[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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