations Part 121 service to 
determine whether potential fuel tank ignition sources exist that are 
similar to those found in the Boeing 747. The survey should include 
removing wires from fuel probes and examining the wires for damage. 
Repair or replacement procedures for any damaged wires that are found 
should be developed.
    A-98-38: Require in Boeing 747 airplanes, and in other airplanes 
with fuel quantity indication system (FQIS) wire installations that are 
co-routed with wires that may be powered, the physical separation and 
electrical shielding of FQIS wires to the maximum extent possible.
    A-98-39: Require, in all applicable transport airplane fuel tanks, 
surge protection systems to prevent electrical power surges from 
entering fuel tanks through fuel quantity indication system wires.

Service History

    The FAA has also reviewed service difficulty reports for the 
transport airplane fleet and evaluated the certification and design 
practices utilized on these previously certificated airplanes. In 
addition, an inspection of fuel tanks on Boeing 747 airplanes was 
initiated. Representatives from the Air Transport Association (ATA), 
Association of European Airlines (AEA), the Association of Asia Pacific 
Airlines (AAPA), the Aerospace Industries Association of America, and 
the Association Europeenne de Constructeurs de Materiel Aerospatial 
(AECMA) initiated a joint effort to inspect and evaluate the condition 
of the fuel tank system installations on a representative sample of 
airplanes within the transport fleet. Data from initial inspections 
conducted as part of this effort and shared with the FAA have assisted 
in establishing a basis for developing corrective action for airplanes 
within the transport fleet. In addition to the results from these 
inspections, the FAA has received reports of anomalies on in-service 
airplanes that have necessitated actions to preclude development of 
ignition sources in or adjacent to airplane fuel tanks. The following 
provides a summary of findings from design evaluations, service 
difficulty reports, and a review of current airplane maintenance 
practices.

Aging Airplane Related Phenomena

    Fuel tank inspections initiated as part of the Boeing 747 accident 
investigation identified aging of fuel tank system components, 
contamination, corrosion of components and copper-sulfur deposits on 
components as possible conditions that could contribute to development 
of ignition sources within the fuel tanks. Results of detailed 
inspection of the fuel pump wiring on several Boeing 747 airplanes 
showed debris within the fuel tanks consisting of lockwire, rivets, and 
metal shavings. Debris was also found inside scavenge pumps. Corrosion 
and damage to insulation on FQIS probe wiring was found on wiring of 6 
out of 8 probes removed from in-service airplanes. In addition, 
inspection of airplane fuel tank system components from out-of-service 
(retired) airplanes, initiated following the accident, revealed damaged 
wiring and corrosion buildup of conductive copper-sulfur deposits on 
the FQIS wiring on some Boeing 747 airplanes. The conductive deposits 
or damaged wiring may result in a location where arcing could occur if 
high power electrical energy was transmitted to the FQIS wiring from 
another airplane source. While the effects of corrosion on fuel tank 
system safety have not been fully evaluated, the FAA is developing a 
research program to obtain a better understanding of the effects of 
copper-sulfur deposits and corrosion on airplane fuel tank system 
safety.
    Wear or chafing of electrical power wires routed in conduits that 
are located inside fuel tanks can result in arcing through the 
conduits. On December 9, 1997, the FAA issued Airworthiness Directive 
(AD) 96-26-06, applicable to certain Boeing 747 airplanes, which 
required inspection of electrical wiring routed within conduits to fuel 
pumps located in the wing fuel tanks and replacement of any damaged 
wiring. Inspection reports indicated that many instances of wear had 
occurred on Teflon sleeves installed over the wiring to protect it from 
damage and possible arcing to the conduit.
    Inspections of wiring to fuel pumps on Boeing 737 airplanes with 
over 35,000 flight hours have shown significant wear to the insulation 
of wires inside conduits that are located in fuel tanks. In nine 
reported cases, wear resulted in arcing to the fuel pump wire conduit 
on airplanes with greater than 50,000 flight hours. In one case, wear 
resulted in burnthrough of the conduit into the interior of the 737 
main tank fuel cell. On May 14, 1998, the FAA issued a telegraphic AD, 
T98-11-52, which required inspection of wiring to Boeing 737 airplane 
fuel pumps routed within electrical conduits and replacement of any 
damaged wiring. Results of these inspections showed that wear of the 
wiring occurred in many instances, particularly on those airplanes with 
high numbers of flight cycles and operating hours.
    The FAA has also received reports of corrosion on bonding jumper 
wires within the fuel tanks on one in-service Airbus A300 airplane. The 
manufacturer investigating this event did not have sufficient evidence 
to determine conclusively the level of damage and corrosion found on 
the jumper wires. Although the airplane was in long-term storage, it 
does not explain why a high number of damaged/corroded jumper wires 
were found concentrated in a specific area of the wing tanks. Further 
inspections of a limited number of other Airbus models did not reveal 
similar extensive corrosion or damage to bonding jumper wires. However, 
they did reveal evidence of the accumulation of copper-sulfur deposits 
around the outer braid of some jumper wires. Tests by the manufacturer 
have shown that these deposits did not affect the bonding function of 
the leads. Airbus has developed a one-time-inspection service bulletin 
for all its airplanes to ascertain the extent of the copper-sulfur 
deposits and to ensure that the level of jumper wire damage found on 
the one A300 airplane is not widespread.
    On March 30, 1998, the FAA received reports of three recent 
instances of electrical arcing within fuel pumps installed in fuel 
tanks on Lockheed L-1011 airplanes. In one case, the electrical arc had 
penetrated the pump and housing and entered the fuel tank. Preliminary 
investigation indicates that features incorporated into the fuel pump 
design that were intended to preclude overheating and arc-through into 
the fuel tank may not have functioned as intended due to discrepancies 
introduced during overhaul of the pumps. Emergency AD 98-08-09 was 
issued April 3, 1998, to specify a minimum quantity of fuel to be 
carried in the fuel tanks for the purpose of

[[Page 58649]]

covering the pumps with liquid fuel and thereby precluding ignition of 
vapors within the fuel tank until such time as terminating corrective 
action could be developed.

Unforeseen Fuel Tank System Failures

    After an extensive review of the Boeing 747 design following the 
July 17, 1996, accident, the FAA determined that during original 
certification of the fuel tank system, the degree of tank contamination 
and the significance of certain failure modes of fuel tank system 
components had not been considered to the degree that more recent 
service experience indicates is needed. For example, in the absence of 
contamination, the FQIS had been shown to preclude creating an arc if 
FQIS wiring were to come in contact with the highest level of 
electrical voltage on the airplane. This was shown by demonstrating 
that the voltage needed to cause an arc in the fuel probes due to an 
electrical short condition was well above any voltage level available 
in the airplane systems. However, recent testing has shown that if 
contamination, such as conductive debris (lock wire, nuts, bolts, steel 
wool, corrosion, copper-sulfur deposits, metal filings, etc.) is placed 
within gaps in the fuel probe, the voltage needed to cause an arc is 
within values that may occur due to a subsequent electrical short or 
induced current on the FQIS probe wiring from electromagnetic 
interference caused by adjacent wiring. These anomalies, by themselves, 
could not lead to an electrical arc within the fuel tanks without the 
presence of an additional failure. If any of these anomalies were 
combined with a subsequent failure within the electrical system that 
creates an electrical short, or if high-intensity radiated fields 
(HIRF) or electrical current flow in adjacent wiring induces EMI 
voltage in the FQIS wiring, sufficient energy could enter the fuel tank 
and cause an ignition source within the tank.
    On November 26, 1997, in Docket No. 97-NM-272-AD, the FAA proposed 
a requirement for operators of Boeing 747-100, -200, and -300 series 
airplanes to install components for the suppression of electrical 
transients and/or the installation of shielding and separation of fuel 
quantity indicating system wiring from other airplane system wiring. 
After reviewing the comments received on the proposed requirements, the 
FAA issued AD 98-20-40 on September 23, 1998 that requires the 
installation of shielding and separation of the electrical wiring of 
the fuel quantity indication system. On April 14, 1998, the FAA 
proposed a similar requirement for Boeing 737-100, -200, -300, -400, 
and -500 series airplanes in Docket No. 98-NM-50-AD, which led to the 
FAA issuing AD 99-03-04 on January 26, 1999. The FAA action required in 
those two airworthiness directives is intended to preclude high levels 
of electrical energy from entering the airplane fuel tank wiring due to 
electromagnetic interference or electrical shorts. All later model 
Boeing 747 and 737 FQIS's have wire separation and fault isolation 
features that may meet the intent of these AD actions. This proposed 
rulemaking will require evaluation of these later designs.
    Other examples of unanticipated failure conditions include 
incidents of parts from fuel pump assemblies impacting or contacting 
the rotating fuel pump impeller. The first design anomaly was 
identified when two incidents of damage to fuel pumps were reported on 
Boeing 767 airplanes. In both cases objects from a fuel pump inlet 
diffuser assembly were ingested into the fuel pump, causing damage to 
the pump impeller and pump housing. The damage could have caused sparks 
or hot debris from the pump to enter the fuel tank. To address this 
unsafe condition, the FAA issued AD 97-19-15. This AD requires revision 
of the airplane flight manual to include procedures to switch off the 
fuel pumps when the center tank approaches empty. The intent of this 
interim action is to maintain liquid fuel over the pump inlet so that 
any debris generated by a failed fuel pump will not come in contact 
with fuel vapors and cause a fuel tank explosion.
    The second design anomaly was reported on Boeing 747-400 series 
airplanes. The reports indicated that inlet adapters of the override/
jettison pumps of the center wing fuel tank were found to be worn. Two 
of the inlet adapters had worn down enough to cause damage to the 
rotating blades of the inducer. The inlet check valves also had 
significant damage. Another operator reported damage to the inlet 
adapter that was so severe that contact had occurred between the steel 
disk of the inlet check valve and the steel screw that holds the 
inducer in place. Wear to the inlet adapters has been attributed to 
contact between the inlet check valve and the adapter. Such excessive 
wear of the inlet adapter can lead to contact between the inlet check 
valve and inducer, which could result in pieces of the check valve 
being ingested into the inducer and damaging the inducer and impellers. 
Contact between the steel disk of the inlet check valve and the steel 
rotating inducer screw can cause sparks. To address this unsafe 
condition, the FAA issued an immediately adopted rule, AD 98-16-19, on 
July 30, 1998.
    Another design anomaly was reported in 1989 when a fuel tank 
ignition event occurred in an auxiliary fuel tank during refueling of a 
Beech 400 airplane. The auxiliary fuel tank had been installed under an 
STC. Polyurethane foam had been installed in portions of the tank to 
minimize the potential of a fuel tank explosion if uncontained engine 
debris penetrated those portions of the tank. The accident 
investigation indicated that electrostatic charging of the foam during 
refueling resulted in ignition of fuel-air vapors in portions of the 
adjacent fuel tank system that did not contain the foam. The fuel vapor 
explosion caused distortion of the tank and fuel leakage from a failed 
fuel line. Modifications to the design, including use of more 
conductive polyurethane foam and installation of a standpipe in the 
refueling system, were incorporated to prevent reoccurrence of 
electrostatic charging and resulting fuel tank ignition source.

Review of Fuel Tank System Maintenance Practices

    In addition to the review of the design features and service 
history of the Boeing 747 and other airplane models in the transport 
airplane fleet, the FAA has also reviewed the current fuel tank system 
maintenance practices for these airplanes.
    Typical transport category airplane fuel tank systems are designed 
with redundancy and fault indication features such that single 
component failures do not result in any significant reduction in 
safety. Therefore, fuel tank systems historically have not had any 
life-limited components or specific detailed inspection requirements, 
unless mandated by airworthiness directives. Most of the components are 
``on condition,'' meaning that some test, check, or other inspection is 
performed to determine continued serviceability, and maintenance is 
performed only if the inspection identifies a condition requiring 
correction. Visual inspection of fuel tank system components is by far 
the predominant method of inspection for components such as boost 
pumps, fuel lines, couplings, wiring, etc. Typically these inspections 
are conducted concurrently with zonal inspections or internal or 
external fuel tank structural inspections. These inspections normally 
do not provide information regarding the continued serviceability of 
components within the fuel tank system, unless the visual inspection 
indicates a potential problem

[[Page 58650]]

area. For example, it would be difficult, if not impossible, to detect 
certain degraded fuel tank system conditions, such as worn wiring 
routed through conduit to fuel pumps, debris inside fuel pumps, 
corrosion to bonding wire interfaces, etc., without dedicated intrusive 
inspections that are much more extensive than those normally conducted.

Listing of Deficiencies

    The list provided below summarizes fuel tank system design 
features, malfunctions, failures, and maintenance related actions that 
have been identified through service experience to result in a 
degradation of the safety features of airplane fuel tank systems. This 
list was developed from service difficulty reports and incident and 
accident reports. These anomalies occurred on in-service transport 
category airplanes contrary to the intent of regulations and policies 
intended to preclude the development of ignition sources within 
airplane fuel tank systems.
    1. Pumps:
     Ingestion of the pump inducer into the pump impeller and 
generation of debris into the fuel tank.
     Pump inlet case degradation, allowing the pump inlet check 
valve to contact the impeller.
     Stator winding failures during operation of the fuel pump. 
Subsequent failure of a second phase of the pump resulting in arcing 
through the fuel pump housing.
     Deactivation of thermal protective features incorporated 
into the windings of pumps due to inappropriate wrapping of the 
windings.
     Omission of cooling port tubes between the pump assembly 
and the pump motor assembly during fuel pump overhaul.
     Extended dry running of fuel pumps in empty fuel tanks, 
which was contrary to the manufacturer's recommended procedures.
     Use of steel impellers that may produce sparks if debris 
enters the pump.
     Debris lodged inside pumps.
     Arcing due to the exposure of electrical connections 
within the pump housing that have been designed with inadequate 
clearance to the pump cover.
     Thermal switches resetting over time to a higher trip 
temperature.
     Flame arrestors falling out of their respective mounting.
     Internal wires coming in contact with the pump rotating 
group, energizing the rotor and arcing at the impeller/adapter 
interface.
     Poor bonding across component interfaces.
     Insufficient ground fault current protection capability.
     Poor bonding of components to structure.
    2. Wiring to pumps in conduits located inside fuel tanks:
     Wear of Teflon sleeving and wiring insulation allowing 
arcing from wire through metallic conduits into fuel tanks.
    3. Fuel pump connectors:
     Electrical arcing at connections within electrical 
connectors due to bent pins or corrosion.
     Fuel leakage and subsequent fuel fire outside of the fuel 
tank caused by corrosion of electrical connectors inside the pump motor 
which lead to electrical arcing through the connector housing 
(connector was located outside the fuel tank).
     Selection of improper materials in connector design.
    4. FQIS wiring:
     Degradation of wire insulation (cracking), corrosion and 
copper-sulfur deposits at electrical connectors.
     Unshielded FQIS wires routed in wire bundles with high 
voltage wires.
    5. FQIS probes:
     Corrosion and copper-sulfur deposits causing reduced 
breakdown voltage in FQIS wiring.
     Terminal block wiring clamp (strain relief) features at 
electrical connections on fuel probes causing damage to wiring 
insulation.
     Contamination in the fuel tanks causing reduced arc path 
between FQIS probe walls (steel wool, lock wire, nuts, rivets, bolts; 
mechanical impact damage to probes).
    6. Bonding straps:
     Corrosion to bonding straps.
     Loose or improperly grounded attachment points.
     Static bonds on fuel tank system plumbing connections 
inside the fuel tank worn due to mechanical wear of the plumbing from 
wing movement and corrosion.
    7. Electrostatic charge:
     Use of non-conductive reticulated polyurethane foam that 
holds electrostatic charge buildup.
     Spraying of fuel into fuel tanks through inappropriately 
designed refueling nozzles or pump cooling flow return methods.

Fuel Tank Flammability

    In addition to the review of potential fuel tank ignition, the FAA 
has undertaken a parallel effort to address the threat of fuel tank 
explosions by eliminating or significantly reducing the presence of 
explosive fuel air mixtures within the fuel tanks of new type designs, 
in-production, and the existing fleet of transport airplanes. On April 
3, 1997, the FAA published a notice in the Federal Register (62 FR 
16014) that requested comments concerning the 1997 NTSB recommendations 
regarding reduced flammability listed earlier in this notice. That 
notice provided significant discussion of service history, background, 
and issues relating to reducing flammability in transport airplane fuel 
tanks. Comments received from that notice indicated that additional 
information was needed before the FAA could initiate rulemaking action 
to address the recommendations.
    On January 23, 1998, the FAA published a notice in the Federal 
Register that established an Aviation Rulemaking Advisory Committee 
(ARAC) working group, the Fuel Tank Harmonization Working Group 
(FTHWG), tasked to achieve this goal. The ARAC consists of interested 
parties, including the public, and provides a public process for advice 
to be given to the FAA concerning development of new regulations. The 
FTHWG evaluated numerous possible means of reducing or eliminating 
hazards associated with explosive vapors in fuel tanks. On July 23, 
1998, the ARAC submitted its report to the FAA. The full report has 
been placed in a docket that was created for this ARAC working group 
(Docket No. FAA-1998-4183). That docket can be reviewed on the U.S. 
Department of Transportation electronic Document Management System on 
the Internet at http://dms.dot.gov. The full report has also been 
placed in the docket for this rulemaking.
    The report provided a recommendation for the FAA to initiate 
rulemaking action to amend Sec. 25.981, applicable to new type design 
airplanes, to include a requirement to limit the time transport 
airplane fuel tanks could operate with flammable vapors in the vapor 
space of the tank. The recommended regulatory text proposed, ``Limiting 
the development of flammable conditions in the fuel tanks, based on the 
intended fuel types, to less than 7 percent of the expected fleet 
operational time, or providing means to mitigate the effects of an 
ignition of fuel vapors within the fuel tanks such that any damage 
caused by an ignition will not prevent continued safe flight and 
landing.'' The report discussed various options of showing compliance 
with this proposal, including managing heat input to the fuel tanks, 
installation of inerting systems or polyurethane fire suppressing foam, 
and suppressing an explosion if one occurred, etc.
    The level of flammability defined in the proposal was established 
based

[[Page 58651]]

upon comparison of the safety record of center wing fuel tanks that, in 
certain airplanes, are heated by equipment located under the tank, and 
unheated fuel tanks located in the wing. The FTHWG concluded that the 
safety record of fuel tanks located in the wings was adequate and that 
if the same level could be achieved in center wing fuel tanks, the 
overall safety objective would be achieved. Results from thermal 
analyses documented in the report indicate that center wing fuel tanks 
that are heated by air conditioning equipment located beneath them are 
flammable, on a fleet average basis, for up to 30 percent of the fleet 
operating time.
    During the ARAC process it was also determined that certain 
airplane types do not locate heat sources adjacent to the fuel tanks. 
These airplanes provide significantly reduced flammability exposure, 
near the 5 percent value of the wing tanks. The group therefore 
determined that it would be feasible to design new airplanes such that 
fuel tank operation in the flammable range would be limited to near 
that of the wing fuel tanks. The primary method of compliance with the 
requirement proposed by the ARAC would likely be to control heat 
transfer into and out of fuel tanks such that heating of the fuel would 
not occur. Design features such as locating the air conditioning 
equipment away from the fuel tanks, providing ventilation of the air 
conditioning bay to limit heating and cool fuel tanks, and/or 
insulating the tanks from heat sources, would be practical means of 
complying with the regulation proposed by the ARAC.
    In addition to its recommendation to revise Sec. 25.981, the ARAC 
also recommended that the FAA continue to evaluate means for minimizing 
the development of flammable vapors within the fuel tanks to determine 
whether other alternatives, such as ground based inerting of fuel 
tanks, could be shown to be cost effective.

Discussion of the Proposal

    The FAA review of the service history, design features, and 
maintenance instructions of the transport airplane fleet indicates that 
aging of fuel tank system components and unforeseen fuel tank system 
failures and malfunctions have become a safety issue for the fleet of 
turbine-powered transport category airplanes. The FAA proposes to amend 
the current regulations in four areas.
    The first area of concern encompasses the possibility of the 
development of ignition sources within the existing transport airplane 
fleet. Many of the design practices used on airplanes in the existing 
fleet are similar. Therefore anomalies that have developed on specific 
airplane models within the fleet could develop on other airplane 
models. As a result, the FAA considers that a one-time design review of 
the fuel tank system for transport airplane models in the current fleet 
is needed.
    The second area of concern encompasses the need to require the 
design of future transport category airplanes to more completely 
address potential failures in the fuel tank system that could result in 
an ignition source in the fuel tank system.
    Third, certain airplane types are designed with heat sources 
adjacent to the fuel tank, which results in heating of the fuel and a 
significant increase in the formation of flammable vapors in the tank. 
The FAA considers that fuel tank safety can be enhanced by reducing the 
time fuel tanks operate with flammable vapors in the tank and is 
therefore proposing a requirement to provide means to minimize the 
development of flammable vapors in fuel tanks or provide means to 
prevent catastrophic damage if ignition does occur.
    Fourth, the FAA considers that it is necessary to impose 
operational requirements so that any required maintenance or inspection 
actions will be included in each operator's FAA-approved program.

Proposed SFAR

    Historically, the FAA has worked together with the TC holders when 
safety issues arise to identify solutions and actions that need to be 
taken. Some of the safety issues that have been addressed by this 
voluntary cooperative process include those involving aging aircraft 
structure, thrust reversers, cargo doors, and wing icing protection. 
While some manufacturers have aggressively completed these safety 
reviews, others have not applied the resources necessary to complete 
these reviews in a timely manner, which delayed the adoption of 
corrective action. Although these efforts have frequently been 
successful in achieving the desired safety objectives, a more uniform 
and expeditious response is considered necessary to address fuel tank 
safety issues.
    While maintaining the benefits of FAA-TC holder cooperation, the 
FAA considers that a Special Federal Aviation Regulation (SFAR) 
provides a means for the FAA to establish clear expectations and 
standards, as well as a timeframe within which the design approval 
holders and the public can be confident that fuel tank safety issues on 
the affected airplanes will be uniformly examined.
    This proposed rulemaking is intended to ensure that the design 
approval holder completes a comprehensive assessment of the fuel tank 
system and develops any required inspections, maintenance instructions, 
or modifications.

Safety Review

    The proposed SFAR would require the design approval holder to 
perform a safety review of the fuel tank system to show that fuel tank 
fires or explosions will not occur on airplanes of the approved design. 
In conducting the review, the design approval holder would be required 
to demonstrate compliance with the standards proposed in this notice 
for Sec. 25.981(a) and (b) (discussed below) and the existing standards 
of Sec. 25.901. As part of this review, the design approval holder 
would be required to submit a report to the cognizant FAA Aircraft 
Certification Office (ACO) that substantiates that the fuel tank system 
is fail-safe.
    The FAA intends that those failure conditions listed previously in 
this notice, and any other foreseeable failures, should be assumed when 
performing the system safety analysis needed to substantiate that the 
fuel tank system design is fail-safe. The system safety analysis should 
be prepared considering all airplane inflight, ground, service, and 
maintenance conditions, assuming that an explosive fuel air mixture is 
present in the fuel tanks at all times, unless the fuel tank has been 
purged of fuel vapor for maintenance. The design approval holder would 
be expected to develop a failure modes and effects analysis (FMEA) for 
all components in the fuel tank system. Analysis of the FMEA would then 
be used to determine whether single failures, alone or in combination 
with foreseeable latent failures, could cause an ignition source to 
exist in a fuel tank. A subsequent quantitative fault tree analysis 
should then be developed to determine whether combinations of failures 
expected to occur in the life of the affected fleet could cause an 
ignition source to exist in a fuel tank system.
    Because fuel tank systems typically have few components within the 
fuel tank, the number of possible sources of ignition is limited. The 
system safety analysis required by this proposed rule would include all 
components or systems that could introduce a source of fuel tank 
ignition. This may require analysis of not only the fuel tank system 
components, (e.g., pumps, fuel pump power supplies, fuel valves, fuel 
quantity indication system probes,

[[Page 58652]]

wiring, compensators, densitometers, fuel level sensors, etc.), but 
also other airplane systems that may affect the fuel tank system. For 
example, failures in airplane wiring or electromagnetic interference 
from other airplane systems could cause an ignition source in the 
airplane fuel tank system under certain conditions and therefore would 
have to be included in the system safety analysis. A proposed revision 
to AC 25.981-1A, discussed later in this document, is being developed 
to provide guidance on performing the safety review.
    The intent of the design review proposed in this notice is to 
assure that each fuel tank system design that is affected by this 
action will be fully assessed and that the design approval holder 
identifies any required modifications, added flight deck or maintenance 
indications, and/or maintenance actions necessary to meet the fail-safe 
criteria.

Maintenance Instructions

    The FAA anticipates that the safety review would identify critical 
areas of the fuel tank and other related systems that would require 
maintenance actions to account for the affects of aging, wear, 
corrosion, and possible contamination on the fuel tank system. For 
example, service history indicates that copper-sulfur deposits may form 
on fuel tank components, including bonding straps and FQIS components, 
which could degrade the intended design capabilities by providing a 
mechanism by which arcing could occur. Therefore, it might be necessary 
to provide maintenance instructions to identify and eliminate such 
deposits.
    The proposed SFAR would require that the design approval holder 
develop any specific maintenance and inspection instructions necessary 
to maintain the design features required to preclude the existence or 
development of an ignition source within the fuel tank system. These 
instructions would have to be established to ensure that an ignition 
source will not develop throughout the remaining operational life of 
the airplane.

Possible Airworthiness Directives

    The design review may also result in identification of unsafe 
conditions on certain airplane models that would require issuance of 
airworthiness directives. For example, as discussed previously in this 
notice, the FAA has required or proposed requirements for design 
changes to the Boeing 737, 747, and 767; Boeing Douglas Products 
Division DC-10 and Lockheed L-1011 airplanes. Design practices utilized 
on these models may be similar to those of other airplane types; 
therefore, the FAA expects that modifications to airplanes with similar 
design features may also be required.
    The number and scope of any possible AD's may vary by airplane type 
design. For example, wiring separation and shielding of FQIS wires on 
newer technology airplanes significantly reduces the likelihood of an 
electrical short causing an electrical arc in the fuel tank; many newer 
transport airplanes do not route electrical power wiring to fuel pumps 
inside the airplane fuel tanks. Therefore, some airplane models may not 
require significant modifications or additional dedicated maintenance 
procedures. Other models may require significant modifications or more 
maintenance. For example, the FQIS wiring on some older technology 
airplanes is routed in wire bundles with high voltage power supply 
wires. The original failure analyses conducted on these airplane types 
did not consider the possibility that the fuel quantity indication 
system may become degraded allowing a significantly lower voltage level 
to produce a spark inside the fuel tank. Causes of degradation observed 
in service include aging, corrosion, or undetected contamination of the 
system. As previously discussed, the FAA has issued AD actions for 
certain Boeing 737 and 747 airplanes to address this condition. 
Modification of similar types of installations on other airplane models 
may be required to address this unsafe condition and to achieve a fail-
safe design.
    It should be noted that any design changes may, in themselves, 
require maintenance actions. For example, transient protection devices 
typically require scheduled maintenance in order to detect latent 
failure of the suppression feature. As a part of the required design 
review, the manufacturer would define the necessary maintenance 
procedures and intervals for any required maintenance actions.

Applicability of the Proposed SFAR

    As proposed, the SFAR would apply to holders of TCs, and STCs for 
modifications that affect the fuel tank systems of turbine-powered 
transport category airplanes, for which the TC was issued after January 
1, 1958, and the airplane has a maximum type certificated passenger 
capacity of 30 or more, or a maximum type certificated payload capacity 
of 7500 pounds or more. The SFAR would also apply to applicants for 
type certificates, amendments to a type certificate, and supplemental 
type certificates affecting the fuel tank systems for those airplanes 
identified above if the application was filed before the effective date 
of the proposed SFAR and the certificate was not issued before the 
effective date of the SFAR. The FAA has determined that turbine-powered 
airplanes, regardless of whether they are turboprops or turbojets, 
should be subject to the rule, because the potential for ignition 
sources in fuel tank systems is unrelated to the engine design. This 
would result in the coverage of the large transport category airplanes 
where the safety benefits and public interest are greatest. This action 
would affect approximately 6,000 U.S. registered airplanes in part 91, 
121, 125, and 129 operations.
    The date January 1, 1958, was chosen so that only turbine-powered 
airplanes, except for a few 1953-1958 vintage Convair 340s and 440s 
converted from reciprocating power, would be included. No 
reciprocating-powered transport category airplanes are known to be used 
currently in passenger service, and the few remaining in cargo service 
would be excluded. Compliance is not proposed for those older airplanes 
because their advanced age and small numbers would likely make 
compliance impractical from an economic standpoint. This is consistent 
with similar exclusions made for those airplanes from other 
requirements applicable to existing airplanes, such as the regulations 
adopted for flammability of seat cushions (49 FR 43188, October 24, 
1984); flammability of cabin interior components (51 FR 26206, July 21, 
1986); cargo compartment liners (54 FR 7384, February 17, 1989); access 
to passenger emergency exits (57 FR 19244, May 4, 1992); and Class D 
cargo or baggage compartments (63 FR 8032, February 17, 1998).
    In order to achieve the benefits of this rulemaking for large 
transport airplanes as quickly as possible, the FAA has decided to 
proceed with this rulemaking with the applicability of the SFAR limited 
to airplanes with a maximum certificated passenger capacity of at least 
30 or at least 7,500 pounds payload. Compliance is not proposed for 
smaller airplanes because it is not clear at this time that the 
possible benefits for those airplanes would be commensurate with the 
costs involved. However, the FAA intends to undertake a full regulatory 
evaluation of applying these requirements to small transport category 
and commuter category airplanes to determine the merits of subsequently 
extending the rule to airplanes with a passenger capacity of fewer than 
30 and less than 7,500 pounds payload. Therefore, the FAA specifically 
requests comments as to the feasibility of

[[Page 58653]]

requiring holders of type certificates issued prior to January 1, 1958, 
or for airplanes having a passenger capacity of fewer than 30 and less 
than 7,500 pounds payload, to comply and the safety benefits likely to 
be realized.

Supplemental Type Certificates (STC)

    The FAA considers that this rule should apply to STC holders as 
well, because a significant number of STCs effect changes to fuel tank 
systems, and the objectives of this proposed rule would not be achieved 
unless these systems are also reviewed and their safety ensured. The 
service experience noted in the background of this proposed rule 
indicates modifications to airplane fuel tank systems incorporated by 
STCs may affect the safety of the fuel tank system.
    Modifications that could affect the fuel tank system include those 
that could result in an ignition source in the fuel tank. Examples 
include installation of auxiliary fuel tanks and installation of, or 
modification to, other systems such as the fuel quantity indication 
system, the fuel pump system (including electrical power supply), 
airplane refueling system, any electrical wiring routed within or 
adjacent to the fuel tank, and fuel level sensors or float switches. 
Modifications to systems or components located outside the fuel tank 
system may also affect fuel tank safety. For example, installation of 
electrical wiring for other systems that was inappropriately routed 
with FQIS wiring could violate the wiring separation requirements of 
the type design. Therefore, the FAA intends that a fuel tank system 
safety review be conducted for any modification to the airplane that 
may affect the safety of the fuel tank system. The level of evaluation 
that is intended would be dependent upon the type of modification. In 
most cases a simple qualitative evaluation of the modification in 
relation to the fuel tank system, and a statement that the change has 
no effect on the fuel tank system, would be all that is necessary. In 
other cases where the initial qualitative assessment shows that the 
modification may affect the fuel tank system, a more detailed safety 
review would be required.
    Design approvals for modification to airplane fuel tank systems 
approved by STCs require the applicant to have knowledge of the 
airplane fuel tank system in which the modification is installed. The 
majority of these approvals are held by the original airframe 
manufacturers or airplane modifiers that specialize in fuel tank system 
modifications, such as installation of auxiliary fuel tanks. Therefore, 
the FAA expects that the data needed to complete the safety review 
proposed in this notice would be available to the STC holder.

Compliance

    This notice proposes a 12-month compliance time from the effective 
date of the final rule, or within 12 months after the issuance of a 
certificate for which application was filed before the effective date 
of this SFAR, whichever is later, for design approval holders to 
conduct the safety review and develop the compliance documentation and 
any required maintenance and inspection instructions. The FAA would 
expect each design approval holder to work with the cognizant FAA 
Aircraft Certification Office (ACO) and Aircraft Evaluation Group (AEG) 
to develop a plan to complete the safety review and develop the 
required maintenance and inspection instructions within the 12 month 
period. The plan should include periodic reviews with the ACO and AEG 
of the ongoing safety review and the associated maintenance and 
inspection instructions.
    During the proposed 12-month compliance period, the FAA is 
committed to working with the affected design approval holders to 
assist them in complying with the requirements of this proposed SFAR. 
However, failure to comply within the specified time would constitute a 
violation of the proposed requirements and may subject the violator to 
certificate action to amend, suspend, or revoke the affected 
certificate in accordance with 49 U.S.C. Sec. 44709. It may also 
subject the violator to a civil penalty of not more than $1,100 per day 
until the SFAR is complied with, in accordance with 49 U.S.C. 
Sec. 46301.

Proposed Operating Requirements

    This proposed rule would require that affected operators 
incorporate FAA-approved fuel tank system maintenance and inspection 
instructions in their maintenance or inspection program within 18 
months of the effective date of the proposed rule. If the design 
approval holder has complied with the SFAR and developed an FAA-
approved program, the operator could incorporate that program to meet 
the proposed requirement. The operator would also have the option of 
developing its own program independently, and would be ultimately 
responsible for having an FAA-approved program, regardless of the 
action taken by the design approval holder.
    The proposed rule would prohibit the operation of certain transport 
category airplanes operated under parts 91, 121, 125, and 129 beyond a 
specified compliance time, unless the operator of those airplanes has 
incorporated FAA-approved fuel tank maintenance and inspection 
instructions in its maintenance or inspection program, as applicable. 
The proposed regulation would require that the maintenance and 
inspection instructions be approved by the Administrator; for the 
purposes of this rule, the Administrator is considered to be the 
manager of the cognizant FAA ACO.
    The operator would need to consider the following:
    1. The fuel tank system maintenance and inspection instructions 
that would be incorporated into the operator's existing maintenance or 
inspection program would need to be approved by the FAA ACO having 
cognizance over the TC of the airplane. If the operator can establish 
that the existing maintenance and inspection instructions fulfill the 
requirements of this proposed rule, then the ACO may approve the 
operator's existing maintenance and inspection instructions without 
change.
    2. The means by which the FAA-approved fuel tank system maintenance 
and inspection instructions would be incorporated into a certificate 
holder's FAA-approved maintenance or inspection program would be 
subject to approval by the certificate holder's principal maintenance 
inspector (PMI) or other cognizant airworthiness inspector. The FAA 
intends that any escalation to the FAA-approved inspection intervals 
would require the operator to receive FAA approval of the amended 
program. Any request for escalation to the FAA approved inspection 
intervals would need to include data to substantiate that the proposed 
interval will provide the level of safety intended by the original 
approval. If inspection results and service experience indicate that 
additional or more frequent inspections are necessary, the FAA may 
issue AD's to mandate such changes to the inspection program.
    3. This rule would not impose any new reporting requirements; 
however, normal reporting required under 14 CFR Secs. 121.703 and 
125.409 would still apply.
    4. This rule would not impose any new FAA recordkeeping 
requirements. However, as with all maintenance, the current operating 
regulations (e.g., 14 CFR Secs. 121.380 and 91.417) already impose 
recordkeeping requirements that would apply to the actions required by 
this proposed rule. When incorporating the fuel tank system maintenance 
and inspection instructions into its

[[Page 58654]]

approved maintenance or inspection program, each operator should 
address the means by which it will comply with these recordkeeping 
requirements. That means of compliance, along with the remainder of the 
program, would be subject to approval by the cognizant PMI or other 
cognizant airworthiness inspector.
    5. The maintenance and inspection instructions developed by the TC 
holder under the proposed rule generally would not apply to fuel tank 
systems modified by an STC, including any auxiliary fuel tank 
installations or other modifications. The operator, however, would 
still be responsible to incorporate specific maintenance and inspection 
instructions applicable to the entire fuel tank system that meet the 
requirements of this proposed rulemaking. This means that the operator 
should evaluate the fuel tank systems and any alterations to the fuel 
tank system and then develop, submit, and gain FAA approval of the 
maintenance and inspection instructions to evaluate repairs to such 
fuel tank systems.
    The FAA recognizes that operators may not have the resources to 
develop maintenance or inspection instructions for the airplane fuel 
tank system. The proposed rule would therefore require the TC and STC 
holders to develop fuel tank system maintenance and inspection 
instructions that may be used by operators. If however, the STC holder 
is out of business or otherwise unavailable, the operator would 
independently have to acquire the FAA-approved inspection instructions. 
To keep the airplanes in service, operators, either individually or as 
a group, could hire the necessary expertise to develop and gain 
approval of maintenance and inspection instructions. Guidance on how to 
comply with this aspect of the proposed rule would be provided in the 
planned revision to AC 25.981-1A.
    After the PMI having oversight responsibilities is satisfied that 
the operator's continued airworthiness maintenance or inspection 
program contains all of the elements of the FAA-approved fuel tank 
system maintenance and inspection instructions, the airworthiness 
inspector would approve the maintenance or inspection program revision. 
This approval would have the effect of requiring compliance with the 
maintenance and inspection instructions.

Applicability of the Proposed Operating Requirements

    This proposed rule would prohibit the operation of certain 
transport category airplanes operated under 14 CFR parts 91, 121, 125, 
and 129 beyond a specified compliance time, unless the operator of 
those airplanes has incorporated FAA-approved specific maintenance and 
inspection instructions applicable to the fuel tank system in its 
approved maintenance or inspection program, as applicable. The 
operational applicability was established so that all airplane types 
affected by the SFAR, regardless of type of operation, would be subject 
to FAA approved fuel tank system maintenance and inspection procedures. 
As discussed earlier, this proposed rulemaking would include each 
turbine-powered transport category airplane model, provided its TC was 
issued after January 1, 1958, and it has a maximum type certificated 
passenger capacity of 30 or more, or a maximum type certificated 
payload capacity of 7,500 pounds or more.

Field Approvals

    A significant number of changes to other transport category 
airplane fuel tank systems have been incorporated through field 
approvals issued to the operators of those airplanes. These changes may 
also significantly affect the safety of the fuel tank system. The 
operator of any airplane with such changes would be required to develop 
the fuel tank system maintenance and inspection program instructions 
and submit it to the FAA for approval, together with the necessary 
substantiation of compliance with the design review requirements of the 
SFAR.

Compliance

    This notice proposes an 18 month compliance time from the effective 
date of the final rule for operators to incorporate FAA-approved long 
term fuel tank system maintenance and inspection instructions into 
their approved program. The FAA would expect each operator to work with 
the airplane TC holder or STC holder to develop a plan to implement the 
required maintenance and inspection instructions within the 18 month 
period. The plan should include periodic reviews with the cognizant ACO 
and AEG that would approve the associated maintenance and inspection 
instructions.

Proposed Changes to Part 25

    Currently, Sec. 25.981 defines limits on surface temperatures 
within transport airplane fuel tank systems. In order to address future 
airplane designs, the FAA proposes to revise Sec. 25.981 to address 
both prevention of ignition sources in fuel tanks and reduction in the 
time fuel tanks contain flammable vapors. The first proposal would 
explicitly include a requirement for effectively precluding ignition 
sources within the fuel tank systems of transport category airplanes. 
The second proposal would require minimizing the formation of flammable 
vapors in the fuel tanks.

Fuel Tank Ignition Source Proposal

    The title of Sec. 25.981 would be changed from ``Fuel tank 
temperature'' to ``Fuel tank ignition prevention.'' The FAA proposes to 
retain the substance of existing paragraph (a), which requires the 
applicant to determine the highest temperature that allows a safe 
margin below the lowest expected auto ignition temperature of the fuel; 
and the existing paragraph (b), which requires precluding the 
temperature in the fuel tank from exceeding the temperature determined 
under paragraph (a). These requirements are redesignated as (a)(1) and 
(2) respectively.
    Compliance with these paragraphs requires the determination of the 
fuel flammability characteristics of the fuels approved for use. Fuels 
approved for use on transport category airplanes have differing 
flammability characteristics. The fuel with the lowest autoignition 
temperature is JET A (kerosene), which has an autoignition temperature 
of approximately 450  deg.F at sea level. The autoignition temperature 
of JP-4 is approximately 470  deg.F at sea level. Under the same 
atmospheric conditions the autoignition temperature of gasoline is 
approximately 800  deg.F. The autoignition temperature of these fuels 
increases at increasing altitudes (lower pressures). For the purposes 
of this rule the lowest temperature at which autoignition can occur for 
the most critical fuel approved for use should be determined. The FAA 
intends that a temperature providing a safe margin is at least 50 
deg.F below the lowest expected autoignition temperature of the fuel 
throughout the altitude and temperature envelopes approved for the 
airplane type for which approval is requested.
    This proposal would also add a new paragraph (a)(3) to require that 
a safety analysis be performed to demonstrate that the presence of an 
ignition source in the fuel tank system could not result from any 
single failure, from any single failure in combination with any latent 
failure condition not shown to be extremely remote, or from any 
combination of failures not shown to be extremely improbable.
    These new requirements define three scenarios that must be 
addressed in order to show compliance with the proposed paragraph 
(a)(3). The first scenario is that any single failure, regardless of 
the probability of occurrence of the failure, must not cause

[[Page 58655]]

an ignition source. The second scenario is that any single failure, 
regardless of the probability occurrence, in combination with any 
latent failure condition not shown to be at least extremely remote 
(i.e., not shown to be extremely remote or extremely improbable), must 
not cause an ignition source. The third scenario is that any 
combination of failures not shown to be extremely improbable must not 
cause an ignition source.
    For the purpose of this proposed rule, ``extremely remote'' failure 
conditions are those not anticipated to occur to each airplane during 
its total life, but which may occur a few times when considering the 
total operational life of all airplanes of the type. This definition is 
consistent with that proposed by the Aviation Rulemaking Advisory 
Committee (ARAC) for a revision to FAA AC 25.1309-1A and that currently 
used by the Joint Aviation Authorities (JAA) in AMJ 25.1309. 
``Extremely improbable'' failure conditions are those so unlikely that 
they are not anticipated to occur during the entire operational life of 
all airplanes of one type. This definition is consistent with the 
definition provided in FAA AC 25.1309-1A and retained in the draft 
revision to AC 25.1309-1A proposed by the ARAC.
    The severity of the external environmental conditions that should 
be considered when demonstrating compliance with this proposed rule are 
those established by certification regulations and special conditions 
(e.g., HIRF), regardless of the associated probability. The proposed 
regulation would also require that the effects of manufacturing 
variability, aging, wear, and likely damage be taken into account when 
demonstrating compliance.
    The proposed requirements are consistent with the general 
powerplant installation failure analysis requirements of Sec. 25.901(c) 
and the systems failure analysis requirements of Sec. 25.1309 as they 
have been applied to powerplant installations. This proposal is needed 
because the general requirements of Secs. 25.901 and 25.1309 have not 
been consistently applied and documented when showing that ignition 
sources are precluded from transport category airplane fuel tanks. 
Compliance with the proposed revision to Sec. 25.981 would require 
analysis of the airplane fuel tank system using analytical methods and 
documentation currently used by the aviation industry in demonstrating 
compliance with Secs. 25.901 and 25.1309. In order to eliminate any 
ambiguity as to the necessary methods of compliance, the proposed rule 
explicitly requires that the existence of latent failures be assumed 
unless they are extremely remote, which is currently required under 
Sec. 25.901, but not under Sec. 25.1309. The analysis should be 
conducted assuming design deficiencies listed in the background section 
of this notice, and any other failure modes identified within the fuel 
tank system functional hazard assessment.
    Based upon the evaluations required by paragraph (a), a new 
requirement would be added to paragraph (b) to require that critical 
design configuration control limitations, inspections, or other 
procedures be established as necessary to prevent development of 
ignition sources within the fuel tank system, and that they be included 
in the Airworthiness Limitations section of the ICA required by 
Sec. 25.1529. This requirement would be similar to that contained in 
Sec. 25.571 for airplane structure. Appendix H to part 25 would also be 
revised to add a requirement to provide any mandatory fuel tank system 
inspections or maintenance actions in the limitations section of the 
ICA.
    Critical design configuration control limitations include any 
information necessary to maintain those design features that have been 
defined in the original type design as needed to preclude development 
of ignition sources. This information is essential to ensure that 
maintenance, repairs or alterations do not unintentionally violate the 
integrity of the original fuel tank system type design. An example of a 
critical design configuration control limitation for current designs 
discussed previously would be maintaining wire separation between FQIS 
wiring and other high power electrical circuits. The original design 
approval holder must define a method of ensuring that this essential 
information will be evident to those that may perform and approve such 
repairs and alterations. Placards, decals or other visible means must 
be placed in areas of the airplane where these actions may degrade the 
integrity of the design configuration. In addition, this information 
should be communicated by statements in appropriate manuals, such as 
Wiring Diagram Manuals.

Flammability Proposal

    The FAA agrees with the intent of the recommended regulatory text 
recommended by the ARAC. However, due to the short timeframe that the 
ARAC was provided to complete the tasking, sufficient detailed economic 
evaluation was not completed to determine if practical means, such as 
ground based inerting, were available to reduce the exposure below the 
specific value of 7 percent of the operational time included in the 
ARAC proposal. In addition the 7 percent level of flammability proposed 
by the FTHWG does not minimize flammability on certain applications, 
while in other applications, such as very short haul operations, it may 
not be practical to achieve. Therefore, the FAA is proposing a more 
objective regulation that is intended to minimize exposure to operation 
with flammable conditions in the fuel tanks.
    As discussed previously, the ARAC has submitted a recommendation to 
the FAA that the FAA continue to evaluate means for minimizing the 
development of flammable vapors within the fuel tanks. Development of a 
definitive standard to address this recommendation will require a 
significant research effort that will likely take some time to 
complete. In the meantime, however, the FAA is aware that historically 
certain design methods have been found acceptable that, when compared 
to readily available alternative methods, increase the likelihood that 
flammable vapors will develop in the fuel tanks. For example, in some 
designs, including the Boeing 747, air conditioning packs have been 
located immediately below a fuel tank without provisions to reduce 
transfer of heat from the packs to the tank.
    Therefore, in order to preclude the future use of such design 
practices, this proposal would revise Sec. 25.981 to add a requirement 
that fuel tank installations be designed to minimize the development of 
flammable vapors in the fuel tanks. Alternatively, if an applicant 
concludes that such minimization is not advantageous, it may propose 
means to mitigate the effects of an ignition of fuel vapors in the fuel 
tanks. For example, such means might include installation of fire 
suppressing polyurethane foam or installation of an explosion 
suppression system.
    This proposal is not intended to prevent the development of 
flammable vapors in fuel tanks because total prevention has currently 
not been found to be feasible. Rather, it is intended as an interim 
measure to preclude, in new designs, the use of design methods that 
result in a relatively high likelihood that flammable vapors will 
develop in fuel tanks when other practicable design methods are 
available that can reduce the likelihood of such development. For 
example, the proposal would not prohibit installation of fuel tanks in 
the cargo compartment, placing heat exchangers in fuel tanks, or 
locating a fuel tank in the center wing. The proposal would, however, 
require that practical means, such as transferring

[[Page 58656]]

heat from the fuel tank (e.g., use of ventilation or cooling air), be 
incorporated into the airplane design if heat sources were placed in or 
near the fuel tanks that significantly increased the formation of 
flammable fuel vapors in the tank, or if the tank is located in an area 
of the airplane where little or no cooling occurs. The intent of the 
proposal is to require that fuel tanks are not heated, and cool at a 
rate equivalent to that of a wing tank in the transport airplane being 
evaluated. This may require incorporating design features to increase 
or provide ventilation means for fuel tanks located in the center wing 
box, horizontal stabilizer, or auxiliary fuel tanks located in the 
cargo compartment. At such time as the FAA has completed the necessary 
research and identified an appropriate definitive standard to address 
this issue, new rulemaking would be considered to revise the standard 
proposed in this rulemaking.

Applicability of Proposed Part 25 Change

    The proposed amendments to part 25 would apply to all transport 
category airplane models for which an application for type 
certification is made after the effective date of the rule, regardless 
of passenger capacity or size. In addition, as currently required by 
the provisions of Sec. 21.50, applicants for any future changes to 
existing part 25 type certificated airplanes, including STCs, that 
could introduce an ignition source in the fuel tank system would be 
required to provide any necessary Instructions for Continued 
Airworthiness, as required by Sec. 25.1529 and the proposed change to 
the Airworthiness Limitations section, paragraph H25.4 of Appendix H. 
In cases where it is determined that the existing ICA are adequate for 
the continued airworthiness of the altered product, then it should be 
noted on the STC, PMA supplement, or major alteration approval.

FAA Advisory Material

    In addition to the amendments proposed in this notice, the FAA is 
developing a proposed revision to AC 25.981-1A, ``Guidelines for 
Substantiating Compliance With the Fuel Tank Temperature 
Requirements.'' The proposed revision will include consideration of 
failure conditions that could result in sources of ignition of vapors 
within fuel tanks. The revised AC will provide guidance on how to 
substantiate that ignition sources will not be present in airplane fuel 
tank systems following failures or malfunctions of airplane components 
or systems. This AC will also include guidance for developing any 
limitations for the ICA that may be generated by the fuel tank system 
safety assessment. Public comments concerning the proposed AC will be 
requested by separate notice published in the Federal Register.

Future Regulatory Actions

    The ARAC report discussed earlier does not recommend specific 
actions to eliminate or significantly reduce the flammability of fuel 
tanks in current production and the existing fleet of transport 
airplanes. The report, however, recommends that the FAA continue to 
investigate means to achieve a cost-effective reduction in flammability 
exposure for these airplanes. The FAA has reviewed the report and 
established research programs to support the further evaluation needed 
to establish the practicality of methods for achieving reduced 
flammability exposure for newly manufactured and the existing fleet of 
transport airplanes. The FAA intends to initiate rulemaking to address 
these airplanes if practical means are established.

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

    Proposed 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 requires agencies 
to analyze the economic impact of regulatory changes on small entities. 
Third, the Office of Management and Budget directs agencies to assess 
the effects of regulatory changes on international trade. And 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). In conducting these 
analyses, the FAA has determined that this proposed rulemaking: (1) 
would generate benefits that justify its costs as required by Executive 
Order 12866 and would be a ``significant regulatory action'' as defined 
in DOT's Regulatory Policies and Procedures; (2) would have a 
significant economic impact on a substantial number of small entities; 
(3) would have minimal effects on international trade; and (4) would 
not contain a significant intergovernmental or private sector mandate. 
These analyses, available in the docket, are summarized as follows.

Affected Industries

    Based on 1996 data, the proposal would affect 6,006 airplanes, of 
which 5,700 airplanes are operated by 114 air carriers under part 121 
service, 193 airplanes are operated by 7 carriers that operate under 
both part 121 and part 135, 22 airplanes are operated by 10 carriers 
under part 125 service, and 91 airplanes are operated by 23 carriers 
operating U.S.-registered airplanes under part 129. At this time, the 
FAA does not have information on airplanes operating under part 91 that 
would be affected by the proposed rulemaking; however, the FAA believes 
that very few airplanes operating under part 91 would be affected by 
the proposal.
    The proposed rule would also affect 12 manufacturers holding 35 
type certificates (TCs) and 26 manufacturers and airlines holding 168 
supplemental type certificates (STCs). The proposed rule would also 
affect manufacturers of future, new part 25 type certificated airplane 
models and holders of future, new part 25 supplemental type 
certificates for new fuel tank systems. At this time, the FAA cannot 
predict the number of new airplane models. Based on the past 10 years 
average, the FAA anticipates that about 17 new fuel tank system STCs 
would be granted annually. The FAA requests comments on these estimates 
and requests that commenters provide clear supporting additional 
information.

Benefits

    In order to quantify the benefits from preventing future fuel tank 
explosions, the FAA assumes that the potential U.S. fuel tank explosion 
rate due to an unknown internal fuel tank ignition source is similar to 
the worldwide fleet explosion rate over the past 10 years. On that 
basis, the FAA estimates that if no preventative actions were to be 
taken, between one and two (the expected value would be 1.25) fuel tank 
explosions would be expected to occur during the next 10 years in U.S. 
operations.
    By way of illustrating the potential effectiveness of an enhanced 
fuel tank system inspection program, on May 14, 1998, the FAA issued AD 
T98-11-52 requiring the inspection of fuel boost pump wires in the 
center wing tank of all Boeing 737's with more than 30,000

[[Page 58657]]

hours. Of the 599 airplanes inspected as of June 30, 1998, 273 wire 
bundles had noticeable chafing to wire insulation, 33 had significant 
(greater than 50 percent) insulation chafing, 8 had arcing on the cable 
but not through the conduit, while 2 had arcing through the conduit 
into the fuel tank.
    In light of the findings from these inspections, the FAA believes 
that better fuel tank system inspections would be a significant factor 
in discovering potential fuel tank ignition sources. The FAA 
anticipates that compliance with the proposal would prevent between 75 
percent and 90 percent of the potential future fuel tank explosions 
from unknown ignition sources.
    Using a value of $2.7 million to prevent a fatality, a value of the 
destroyed airplane of $20 million, an average of $30 million for an FAA 
investigation of an explosion, and assuming the proposal would prevent 
between 75 percent and 90 percent of these potential fuel tank 
explosions from an unknown ignition source, the potential present value 
of the expected benefits discounted over 10 years at 7 percent would be 
between $260 million and $520 million.
    In addition, the proposed part 25 change would reduce the length of 
time that an explosive atmosphere would exist in the fuel tank during 
certain operations for new part 25 type certificated airplanes and for 
new fuel tank system STCs. At this time, the FAA cannot quantify these 
potential benefits, but they are not expected to be considerable in the 
immediate future. The FAA expects that these benefits would increase 
over time as new part 25 type certificated airplanes replace the older 
part 25 type certificated airplanes in the fleet.

Compliance Costs

    The proposal consists of three parts. The first two are separate 
but interrelated parts, each of which would impose costs on the 
industry. The first is the proposed SFAR. The second is the proposed 
operational rules changes from the recommendations following the SFAR. 
The third part is the proposed part 25 change.
    The compliance costs for the proposed SFAR would be due to the 
requirement for the design approval holder to complete a comprehensive 
fuel tank system design assessment and to provide recommendations for 
the inspections and model-specific service instructions within one year 
from the SFAR's effective date. The assessment may identify conditions 
that would be addressed by specific service bulletins or unsafe 
conditions that would result in FAA issuance of an airworthiness 
directive (AD). However, those future costs would be the result of 
compliance with the service bulletin or the AD and are not costs of 
compliance with the proposed rulemaking. Those costs would be estimated 
for each individual AD, when proposed. In addition, the compliance 
costs do not include the compliance costs from an existing fuel tank 
AD.
    The compliance costs for the proposed operational rule changes 
would be due to the requirement for the air carrier to incorporate 
these recommendations into its fuel tank system inspection and 
maintenance program within 18 months from the proposal's effective 
date. These compliance costs do not include the costs to repair and 
replace equipment and wiring that is found to need repair or 
replacement during the inspection. Although these costs are likely to 
be substantial, they are attributable to existing FAA regulations that 
require such repairs and replacements be made to assure the airplane's 
continued airworthiness.
    The FAA anticipates that the proposed part 25 change would have a 
minimal effect on the cost of future type certificated airplanes 
because compliance with the proposed change would be done during the 
design phase of the airplane model before any new airplanes would be 
manufactured.
    In addition, the FAA determines, after discussion with industry 
representatives, that the proposed part 25 changes would have a minimal 
impact on future fuel tank system STCs because current industry design 
practices could be adapted to allow compliance with the proposed 
requirement.

Costs of Fuel Tank System Design Assessments--New SFAR

    The FAA has determined that 35 TCs and 68 fuel tank system STCs 
(many of the 168 STCs duplicate other STCs) would need a fuel tank 
system design assessment. Depending upon the complexity of the fuel 
tank system and the number of tanks, the FAA has estimated that a fuel 
tank system design assessment would take between 0.5 to 2 engineer 
years for a TC holder and an average of 0.25 engineer years for an STC 
holder. The FAA estimates that developing manual revisions and service 
bulletins would take between 0.25 to 1 engineer years for a TC holder 
and an average of 0.1 engineer years for an STC holder. In addition, 
the FAA and the TC or STC holder would each spend between 1 day and 5 
days to review, revise, and approve the assessment and the changes to 
the manual.
    Using a total engineer compensation rate (salary and fringe 
benefits plus a mark-up for hours spent by management, legal, etc. on 
the assessment) of $100 an hour, the FAA estimates that the one-time 
fuel tank system design assessment would cost TC holders a total of 
$9.5 million, it would cost STC holders a total of $4.9 million, and it 
would cost the FAA about $220,000.
    The FAA requests comments on the assumptions and the methodology 
and also requests that commenters provide additional data.

Costs of Fuel Tank System Inspections--Operational Rule Changes

    Methodology: The costs to air carriers of complying with the 
operational requirements proposed for Parts 91, 121, 125, and 129 would 
be the additional (incremental) labor hours and additional airplane 
out-of-service time to perform the enhanced fuel tank system 
maintenance and inspections. However, the costs of the fuel tank system 
inspections that have been required by recent ADs are not included as a 
cost of complying with the proposed operational amendments.
    The FAA intends that any additional fuel tank system inspection and 
maintenance actions resulting from the SFAR review would occur during 
an airplane's regularly scheduled major maintenance checks. From a 
safety standpoint, repeated entry increases the risk of damage to the 
airplane. Thus, the proposal would not require air carriers to alter 
their maintenance schedules, and the FAA anticipates that few or no 
airplanes would be taken out of service solely to comply with the 
proposal unless an immediate safety concern is identified. In that 
case, corrective action would be mandated by an AD.
    The FAA anticipates that the proposal would require additional time 
out of service and man-hours to complete a fuel tank system inspection 
and equipment and wiring testing.
    The FAA-estimated number of additional hours (for both man-hours 
and time out of service) to perform each of the various inspections is 
derived primarily from the available service bulletins and from 
discussions with airline maintenance engineers. For those turbojet 
models that have not been the subject of a fuel tank system inspection 
service bulletin, the FAA adopted the estimated hours from existing 
service bulletins of similar types of turbojet models. Although there 
have been no fuel tank system inspection service bulletins for 
turboprops, the FAA

[[Page 58658]]

received information concerning the estimated fuel tank system 
inspection time for a turboprop from commuter airline maintenance 
personnel. Based on this information and an FAA analysis that turboprop 
fuel tanks are smaller and have less equipment than turbojet fuel 
tanks, the FAA estimates that a turboprop fuel tank system inspection 
would take between one-third to one-half of the time it would take for 
the turbojet fuel tank system inspections defined in available 
bulletins.
    The FAA requests comments on these estimates and that commenters 
provide supporting data.
    Estimated Compliance Costs: The following cost and hour estimates 
are summaries of the Regulatory Evaluation of the proposal. The 
detailed estimated compliance costs, including all assumptions and the 
spreadsheet used for the calculations, are in that document, which is 
available in the docket.
    The incremental cost of complying with the operational proposals 
would consist of the following four components: (1) the labor hours to 
incorporate the recommendations into the inspections manual; (2) the 
labor hours needed to perform the fuel tank system inspection; (3) the 
cost of the additional downtime required to complete the inspection; 
and (4) the increased documentation and reporting of the inspection and 
subsequent findings.
    The FAA estimates that it would take an average of 5 engineer days 
to incorporate the recommendations into the inspections manual, for a 
cost of about $4,000 per airplane model per operator, with a total cost 
of about $1.16 million.
    The FAA estimates that the increased number of labor hours per 
airplane resulting from the enhanced fuel tank system inspection and 
maintenance would range from 19 hours to 110 hours in the first three 
years, and would decline to 9 hours to 60 hours beginning in the fourth 
year. Using a total compensation rate (wages plus fringe benefits) of 
$70 an hour for maintenance personnel, the FAA estimates that the 
annual per airplane costs of compliance would range from $1,330 to 
$7,700 in each of the first 3 years and from $630 to $4,200 in each 
year thereafter.
    The FAA estimates that the total annual inspection costs would be 
about $21.1 million during the first year, increasing by 4.3 percent 
per year from the projected increase in airline operations until the 
fourth year, when it would decline to about $10.1 million increasing by 
4.3 percent each year thereafter. The present value of the total 
operational cost, discounted at 7 percent over 10 years, would be about 
$100 million.
    As noted earlier, equipment costs would not be attributed to the 
proposal but rather to the existing FAA airworthiness requirements. For 
example, inspecting fuel boost pump wiring may involve its disassembly 
and then reinstallation. Regardless of the wiring's condition, the cost 
of complying with the proposal would include reinstallation time. 
However, if the inspection or testing revealed the need for new wiring, 
the new wiring cost is not attributed to the proposal.
    The proposal would increase out-of-service time because only a 
limited number of maintenance employees can work inside of a fuel tank 
at any point in time, and thereby would not allow air carriers the 
flexibility to perform the fuel tank system inspections during 
regularly scheduled major maintenance checks. Thus, the time to open 
the tank, drain the fuel, vent the tank, and close the tank are not 
costs attributed to the proposal because those activities are necessary 
to complete a scheduled maintenance check. On that basis, the FAA 
estimates that this annual increase in out-of-service time would be 
between 11.5 hours and 32 hours per airplane for each of the first 3 
years and then decline to 10 to 25 hours per airplane in each year 
thereafter.
    The economic cost of out-of-service time is lost net revenue, which 
is computed using the Office of Management and Budget (OMB) 
determination that the average annual risk-free productive rate of 
return on capital is 7 percent of the average value of that airplane 
model. Thus, out-of-service lost net revenue per fuel tank system 
inspection ranges from $50 to $9,750 per airplane, depending upon the 
airplane model. Assuming one major inspection per year, the total 
annual out-of-service lost net revenue would be about $6.4 million 
during the first year, increasing by 4.3 percent per year until the 
fourth year when it would decline to about $2.95 million but increase 
by 4.3 percent each year thereafter. The present value of this total 
lost net revenue, discounted at 7 percent over 10 years, would be about 
$35.6 million.
    The FAA estimates that the increased annual documentation and 
reporting time would be one hour of recordkeeping for every 8 hours of 
labor time in the first three years, and one hour of recordkeeping for 
every 10 hours of labor time in every year thereafter. Thus, the per 
airplane annual documentation cost would be between $150 and $850 in 
the first three years becoming $100 to $540 each year thereafter.
    To estimate the total documentation cost, it is noted that there is 
a voluntary industry program to inspect certain airplane model fuel 
tanks and report the findings and corrective actions taken to the 
manufacturer. The reporting costs of compliance associated with the 
proposal would not include these airplanes. On that basis, the FAA 
estimates that the present value of the total recordkeeping cost 
discounted at 7 percent for 10 years would be about $17.4 million.

Costs of Future Fuel Tank System Design Changes--Revised Part 25

    The FAA anticipates that these discounted costs would be minimal 
for new type certificated airplanes because these design costs would be 
incurred in the future by airplane models yet to be designed. After 
consultation with industry, the FAA also anticipates that these 
discounted costs would be minimal for future fuel tank system design 
supplemental type certificates because the existing systems would 
largely be in compliance. The FAA requests comments and supporting data 
on these determinations.

Total Costs of Proposed SFAR and Proposed Operational Rules Changes

    Thus, the FAA estimates that the present value of the total cost of 
complying with the proposed SFAR and the proposed operational rules 
changes discounted over 10 years at 7 percent would be about $170 
million.

Benefit-Cost Comparison of the Proposed Part 25 Change

    Although the FAA does not have quantified costs and benefits from 
the proposed part 25 changes at this time, the FAA believes that the 
future benefits would likely be greater than the future costs. The FAA 
requests comments and additional data on this determination.

Benefit-Cost Comparison of the Proposed SFAR and the Proposed 
Operational Rules Changes

    In comparing the estimated benefits and costs, the FAA determines 
that using the lowest expected benefit estimate, the expected present 
value of the benefits ($260 million) would be about 50 percent greater 
than the present value of the total compliance costs ($170 million). 
Thus, the FAA concludes that the proposed SFAR and the proposed 
operational rules changes would be cost-beneficial.

[[Page 58659]]

Regulatory Flexibility Determination

    The Regulatory Flexibility Act of 1980 establishes ``as a principle 
of regulatory issuance that agencies shall endeavor, consistent with 
the objective of the rule and of applicable statutes, to fit regulatory 
and informational requirements to the scale of the business, 
organizations, and governmental jurisdictions subject to regulation.'' 
To achieve that principle, the Act requires agencies to solicit and 
consider flexible regulatory proposals and to explain the rationale for 
their actions. The Act 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 proposed or 
final rule will have a significant economic impact on a substantial 
number of small entities. If the determination finds that it will, the 
agency must prepare a Regulatory Flexibility Analysis (RFA) as 
described in the Act.
    However, if an agency determines that a proposed or final rule is 
not expected to have a significant economic impact on a substantial 
number of small entities, section 605(b) of the 1980 Act provides that 
the head of the agency may so certify, and an RFA is not required. The 
certification must include a statement providing the factual basis for 
this determination, and the reasoning should be clear. Recently, the 
Office of Advocacy of the Small Business Administration (SBA) published 
new guidance for Federal agencies in responding to the requirements of 
the Regulatory Flexibility Act, as amended.
    Application of that guidance to the proposed part 25 change would 
only affect future airplane manufacturers; and currently all 
manufacturers of part 25 type certificated airplanes are considered to 
be large manufacturers. Although the proposed changes to part 25 would 
also affect future fuel tank system STCs, industry sources indicate 
that current industry designs would meet the proposed requirement. 
Thus, the FAA certifies that the proposed part 25 change would not have 
a significant economic impact on a substantial number of small airplane 
manufacturing entities.
    However, application of that guidance to the proposed SFAR and to 
the proposed operational rule changes indicates that it would have a 
significant economic impact on a substantial number of small air 
carrier entities that have one to nineteen airplanes. Accordingly, a 
complete preliminary regulatory flexibility analysis was conducted for 
those two elements of the proposal and is summarized as follows.
    1. Reasons why the FAA is considering the proposed rule. This 
proposed action is being considered in order to prevent airplane 
explosions and the resultant loss of life (as evidenced by TWA Flight 
800). Existing fuel tank system inspection programs may not provide 
comprehensive, systematic prevention and control of ignition sources in 
airplane fuel tanks.
    2. The objectives and legal basis for the proposal. The objective 
of the proposal is to ensure the continuing airworthiness of airplanes 
certificated with 30 or more passengers or with a payload of 7,500 
pounds or more. The design approval holder [including type certificates 
(TC) and supplemental type certificates (STC)] would be required to 
perform a design fuel tank system assessment and provide 
recommendations and instructions concerning fuel tank system 
inspections and equipment and wiring testing to the operators of those 
airplanes, as well as to create service bulletins and provide data to 
the FAA to support any needed ADs. An operator working under part 91, 
under part 121, under part 125, and all U.S.-registered airplanes used 
in scheduled passenger carrying operations under part 129, would be 
required to incorporate these recommendations or other approved 
instructions into the inspection manual and to perform these 
inspections and tests. The legal basis for the proposal is found in 49 
U.S.C. 44901 et seq. As a matter of policy, the FAA must, as its 
highest priority (49 U.S.C. 40101(d)), maintain and enhance safety and 
security in air commerce.
    3. All relevant federal rules that may duplicate, overlap, or 
conflict with the proposal. The FAA is unaware of any federal rules 
that would duplicate, overlap, or conflict with the proposal.
    4. A description and an estimate of the number of small entities to 
which the proposal would apply. The proposal would apply to the 
operators of all airplanes certificated with 30 or more passengers or a 
7,500 pound or more payload operated under part 91, part 121, part 125, 
and all U.S.-registered airplanes operated under part 129. Standard 
industrial classification (SIC) coding does not exactly coincide with 
the subsets of operators who could be affected by the proposal. 
Nevertheless, using data from the SBA, the distributions of employment 
size and estimated receipts for all scheduled air transportation firms 
(SIC Code 4512), given in Table 1 below, are representative of the 
operators who would be affected by the proposal.
    5. The projected reporting, recordkeeping, and other compliance 
requirements of the proposal. The proposal would not impose any 
incremental recordkeeping authority. Existing 14 CFR part 43, in part, 
already prescribes the content, form, and disposition of maintenance, 
preventive maintenance, rebuilding, and alteration records for any 
aircraft having a U.S. airworthiness certificate or any foreign 
registered aircraft used in common carriage under part 121. The FAA 
recognizes, however, that the proposal would necessitate additional 
inspection and testing work, and consequently would also require the 
completion of the additional recordkeeping associated with that 
additional work.
    The FAA estimates that each 8 additional hours of actual inspection 
and testing required under the proposal would require one additional 
hour for reporting and recordkeeping (7.5 recordkeeping minutes per 
inspection hour). This recordkeeping would be performed by the holder 
of an FAA-approved repairman or maintenance certificate. The projected 
recordkeeping and reporting costs of the proposal are included as part 
of the overall costs computed in the evaluation and included below in 
the Regulatory Flexibility Cost Analysis.

                                Table 1.
------------------------------------------------------------------------
                                                             Estimated
  Operator Category  (No. of employees)      Number of     receipts  (in
                                               firms          $1,000)
------------------------------------------------------------------------
0-4.....................................             153         193,166
5-9.....................................              57         145,131
10-19...................................              56         198,105
20-99...................................             107       1,347,711
101-499.................................              74       3,137,624
500+....................................              73     112,163,942
                                         -------------------------------
    Total...............................             520     117,185,679
------------------------------------------------------------------------

    Table 2 categorizes the estimated number of operators by number of 
airplanes that would be affected by the proposal and provides an 
estimate of the total number of affected airplanes in that operator 
category. Based on existing operator/airplane distributions, the FAA 
estimates that 131 U.S. operators would be subject to the proposal. 
(Note that this excludes the 19 non-U.S. owners of U.S.-registered 
airplanes that would be affected by the proposal. It should also be 
noted that Table 2 excludes Boeing 747 models, and, therefore, 
operators who exclusively fly Boeing 747s.)

[[Page 58660]]



                                Table 2.
------------------------------------------------------------------------
                                              No. of       Total No. of
            Operator category                operators       airplanes
------------------------------------------------------------------------
0-4.....................................              48              93
5-9.....................................              17             108
10-19...................................              22             271
20-29...................................              13             277
30-39...................................               4             145
40-49...................................               5             220
                                         -------------------------------
    Total 0-50..........................             109           1,114
50+.....................................              22           4,594
                                         -------------------------------
    U.S. Total..........................             131           5,708
Non-U.S.................................              23              62
                                         -------------------------------
    Total...............................             154           5,770
------------------------------------------------------------------------

    6. Regulatory Flexibility Cost Analysis. The proposal would consist 
of two actions affecting small business expenses. The first action, the 
proposed SFAR, would require all design approval TC holders and fuel 
tank system STC holders: (1) to complete a fuel tank system design 
assessment and to generate future service bulletins and provide data to 
the FAA; and (2) to provide operators with recommendations for fuel 
tank system inspections, testing, and maintenance. The second action, 
the proposed operational rules changes, would require that operators 
incorporate these recommendations for an enhanced fuel tank system 
inspection and equipment and wiring testing into the inspection and 
maintenance manuals. This proposal would apply to both existing and 
future production airplanes and to future TCs and STCs. This Regulatory 
Flexibility Cost Analysis focuses on the costs to operators of existing 
and future production airplanes, because almost 99 percent of the 
estimated costs of the proposal would be incurred by operators of those 
airplanes.
    Table 3 summarizes the results for the total annualized compliance 
costs for U.S. operators only and also provides the estimated cost per 
operator and per airplane by each operator size category.

                                                    Table 3.
----------------------------------------------------------------------------------------------------------------
                                                                                   Per operator    Per airplane
              Operator category  (No. of airplanes)                Total  costs        cost            cost
----------------------------------------------------------------------------------------------------------------
0-4.............................................................        $293,000          $6,100          $3,150
5-9.............................................................         275,000          16,175           2,550
10-19...........................................................       1,123,000          51,050           4,150
20-29...........................................................         784,000          60,300           2,825
30-39...........................................................         234,000          58,500           1,600
40-49...........................................................         262,000          52,400           1,200
                                                                 -----------------------------------------------
    Total 0-4...................................................       2,971,000          27,250           2,675
50+.............................................................      17,820,000         810,000           3,775
                                                                 -----------------------------------------------
    Total.......................................................      20,791,000         158,700           3,650
----------------------------------------------------------------------------------------------------------------

    7. Affordability Analysis. Although the FAA lacks financial data 
for most of the smallest operators, if the average operating revenues, 
calculated to be about $1.25 million for the category of 0 to 4 
employees from Table 1, are compared to the average annualized 
compliance costs from Table 3 (an admittedly crude method), it appears 
that the average operator would pay no more than 0.5 percent of 
operating revenues, based on an average annual risk-free return of 7 
percent of the value of the airplane, to comply with the proposal. On 
that basis, most small entities would be able to offset the incremental 
compliance costs. Nevertheless, it is likely that there would be some 
of the very small operators (those with 1 to 9 affected airplanes) that 
may have difficulties in offsetting these incremental costs. However, 
due to the unavailability of current financial data from the Department 
of Transportation on these smallest operators, the FAA cannot more 
definitively determine the potential impact on these smallest affected 
operators. The FAA solicits comments on these costs and requests that 
all comments be accompanied with clear supporting data.
    8. Disproportionality analysis. The principle factors determining 
the compliance cost for an operator would be the type of airplane model 
in the operator's fleet and the number of airplanes that would be 
affected by the proposal. As noted in the compliance cost section, the 
cost to inspect the fuel tank system of larger transport category 
airplane models would be 3 to 4 times more than the cost for a small 
transport category turboprop. Consequently, as seen in Table 3, the 
average per airplane compliance cost for operators with more than 50 
airplanes is generally higher than the average cost per airplane for 
operators with fewer than 50 airplanes. This is due to the predominance 
of turboprops in the 30-50 airplane fleets, which would have the lowest 
compliance costs. However the per airplane cost for operators with 1 to 
29 airplanes is higher than for the 30 to 50 airplane operators. Many 
of the smallest operators with fewer airplanes are cargo

[[Page 58661]]

operators utilizing larger and older turbojets, and they have fewer 
airplanes available to average the fixed costs associated with 
compliance with the proposal. Nevertheless, in general, the average 
compliance cost per airplane is relatively consistent for operators 
with fewer than 50 affected airplanes. Further, the compliance cost 
relative to these airplanes operating revenues would be relatively 
small. As a result, the FAA does not believe that small entities, as a 
group, would be disadvantaged relative to large air carriers due solely 
to the slight disproportionate cost effects from compliance with the 
proposal.
    9. Competitiveness Analysis. The proposal would likely impose 
significant costs on some of the smallest air carriers (those with 1 to 
19 airplanes) and, as a consequence, may affect the relative position 
of these carriers in their markets. However, most of these smallest air 
carriers operate in ``niche'' markets in which the competition that 
occurs arises from other small operators using largely similar 
equipment and often competing on the basis of service rather than on 
the basis of price. In such markets, the number of competitors is very 
limited. For example, Atlas Air specializes in supplying international 
air cargo by using large all-cargo airplanes to carry bulky cargo, like 
oil rig equipment. Similarly, Northern Air Cargo specializes in mail 
and air cargo to rural Alaska.
    The FAA believes that most of the markets served by these smallest 
air carriers are low-volume niche markets that larger air carriers have 
in many cases abandoned, because the larger air carriers' fleets have 
been designed for high-volume markets. Further, larger air carriers 
would not be interested in servicing most of these markets because they 
cannot compete on a cost basis. Thus, these smallest operators would be 
able to avoid direct competition with larger air carriers. As a result, 
to the extent that there would be adverse competitiveness effects, they 
would likely be minimal and they would occur with other similar-sized 
(1 to 19) air carriers. On that basis, the FAA concludes that small air 
carriers would not lose market share to larger air carriers.
    The proposal would not impose significant compliance costs on a 
substantial number of small operators that have 20 or more airplanes 
that would be affected by the proposal. These operators include large 
regionals, medium regionals, commuter airlines, and air cargo carriers. 
To some extent, these operators avoid direct competition with major 
carriers. However, in those markets where there is competition between 
the small entities and the larger air carriers, the proposal would have 
minimal competitive impact, because the per airplane compliance cost 
for a given airplane model would be roughly the same for a large and a 
small operator.
    10. Business Closure Analysis. The FAA is unable to determine with 
certainty the extent to which small entities that would be 
significantly affected by the proposal would have to close their 
operations. Many of the very small operations (1 to 4 airplanes) 
operate very close to the margin, as evidenced by the constant exit 
from and entry into air carrier service of these types of air carriers. 
Consequently, in the absence of financial data, it is difficult to 
determine the extent to which the proposal would make the difference in 
an entity's remaining in business.
    11. Description of Alternatives. In the general course of 
promulgating the proposed rule, the FAA has considered four approaches. 
The three alternatives to the proposed rule are described below. In 
formulating the alternatives, the FAA focused on its responsibility for 
aviation safety and its particular obligation under 49 U.S.C. 44717 to 
ensure the continuing airworthiness of airplanes. The three primary 
alternatives to the proposal considered by the FAA varied with respect 
to the number of airplanes to be included in the proposal. The proposed 
rule would limit the potential impact on airplanes most likely to be 
used by small entities, while meeting the Agency's safety 
responsibility.
    Alternative 1: Require all airplanes in commercial service with 
more than 10 seats to be covered by the proposal.
    Alternative 1 would require all airplanes operating under part 91, 
121, 125, and 129 to comply with the proposal. This would also include 
operators supplying on-demand service under part 135. The FAA estimates 
that about 45 additional airplane models, about 2,360 additional 
airplanes, and about 550 additional operators would be covered by this 
proposed alternative. The airplane operation is not the principal 
business for many of these additional operators. In estimating these 
potential compliance costs, the FAA assumes that, due to their small 
fuel tanks and relative straightforward fuel systems, these airplanes 
would need one-half of the time reported for the smallest part 25 
turboprop to complete the fuel tank system design assessment. In 
addition, the FAA assumes that it would also take one-quarter of the 
time reported for the smallest part 25 turboprop to complete the 
enhanced fuel tank system inspection and maintenance and wiring 
testing. Further, the FAA assumes that the out-of-service time would be 
one-half of the labor time to complete the inspection and testing. 
However, there would be no out-of-service time for part 135 on-demand 
airplanes because those operators would normally schedule maintenance 
when there was no activity. For the other operators, the FAA estimates 
the value of the average airplane would be about $750,000.
    The FAA estimates that the total additional compliance costs of 
including these operators (including the fuel tank system design 
assessment cost) would be about $7.4 million in the first-year, 
becoming about $1.1 million in the fourth year. The total compliance 
cost, discounted over 10 years at 7 percent, would be about $17.1 
million. The annualized cost, discounted over 10 years at 7 percent, 
would be about $2.4 million.
    This proposed alternative would not significantly increase the 
expected quantitative benefits because there have been no in-flight 
fuel tank explosions of these airplanes. In light of the absence of a 
fuel tank explosion accident history, the FAA does not believe at this 
time that the increased cost from including these smaller airplanes 
would be met with a commensurate level of benefits.
    The FAA requests comments on these estimates and requests 
commenters to provide supporting data for the comments.
    Alternative 2: Require all airplanes in commercial service with 30 
or more seats (the proposed rule), plus all airplanes with 10 or more 
seats in scheduled commercial service, to be covered by the proposal.
    Alternative 2 would add the requirement for all airplanes with 10 
or more seats in scheduled commercial service operating under part 91, 
part 121, part 125, and part 129 to comply with the proposal. The FAA 
estimates that 30 additional airplane models, 724 additional airplanes, 
and about 84 additional operators would be covered by this proposed 
alternative. However, 35 of the 84 additional operators would already 
have airplanes that would be covered by the proposal. In estimating 
these potential compliance costs, the FAA makes the same assumptions 
that were described under Alternative 1.
    On that basis, the FAA estimates that the additional compliance 
costs of including these operators (including the fuel tank system 
design assessment cost) would be about $2.7 million in the first-year 
and about $340,000 in the fourth

[[Page 58662]]

year. The total compliance cost, discounted over 10 years at 7 percent, 
would be about $5.7 million. The annualized cost, discounted over 10 
years at 7 percent, would be about $806,000. However, as also described 
under Alternative 1, this proposed alternative would not significantly 
increase the expected quantitative benefits because there have been no 
in-flight fuel tank explosions of these airplanes.
    The FAA requests comments on these estimates and requests 
commenters to provide supporting data for the comments.
    Alternative 3: Require that only turbojet airplanes in commercial 
service be covered by the proposal.
    This alternative would allow 1,034 turboprop airplanes certificated 
under part 25 to be exempt from the proposal's requirements. By doing 
so, it would reduce the first year cost of compliance to all of these 
exempted airplanes by about $1.8 million, becoming about $545,000 in 
the fourth year. The total compliance cost savings, discounted over 10 
years at 7 percent, would be about $8.3 million. The total annualized 
cost savings, discounted over 10 years at 7 percent, would be about 
$1.2 million.
    Although there have been no in-flight fuel tank explosions 
associated with these part 25 turboprop airplane models, the FAA 
believes that the underlying fuel tank system risk is similar to those 
of the larger turbojets. On that basis, as the FAA's estimated overall 
benefits are larger than its estimated overall costs, by extrapolation, 
removing 20 percent of the population at risk from the proposed rule 
would remove 20 percent of both the benefits and costs. As the benefits 
are estimated to be greater than the costs, the result would be a 
reduction in the net dollar benefits and higher safety risk. Finally, 
these airplanes are part 25 certificated and the FAA considers that the 
same level of safety should be applied to all part 25 certificated 
airplanes. Thus, as a result of performing the regulatory flexibility 
analysis and addressing the concerns of the SBA, the FAA believes that, 
in comparison to the two higher cost alternatives and the one lower 
cost alternative evaluated by the FAA, the proposal would provide the 
necessary level of safety in the most cost-effective manner.
    12. Special Considerations. As seen in Table 3, on a proportional 
basis the proposal would have a slightly greater impact on larger air 
carriers. The per airplane annualized cost for a large operator with 50 
or more airplanes would be $3,775, where it would be about $2,675 for a 
smaller operator. However, this difference is relatively small, and the 
FAA concludes that the proposal would not alter the competitiveness of 
small air carriers relative to larger air carriers.
    13. Conclusion. For a small operator with an airplane worth $5 
million, an annualized cost of $2,675 would be equal to about three 
days of lost net revenue, based on an average annual risk-free 
productive rate of return on capital of 7 percent. However, the FAA 
also considers that even for small operators of these affected 
airplanes, the safety benefits would be greater than the compliance 
costs. The FAA requests comments on this analysis and requests 
commenters to supply supporting data for the comments.

International Trade Impact Assessment

    Consistent with the Administration's belief in the general 
superiority, desirability, and efficacy of free trade, it is the policy 
of the Administrator to remove or diminish, to the extent feasible, 
barriers to international trade, including both barriers affecting the 
export of American goods and services to foreign countries and those 
affecting the import of foreign goods and services into the United 
States.
    In accordance with that policy, the FAA is committed to develop as 
much as possible its aviation standards and practices in harmony with 
its trading partners. Significant cost savings can result from this, 
both to American companies doing business in foreign markets, and 
foreign companies doing business in the United States.
    This proposed rule would have little or no impact on international 
trade. The proposed part 25 change would equally affect all future part 
25 airplanes, wherever manufactured, that would be registered in the 
United States. Although the proposed operational rules changes would 
affect only U.S. registered airplanes, the net effect is expected to be 
small and the European Joint Aviation Authorities may consider similar 
regulations.

Unfunded Mandates Assessment

    Title II of the Unfunded Mandates Reform Act of 1995 (the Act), 
enacted as Public Law 104-4 on March 22, 1995, requires each Federal 
agency, to the extent permitted by law, to prepare a written assessment 
of the effects of any Federal mandate in a proposed or final agency 
rule that may result in the expenditure by State, local, and tribal 
governments, in the aggregate, or by the private sector, of $100 
million or more (adjusted annually for inflation) in any one year. 
Section 204(a) of the Act, 2 U.S.C. 1534(a), requires the Federal 
agency to develop an effective process to permit timely input by 
elected officers (or their designees) of State, local, and tribal 
governments on a proposed ``significant intergovernmental mandate.'' A 
``significant intergovernmental mandate'' under the Act is any 
provision in a Federal agency regulation that will impose an 
enforceable duty upon State, local, and tribal governments, in the 
aggregate, of $100 million (adjusted annually for inflation) in any one 
year. Section 203 of the Act, 2 U.S.C. 1533, which supplements section 
204(a), provides that before establishing any regulatory requirements 
that might significantly or uniquely affect small governments, the 
agency shall have developed a plan that, among other things, provides 
for notice to potentially affected small governments, if any, and for a 
meaningful and timely opportunity to provide input in the development 
of regulatory proposals.
    The FAA determines that this proposed rule would not contain a 
significant intergovernmental or private sector mandate as defined by 
the Act.

Federalism Implications

    The regulations proposed herein will not have substantial direct 
effects on the States, or on the relationship between the national 
government and the States, or on the distribution of power and 
responsibility among the various levels of the government. Therefore, 
in accordance with Executive Order 12612, it is determined that this 
proposed rule would not have significant federalism implications to 
warrant the preparation of a Federalism Assessment.

International Civil Aviation Organization (ICAO) and Joint Aviation 
Regulations

    In keeping with U.S. obligations under the Convention on 
International Civil Aviation, it is FAA policy to comply with ICAO 
Standards and Recommended Practices to the maximum extent practicable. 
The FAA has determined that this proposed rule would not conflict with 
any international agreement of the United States.

Paperwork Reduction Act

    There are no new requirements for information collection associated 
with this proposed rule that would require approval from the Office of 
Management and Budget pursuant to the Paperwork Reduction Act of 1995 
(44 U.S.C. 3507(d)).

[[Page 58663]]

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 a 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 proposed 
rule would apply to the operation of certain transport category 
airplanes under parts 91, 121, 125, and 129 of Title 14, it could, if 
adopted, affect intrastate aviation in Alaska. The FAA therefore 
specifically requests comments on whether there is justification for 
applying the proposed rule differently to intrastate operations in 
Alaska.

List of Subjects

14 CFR Parts 21, 25, 91, 125 and 129

    Aircraft, Aviation safety, Reporting and recordkeeping 
requirements.

14 CFR Part 121

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

The Proposed Amendment

    In consideration of the foregoing, the Federal Aviation 
Administration proposes to amend parts 21, 25, 91, 121, 125, and 129 of 
Title 14, Code of Federal Regulations, as follows:

PART 21--CERTIFICATION PROCEDURES FOR PRODUCTS AND PARTS

    1. The authority citation for part 21 continues to read as follows:

    Authority: 42 U.S.C. 7572; 40105; 40113; 44701-44702, 44707. 
44709, 44711, 44713, 44715, 45303.

    2. In part 21, add SFAR No. XX to read as follows:

Special Federal Aviation Regulations

* * * * *

SFAR No. XX--Fuel Tank System Fault Tolerance Evaluation 
Requirements

    1. Applicability. This SFAR applies to the holders of type 
certificates, and supplemental type certificates affecting the 
airplane fuel tank system, for turbine-powered transport category 
airplanes, provided the type certificate was issued after January 1, 
1958, and the airplane has a maximum type certificated passenger 
capacity of 30 or more, or a maximum type certificated payload 
capacity of 7500 pounds or more. This SFAR also applies to 
applicants for type certificates, amendments to a type certificate, 
and supplemental type certificates affecting the fuel tank systems 
for those airplanes identified above, if the application was filed 
before the effective date of this SFAR and the certificate was not 
issued before the effective date of this SFAR.
    2. Compliance: No later than [12 months after the effective date 
of the final rule], or within 12 months after the issuance of a 
certificate for which application was filed before [effective date 
of the final rule], whichever is later, each type certificate 
holder, or supplemental type certificate holder of a modification 
affecting the airplane fuel tank system, must accomplish the 
following:
    (a) Conduct a safety review of the airplane fuel tank system to 
determine that the design meets the requirements of Secs. 25.901 and 
25.981(a) and (b) of this chapter. If the current design does not 
meet these requirements, develop all design changes necessary to the 
fuel tank system to meet these requirements.
    (b) Develop all maintenance and inspection instructions 
necessary to maintain the design features required to preclude the 
existence or development of an ignition source within the fuel tank 
system of the airplane.
    (c) Submit a report for approval of the Administrator that:
    (1) Provides substantiation that the airplane fuel tank system 
design, including all necessary design changes, meets the 
requirements of Secs. 25.901 and 25.981(a) and (b) of this chapter; 
and
    (2) Contains all maintenance and inspection instructions 
necessary to maintain the design features required to preclude the 
existence or development of an ignition source within the fuel tank 
system throughout the full operational life of the airplane.

PART 25--AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY AIRPLANES

    3. The authority citation for part 25 continues to read:

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

    4. Section 25.981 is revised to read as follows:


Sec. 25.981  Fuel tank ignition prevention.

    (a) No ignition source may be present at each point in the fuel 
tank or fuel tank system where catastrophic failure could occur due to 
ignition of fuel or vapors. This must be shown by:
    (1) Determining the highest temperature allowing a safe margin 
below the lowest expected autoignition temperature of the fuel in the 
fuel tanks.
    (2) Demonstrating that no temperature at each place inside each 
fuel tank where fuel ignition is possible will exceed the temperature 
determined under paragraph (a)(1) of this section. This must be 
verified under all probable operating, failure and malfunction 
conditions of each component whose operation, failure or malfunction 
could increase the temperature inside the tank.
    (3) Demonstrating that an ignition source could not result from 
each single failure, from each single failure in combination with each 
latent failure condition not shown to be extremely remote, and from all 
combinations of failures not shown to be extremely improbable. The 
effects of manufacturing variability, aging, wear, corrosion, and 
likely damage must be considered.
    (b) Based on the evaluations required by this section, critical 
design configuration control limitations, inspections or other 
procedures must be established as necessary to prevent development of 
ignition sources within the fuel tank system and must be included in 
the Airworthiness Limitations section of the ICA required by 
Sec. 25.1529. Placards, decals or other visible means must be placed in 
areas of the airplane where maintenance, repairs or alterations may 
violate the critical design configuration limitations.
    (c) The fuel tank installation must include--
    (1) Means to minimize the development of flammable vapors in the 
fuel tanks; or
    (2) Means to mitigate the effects of an ignition of fuel vapors 
within fuel tanks such that no damage caused by an ignition will 
prevent continued safe flight and landing.
    5. Paragraph H25.4 of Appendix H is revised to read as follows:

Appendix H To Part 25--Instructions for Continued Airworthiness

    H25.4  Airworthiness Limitations section.
    (a) The Instructions for Continued Airworthiness must contain a 
section titled Airworthiness Limitations that is segregated and 
clearly distinguishable from the rest of the document. This section 
must set forth--
    (1) Each mandatory replacement time, structural inspection 
interval, and related structural inspection procedures approved 
under Sec. 25.571; and
    (2) each mandatory replacement time, inspection interval, 
related inspection procedure, and all critical design configuration 
control limitations approved under Sec. 25.981 for the fuel tank 
system.
    (b) If the Instructions for Continued Airworthiness consist of 
multiple documents, the section required by this paragraph must be 
included in the principle manual. This section must contain a 
legible statement in a prominent location that reads: ``The 
Airworthiness Limitations section is FAA-approved and specifies 
maintenance required under Secs. 43.16 and 91.403 of the Federal 
Aviation Regulations, unless an alternative program has been FAA 
approved.''

[[Page 58664]]

PART 91--GENERAL OPERATING AND FLIGHT RULES

    6. The authority citation for part 91 continues to read as follows:

    Authority: 49 U.S.C. 1301(7), 1303, 1344, 1348, 1352 through 
1355, 1401, 1421 through 1431, 1471, 1472, 1502, 1510, 1522, and 
2121 through 2125; Articles 12, 29, 31, and 32(a) of the Convention 
on International Civil Aviation (61 Stat. 1180); 42 U.S.C. 4321 et. 
seq.; E.O. 11514; 49 U.S.C. 106(g) (Revised Pub. L. 97-449, January 
21, 1983).

    7. By adding a new Sec. 91.410 to read as follows:


Sec. 91.410  Fuel tank system maintenance and inspection instructions.

    After [18 months after the effective date of the final rule], no 
person may operate a turbine-powered transport category airplane with a 
type certificate issued after January 1, 1958, and a maximum type 
certificated passenger capacity of 30 or more, or a maximum type 
certificated payload capacity of 7,500 pounds or more, unless 
instructions for maintenance and inspection of the fuel tank system are 
incorporated into its inspection program. Those instructions must be 
approved by the Administrator. Thereafter, the approved instructions 
can be revised only with the approval of the Administrator.

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

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

    Authority: 49 U.S.C. 106(g), 40113, 40119, 44101, 44701-44702, 
44705, 44709-44711, 44713, 44716-44717, 44722, 44901, 44903-44904, 
44912, 46105.

    9. By adding a new Sec. 121.370 to read as follows:


Sec. 121.370  Fuel tank system maintenance and inspection instructions.

    After [18 months after the effective date of the final rule], no 
certificate holder may operate a turbine-powered transport category 
airplane with a type certificate issued after January 1, 1958, and a 
maximum type certificated passenger capacity of 30 or more, or a 
maximum type certificated payload capacity of 7500 pounds or more, 
unless instructions for maintenance and inspection of the fuel tank 
system are incorporated in its maintenance program. Those instructions 
must be approved by the Administrator. Thereafter, the approved 
instructions can be revised only with the approval of the 
Administrator.

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

    10. 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.

    11. By adding a new Sec. 125.248 to read as follows:


Sec. 125.248  Fuel tank system maintenance and inspection instructions.

    After [18 months after the effective date of the final rule], no 
certificate holder may operate a turbine-powered transport category 
airplane with a type certificate issued after January 1, 1958, and a 
maximum type certificated passenger capacity of 30 or more, or a 
maximum type certificated payload capacity of 7500 pounds or more 
unless instructions for maintenance and inspection of the fuel tank 
system are incorporated in its inspection program. Those instructions 
must be approved by the Administrator. Thereafter, the approved 
instructions can be revised only with the approval of the 
Administrator.

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

    12. The authority citation for part 129 continues to read:

    Authority: 49 U.S.C. 106(g), 40104-40105, 40113, 40119, 44701-
44702, 44712, 44716-44717, 44722, 44901-44904, 44906.

    13. By amending Sec. 129.14 by adding a new paragraph (c) to read 
as follows:


Sec. 129.14  Maintenance program and minimum equipment list 
requirements for U.S.-registered airplanes.

* * * * *
    (c) For turbine-powered transport category airplanes with a type 
certificate issued after January 1, 1958, and a maximum type 
certificated passenger capacity of 30 or more, or a maximum type 
certificated payload capacity of 7500 pounds or more, no later than [18 
months after the effective date of the final rule], the program 
required by paragraph (a) of this section must include instructions for 
maintenance and inspection of the fuel tank systems. Those instructions 
must be approved by the Administrator. Thereafter the approved 
instructions can be revised only with the approval of the 
Administrator.

    Issued in Washington, D.C., on October 26, 1999.
Elizabeth Erickson,
Director, Aircraft Certification Service.
[FR Doc. 99-28348 Filed 10-28-99; 8:45 am]
BILLING CODE 4910-13-U