[Federal Register: September 26, 2007 (Volume 72, Number 186)]
[Rules and Regulations]
[Page 54529-54530]
From the Federal Register Online via GPO Access [wais.access.gpo.gov]
[DOCID:fr26se07-4]
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DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 25
[Docket No. NM367 Special Conditions No. 25-363-SC]
Special Conditions: Boeing Model 787-8 Airplane; Tire Debris
Penetration 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 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 include wing fuel tanks constructed of carbon fiber
composite materials. For these design features, the applicable
airworthiness regulations do not contain adequate or appropriate safety
standards. 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
standards. Additional special conditions will be issued for other novel
or unusual design features of the Boeing Model 787-8 airplanes.
DATES: Effective Date: October 26, 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 pursuant to 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 use carbon fiber composite materials for most of the
wing fuel tank structure. 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 the exposed wing surfaces.
The FAA issues these special conditions to maintain the level of
safety envisioned in the existing airworthiness standards by
establishing a standard for resistance to potential tire debris impacts
to the 787 contiguous wing surfaces.
Discussion
Historically, 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 one incident, in Honolulu, Hawaii, a tire on a Boeing Model 747
burst and tire debris penetrated a fuel tank access cover, causing a
substantial fuel leak. Takeoff was aborted and passengers were
evacuated down the emergency chutes into pools of fuel which
fortunately had not ignited. This accident highlighted deficiencies in
the then-existing title 14 CFR part 25 regulations pertaining to fuel
retention following impact to fuel tanks by tire fragments.
After a subsequent Boeing Model 737 accident in Manchester,
England, in which a fuel tank access panel was penetrated by engine
debris, the FAA
[[Page 54530]]
amended Sec. 25.963 to require that fuel tank access panels be
resistant to both tire and engine debris. An amendment to 14 CFR part
121 required operators to modify their existing fleets of airplanes
with impact resistant fuel access panels. The amendment only addressed
fuel tank access panels since service experience at the time indicated
that the lower wing skin of a conventional, subsonic airplane provided
adequate, inherent capability to resist tire and engine debris threats.
Section 25.963(e) requires showing by analysis or tests that fuel tank
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 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 wing basic structures meet some higher
standard.
However, in another event in 2000, on the Concorde airplane, an
unanticipated failure mode occurred when tire debris impacted the fuel
tank. The initial impact of the tire debris did not penetrate the fuel
tank, but a pressure wave caused by the tire impact caused the fuel
tank to rupture. Regulatory authorities subsequently required
modifications to Concorde airplanes to add a means to retain fuel if
the primary fuel retention means was damaged.
In order to maintain the level of safety envisioned by Sec.
25.963(e), 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 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 this hazard will be addressed on
the 787 under the existing requirements of Sec. 25.903(d). Section
25.903(d) requires minimizing the hazards from uncontained engine
debris.
Discussion of Comments
Notice of Proposed Special Conditions No. 25-07-04-SC for the 787
was published in the Federal Register on June 11, 2007 (72 FR 32023).
One comment was received from Airbus. Airbus referred to the discussion
of the Concorde airplane, in which we said, ``The skin on the unique
delta wing design of this supersonic airplane is made of titanium, with
a thickness much less than that of the skin on a conventional subsonic
airplane.'' Airbus informed us that the wing skin of the Concorde is
made of aluminum rather than titanium. We thank the commenter for that
information. The difference in material on the Concorde does not affect
these special conditions, however, and the commenter did not request a
change. These special conditions are adopted as proposed.
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.
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 the Boeing Model 787-8 airplane.
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 located
within the tire debris impact area, 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 September 14, 2007.
Ali Bahrami,
Manager, Transport Airplane Directorate, Aircraft Certification
Service.
[FR Doc. E7-18931 Filed 9-25-07; 8:45 am]
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