[Federal Register Volume 64, Number 13 (Thursday, January 21, 1999)]
[Rules and Regulations]
[Pages 3201-3202]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 99-1352]



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 Rules and Regulations
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  Federal Register / Vol. 64, No. 13 / Thursday, January 21, 1999 / 
Rules and Regulations  

[[Page 3201]]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 25

[Docket No. NM151; Special Conditions No. 25-142-SC]


Special Conditions: Boeing Model 757-300 Sudden Engine Stoppage

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Final special conditions.

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SUMMARY: These special conditions are issued for the Boeing Model 757-
300 airplane. This airplane will have a novel or unusual design feature 
associated with sudden engine stoppage. 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.

EFFECTIVE DATE: January 14, 1999.

FOR FURTHER INFORMATION CONTACT: Joe Jacobsen, FAA, Standardization 
Branch, ANM-113, Transport Airplane Directorate, Aircraft Certification 
Service, 1601 Lind Avenue SW., Renton, Washington, 98055-4056; 
telephone (425) 227-2011; facsimile (425) 227-1149.

SUPPLEMENTARY INFORMATION:

Background

    On February 21, 1996, Boeing applied for an amendment to Type 
Certificate No. A2NM to include the new Model 757-300 airplane, a 
derivative of the Model 757-200 currently approved under Type 
Certificate No. A2NM. The Model 757-300 airplane is a swept wing, 
conventional tail, twin engine, turbofan powered transport. Each engine 
will be capable of delivering 43,100 pounds of thrust. The airframe has 
been strengthened to accommodate the increased design loads and 
weights. The airplane has a seating capacity of up to 295, and a 
maximum takeoff weight of 270,000 pounds (122,470 Kg).

Type Certification Basis

    Under the provisions of 14 CFR 21.101, Boeing must show that the 
Model 757-300 airplane meets the applicable provisions of the 
regulations incorporated by reference in Type Certificate No. A2NM, or 
the applicable regulations in effect on the date of application for the 
change to the Model 757-300. The regulations incorporated by reference 
in the type certificate are commonly referred to as the ``original type 
certification basis.'' The regulations incorporated by reference in 
Type Certificate No. A2NM include part 25, as amended by Amendments 25-
1 through 25-45, and certain other later amended sections of part 25 
that are not relevant to these special conditions. In addition, Boeing 
has chosen to comply with the applicable regulations in effect on 
February 21, 1996; specifically part 25 as amended by Amendments 25-1 
through 25-85 and certain other earlier amended sections of part 25 
that are not relevant to these special conditions. Three exemptions 
have been granted. These special conditions form an additional part of 
the type certification basis.
    If the Administrator finds that the applicable airworthiness 
regulations (i.e., part 25, as amended) do not contain adequate or 
appropriate safety standards for the Boeing Model 757-300 airplane 
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 Model 757-300 airplane must comply with the fuel vent 
and exhaust emission requirements of part 34, effective September 10, 
1990, plus any amendments in effect at the time of certification; and 
the noise certification requirements of part 36, effective December 1, 
1969, as amended by Amendment 36-1 through the amendment in effect at 
the time of certification.
    Special conditions, as appropriate, are issued in accordance with 
14 CFR 11.49 after public notice, as required by Secs. 11.28 and 
11.29(b), and become part of the type certification basis in accordance 
with Sec. 21.101(b)(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 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 the provisions of Sec. 21.101(a)(1).

Novel or Unusual Design Features

    The engine proposed for the Boeing Model 757-300 airplane is a 
high-bypass ratio fan jet engine that will not seize and produce 
transient torque loads in the same manner that is envisioned by current 
Sec. 25.361(b)(1) related to ``sudden engine stoppage.''

Discussion

    For the engine proposed for the Model 757-300 airplanes, the limit 
engine torque load imposed by sudden engine stoppage due to malfunction 
or structural failure (such as compressor jamming) has been a specific 
requirement for transport category airplanes since 1957. The size, 
configuration, and failure modes of jet engines has changed 
considerably from those envisioned in 14 CFR 25.361(b) when the engine 
seizure requirement was first adopted. Engines have grown much larger 
and are now designed with large bypass fans capable of producing much 
higher torque loads if they become jammed.
    Relative to the engine configuration that existed when the rule was 
developed in 1957, the present generation of engines are sufficiently 
different and novel to justify issuance of a special condition to 
establish appropriate design standards. The latest generation of jet 
engines are capable of producing engine seizure torque loads that are 
significantly higher than previous generations of engines.
    The FAA is developing a new regulation and a new advisory circular 
that will provide more comprehensive criteria for treating engine 
torque loads resulting from sudden engine stoppage. In the meantime, a 
special condition is needed to establish appropriate criteria for the 
Boeing Model 757-300 airplane.

[[Page 3202]]

Limit Engine Torque Loads for Sudden Engine Stoppage

    In order to maintain the level of safety envisioned by 
Sec. 25.361(b), more comprehensive criteria are needed for the new 
generation of high bypass engines. These special conditions distinguish 
between the more common seizure events and those rare seizure events 
resulting from structural failures in the engine. For these more rare 
but severe seizure events, the criteria would allow some deformation in 
the engine supporting structure (ultimate load design) in order to 
absorb the higher energy associated with the high bypass engines, while 
at the same time protecting the adjacent primary structure in the wing 
and fuselage by applying a higher factor of safety to the maximum 
torque load imposed by sudden engine stoppage due to a structural 
failure.

Discussion of Comments

    Notice of proposed special conditions No. 25-98-04-SC for the 
Boeing Model 757-300 airplanes was published in the Federal Register on 
December 10, 1998 (63 FR 68211). No comments were received, and the 
special conditions are adopted as proposed.

Applicability

    As discussed above, these special conditions are applicable to the 
Boeing Model 757-300. 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 under the provisions of Sec. 21.101(a)(1).
    Under standard practice, the effective date of final special 
conditions is 30 days after the date of publication in the Federal 
Register; however, as the certification date for the Boeing Model 757-
300 is imminent, the FAA finds that good cause exists to make these 
special conditions effective upon issuance.

Conclusion

    This action affects only certain novel or unusual design features 
on one model series of airplanes. It is not a rule of general 
applicability, and it affects only the applicant who 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 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 757-300 airplanes.
    1. Engine Torque Loads. In lieu of compliance with Sec. 25.361(b), 
compliance with the following special condition is proposed:
    (a) For turbine engine installations, the mounts and local 
supporting structure must be designed to withstand each of the 
following:
    (1) The maximum torque load, considered as limit, imposed by:
    (i) sudden deceleration of the engine due to a malfunction that 
could result in a temporary loss of power or thrust capability, and 
that could cause a shutdown due to vibrations; and
    (ii) the maximum acceleration of the engine.
    (2) The maximum torque load, considered as ultimate, imposed by 
sudden engine stoppage due to a structural failure, including fan blade 
failure.
    (3) The load condition defined in paragraph (a)(2) of this section 
is also assumed to act on adjacent airframe structure, such as the wing 
and fuselage. This load condition is multiplied by a factor of 1.25 to 
obtain ultimate loads when the load is applied to the adjacent wing and 
fuselage supporting structure.

    Issued in Renton, Washington, on January 14, 1999.
John J. Hickey,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service, ANM-100.
[FR Doc. 99-1352 Filed 1-20-99; 8:45 am]
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