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[Federal Register Volume 79, Number 177 (Friday, September 12, 2014)]
[Rules and Regulations]
[Pages 54576-54577]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: 2014-21786]

[[Page 54576]]

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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 25

[Docket No. FAA-2014-0329; Special Conditions No. 25-560-SC]

Special Conditions: Bombardier Aerospace, Models BD-500-1A10 and 
BD-500-1A11 Series Airplanes; Tire Debris Impacts to Fuel Tanks

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Final special conditions.

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SUMMARY: These special conditions are issued for the Bombardier 
Aerospace, Models BD-500-1A10 and BD-500-1A11 series airplanes. These 
airplanes will have a novel or unusual design feature associated with 
the use of carbon fiber reinforced plastic (CFRP) for most of the wing 
fuel tank structure, which, when impacted by tire debris, may resist 
penetration or rupture differently from aluminum wing skins. The 
applicable airworthiness regulations do not contain adequate or 
appropriate safety standards for this design feature. 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: October 14, 2014.

FOR FURTHER INFORMATION CONTACT: Margaret Langsted, FAA, Propulsion and 
Mechanical Systems Branch, ANM-112, Transport Airplane Directorate, 
Aircraft Certification Service, 1601 Lind Avenue SW., Renton, 
Washington, 98057-3356; telephone 425-227-2677; facsimile 425-227-1149.

SUPPLEMENTARY INFORMATION:

Background

    On December 10, 2009, Bombardier Aerospace applied for a type 
certificate for their new Models BD-500-1A10 and BD-500-1A11 series 
airplanes (hereafter collectively referred to as ``CSeries''). The 
CSeries airplanes are swept-wing monoplanes with an aluminum alloy 
fuselage sized for 5-abreast seating. Passenger capacity is designated 
as 110 for the Model BD-500-1A10 and 125 for the Model BD-500-1A11. 
Maximum takeoff weight is 131,000 pounds for the Model BD-500-1A10 and 
144,000 pounds for the Model BD-500-1A11.

Type Certification Basis

    Under the provisions of Title 14, Code of Federal Regulations (14 
CFR) 21.17, Bombardier Aerospace must show that the CSeries airplanes 
meet the applicable provisions of part 25, as amended by Amendments 25-
1 through 25-129 thereto.
    If the Administrator finds that the applicable airworthiness 
regulations (i.e., 14 CFR part 25) do not contain adequate or 
appropriate safety standards for the CSeries 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 CSeries airplanes 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, and 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 CSeries airplanes will incorporate the following novel or 
unusual design features: The use of carbon fiber reinforced plastic 
(CFRP) for most of the wing fuel tank structure. The ability of 
aluminum wing skins to resist penetration or rupture when impacted by 
tire debris is understood from extensive experience, but the ability of 
CFRP construction to resist these hazards has not been established. 
There are no existing regulations that adequately establish a level of 
safety with respect to the performance of the composite materials used 
in the construction of wing fuel tanks. It requires the consideration 
of fuel tank penetration, fuel leaks, discrete source damage tolerance, 
and the effects of shock waves generated by tire debris impact.

Discussion

    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. The Concorde accident in 
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 lower wing surface by tire debris 
induced pressure waves within the fuel tank that resulted in fuel 
leakage and fire. Regulatory authorities subsequently required 
modifications to the Concorde to improve impact resistance of the lower 
wing or means to retain fuel if the primary fuel retention means is 
damaged.
    In another incident, a Boeing Model 747 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 chutes into pools of fuel that 
fortunately had not ignited.
    These accidents highlight deficiencies in the existing regulations 
pertaining to fuel retention following impact of the fuel tanks by tire 
fragments. Following a 1985 Boeing Model 737 accident in Manchester, 
England, in which a fuel tank access panel was penetrated by engine 
debris, the FAA amended 14 CFR 25.963 to require fuel tank access 
panels that are resistant to both tire and engine debris (engine debris 
is addressed elsewhere). This regulation, Sec.  25.963(e), only 
addressed the fuel tank access covers since 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, that 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, Fuel 
Tank Access Covers, describes 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, because of the inherent ability of 
conventional aluminum wing skins to resist penetration by tire debris. 
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 structure is more capable of 
resisting tire impact debris than fuel tank access covers.
    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. To maintain the level of safety envisioned by 14 CFR 
25.963(e), these special conditions

[[Page 54577]]

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. It takes into account that 
new construction methods and materials will not necessarily yield 
debris resistance that has historically been shown as adequate. The 
standard in these special conditions is based on the defined tire 
impact areas and tire fragment characteristics.
    In addition, despite practical design considerations, some uncommon 
debris larger than that defined in paragraph 2 may cause a fuel leak 
within the defined area, so paragraph 3 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 2 of these special 
conditions. Consideration of leaks caused by larger tire fragments is 
needed to ensure that an adequate level of safety is provided.

Discussion of Comments

    Notice of proposed special conditions No. 25-14-03-SC for the 
Bombardier Aerospace CSeries airplanes was published in the Federal 
Register on June 3, 2014, (79 FR 31886). No comments were received, and 
the special conditions are adopted as proposed.

Applicability

    As discussed above, these special conditions are applicable to the 
BD-500-1A10 and BD-500-1A11 series airplanes. Should Bombardier 
Aerospace 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 feature, these special conditions would 
apply to that model as well.

Conclusion

    This action affects only certain novel or unusual design features 
on one model series of 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

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 Bombardier Aerospace Models BD-500-
1A10 and BD-500-1A11 series airplanes.

Tire Debris Impacts to Fuel Tanks

    1. 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 a--
    a. Running leak,
    b. Dripping leak, or
    c. 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.
    2. Compliance with paragraph 1 must be shown by analysis or tests 
assuming all of the following:
    a. The tire debris fragment size is 1 percent of the tire mass.
    b. 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).
    c. The tire debris fragment load is distributed over an area on the 
fuel tank surface equal to 1\1/2\ percent of the total tire tread area.
    3. Fuel leaks caused by impact from tire debris larger than that 
specified in paragraph 2, from any portion of a fuel tank or fuel 
system component located within the tire debris impact area defined in 
paragraph 1, may not result in hazardous quantities of fuel entering 
any of the following areas of the airplane:
    a. Engine inlet,
    b. Auxiliary power unit inlet, or
    c. 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.

    Issued in Renton, Washington, on September 3, 2014.
Michael Kaszycki,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 2014-21786 Filed 9-11-14; 8:45 am]
BILLING CODE 4910-13-P
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