Special Conditions: Boeing Model 747-8/-8F Airplane, Additional Airframe Structural Design Requirements Related to Sudden Engine Stoppage Due to Fan Blade Failures, 15888-15889 [E9-7909]

Agencies

• Federal Aviation Administration
• DEPARTMENT OF TRANSPORTATION

[Federal Register Volume 74, Number 66 (Wednesday, April 8, 2009)]
[Proposed Rules]
[Pages 15888-15889]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: E9-7909]


========================================================================
Proposed Rules
                                                Federal Register
________________________________________________________________________

This section of the FEDERAL REGISTER contains notices to the public of 
the proposed issuance of rules and regulations. The purpose of these 
notices is to give interested persons an opportunity to participate in 
the rule making prior to the adoption of the final rules.

========================================================================


Federal Register / Vol. 74, No. 66 / Wednesday, April 8, 2009 / 
Proposed Rules

[[Page 15888]]



DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 25

[Docket No. NM399 Special Conditions No. 25-09-02-SC]


Special Conditions: Boeing Model 747-8/-8F Airplane, Additional 
Airframe Structural Design Requirements Related to Sudden Engine 
Stoppage Due to Fan Blade Failures

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Notice of proposed special conditions.

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

SUMMARY: This document proposes special conditions for the Boeing Model 
747-8/-8F 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 design 
features include larger engines with large bypass fans capable of 
producing much larger and more complex dynamic loads. 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 747-8/-8F airplanes.

DATES: Comments must be received on or before May 26, 2009.

ADDRESSES: Comments on this proposal may be mailed in duplicate to: 
Federal Aviation Administration, Transport Airplane Directorate, 
Attention: Rules Docket (ANM-113), Docket No. NM399, 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. NM399. 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: Mark Freisthler, FAA, Airframe & Cabin 
Safety Branch, ANM-115, Transport Airplane Directorate, Aircraft 
Certification Service, 1601 Lind Avenue, SW., Renton, Washington 98057-
3356; telephone (425) 227-1119; facsimile (425) 227-1149.

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 proposed 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 November 4, 2005, The Boeing Company, PO Box 3707, Seattle, WA, 
98124, applied for an amendment to Type Certificate Number A20WE to 
include the new Model 747-8 passenger airplane and the new Model 747-8F 
freighter airplane. The Model 747-8 and the Model 747-8F are 
derivatives of the 747-400 and the 747-400F, respectively. Both the 
Model 747-8 and the Model 747-8F are four-engine jet transport 
airplanes that will have a maximum takeoff weight of 970,000 pounds and 
new General Electric GEnx -2B67 engines. The Model 747-8 will have two 
flight crew and the capacity to carry 660 passengers. The Model 747-8F 
will have two flight crew and a zero passenger capacity, although 
Boeing has submitted a petition for exemption to allow the carriage of 
supernumeraries.

Type Certification Basis

    Under the provisions of 14 CFR 21.101, Boeing must show that the 
Model 747-8 and 747-8F airplanes (hereafter referred as 747-8/-8F) meet 
the applicable provisions of part 25, as amended by Amendments 25-1 
through 25-117, except for earlier amendments as agreed upon by the 
FAA. These regulations will be incorporated into Type Certificate No. 
A20WE after type certification approval of the 747-8/-8F.
    In addition, the certification basis includes other regulations, 
special conditions and exemptions that are not relevant to these 
proposed special conditions. Type Certificate No. A20WE will be updated 
to include a complete description of the certification basis for these 
model airplanes.
    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 747-8/-8F because of a novel or 
unusual design feature, special conditions are prescribed under the 
provisions of Sec.  21.16.
    In addition to the applicable airworthiness regulations and special 
conditions, the 747-8/-8F 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.
    Special conditions, as defined in Sec.  11.19, are issued under 
Sec.  11.38, and become part of the type certification basis under 
Sec.  21.101.
    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, or should any other model already 
included on the same type certificate be modified to incorporate the 
same or similar novel or unusual design feature, the special

[[Page 15889]]

conditions would also apply to the other model under Sec.  21.101.

Novel or Unusual Design Features

    The Boeing Model 747-8/-8F airplane will incorporate the following 
novel or unusual design features: high-bypass engines with a fan 
diameter approximately twelve percent greater than those currently 
installed on other Boeing Model 747 airplanes.

Discussion

    High-bypass engines with a fan diameter approximately twelve 
percent greater than those currently installed on other Boeing Model 
747 airplanes, such as the 747-400 series were not envisioned when 
Sec.  25.361 was adopted in 1965. Section 25.361 addresses loads 
imposed by engine seizure. Because of the higher inertia of the 
rotating components, worst case engine seizure events become 
increasingly more severe with increasing engine size.
    Typically the design torque loads associated with typical failure 
scenarios have been estimated by the engine manufacturer. These loads 
are used by the airframe manufacturer as limit loads. Section 25.305 
requires that supporting structure be able to support limit loads 
without detrimental permanent deformation, meaning that supporting 
structure should remain serviceable after a limit load event. Limit 
loads are expected to occur about once in the lifetime of any airplane. 
For turbine engine installations, Sec.  25.361(b)(1) requires that the 
engine mounts and supporting structures be designed to withstand a 
``limit engine torque load imposed by sudden engine stoppage due to 
malfunction or structural failure.''
    Since Sec.  25.361(b)(1) was adopted the size, configuration, and 
failure modes of turbine engines have changed significantly. Current 
engines are much larger and are designed with large bypass fans. In the 
failure event prescribed by Sec.  25.361 they produce much higher 
transient loads on the engine mounts and supporting structure than 
previous designs. At the same time, the likelihood of such an event 
occurring in modern engines has become less. The service history of 
modern turbine engines shows that engine seizures are rare events, much 
less than what is typically expected for ``limit'' loads. While it is 
important for the airplane to be able to support such rare loads safely 
without failure, it is unrealistic to expect that no permanent 
deformation will occur.
    Given this situation, the Aviation Rulemaking Advisory Committee 
(ARAC) has proposed a design standard for today's large engines. For 
the commonly occurring deceleration events, the proposed standard would 
require engine mounts and structures to support maximum torques without 
detrimental permanent deformation. For the rare-but-severe engine 
seizure events such as loss of any fan, compressor, or turbine blade, 
the proposed standard would require engine mounts and structures to 
support maximum torques without failure, but allow for some deformation 
in the structure.
    The FAA concludes that modern large engines, including those on the 
747-8/-8F, are novel and unusual compared to those envisioned when 
Sec.  25.361(b)(1) was adopted and thus warrant special conditions. 
These proposed special conditions contain design criteria recommended 
by ARAC.

Applicability

    As discussed above, these proposed special conditions are 
applicable to Boeing Model 747-8/-8F airplanes. 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 Boeing Model 747-8/-8F 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 proposed Special Conditions is as 
follows:

    Authority:  49 U.S.C. 106(g), 40113, 44701, 44702, 44704.

The Proposed Special Conditions

    Accordingly, pursuant to the authority delegated to me by the 
Administrator, the Federal Aviation Administration (FAA) proposes the 
following special conditions as part of the type certification basis 
for the 747-8/-8F airplanes.
    In lieu of Sec.  25.361(b) the following special conditions are 
proposed:
    1. For turbine engine installations, the engine mounts, pylons and 
supporting airframe primary structure (such as the affected wing and 
fuselage primary structure) must be designed to withstand 1g level 
flight loads acting simultaneously with the maximum torque load, 
considered as limit load, imposed by each of the following:
    (a) Sudden engine deceleration due to a malfunction which could 
result in a temporary loss of power or thrust; and
    (b) The maximum acceleration of the engine.
    2. For auxiliary power unit installations, the power unit mounts 
and supporting airframe primary structure (such as the affected 
fuselage primary structure) must be designed to withstand 1g level 
flight loads acting simultaneously with the maximum torque load, 
considered as limit load, imposed by each of the following:
    (a) Sudden auxiliary power unit deceleration due to malfunction or 
structural failure; and
    (b) The maximum acceleration of the power unit.
    3. For turbine engine installations, the engine mounts, pylons and 
supporting airframe primary structure (such as the affected wing and 
fuselage primary structure) must be designed to withstand 1g flight 
loads acting simultaneously with the transient dynamic loads, 
considered as ultimate load, imposed by each of the following:
    (a) Sudden engine stoppage due to the loss of any fan, compressor, 
or turbine blade; and separately
    (b) Where applicable to a specific engine design, any other engine 
structural failure that results in higher loads.
    4. The ultimate loads developed from the conditions specified in 
paragraphs 3(a) and 3(b) are to be multiplied by a factor of 1.0 when 
applied to engine mounts and pylons and multiplied by a factor of 1.25 
when applied to the supporting airframe primary structure (such as the 
affected wing and fuselage primary structure). In addition, the 
airplane must be capable of continued safe flight considering the 
aerodynamic effects on controllability due to any permanent deformation 
that results from the conditions specified in paragraph 3, above.

    Issued in Renton, Washington, on January 22, 2009.
Ali Bahrami,
Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
 [FR Doc. E9-7909 Filed 4-7-09; 8:45 am]
BILLING CODE 4910-13-P