[Federal Register Volume 72, Number 196 (Thursday, October 11, 2007)]
[Rules and Regulations]
[Pages 57844-57848]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: E7-20031]


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

DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 25

[Docket No. NM366 Special Conditions No. 25-348-SC]


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

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Final special conditions.

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

SUMMARY: These special conditions are issued 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 postcrash fire safety. These special 
conditions contain the additional safety standards that the 
Administrator considers necessary to

[[Page 57845]]

establish a level of safety equivalent to that established by the 
existing standards. We will issue additional special conditions for 
other novel or unusual design features of the Boeing Model 787-8 
airplanes.

DATES: Effective Date: November 13, 2007.

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:

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 Title 14 Code of Federal Regulations (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 25-115. 
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 14 CFR part 36. The FAA must also issue a finding of regulatory 
adequacy under section 611 of Public Law 92-574, the ``Noise Control 
Act of 1972.''
    The FAA issues special conditions, as defined in 14 CFR 11.19, 
under Sec.  11.38, and they become part of the type certification basis 
under 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 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 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 not 
built mainly with aluminum materials for the fuel tank structure. 
Instead it will use chiefly 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 postcrash fires 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 postcrash fire safety. Use of 
composite structure is new and novel compared to the designs envisioned 
when the applicable regulations were written. Because of this, Boeing 
must present additional confirmation by test and analysis 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 postcrash fire 
passenger survivability is dependent on the time available for 
passenger evacuation before 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 because 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 tried to harmonize the requirements of 
Sec.  25.963 for 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.
---------------------------------------------------------------------------

    \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.
---------------------------------------------------------------------------

    As with previous Boeing airplane designs with underwing mounted 
engines, the wing tanks and center tanks are located in proximity to 
the passengers and near the engines. Experience indicates postcrash 
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 postcrash fire conditions has 
been shown 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

[[Page 57846]]

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 14 CFR part 1 and AC 20-135.
     The heat absorption capacity of aluminum and fuel will 
prevent burn-through or wing collapse for a time interval that will 
generally exceed the passenger evacuation time.
    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 
postcrash fire safety performance of wing and fuel tank skin or 
structure.

Discussion of 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 postcrash survivability to enable occupants to 
safely evacuate in the event that the wings are exposed to a large 
fuel-fed fire. Factors in fuel tank survivability are the structural 
integrity of the wing and tank, flammability of the tank, burn-through 
resistance of the wing skin, and the presence of auto-ignition threats 
during exposure to a fire. The FAA assessed postcrash survival time 
during the adoption of Amendment 25-111 for fuselage burn-through 
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.) There is little benefit in requiring the design to prevent wing 
skin burn-through beyond five minutes, due to the effects of the fuel 
fire itself on the rest of the airplane. 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, AC 20-135 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 postcrash 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.

Discussion of Comments

    Notice of Proposed Special Conditions No. 25-07-03-SC for the 787 
was published in the Federal Register on April 9, 2007 (72 FR 17441). 
Two comments were received from the Air Line Pilots Association, 
International (ALPA), two from Airbus, and several from members of the 
public.
    Comment 1--Air Line Pilots Association (ALPA). The Air Line Pilots 
Association, International questioned whether the 787 will be required 
to comply with any and all rules related to fuel tank inerting/
flammability requirements of 14 CFR parts 25 and 121 and the guidance 
in Advisory Circular 25.981-2A.
    FAA Response. The 787 will be required to meet the current 
requirements for the certification basis of the airplane that include 
fuel vapor flammability standards, and we will be proposing additional 
requirements within special conditions for a nitrogen inerting system. 
The certification basis for the 787 includes Amendment 25-102, which 
includes the Sec.  25.981(c) requirement for minimization of fuel tank 
flammability. In the preamble to Amendment 25-102 we described the 
intended level of flammability to be equivalent to an unheated aluminum 
wing fuel tank. The composite fuel tank structure of the 787 does not 
inherently meet this flammability standard because of the difference in 
thermal conductivity between composite materials and aluminum. Boeing 
has proposed a design that includes a nitrogen inerting system to meet 
the flammability standard. Because of this novel and unique feature 
that provides nitrogen enriched air to all fuel tanks, we will be 
publishing proposed special conditions for public comment.
    We have made no changes to these special conditions as a result of 
this comment.
    Comment 2--ALPA. ALPA also commented that it is important to 
determine the characteristics of composites after prolonged exposure to 
moisture of any kind (humidity, liquid, deicing fluid, fuel etc.) and 
stated that the FAA must conduct or endorse research to determine 
whether composite materials are susceptible to absorbing liquids during 
prolonged exposure. The commenter also stated that research must be 
done to determine effects of water (or other liquid) intrusion on the 
aircraft weight, controllability, flammability, and survivability.
    FAA Response. The FAA concurs with the concerns of the commenter 
and has discussed these items with the applicant. The existing 
airworthiness regulations for certification require that all parts and 
components be qualified for all foreseeable environmental conditions as 
installed on the airplane. Therefore, as part of the material 
certification and approval, the composite material is required to be 
subjected to accelerated environmental exposure to all liquids 
anticipated to be in contact with the material for the life of the 
aircraft. This includes but is not limited to water, salt spray, fuel, 
hydraulic fluid, and de-icing fluids. Any material effects due to this 
exposure testing will have to be considered in showing the material's 
ability to perform its intended function, including consideration for 
the life and performance of the material. These environmental 
qualifications are required by existing airworthiness regulations and 
are therefore not required to be included in the special conditions for 
composite structure. We have made no changes to these special 
conditions as a result of this comment.
    Comment 3--Airbus. Airbus noted a reference in the proposed special 
conditions to testing conducted at the FAA Technical Center that 
demonstrated aluminum fuel tank performance under postcrash fire 
conditions. The commenter requested access to the documentation for 
review of the test data to understand the applied conditions and 
parameters of the test.
    FAA Response. The noted reports are available to the public via the 
FAA

[[Page 57847]]

Technical Center Website for Fire Safety at http://www.fire.tc.faa.gov/
. The document we were referring to in the proposed special conditions 
was document FAA-RD-75-119, Investigation of Aircraft Fuel Tank 
Explosions and Nitrogen Inerting Requirements During Ground Fires. We 
have made no changes to these special conditions as a result of this 
comment.
    Comment 4--Airbus. Airbus also requested clarification of the 
following statement on page 17443 of the Federal Register, under the 
heading ``Discussion of Proposed Special Conditions:'' * * * AC 20-135 
indicates that, when aluminum is used for fuel tanks, the tank should 
withstand the effects of fire for 5 minutes without failure.'' Airbus 
said this statement needed clarification, because the actual language 
in the AC discusses fire resistance of a number of elements, but does 
not consider the fuel tank as a whole.
    FAA Response. The commenter is correct that AC 20-135 does not 
specifically refer to demonstrating that the fuel tank as a whole is 
fire resistant. In the past fuel tanks have typically been constructed 
of aluminum, which is considered to be fire resistant. AC 20-135 
provides general guidance on how materials can be shown to be fire 
resistant if they can withstand the effects of fire for 5 minutes. 
These special conditions require that the fuel tank be shown to meet 
fire resistance standards and one means of showing a material meets 
these standards is described in the AC. Since the fuel tank is 
constructed of composite materials, we consider the guidance in the AC 
to be applicable to the fuel tank as a whole. We've made no change to 
these special conditions as a result of this comment.
    The following four comments, received from the public, were outside 
the scope of these special conditions.
    Comment 5. One commenter requested that the FAA and foreign 
authorities pursue rulemaking activities to develop specific rules 
related to use of composite materials for basic airframe structure.
    FAA Response. Although this comment does not address the context of 
these special conditions, we agree that current transport category 
rules do not adequately address the unique aspects of composite 
structure. These special conditions, and others for the 787 and other 
certification projects involving composite structure, are the first 
steps in establishing new airworthiness standards. We anticipate that 
these special conditions will be followed by rulemaking activity to 
establish similar standards in the applicable sub-parts of part 25. The 
FAA cannot comment on the position of other foreign authorities in this 
regard. No change to the special conditions is required.
    Comment 6. This commenter also requested that the scope of the 
special conditions be expanded to include evaluation of the fuselage, 
wing, and fuel tank to simulate actual survivable crash conditions 
during a fuel fed fire with respect to fire, smoke, and toxicity and 
passenger survivability. The commenter requested that the special 
conditions address fire, smoke, and toxicity environments within the 
fuselage interior during an external fuel fed fire.
    FAA Response. While we agree with the commenter that these are 
important considerations, the FAA has determined that this comment is 
outside the scope of these special conditions because they are limited 
to performance of the wing and fuel tank structure during a postcrash 
ground fire. The performance of the fuselage barrel and interiors 
during a fuel-fed fire is already addressed by existing regulations 
(reference 14 CFR 25.853, 25.855, and 25.856 and Appendix F for current 
standards for airplane interior fire safety). We have determined that 
existing regulations for a fuel-fed external fire are adequate to 
address cabin interiors, including those issues suggested by the 
commenter, and special conditions are not warranted. In addition, while 
full scale fire tests of the wing and fuselage were considered by the 
FAA, we determined that requiring a large scale fire test could be 
overly prescriptive. The means of complying with the objectives of 
these special conditions will be reviewed and approved by the FAA. In 
addition, although the performance standards for the wing and fuselage 
were developed independently, they have a common objective of 
preserving the current level of safety provided by aluminum airplanes. 
After reviewing this comment, we have determined that no change to the 
special conditions is required.
    Comment 7. This commenter has noted that burn-through tests at the 
component level do not address high lateral fire burning rates or fire 
and smoke ingress into the cabin. The commenter suggested testing 
should be expanded to include a full scale fire test of a fuselage 
barrel section with all exits opened and slides deployed throughout the 
test.
    FAA Response. The FAA has determined that the requirements for the 
smoke, toxicity, and fire resistance of the fuselage materials are 
adequately addressed by the current regulations and, therefore, 
inclusion in these special conditions is unwarranted. The intent and 
scope of these special conditions was to ensure that the wing and fuel 
tank structure will not pose an additional hazard to passengers and 
crew during postcrash fire scenarios because of the introduction of 
composite materials. Cabin safety special conditions have been 
developed and published for comment in Special Conditions No. 25-07-09-
SC, Docket No. NM373, published April 26, 2007 (72 FR 20774). Those 
special conditions require that the 787 provide the same level of in-
flight survivability as a conventional aluminum fuselage airplane. This 
includes its thermal/acoustic insulation meeting requirements of Sec.  
25.856(a). Those special conditions state that resistance to flame 
propagation must be shown, and all products of combustion that may 
result must be evaluated for toxicity and found acceptable.
    We have made no changes to these special conditions as a result of 
this comment.
    Comment 8. Another commenter provided extensive background 
information on the current level of safety provided by the 
crashworthiness of aluminum transport category airframes. This 
commenter expressed concern that the introduction of a composite 
fuselage will reduce the crashworthiness of transport airplanes. The 
commenter further requested that we impose a fuselage drop test for the 
787 to ensure that the current level of safety provided by an aluminum 
fuselage is provided by the composite materials used in the 
construction of the 787 fuselage.
    FAA Response: We would like to note that the scope of these special 
conditions is limited to the fire safety provisions of the fuel tanks 
and wing structure during a fuel-fed ground fire. These special 
conditions are not intended to address the structural crashworthiness 
of the airframe. We have considered the impact of composites on 
airframe crashworthiness and have proposed Special Conditions 25-07-05-
SC, published on June 11, 2007, in the Federal Register (72 FR 32021). 
As stated in those special conditions, ``The Boeing Model 787-8 must 
provide an equivalent level of occupant safety and survivability to 
that provided by previously certificated wide-body transports of 
similar size under foreseeable survivable impact events for the 
following four criteria. In order to demonstrate an equivalent level of 
occupant safety and survivability, the applicant must demonstrate that 
the

[[Page 57848]]

Model 787-8 meets the following criteria for a range of airplane 
vertical descent velocities up to 30 ft/sec * * *'' The FAA considers 
that proposed Special Conditions 25-07-05-SC adequately addresses the 
commenter's concerns for crashworthiness and we note that the commenter 
had opportunity to submit comments to that proposal as well. We have 
made no changes to these special conditions as a result of this 
comment.

Applicability

    As discussed above, these 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 on the same type certificate 
incorporating the same novel or unusual design features, these special 
conditions would apply to that model as well.

Conclusion

    This action affects only certain novel or unusual design features 
of the 787. It is not a rule of general applicability.

List of Subjects in 14 CFR Part 25

    Aircraft, Aviation safety, Reporting and recordkeeping 
requirements.

0
The authority citation for these special conditions is as follows:

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

The Special Conditions

0
Accordingly, pursuant to the authority delegated to me by the 
Administrator, the following special conditions are issued as part of 
the type certification basis for the Boeing Model 787-8 airplane.

    In addition to complying with 14 CFR part 25 regulations 
governing the fire-safety performance of the fuel tanks, wings, and 
nacelle, the Boeing Model 787-8 must demonstrate acceptable 
postcrash 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 September 28, 2007.
Ali Bahrami,
Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. E7-20031 Filed 10-10-07; 8:45 am]
BILLING CODE 4910-13-P