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[Federal Register Volume 74, Number 154 (Wednesday, August 12, 2009)]
[Rules and Regulations]
[Pages 40482-40484]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: E9-19249]

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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 25

[Docket No. NM399; Special Conditions No. 25-387-SC]

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

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Final special conditions.

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SUMMARY: These special conditions are issued for Boeing Model 747-8/-8F 
airplanes. These airplanes will have a novel or unusual design 
feature(s) associated with an increased engine size when compared to 
previous model airplanes. These larger engines with larger bypass fans 
are capable of producing higher and more complex dynamic loads than 
previously experienced in older designs. 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: Effective Date: September 11, 2009.

FOR FURTHER INFORMATION CONTACT: Mark Freisthler, FAA, Airframe & Cabin

[[Page 40483]]

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:

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 Title 14 Code of Federal Regulations (14 
CFR) 21.101, Boeing must show that the Model 747-8 and 747-8F airplanes 
(hereafter referred to as the 747-8/-8F) as changed, continue to meet 
the applicable provisions of 14 CFR 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.
    If the Administrator finds that the applicable airworthiness 
regulations (i.e., 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 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, the special conditions would also apply to the 
other model under Sec.  21.101.

Novel or Unusual Design Features

    The Boeing Model 747-8/-8F airplanes 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 special conditions contain design criteria recommended by the 
ARAC.

Discussion of Comments

    Notice of proposed special conditions No. 25-09-02-SC for the 
Boeing Model 747-8 and 747-8F airplanes was published in the Federal 
Register on April 8, 2009 (74 FR 15888). No comments were received and 
the special conditions are adopted as proposed.

Applicability

    As discussed above, these 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, the special 
conditions would apply to that model as well.

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.

0
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

[[Page 40484]]

747-8/-8F airplanes. The following special conditions are in lieu of 
Sec.  25.361(b):
    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 July 29, 2009.
Ali Bahrami,
Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. E9-19249 Filed 8-11-09; 8:45 am]
BILLING CODE 4910-13-P
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