[Federal Register Volume 64, Number 184 (Thursday, September 23, 1999)]
[Rules and Regulations]
[Pages 51423-51424]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 99-24793]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 25

[Docket No. NM157; Special Conditions No. 25-149-SC]


Special Conditions: Boeing Model 767-400ER; 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 767-
400ER airplane. This airplane will have a novel or unusual design 
feature(s) 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: September 16, 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 January 14, 1997, Boeing Commercial Airplane Group applied for 
an amendment to Type Certificate No. A1NM to include the new Model 767-
400ER. The Model 767-400ER, which is a derivative of the Model 767-200/
-300 series airplanes currently approved under Type Certificate No. 
A1NM, is a swept wing, conventional-tail twin engine, turbofan-powered 
transport. The airframe has been strengthened to accommodate the 
increased design loads and weights. The airplane has a seating capacity 
of up to 375, and a maximum takeoff weight of 450,000 pounds (204,120 
Kg). Each engine will be capable of delivering 62,000 pounds of thrust. 
The flight controls are unchanged beyond those changes deemed necessary 
to accommodate the stretched configuration.

Type Certification Basis

    Under the provisions of 14 CFR 21.101, Boeing must show that the 
Model 767-400ER airplane meets the applicable provisions of the 
regulations incorporated by reference in Type Certificate No. A1NM, or 
the applicable regulations in effect on the date of application for the 
change to the Model 767-400ER. 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. A1NM include 14 CFR part 25, as 
amended by Amendments 25-1 through 25-45 with a few exceptions, 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 January 14, 1997; 
specifically part 25 as amended by Amendments 25-1 through 25-89 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 767-400ER airplane 
because of a novel or unusual design feature, special conditions are 
prescribed under the provisions of 21.16.
    In addition to the applicable airworthiness regulations and special 
conditions, the Model 767-400ER airplane must comply with the fuel vent 
and exhaust emission requirements of 14 CFR part 34, effective 
September 10, 1990, plus any amendments in effect at the time of 
certification; and the noise certification requirements of 14 CFR 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 11.28 and 11.29(b), 
and become part of the type certification basis in accordance with 
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, the special conditions would also apply to the 
other model under the provisions of 21.101(a)(1).

Novel or Unusual Design Features

    The engine proposed for the Boeing Model 767-400ER airplane will 
incorporate the unusual design feature of a high-bypass ratio fan jet 
engine that will not necessarily seize and produce transient engine 
loads in the same manner that is envisioned by current 
Sec. 25.361(b)(1) related to ``sudden engine stoppage.''

Discussion of Comments

    Notice of Proposed Special Conditions No. 25-99-05-SC for the 
Boeing Model 767-400ER airplanes was published in the Federal Register 
on May 20, 1999 (64 FR 27478). Two comments were received. One 
commenter objects to the proposed special condition because it allows 
engine support structures to be subjected to loads beyond limit loads 
in the event of sudden engine stoppage. The commenter further states 
that such a reduction in the robustness of the engine support structure 
without hard data to justify it is not appropriate. The FAA has 
reviewed the notice, and has concluded that it was not put forth in a 
manner that fully reflected the

[[Page 51424]]

improvement in safety that was intended. The existing 25.361(b) 
requires the consideration of a pure torque condition with no 
consideration of other combined loads (e.g. lateral loads) that are 
associated with engine failures. Furthermore, this pure torque load is 
treated as a simple static limit load condition without regard to any 
dynamic amplification. Then, the ultimate design load is determined by 
using a safety factor of 1.5 on the static torque load. In the past, 
the engine manufacturers estimated the pure limit torque load condition 
based on typical failure loads and provided them to the airframe 
manufacturer. These design limit loads did not necessarily reflect the 
worst possible failure condition and did not include the possible 
effects of dynamic amplification. The FAA considers that engines have 
evolved to a point that such a simplified approach, developed over 40 
years ago for the first turbojet engines, is no longer appropriate for 
modern high bypass turbofan engines. The FAA and the industry 
(including both the engine and airframe manufacturers) have continued 
to address this issue, and to refine the necessary design approach, 
since the first special conditions were issued on this subject for 
other similar airplane types. The design approach now contains a more 
rational treatment of sudden engine stoppage events. The airframe 
manufacturers had already begun to employ the improved criteria, even 
though the FAA had not updated the special condition at the time that 
Notice No. 25-99-05-SC was published.
    Another commenter, who is familiar with the more rational approach 
developed by the FAA and industry, was also concerned that it was not 
reflected in Notice No. 25-99-05-SC. This could allow an interpretation 
that would result in an inadequate level of safety. This commenter 
believes the special condition should be modified to reflect the more 
comprehensive approach that is already in practice in the industry.
    The FAA concurs with these commenters. The special condition is 
modified to reflect the more comprehensive approach associated with 
determination of the load and the method of applying it to the 
airplane. Phrases have been added to the special condition to reflect 
the transient dynamic nature of the loads and the specific types of 
failures that must be included.
    The safety factors associated with these loads remain the same as 
proposed in Notice No. 25-99-05-SC. This is justified because every 
effort is being made to develop the true ultimate transient load time 
history from actual tests of the most extreme conditions of operation 
and with the most severe failures, such as the blade failure tests 
required under 14 CFR 33.94 ``Blade containment and rotor unbalance 
tests.'' The derived loads include all aspects of the transient load, 
including torque and lateral load time histories. This transient 
loading is then applied to the engine mounts, pylon, and airframe 
structure in a comprehensive dynamic analysis.
    The application of this revised special condition will not be an 
undue burden for Boeing since, on their own initiative, they have used 
the more rational criteria in designing the Model 767-400ER.

Applicability

    As discussed above, these special conditions are applicable to the 
Boeing Model 767-400ER. 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 would be 30 days after the date of publication in the 
Federal Register; however, as the certification date for the Boeing 
Model 767-400ER 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 airplane model. 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 767-400ER airplanes.
    1. Engine Failure Loads. In lieu of compliance with Sec. 25.361(b), 
the following special condition applies:
    a. For turbine engine installations, the engine mounts, pylons and 
adjacent supporting airframe structure must be designed to withstand 1g 
level flight loads acting simultaneously with the maximum limit torque 
loads imposed by each of the following:
    (1) Sudden engine deceleration due to a malfunction which could 
result in a temporary loss of power or thrust,
    (2) The maximum acceleration of the engine.
    b. For auxiliary power unit installations, the power unit mounts 
and adjacent supporting airframe structure must be designed to 
withstand 1g level flight loads acting simultaneously with the maximum 
limit torque loads imposed by each of the following:
    (1) Sudden auxiliary power unit deceleration due to malfunction or 
structural failure; and
    (2) The maximum acceleration of the power unit.
    c. For engine supporting structure, an ultimate loading condition 
must be considered that combines 1g flight loads with the transient 
dynamic loads resulting from:
    (1) The loss of any fan, compressor, or turbine blade; and 
separately
    (2) Where applicable to a specific engine design, any other engine 
structural failure that results in higher loads.
    d. The ultimate loads developed from the conditions specified in 
paragraphs (c)(1) and (c)(2) 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 adjacent supporting airframe structure.

    Issued in Renton, Washington on September 16, 1999.
Vi L. Lipski,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service, ANM-100.
[FR Doc. 99-24793 Filed 9-22-99; 8:45 am]
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