Document ID: FAA-2018-1017-0001
Agency: faa
Document Type: Rule
Title: Special Conditions: Boeing Model 777-9 Airplanes; Post-Crash Fire Survivability, Airplane Level of Safety Provided by Composite Fuel-Tank Structure
Posted Date: 2019-02-27T05:00Z

[Federal Register Volume 84, Number 39 (Wednesday, February 27, 2019)]
[Rules and Regulations]
[Pages 6313-6315]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2019-03343]

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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 25

[Docket No. FAA-2018-1017; Special Conditions No. 25-741-SC]

Special Conditions: Boeing Model 777-9 Airplanes; Post-Crash Fire 
Survivability, Airplane Level of Safety Provided by Composite Fuel-Tank 
Structure

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Final special conditions; request for comments.

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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-tank structure as it 
relates to post-crash fire survivability. The applicable airworthiness 
regulations do not contain adequate or appropriate safety standards for 
this design feature. 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.

DATES: This action is effective on Boeing on February 27, 2019. Send 
comments on or before April 15, 2019.

ADDRESSES: Send comments identified by Docket No. FAA-2018-1017 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 
suzanne.lucier@faa.gov.

SUPPLEMENTARY INFORMATION: The FAA has determined that notice of, and 
opportunity for prior public comment on, these special conditions is 
impracticable because 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 Model 777-9 airplane meets the 
applicable

[[Page 6314]]

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-tank structure as it relates to post-crash fire 
survivability.

Discussion

    As with previous applicant airplane designs with underwing-mounted 
engines, the wing tanks and center tanks are located in proximity to 
the passengers and near the engines. Experience indicates post-crash 
survivability is greatly influenced by the size and intensity of any 
fire that occurs. Tests conducted at the FAA Technical Center have 
shown the ability of aluminum wing surfaces to withstand post-crash 
fire conditions. These tests have verified adequate dissipation of heat 
across wetted aluminum fuel-tank surfaces so that localized hot spots 
do not occur, thus minimizing the threat of explosion. This inherent 
capability of aluminum to dissipate heat also allows the wing lower 
surface to retain its load-carrying characteristics during a fuel-fed 
ground fire. These properties significantly delay wing collapse and 
burn-through for a time interval that usually exceeds evacuation times. 
In addition, as an aluminum fuel tank is heated with significant 
quantities of fuel inside, fuel vapor accumulates in the ullage space, 
exceeding the upper flammability limit relatively quickly, and thus 
reducing the threat of a fuel-tank explosion prior to fuel-tank burn-
through. The service history of conventional aluminum airplanes has 
shown that fuel-tank explosions caused by ground fires have been rare 
on airplanes configured with flame arrestors in the fuel-tank vent 
lines. Fuel tanks constructed with composite materials, a new 
technology, may or may not have equivalent capability.
    Current regulations were developed and have evolved under the 
assumption that wing construction would be of aluminum materials, which 
provide inherent properties. Current regulations may not be adequate 
when applied to airplanes constructed of different materials.
    Aluminum has the following properties with respect to fuel tanks 
and fuel-fed external fires.
    Aluminum is highly thermally conductive. It readily transmits the 
heat of a fuel-fed external fire to fuel in the tank. This has the 
benefit of rapidly driving the fuel-tank ullage to exceed the upper 
flammability limit prior to burn-through of the fuel-tank skin, or 
heating of the wing upper surface above the auto-ignition temperature. 
This greatly reduces the threat of fuel-tank explosion.
    Aluminum panels at thicknesses previously used in wing lower 
surfaces of large transport-category airplanes have been fire resistant 
as defined in 14 CFR part 1, and Advisory Circular (AC) 20-135, 
``Powerplant Installation and Propulsion System Component Fire 
Protection Test Methods, Standards and Criteria.''
    The heat-absorption capacity of both aluminum and fuel prevent 
burn-through and wing collapse for a time interval that generally 
exceeds the passenger evacuation time.
    The extensive use of composite materials in the design of the 
Boeing Model 777-9 airplane wing and fuel-tank structure is considered 
a major change from conventional and traditional methods of 
construction. The applicable airworthiness regulations do not contain 
specific standards for post-crash fire-safety performance of wing and 
fuel-tank skin or structure.
    To provide the same level of safety as exists with conventional 
airplane construction, the applicant must demonstrate that the airplane 
has sufficient post-crash survivability to enable occupants to safely 
evacuate in the event that the wings are exposed to a large fuel-fed 
fire. Factors in fuel-tank survivability are the structural integrity 
of the wing and tank, flammability of the tank, burn-through resistance 
of the wing skin, and the presence of auto-ignition threats during 
exposure to a fire. The FAA assessed post-crash survival time during 
the adoption of Amendment 25-111 for fuselage burn-through protection. 
Studies conducted by and on behalf of the FAA indicated that, following 
a survivable accident, prevention of fuselage burn-through for 
approximately 5 minutes can significantly enhance survivability. (See 
report numbers DOT/FAA/AR-99/57 and DOT/FAA/AR-02/49.) Research reveals 
little benefit in requiring wing-skin design to prevent wing-skin burn-
through beyond five minutes, due to the effects of the fuel fire itself 
on the rest of the airplane. That assessment was carried out based on 
accidents involving airplanes with conventional fuel tanks, and 
considering the ability of ground personnel to rescue occupants. In 
addition, AC 20-135 indicates that, when aluminum is used for fuel 
tanks, the tank should withstand the effects of fire for 5 minutes 
without failure. Therefore, to be consistent with existing capability 
and related requirements, the applicant airplane fuel tanks must be 
capable of resisting a post-crash fire for at least 5 minutes. In 
demonstrating compliance, the applicant must address a range of fuel 
loads from minimum to maximum, as well as any other critical fuel load.
    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.

[[Page 6315]]

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.
    In addition to complying with 14 CFR part 25 regulations governing 
the fire-safety performance of the fuel tanks, wings, and nacelle, the 
Boeing Model 777-9 airplane must demonstrate acceptable post-crash 
survivability in the event the wings are exposed to a large fuel-fed 
ground fire. Boeing must demonstrate that the wing and fuel-tank design 
can endure an external fuel-fed pool fire for at least 5 minutes. This 
must be demonstrated for minimum fuel loads (not less than reserve fuel 
levels) and maximum fuel loads (maximum-range fuel quantities), and 
other identified critical fuel loads. Considerations must include fuel-
tank flammability, burn-through resistance, wing structural-strength-
retention properties, and auto-ignition threats during a ground-fire 
event for the required duration.

    Issued in Des Moines, Washington, on February 19, 2019.
Victor Wicklund,
Manager, Transport Standards Branch, Policy and Innovation Division, 
Aircraft Certification Service.
[FR Doc. 2019-03343 Filed 2-26-19; 8:45 am]
 BILLING CODE 4910-13-P