[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]
-----------------------------------------------------------------------
DEPARTMENT OF TRANSPORTATION
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.
SUPPLEMENTARY INFORMATION:
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.
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
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
time.
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
airplane.
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
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
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.
Discussion
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
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 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
provided.
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.
Applicability
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.
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 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
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 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
Service.
[FR Doc. 2014-00450 Filed 1-13-14; 8:45 am]
BILLING CODE 4910-13-P