[Federal Register Volume 79, Number 9 (Tuesday, January 14, 2014)]
[Proposed Rules]
[Pages 2388-2390]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2014-00450]



Federal Aviation Administration

14 CFR Part 25

[Docket No. FAA-2013-0907; Notice No. 25-13-19-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: Notice of proposed special conditions.


SUMMARY: This action proposes special conditions for the Airbus Model 
A350-900 series airplane. These airplanes will have a novel or unusual 
design feature

[[Page 2389]]

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. 
There are no current airworthiness standards specifically addressing 
this hazard for all exposed wing surfaces. 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.

DATES: Send your comments on or before February 28, 2014.

ADDRESSES: Send comments identified by docket number FAA-2013-0907 
using any of the following methods:
     Federal eRegulations Portal: Go to http://www.regulations.gov/ and follow the online instructions for sending 
your comments electronically.
     Mail: Send comments to Docket Operations, M-30, U.S. 
Department of Transportation (DOT), 1200 New Jersey Avenue SE., Room 
W12-140, West Building Ground Floor, Washington, DC, 20590-0001.
     Hand Delivery or Courier: Take comments to Docket 
Operations in Room W12-140 of the West Building Ground Floor at 1200 
New Jersey Avenue SE., Washington, DC, between 9 a.m. and 5 p.m., 
Monday through Friday, except federal holidays.
     Fax: Fax comments to Docket Operations at 202-493-2251.
    Privacy: The FAA will post all comments it receives, without 
change, to http://www.regulations.gov/, including any personal 
information the commenter provides. Using the search function of the 
docket Web site, anyone can find and read the electronic form of all 
comments received into any FAA docket, including the name of the 
individual sending the comment (or signing the comment for an 
association, business, labor union, etc.). DOT's complete Privacy Act 
Statement can be found in the Federal Register published on April 11, 
2000 (65 FR 19477-19478), as well as at http://DocketsInfo.dot.gov/.
    Docket: Background documents or comments received may be read at 
http://www.regulations.gov/ at any time. Follow the online instructions 
for accessing the docket or go to the Docket Operations in Room W12-140 
of the West Building Ground Floor at 1200 New Jersey Avenue SE., 
Washington, DC, between 9 a.m. and 5 p.m., Monday through Friday, 
except federal holidays.

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.


Comments Invited

    We invite interested people to take part in this rulemaking by 
sending 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 will consider all comments we receive on or before the closing 
date for comments. We may change these proposed special conditions 
based on the comments we receive.


    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 
June 28, 2009. The Model A350-900 series has a conventional layout with 
twin wing-mounted Rolls-Royce Trent 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 configuration will accommodate 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. Airbus proposes the Model A350-900 
series to be certified for extended operations (ETOPS) beyond 180 
minutes at entry into service for up to a 420 minute maximum diversion 
    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 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 accident in Manchester, 
England, in which a fuel tank access panel 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 panels that are 
resistant to both tire and engine debris (engine debris is addressed 
outside of this proposed special condition). Modifications to the 
access covers were required of the existing fleet by an amendment to 
part 121. 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, 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 
    There were several previous accidents from burst tires that damaged 
the fuel tank and wings in the Concorde. In 1979 a burst main gear tire 
put a hole through the wing and caused 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 
caused some 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

[[Page 2390]]

wing, or means to retain fuel if the primary fuel retention means is 
    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 
meets the applicable provisions of part 25, as amended by Amendments 
25-1 through 25-129.
    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 proposed special conditions would 
also apply to the other model under Sec.  21.101.
    In addition to the applicable airworthiness regulations and 
proposed special conditions, the Model A350-900 series 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 Sec.  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 will incorporate the following 
novel or unusual design features: CFRP materials for most of the wing 
fuel tank structure.


    In order 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. It takes 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 proposed special conditions are based on the defined 
tire impact areas and tire fragment characteristics described in AC 
    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 proposed 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 proposed 
special conditions. Consideration of leaks caused by larger tire 
fragments is needed to ensure that an adequate level of safety is 

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


    As discussed above, these proposed 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 proposed special conditions would apply to that model as well.


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

List of Subjects in 14 CFR Part 25

    Aircraft, Aviation safety, Reporting, and recordkeeping 

    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 Federal Aviation Administration (FAA) proposes the 
following special conditions as part of the type certification basis 
for Airbus Model A350-900 series airplanes.

Debris Impacts to Fuel Tanks

    (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 
    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 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\1/2\ 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.

    Issued in Renton, Washington, on October 22, 2013.
Stephen P. Boyd,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
[FR Doc. 2014-00450 Filed 1-13-14; 8:45 am]