Special Conditions: Airbus Model A380-800 Airplane, Transient Engine Failure Loads, 61869-61871 [E6-17534]

Agencies

• Federal Aviation Administration
• DEPARTMENT OF TRANSPORTATION

[Federal Register Volume 71, Number 203 (Friday, October 20, 2006)]
[Rules and Regulations]
[Pages 61869-61871]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: E6-17534]



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Federal Register / Vol. 71, No. 203 / Friday, October 20, 2006 / 
Rules and Regulations

[[Page 61869]]



DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 25

[Docket No. NM322; Special Condition No. 25-333-SC]


Special Conditions: Airbus Model A380-800 Airplane, Transient 
Engine Failure Loads

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Final special conditions.

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SUMMARY: These special conditions are issued for the Airbus A380-800 
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. Some of these novel or 
unusual design features are associated with the high bypass engines 
used on the Model A380. For these design features, the applicable 
airworthiness regulations do not contain adequate or appropriate safety 
standards regarding transient engine failure 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 Airbus Model A380-800 airplane.

DATES: Effective Date: The effective date of these special conditions 
is October 6, 2006.

FOR FURTHER INFORMATION CONTACT: Holly Thorson, FAA, International 
Branch, ANM-116, Transport Airplane Directorate, Aircraft Certification 
Service, 1601 Lind Avenue, SW., Renton, Washington 98055-4056; 
telephone (425) 227-1357; facsimile (425) 227-1149.

SUPPLEMENTARY INFORMATION:

Background

    Airbus applied for FAA certification/validation of the 
provisionally-designated Model A3XX-100 in its letter AI/L 810.0223/98, 
dated August 12, 1998, to the FAA. Application for certification by the 
Joint Aviation Authorities (JAA) of Europe had been made on January 16, 
1998, reference AI/L 810.0019/98. In its letter to the FAA, Airbus 
requested an extension to the 5-year period for type certification in 
accordance with 14 CFR 21.17(c).
    The request was for an extension to a 7-year period, using the date 
of the initial application letter to the JAA as the reference date. The 
reason given by Airbus for the request for extension is related to the 
technical challenge, complexity, and the number of new and novel 
features on the airplane. On November 12, 1998, the Manager, Aircraft 
Engineering Division, AIR-100, granted Airbus' request for the 7-year 
period, based on the date of application to the JAA.
    In its letter AI/LE-A 828.0040/99 Issue 3, dated July 20, 2001, 
Airbus stated that its target date for type certification of the Model 
A380-800 had been moved from May 2005, to January 2006, to match the 
delivery date of the first production airplane. In a subsequent letter 
(AI/L 810.0223/98 issue 3, dated January 27, 2006), Airbus stated that 
its target date for type certification is October 2, 2006. In 
accordance with 14 CFR 21.17(d)(2), Airbus chose a new application date 
of December 20, 1999, and requested that the 7-year certification 
period which had already been approved be continued. The FAA has 
reviewed the part 25 certification basis for the Model A380-800 
airplane, and no changes are required based on the new application 
date.
    The Model A380-800 airplane will be an all-new, four-engine jet 
transport airplane with a full-length double-deck, two-aisle cabin. The 
maximum takeoff weight will be 1.235 million pounds with a typical 
three-class layout of 555 passengers.

Type Certification Basis

    Under the provisions of 14 CFR 21.17, Airbus must show that the 
Model A380-800 airplane meets the applicable provisions of 14 CFR part 
25, as amended by Amendments 25-1 through 25-98. If the Administrator 
finds that the applicable airworthiness regulations do not contain 
adequate or appropriate safety standards for the Airbus A380-800 
airplane because of novel or unusual design features, special 
conditions are prescribed under the provisions of 14 CFR 21.16.
    In addition to the applicable airworthiness regulations and special 
conditions, the Airbus Model A380-800 airplane 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. In addition, the 
FAA must issue a finding of regulatory adequacy pursuant to section 611 
of Public Law 93-574, the ``Noise Control Act of 1972.''
    Special conditions, as defined in 14 CFR 11.19, are issued in 
accordance with 14 CFR 11.38 and become part of the type certification 
basis in accordance with 14 CFR 21.17(a)(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, the special conditions would also apply to the 
other model under the provisions of 14 CFR 21.101.

Discussion of Novel or Unusual Design Features

    The Model A380 will have very large high bypass ratio engines with 
110 inch diameter bypass fans, representing the latest in a trend 
toward increasing engine size. Engines of this size were not envisioned 
when Sec.  25.361--pertaining to loads imposed by engine seizure--was 
adopted in 1965. Worst case engine seizure events become increasingly 
more severe with increasing engine size because of the higher inertia 
of the rotating components.
    Section 25.361(b)(1) requires that for turbine engine 
installations, the engine mounts and the supporting structures must be 
designed to withstand a ``limit engine torque load imposed by sudden 
engine stoppage due to malfunction or structural failure.'' Limit loads 
are expected to occur about once in the lifetime of any airplane. 
Section 25.305 requires that supporting structures be able to support 
limit loads without detrimental permanent deformation, meaning that the 
supporting structures

[[Page 61870]]

should remain serviceable after a limit load event.
    Since the adoption of Sec.  25.361(b)(1), the size, configuration, 
and failure modes of jet engines have changed considerably. Current 
engines are much larger and are designed with large bypass fans. In the 
event of a structural failure, these engines are capable of producing 
much higher transient loads on the engine mounts and supporting 
structures.
    As a result, modern high bypass engines are subject to certain 
rare-but-severe engine seizure events. Service history shows that such 
events occur far less frequently than limit load events. Although 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) \1\ has proposed a design standard for today's large engines. 
For the commonly-occurring deceleration events, the proposed standard 
requires engine mounts and structures to support maximum torques 
without detrimental permanent deformation. For the rare-but-severe 
engine seizure events (i.e., loss of any fan, compressor, or turbine 
blade), the proposed standard requires engine mounts and structures to 
support maximum torques without failure, but allows for some 
deformation in the structure.
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    \1\ Industry members of the ARAC group included Embraer, 
Dassault Aviation, Airbus, Gulfstream, Lockheed Martin, Boeing, 
Cessna, Bombardier, Raytheon, Rolls Royce, Pratt & Whitney, and 
General Electric. In addition to the FAA, aviation authorities 
included CAA-UK, Transport Canada, DGAC-France, CTA-Brazil, and CAA-
Netherlands.
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    The FAA concludes that modern large engines, including those on the 
Model A380, are novel and unusual compared to those envisioned when 
Sec.  25.361(b)(1) was adopted and thus warrant special conditions. The 
special conditions contain design criteria, as recommended by the ARAC.
    The ARAC proposal would revise the wording of Sec.  25.361(b), 
including Sec. Sec.  25.361(b)(1) and (b)(2), removing the language 
pertaining to structural failures and moving it to a separate 
requirement that discusses the reduced factors of safety that apply to 
these failures. The revised wording of Sec.  25.361(b) would also 
include non-substantive changes recommended by ARAC to clarify the 
existing requirement. The FAA is using this ARAC text in these special 
conditions, because it clarifies the supplementary conditions for 
engine torque.

Discussion of Comments

    Notice of Proposed Special Conditions No. 25-05-17-SC, pertaining 
to transient engine failure loads, was published in the Federal 
Register on August 9, 2005 (70 FR 46104). Comments were received from 
the Boeing Company and the Airline Pilots Association (ALPA).
    Requested change 1: The Boeing Company recommends that the proposed 
special conditions be withdrawn, for the following reasons:
    (1) The engines on the Model A380 are not novel or unusual design 
features, and
    (2) The proposed special conditions would provide a level of safety 
greater than that established by the regulations, rather than an 
equivalent level as safety, as specified by Sec.  21.16.
    Specifically, Boeing states the following:
    ``These proposed Special Conditions address transient engine loads 
resulting from sudden engine stoppage, because of the large size of the 
engines being used on the Model A380. The FAA references a report 
submitted by the Aviation Rulemaking Advisory Committee (ARAC) that 
addresses design standards for large engines and contains suggested 
associated regulatory changes. The FAA has taken the ARAC-proposed 
regulations and has applied them, essentially verbatim, to the Model 
A380 as Special Conditions.
    ``We consider this `general rulemaking by Special Conditions.' The 
engines on the Model A380 are not novel or unusual compared to other 
large engines used on other large transports.
    ``In addition, 14 CFR Sec.  25.361 already contains engine torque 
standards. Section 21.16 enables the FAA to issue special conditions 
``to establish a level of safety equivalent to that established in the 
regulations.'' It does not authorize the FAA to issue special 
conditions to upgrade a level of safety already in the regulations.
    ``In sum, we believe the FAA has failed to comply with two 
necessary conditions for the issuance of a Special Condition, and the 
proposal should be withdrawn.''
    FAA response: The FAA does not agree with this comment. The 
regulation that specifies design criteria pertaining to engine torque 
effects resulting from sudden engine stoppage was developed in 1957 (as 
Civil Aviation Regulations (CAR) 4b.216(a)(4), Amendment 4b-6). In 1964 
the regulation was recodified as 14 CFR 25.361. The design criteria 
were developed for turbojet and low by-pass ratio turbofan engines.
    The new large high-bypass ratio turbofan engines being developed 
for the Model A380 have very large fans that produce failure modes and 
torque loads that were not envisioned when the regulatory design 
criteria were developed. The FAA has determined that this new 
generation of large high-bypass turbofan engines is sufficiently 
different from engines envisioned in 1957 as to justify issuance of 
special conditions to establish appropriate design standards. The 
design standards in these special conditions provide a level of safety 
for large high by-pass turbofan engines equivalent to that which the 
current regulations provide for turbojet or low-bypass ratio turbofan 
engines.
    The fact that the special conditions consist of draft regulations 
proposed by ARAC is not relevant to their suitability or 
appropriateness in this circumstance. The FAA considers the regulations 
proposed by ARAC to be acceptable for addressing the effects of sudden 
engine torque for large high-bypass turbofan engines and has issued 
similar special conditions for other airplane models. Section 21.16 
requires the Administrator to issue special conditions in this 
circumstance and does not restrict her from using language contained in 
the ARAC-proposed regulations.
    Requested change 2: The Airline Pilots Association (ALPA) supports 
the intent of the special conditions, as proposed, but offers the 
following comment:
    ``The subject special condition does not address potentially 
serious aerodynamic effects resulting from a total engine failure and 
seizure. Engine seizure could introduce engine support structure 
deformation that may ultimately affect the aerodynamics of the 
airframe. The special conditions should require some sort of analysis 
to ensure that any drag changes due to a seized engine will not 
adversely affect the support structures of the aerodynamics such that 
safe operation of the aircraft is degraded.''
    FAA response: The FAA agrees. Although not specifically stated, it 
was the intent of the proposed special condition that the airplane be 
capable of continued safe flight after the load conditions specified in 
b.1. Accordingly, the FAA has revised the final special conditions to 
clarify this point.

Applicability

    As discussed above, these special conditions are applicable to the 
Airbus A380-800 airplane. Should Airbus apply at a later date for a 
change to the type certificate to include another model incorporating 
the same novel or

[[Page 61871]]

unusual design features, these 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 Airbus A380-800 airplane. 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 special conditions is as follows:

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

The Special Conditions

0
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 Airbus A380-800 airplane.
    a. In lieu of compliance with Sec.  25.361(b), the following 
special condition applies:
    For turbine engine installations, the engine mounts, pylons, and 
adjacent supporting airframe structure must be designed to withstand 1 
g 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; and
    2. The maximum acceleration of the engine.
    b. In addition to the requirements of 14 CFR part 25, the following 
special condition applies:
    1. For engine supporting structure, an ultimate loading condition 
must be considered that combines 1 g flight loads with the transient 
dynamic loads resulting from:
    (a) The loss of any fan, compressor, or turbine blade; and
    (b) Separately, where applicable to a specific engine design, any 
other engine structural failure that results in higher loads.
    2. The ultimate loads developed from the conditions specified in 
paragraph b.1. above are to be:
    (a) Multiplied by a factor of 1.0 when applied to engine mounts and 
pylons; and
    (b) Multiplied by a factor of 1.25 when applied to adjacent 
supporting airframe structure.
    3. The airplane must be capable of continued safe flight 
considering the aerodynamic effects on controllability due to any 
permanent deformation that results form the conditions specified in 
b.1.

    Issued in Renton, Washington, on October 6, 2006.
Kalene C. Yanamura,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. E6-17534 Filed 10-19-06; 8:45 am]
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