[Federal Register Volume 84, Number 99 (Wednesday, May 22, 2019)]
[Rules and Regulations]
[Pages 23456-23458]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2019-10703]


=======================================================================
-----------------------------------------------------------------------

DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 25

[Docket No. FAA-2018-1015; Special Conditions No. 25-746-SC]


Special Conditions: Boeing Model 777-9 Airplane; Tire Debris 
Penetration of Fuel Tank Structure

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Final special conditions; request for comments.

-----------------------------------------------------------------------

SUMMARY: These special conditions are issued for The Boeing Company 
(Boeing) Model 777-9 airplane. This airplane will have a novel or 
unusual design feature when compared to the state of technology 
envisioned in the airworthiness standards for transport category 
airplanes. This design feature is composite fuel tanks that may be 
subject to tire-debris penetration of the fuel tanks. The applicable 
airworthiness regulations do not contain adequate or appropriate safety 
standards for this design feature. These special conditions

[[Page 23457]]

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: This action is effective on Boeing on May 22, 2019. Send 
comments on or before July 8, 2019.

ADDRESSES: Send comments identified by Docket No. FAA-2018-1015 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 website, 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).
    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 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: Suzanne Lucier, Propulsion and 
Mechanical Systems Section, AIR-672, Transport Standards Branch, Policy 
and Innovation Division, Aircraft Certification Service, Federal 
Aviation Administration, 2200 South 216th Street, Des Moines, 
Washington 98198; telephone and fax 206-231-3173; email 
[email protected].

SUPPLEMENTARY INFORMATION: The substance of these special conditions 
has been published in the Federal Register for public comment in 
several prior instances with no substantive comments received. 
Therefore, the FAA has determined that prior public notice and comment 
are unnecessary, and finds that, for the same reason, good cause exists 
for adopting these special conditions upon publication in the Federal 
Register.

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 by the closing date for 
comments. We may change these special conditions based on the comments 
we receive.

Background

    On March 12, 2015, Boeing applied for an amendment to Type 
Certificate No. T00001SE to include the new 777-9 airplane. This 
airplane, which is a derivative of the Boeing Model 777 airplane 
currently approved under Type Certificate No. T00001SE, is a twin-
engine, transport category airplane with seating for 495 passengers and 
a maximum takeoff weight of 775,000 pounds.

Type Certification Basis

    Under the provisions of title 14, Code of Federal Regulations (14 
CFR) 21.101, Boeing must show that the 777-9 airplane meets the 
applicable provisions of the regulations listed in Type Certificate No. 
T00001SE, or the applicable regulations in effect on the date of 
application for the change, except for earlier amendments as agreed 
upon by the FAA.
    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 Boeing Model 777-9 airplane 
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 novel or 
unusual design feature, or should any other model already included on 
the same type certificate be modified to incorporate the same novel or 
unusual design feature, these special conditions would also apply to 
the other model under Sec.  21.101.
    In addition to the applicable airworthiness regulations and special 
conditions, the Boeing Model 777-9 airplane 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 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.  21.101.

Novel or Unusual Design Features

    The Boeing Model 777-9 airplane will incorporate the following 
novel or unusual design feature:
    Composite fuel tanks that may be subject to tire-debris penetration 
of the fuel tanks.

Discussion

    Accidents or incidents have resulted from uncontrolled fires caused 
by fuel leaks due to fragments of tires or uncontained engine failure 
penetrating or rupturing the undersides of airplane wings. The effects 
of engine debris as a result of uncontained engine failure are not 
included in these special conditions because, for the Boeing Model 777-
9 airplane, this hazard is addressed under the existing requirements of 
Sec.  25.903(d), which requires minimizing the hazards from uncontained 
engine-failure debris.
    In one incident in Honolulu, Hawaii, a tire on a Boeing Model 747 
airplane burst, and tire debris penetrated a fuel-tank access panel, 
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 14 CFR part 25 regulations pertaining to fuel-tank 
fuel retention following tire fragments penetrating fuel tanks.
    After a subsequent Boeing Model 737 airplane accident in 
Manchester, England, in which uncontained engine-failure debris 
penetrated a fuel-tank access panel, the FAA amended Sec.  25.963 to 
require that fuel-tank access panels be resistant to penetration from 
both tire-failure debris and uncontained engine-failure debris. 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, ``Fuel Tank Access Covers,'' defines the region of the 
wing that is vulnerable to impact damage from these sources, and

[[Page 23458]]

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 fuel-tank access covers are installed, 
because of the inherent ability of conventional aluminum wing skins to 
resist tire-debris penetration. Advisory Circular 25.963-1 specifically 
notes, ``The [fuel-tank] access covers, however, need not be more 
impact resistant than the contiguous tank structure,'' highlighting the 
assumption that the basic structures of these wings meet some higher 
standard. An additional amendment to 14 CFR part 121 required operators 
to modify their existing fleets of airplanes with impact-resistant 
fuel-tank access panels. This amendment only addressed fuel-tank access 
panels because service experience at the time indicated that the wing 
skin on the underside of a wing, on conventional, subsonic airplanes, 
provided adequate, inherent capability to resist tire debris and engine 
debris penetration.
    However, after the adoption of the amendments to Sec.  25.963 in 
2000, an unanticipated failure mode occurred on a Concorde airplane 
when tire debris impacted the fuel tank. The initial impact of the tire 
debris did not penetrate the fuel tank, but a pressure wave from the 
debris impact caused the fuel tank to rupture. In September 2001, both 
the French civil-aviation authority (DGAC) and the United Kingdom Civil 
Aviation Authority (CAA) issued airworthiness directives requiring 
modifications to Concorde airplanes, to add a means to retain fuel if 
the primary fuel retention means was damaged.
    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. This standard takes into account that new construction 
methods and materials may not necessarily provide the resistance to 
debris impact that historically has been shown as adequate with 
conventional aluminum wings. 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) of these special 
conditions may cause a fuel leak within the defined area, so paragraph 
(c) of these special conditions also takes into consideration possible 
fuel-leak 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 where composite material is used.
    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.

Applicability

    As discussed above, these special conditions are applicable to the 
Boeing Model 777-9 airplane. 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 feature, these special conditions 
would apply to that model as well.

Conclusion

    This action affects only a certain novel or unusual design feature 
on one model of airplane. It is not a rule of general applicability.

List of Subjects in 14 CFR Part 25

    Aircraft, Aviation safety, Reporting and recordkeeping 
requirements.

Authority Citation

    The authority citation for these special conditions is as follows:

    Authority: 49 U.S.C. 106(f), 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 Boeing Model 777-9 airplanes.
    (a) Tire-debris impact 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 (e.g., 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), above, must be shown by analysis 
or tests assuming all of the following. The tire-debris fragment:
    1. Size is 1 percent of the tire mass.
    2. 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. Load is distributed over an area on the fuel-tank surface equal 
to 1.5 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 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 Des Moines, Washington, on May 13, 2019.
Victor Wicklund,
Manager, Transport Standards Branch, Policy and Innovation Division, 
Aircraft Certification Service.
[FR Doc. 2019-10703 Filed 5-21-19; 8:45 am]
BILLING CODE 4910-13-P