[Federal Register Volume 72, Number 67 (Monday, April 9, 2007)]
[Proposed Rules]
[Pages 17441-17443]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: E7-6542]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 25

[Docket No. NM366 Special Conditions No. 25-07-03-SC]


Special Conditions: Boeing Model 787-8 Airplane; Composite Wing 
and Fuel Tank Structure--Fire Protection Requirements

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Notice of proposed special conditions.

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SUMMARY: This notice proposes special conditions for the Boeing Model 
787-8 airplane. This airplane will have novel or unusual design 
features when compared to the state of technology envisioned in the 
airworthiness standards for transport category airplanes. These novel 
or unusual design features are associated with composite materials 
chosen for the construction of the fuel tank skin and structure. For 
these design features, the applicable airworthiness regulations do not 
contain adequate or appropriate safety standards for wing and fuel tank 
structure with respect to post-crash fire safety. These proposed 
special conditions contain the additional safety standards that the 
Administrator considers necessary to establish a level of safety 
equivalent to that established by the existing airworthiness standards. 
Additional special conditions will be issued for other novel or unusual 
design features of the Boeing Model 787-8 airplanes.

DATES: Comments must be received on or before May 24, 2007.

ADDRESSES: Comments on this proposal may be mailed in duplicate to: 
Federal Aviation Administration, Transport Airplane Directorate, 
Attention: Rules Docket (ANM-113), Docket No. NM366, 1601 Lind Avenue, 
SW., Renton, Washington 98057-3356; or delivered in duplicate to the 
Transport Airplane Directorate at the above address. All comments must 
be marked Docket No. NM366. Comments may be inspected in the Rules 
Docket weekdays, except Federal holidays, between 7:30 a.m. and 4 p.m.

FOR FURTHER INFORMATION CONTACT: Mike Dostert, FAA, Propulsion/
Mechanical Systems, ANM-112, Transport Airplane Directorate, Aircraft 
Certification Service, 1601 Lind Avenue, SW., Renton, Washington 98057-
3356; telephone (425) 227-2132; facsimile (425) 227-1320.

SUPPLEMENTARY INFORMATION:

Comments Invited

    The FAA invites interested persons to participate in this 
rulemaking by submitting written comments, data, or views. The most 
helpful comments reference a specific portion of the special 
conditions, explain the reason for any recommended change, and include 
supporting data. We ask that you send us two copies of written 
comments.
    We will file in the docket all comments we receive as well as a 
report summarizing each substantive public contact with FAA personnel 
concerning these proposed special conditions. The docket is available 
for public inspection before and after the comment closing date. If you 
wish to review the docket in person, go to the address in the ADDRESSES 
section of this notice between 7:30 a.m. and 4 p.m., Monday through 
Friday, except Federal holidays.
    We will consider all comments we receive on or before the closing 
date for comments. We will consider comments filed late if it is 
possible to do so without incurring expense or delay. We may change the 
proposed special conditions based on comments we receive.
    If you want the FAA to acknowledge receipt of your comments on this 
proposal, include with your comments a pre-addressed, stamped postcard 
on which the docket number appears. We will stamp the date on the 
postcard and mail it back to you.

Background

    On March 28, 2003, Boeing applied for an FAA type certificate for 
its new Boeing Model 787-8 passenger airplane. The Boeing Model 787-8 
airplane will be an all-new, two-engine jet transport airplane with a 
two-aisle cabin. The maximum takeoff weight will be 476,000 pounds, 
with a maximum passenger count of 381 passengers.

Type Certification Basis

    Under provisions of 14 CFR 21.17, Boeing must show that Boeing 
Model 787-8 airplanes (hereafter referred to as ``the 787'') meet the 
applicable provisions of 14 CFR part 25, as amended by Amendments 25-1 
through 25-117, except Sec. Sec.  25.809(a) and 25.812, which will 
remain at Amendment 25-

[[Page 17442]]

115. If the Administrator finds that the applicable airworthiness 
regulations do not contain adequate or appropriate safety standards for 
the 787 because of a novel or unusual design feature, special 
conditions are prescribed under provisions of 14 CFR 21.16.
    In addition to the applicable airworthiness regulations and special 
conditions, the 787 must comply with the fuel vent and exhaust emission 
requirements of 14 CFR part 34 and the noise certification requirements 
of part 36. In addition, the FAA must issue a finding of regulatory 
adequacy pursuant to section 611 of Pub. L. 92-574, the ``Noise Control 
Act of 1972.''
    Special conditions, as defined in Sec.  11.19, are issued in 
accordance with Sec.  11.38 and become part of the type certification 
basis in accordance with Sec.  21.17(a)(2).
    Special conditions are initially applicable to the model for which 
they are issued. Should the type certificate for that model be amended 
later to include any other model that incorporates the same or similar 
novel or unusual design feature, the special conditions would also 
apply to the other model under the provisions of Sec.  21.101.

Novel or Unusual Design Features

    The 787 will incorporate a number of novel or unusual design 
features. Because of rapid improvements in airplane technology, the 
applicable airworthiness regulations do not contain adequate or 
appropriate safety standards for these design features. These proposed 
special conditions for the 787 contain the additional safety standards 
that the Administrator considers necessary to establish a level of 
safety equivalent to that established by the existing airworthiness 
standards.
    The 787 will be the first large transport category airplane that 
will not be fabricated primarily with aluminum materials for the fuel 
tank structure. Instead it will use predominantly composite materials 
for the structural elements and skin of the wings and fuel tanks. 
Conventional airplanes with aluminum skin and structure provide a well 
understood level of safety during post-crash fire scenarios with 
respect to fuel tanks. This is based on service history and extensive 
full-scale fire testing. Composites may or may not have capabilities 
equivalent to aluminum, and current regulations do not provide 
objective performance requirements for wing and fuel tank structure 
with respect to post-crash fire safety. Because the use of composite 
structure is new and novel compared to the designs envisioned when the 
applicable regulations were written, additional substantiation by test 
and analysis will be required to show that the 787 provides an 
acceptable level of safety with respect to the performance of the wings 
and fuel tanks during an external fuel-fed fire.
    Although the FAA has previously approved fuel tanks made of 
composite materials that are located in the horizontal stabilizer of 
some airplanes, the composite wing structure of the 787 will introduce 
a new fuel tank construction into service. Advisory Circular (AC) 20-
107A, Composite Aircraft Structure, under the topic of flammability, 
states: ``The existing requirements for flammability and fire 
protection of aircraft structure attempt to minimize the hazard to the 
occupants in the event ignition of flammable fluids or vapors occurs. 
The use of composite structure should not decrease this existing level 
of safety.'' The relevance to the wing structure is that post-crash 
fire passenger survivability is dependent on the time available for 
passenger evacuation prior to fuel tank breach or structural failure. 
Structural failure can be a result of degradation in load-carrying 
capability in the upper or lower wing surface caused by a fuel-fed 
ground fire. Structural failure can also be a result of over-
pressurization caused by ignition of fuel vapors in the fuel tank.
    The FAA has historically developed rules with the assumption that 
the material of construction for wing and fuselage would be aluminum. 
As a representative case, Sec.  25.963 was developed as a result of a 
large fuel-fed fire following the failures of fuel tank access doors 
caused by uncontained engine failures. During the subsequent Aviation 
Rulemaking Advisory Committee (ARAC) harmonization process with the 
JAA,\1\ the structures group attempted to harmonize the requirements of 
Sec.  25.963 regarding the impact and fire resistance of fuel tank 
access panels. Both authorities recognized that existing aluminum wing 
structure provided an acceptable level of safety. Further rulemaking 
has not yet been pursued.
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    \1\ The JAA is the Joint Aviation Authority of Europe and the 
JAR is its Joint Aviation Requirements, the equivalent of our 
Federal Aviation Regulations. In 2003, the European Aviation Safety 
Agency (EASA) was formed, and EASA is now the principal aviation 
regulatory agency in Europe. We intend to work with EASA to ensure 
that our rules are also harmonized with its Certification 
Specifications (CS). But since these efforts in developing 
harmonization of Sec.  25.963 occurred before EASA was formed, it 
was the JAA that was involved with them.
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    As with previous Boeing airplane designs with under-wing mounted 
engines, the wing tanks and center tanks are located in proximity to 
the passengers and near the engines. Past experience indicates post 
crash survivability is greatly influenced by the size and intensity of 
any fire that occurs. The ability of aluminum wing surfaces wetted by 
fuel on their interior surface to withstand post-crash fire conditions 
has been demonstrated by tests conducted at the FAA Technical Center. 
These tests have verified adequate dissipation of heat across wetted 
aluminum fuel tank surfaces so that localized hot spots do not occur, 
thus minimizing the threat of explosion. This inherent capability of 
aluminum to dissipate heat also allows the wing lower surface to retain 
its load carrying characteristics during a fuel-fed ground fire. It 
significantly delays wing collapse or burn-through for a time interval 
that usually exceeds evacuation times. In addition, as an aluminum fuel 
tank is heated with significant quantities of fuel inside, fuel vapor 
accumulates in the ullage space, exceeding the upper flammability limit 
relatively quickly and thus reducing the threat of a fuel tank 
explosion prior to fuel tank burn-through. Service history of 
conventional aluminum airplanes has shown that fuel tank explosions 
caused by ground fires have been rare on airplanes configured with 
flame arrestors in the fuel tank vent lines. Fuel tanks constructed 
with composite materials may or may not have equivalent capability.
    Current regulations were developed and have evolved under the 
assumption that wing construction would be of aluminum materials, which 
provide inherent properties. Current regulations may not be adequate 
when applied to airplanes constructed of different materials. Aluminum 
has the following properties with respect to fuel tanks and fuel-fed 
external fires.
     Aluminum is highly thermally conductive. It readily 
transmits the heat of a fuel-fed external fire to fuel in the tank. 
This has the benefit of rapidly driving the fuel tank ullage to exceed 
the upper flammability limit prior to burn-through of the fuel tank 
skin or heating of the wing upper surface above the auto-ignition 
temperature. This greatly reduces the threat of fuel tank explosion.
     Aluminum panels at thicknesses previously used in wing 
lower surfaces of large transport category airplanes have been fire 
resistant as defined in CFR 14 part 1 and AC 20-135.
     The heat capacity of aluminum and fuel will prevent burn-
through or wing collapse for a time interval that will generally exceed 
the passenger evacuation time.

[[Page 17443]]

    The extensive use of composite materials in the design of the 787 
wing and fuel tank structure is considered a major change from 
conventional and traditional methods of construction. This will be the 
first large transport category airplane to be certificated with this 
level of composite material for these purposes. The applicable 
airworthiness regulations do not contain specific standards for post-
crash fire safety performance of wing and fuel tank skin or structure.

Discussion of Proposed Special Conditions

    In order to provide the same level of safety as exists with 
conventional airplane construction, Boeing must demonstrate that the 
787 has sufficient post-crash survivability, in the event that the 
wings are exposed to a large fuel-fed fire, to enable occupants to 
safely evacuate. Factors in fuel tank survivability are the structural 
integrity of the wing and tank, flammability of the tank, burnthrough 
resistance of the wing skin, and the presence of auto-ignition threats 
during exposure to a fire. The FAA assessed post crash survival time 
during the adoption of amendment 25-111 for fuselage burnthrough 
protection. Studies conducted by and on behalf of the FAA indicated 
that, following a survivable accident, prevention of fuselage burn-
through for approximately 5 minutes can significantly enhance 
survivability. ( See report numbers DOT/FAA/AR-99/57 and DOT/FAA/AR-02/
49.) Beyond five minutes, there is little benefit, due to the effects 
of the fuel fire itself. That assessment was carried out based on 
accidents involving airplanes with conventional fuel tanks, and 
considering the ability of ground personnel to rescue occupants. In 
addition, AC20-135 indicates that, when aluminum is used for fuel 
tanks, the tank should withstand the effects of fire for 5 minutes 
without failure. Therefore, to be consistent with existing capability 
and related requirements, the 787 fuel tanks must be capable of 
resisting a post crash fire for at least 5 minutes. In demonstrating 
compliance, Boeing must address a range of fuel loads from minimum to 
maximum, as well as any other critical fuel load.

Applicability

    As discussed above, these proposed special conditions are 
applicable to the 787. Should Boeing apply at a later date for a change 
to the type certificate to include another model incorporating the same 
novel or unusual design features, these proposed special conditions 
would apply to that model as well under the provisions of Sec.  21.101.

Conclusion

    This action affects only certain novel or unusual design features 
of the 787. It is not a rule of general applicability, and it affects 
only the applicant that applied to the FAA for approval of these 
features on the airplane.

List of Subjects in 14 CFR Part 25

    Aircraft, Aviation safety, Reporting and recordkeeping 
requirements.

    The authority citation for these Special Conditions is as follows:

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

The Proposed Special Conditions

    Accordingly, the Administrator of the Federal Aviation 
Administration (FAA) proposes the following special conditions as part 
of the type certification basis for the Boeing Model 787-8 airplane.

    In addition to complying with part 25 regulations governing the 
fire-safety performance of the fuel tanks, wings, and nacelle, the 
Boeing Model 787-8 must demonstrate acceptable post-crash 
survivability in the event the wings are exposed to a large fuel-fed 
ground fire. Boeing must demonstrate that the wing and fuel tank 
design can endure an external fuel-fed pool fire for at least 5 
minutes. This shall be demonstrated for minimum fuel loads (not less 
than reserve fuel levels) and maximum fuel loads (maximum range fuel 
quantities), and other identified critical fuel loads. 
Considerations shall include fuel tank flammability, burn-through 
resistance, wing structural strength retention properties, and auto-
ignition threats during a ground fire event for the required time 
duration.

    Issued in Renton, Washington, on March 30, 2007.
Ali Bahrami,
Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
 [FR Doc. E7-6542 Filed 4-6-07; 8:45 am]
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