[Federal Register Volume 72, Number 111 (Monday, June 11, 2007)]
[Proposed Rules]
[Pages 32023-32025]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: E7-11150]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 25

[Docket No. NM367 Special Conditions No. 25-07-04-SC]


Special Conditions: Boeing Model 787-8 Airplane; Tire Debris 
Penetration of Fuel Tank Structure

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Notice of proposed special conditions.

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SUMMARY: This notice proposes special conditions 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

[[Page 32024]]

standards for transport category airplanes. These design features 
include wing fuel tanks constructed of carbon fiber composite 
materials. 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. Additional special conditions will be 
issued for other novel or unusual design features of the Boeing Model 
787-8 airplanes.

DATES: Comments must be received on or before July 26, 2007.

ADDRESSES: Comments on this proposal may be mailed in duplicate to: 
Federal Aviation Administration, Transport Airplane Directorate, 
Attention: Rules Docket (ANM-113), Docket No. NM367, 1601 Lind Avenue, 
SW., Renton, Washington 98057-3356; or delivered in duplicate to the 
Transport Airplane Directorate at the above address. All comments must 
be marked Docket No. NM367. Comments may be inspected in the Rules 
Docket weekdays, except Federal holidays, between 7:30 a.m. and 4 p.m.

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:

Comments Invited

    The FAA invites interested persons to participate in this 
rulemaking by submitting 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 ask that you send us two copies of written 
comments.
    We will file in the docket all comments we receive as well as a 
report summarizing each substantive public contact with FAA personnel 
concerning these proposed special conditions. The docket is available 
for public inspection before and after the comment closing date. If you 
wish to review the docket in person, go to the address in the ADDRESSES 
section of this notice between 7:30 a.m. and 4 p.m., Monday through 
Friday, except Federal holidays.
    We will consider all comments we receive on or before the closing 
date for comments. We will consider comments filed late if it is 
possible to do so without incurring expense or delay. We may change the 
proposed special conditions based on comments we receive.
    If you want the FAA to acknowledge receipt of your comments on this 
proposal, include with your comments a pre-addressed, stamped postcard 
on which the docket number appears. We will stamp the date on the 
postcard and mail it back to you.

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 14 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 part 36. In addition, the FAA must issue a finding of regulatory 
adequacy pursuant to section 611 of Public Law 92-574, the ``Noise 
Control Act of 1972.''
    Special conditions, as defined in Sec.  11.19, are issued in 
accordance with Sec.  11.38 and become part of the type certification 
basis in accordance with 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 the provisions of 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 proposed 
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 construction to resist these 
hazards has not been established, and thus there are no current 
airworthiness standards specifically addressing this hazard for all the 
exposed wing surfaces.
    The FAA is proposing these special conditions to maintain the level 
of safety envisioned in the existing airworthiness standards by 
proposing 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 amended Sec.  25.963 to 
require that fuel tank access panels be resistant to both tire and 
engine debris. An amendment to title 14 CFR part 121 required operators 
to modify their existing fleets of airplanes with impact resistant 
access panels. The amendment only addressed fuel tank access covers 
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

[[Page 32025]]

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 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. 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 14 CFR 
25.963(e), these special conditions propose 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 proposed standard is based on 
the defined tire impact areas and tire fragment characteristics 
described in AC 25.963-1.
    In addition, despite practical design considerations, some 
exceptional 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 
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.

Applicability

    As discussed above, these proposed 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 incorporating the same 
novel or unusual design features, these proposed special conditions 
would apply to that model as well under the provisions of Sec.  21.101.

Conclusion

    This action affects only certain novel or unusual design features 
of the 787. It is not a rule of general applicability, and it affects 
only the applicant that applied to the FAA for approval of these 
features on the airplane.

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 Administrator of the Federal Aviation 
Administration (FAA) proposes the following special conditions 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.
    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 May 31, 2007.
Ali Bahrami,
Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. E7-11150 Filed 6-8-07; 8:45 am]
BILLING CODE 4910-13-P