[Federal Register Volume 79, Number 152 (Thursday, August 7, 2014)]
[Rules and Regulations]
[Pages 46167-46168]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2014-18653]



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  Federal Register / Vol. 79, No. 152 / Thursday, August 7, 2014 / 
Rules and Regulations  

[[Page 46167]]



DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 25

[Docket No. FAA-2013-0907; Special Conditions No. 25-541-SC]


Special Conditions: Airbus Model A350-900 Series Airplane; Tire 
Failure--Debris Penetration or Rupture of Fuel-Tank Structure

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Final special conditions.

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SUMMARY: These special conditions are issued for Airbus Model A350-900 
series airplanes. These airplanes will have a novel or unusual design 
feature associated with fuel tanks constructed of carbon-fiber 
reinforced plastic (CFRP) materials located within the tire-impact 
zone, including the wing fuel tanks.
    The ability of aluminum wing skins, as has been conventionally 
used, to resist penetration or rupture when impacted by tire debris, is 
understood from extensive experience. The ability of carbon-fiber 
composite material to resist these hazards has not been established. No 
current airworthiness standards specifically address this hazard for 
all exposed wing surfaces. These 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.

DATES: Effective Date: September 8, 2014.

FOR FURTHER INFORMATION CONTACT: Doug Bryant, Propulsion/Mechanical 
Systems, ANM-112, Transport Airplane Directorate, Aircraft 
Certification Service, 1601 Lind Avenue SW., Renton, Washington, 98057-
3356; telephone (425) 227-2384; facsimile (425) 227-1320.

SUPPLEMENTARY INFORMATION: 

Background

    On August 25, 2008, Airbus applied for a type certificate for their 
new Model A350-900 series airplane. Later, Airbus requested and the FAA 
approved an extension to the application for FAA type certification to 
November 15, 2009. The Model A350-900 series airplane has a 
conventional layout with twin wing-mounted Rolls-Royce Trent XWB 
engines. It features a twin aisle, 9-abreast, economy-class layout, and 
accommodates side-by-side placement of LD-3 containers in the cargo 
compartment. The basic Model A350-900 series airplane configuration 
accommodates 315 passengers in a standard two-class arrangement. The 
design cruise speed is Mach 0.85 with a maximum take-off weight of 
602,000 lbs.
    Accidents have resulted from uncontrolled fires caused by fuel 
leaks following penetration or rupture of the lower wing by fragments 
of tires, or from uncontained engine failure. In a November 1984 
accident, a Boeing Model 747 airplane tire burst during an aborted 
takeoff from Honolulu, Hawaii. That tire debris penetrated a fuel-tank 
access cover, causing substantial fuel leakage. Passengers were 
evacuated down the emergency slides into pools of fuel that fortunately 
had not ignited.
    After an August 1985 Boeing Model 737 airplane accident in 
Manchester, England, in which a fuel-tank access cover was penetrated 
by engine debris creating a fire, the FAA amended Title 14, Code of 
Federal Regulations (14 CFR) 25.963 to require fuel-tank access covers 
that are resistant to both tire and engine debris (engine debris is 
addressed outside of these special conditions). Modifications to the 
access covers were required of the existing fleet by an amendment to 14 
CFR part 121. This regulation, Sec.  25.963(e), only addressed the 
fuel-tank access covers because service experience at the time showed 
that the lower-wing skin of a conventional, subsonic airplane provided 
adequate inherent capability to resist tire and engine debris threats. 
More specifically, this regulation requires showing, by analysis or 
tests, that the access covers ``. . . minimize penetration and 
deformation by tire fragments, low energy engine debris, or other 
likely debris.'' Advisory Circular (AC) 25.963-1 defines the region of 
the wing that is vulnerable to impact damage from these sources and 
provides a method to substantiate that the rule has been met for tire 
fragments. No specific requirements were established for the contiguous 
wing areas into which the access covers are installed. AC 25.963-1 
specifically notes, ``The access covers, however, need not be more 
impact resistant than the contiguous tank structure,'' highlighting the 
assumption that the wing was adequately addressed.
    The Concorde accident in July 2000 is the most notable example. 
That accident demonstrated an unanticipated failure mode in an airplane 
with an unusual transport-airplane configuration. Impact to the thin 
aluminum wing surface by tire debris induced pressure waves within the 
fuel tank that resulted in fuel leakage and fire. The skin on the 
Concorde delta-wing supersonic airplane is made of aluminum, having a 
thickness that is much less than that of a conventional subsonic 
airplane.
    Several previous accidents from burst tires damaged the fuel tank 
and wings on the Concorde. In 1979, a burst main-gear tire put a hole 
through the wing, causing both fuel and hydraulic leaks. In 1980, a 
burst tire damaged the engine and airframe. In July 1993, a main-gear 
tire burst, damaging the wing and causing hydraulic problems. In 
October 1993, a main-gear tire burst, broke the water deflector, and 
created holes in the fuel tank. Fortunately, the fuel did not catch 
fire during any of these events before the July 2000 accident involving 
the Concorde airplane.
    Following the accident in 2000, regulatory authorities required 
modifications to the Concorde aircraft to improve impact resistance of 
the lower wing, or means to retain fuel if the primary fuel retention 
means is damaged.
    These accidents and incidents highlight the need to establish 
standards for fuel-tank designs and configurations that were not 
envisioned when the existing standards in 14 CFR part 25 were issued.

Type Certification Basis

    Under 14 CFR 21.17, Airbus must show that the Model A350-900 series 
airplane meets the applicable provisions of part 25, as amended by 
Amendments 25-1 through 25-129.

[[Page 46168]]

    If the Administrator finds that the applicable airworthiness 
regulations (i.e., 14 CFR part 25) do not contain adequate or 
appropriate safety standards for Model A350-900 series airplanes 
because of a novel or unusual design feature, special conditions are 
prescribed under the provisions of Sec.  21.16.
    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.
    In addition to the applicable airworthiness regulations and special 
conditions, the Model A350-900 series airplane must be shown to 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 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, in 
accordance with Sec.  11.38, and they become part of the type-
certification basis under Sec.  21.17(a)(2).

Novel or Unusual Design Features

    The Airbus Model A350-900 series airplanes will incorporate the 
following novel or unusual design features: CFRP materials for most of 
the wing fuel-tank structure.

Discussion

    To maintain the level of safety prescribed by Sec.  25.963(e) for 
fuel-tank access covers, these special conditions establish a standard 
for resistance to potential tire-debris impacts to the contiguous wing 
surfaces, and require consideration of possible secondary effects of a 
tire impact, such as the induced pressure wave that was a factor in the 
Concorde accident. These special conditions take into account that new 
construction methods and materials may not necessarily provide the 
resistance to debris impact that has historically been shown as 
adequate. These special conditions are based on the defined tire-impact 
areas and tire-fragment characteristics described in AC 25.963-1.
    In addition, despite practical-design considerations, some uncommon 
debris larger than that defined in paragraph (b) may cause a fuel leak 
within the defined area, so paragraph (c) of these special conditions 
also takes into consideration possible leakage paths. Fuel-tank 
surfaces of typical transport airplanes have thick aluminum 
construction in the tire-debris impact areas that is tolerant to tire 
debris larger than that defined in paragraph (b) of these special 
conditions. Consideration of leaks caused by larger tire fragments is 
needed to ensure that an adequate level of safety is provided.

    Note:  While Sec.  25.963 includes consideration of uncontained 
engine debris, the effects of engine debris are not included in 
these special conditions because these related potential hazards are 
addressed on the Model A350-900 series airplane under the existing 
requirements of Sec.  25.903(d). Section 25.903(d) requires 
minimizing the hazards from uncontained engine debris.

    These 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.

Discussion of Comments

    Notice of proposed special conditions No. 25-13-19-SC for the 
Airbus Model A350-900 series airplanes was published in the Federal 
Register on January 14, 2014 (79 FR 2388). No comments were received, 
and the special conditions are adopted as proposed.

Applicability

    As discussed above, these special conditions are applicable to 
Airbus Model A350-900 series airplanes. Should Airbus apply at a later 
date for a change to the type certificate to include another model 
incorporating the same novel or unusual design feature, the special 
conditions would apply to that model as well.

Conclusion

    This action affects only certain novel or unusual design features 
on Airbus Model A350-900 series airplanes. It is not a rule of general 
applicability.

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 Special Conditions

    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 Airbus Model A350-900 series 
airplanes.
    a. Impacts by tire debris to any fuel tank or fuel-system component 
located within 30 degrees to either side of wheel rotational planes may 
not result in penetration or otherwise induce fuel-tank deformation, 
rupture (for example, through propagation of pressure waves), or 
cracking sufficient to allow a hazardous fuel leak. A hazardous fuel 
leak results if debris impact to a fuel tank surface causes--
    1. a running leak,
    2. a dripping leak, or
    3. a leak that, 15 minutes after wiping dry, results in a wetted 
airplane surface exceeding 6 inches in length or diameter.
    The leak must be evaluated under maximum fuel-head pressure.
    b. Compliance with paragraph (a) must be shown by analysis or tests 
assuming all of the following:
    1. The tire-debris fragment size is equal to 1 percent of the tire 
mass.
    2. The tire-debris fragment is propelled at a tangential speed that 
could be attained by a tire tread at the Airplane Flight Manual 
airplane rotational speed (VR at maximum gross weight).
    3. The tire-debris fragment load is distributed over an area on the 
fuel-tank surface equal to 1.5 percent of the total tire-tread area.
    c. Fuel leaks caused by impact from tire debris larger than that 
specified in paragraph (b), from any portion of a fuel tank or fuel-
system component located within the tire-debris impact area defined in 
paragraph (a), may not result in hazardous quantities of fuel entering 
any of the following areas of the airplane:
    1. Engine inlet,
    2. APU inlet, or
    3. Cabin-air inlet.
    This must be shown by test or analysis, or a combination of both, 
for each approved engine forward-thrust condition, and each approved 
reverse-thrust condition.

Jeffrey E. Duven,
Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 2014-18653 Filed 8-6-14; 8:45 am]
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