
[Federal Register Volume 79, Number 152 (Thursday, August 7, 2014)]
[Rules and Regulations]
[Pages 46169-46170]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: 2014-18657]



[[Page 46169]]

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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 25

[Docket No. FAA-2013-0897; Special Conditions No. 25-523-SC]


Special Conditions: Airbus Model A350-900 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 Airbus Model A350-900 
airplanes. These airplanes will have a novel or unusual design feature 
associated with the new generation of high-bypass engines and the 
potential loads resulting from extreme engine-failure conditions.
    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 8, 2014.

FOR FURTHER INFORMATION CONTACT: Todd Martin, FAA, Airframe and Cabin 
Safety Branch, ANM-115, Transport Airplane Directorate, Aircraft 
Certification Service, 1601 Lind Avenue SW., Renton, Washington 98057-
3356; telephone (425) 227-1178; facsimile (425) 227-1320.

SUPPLEMENTARY INFORMATION: 

Background

    On August 25, 2008, Airbus applied for a type certificate for their 
new Model A350-900 airplane. Later, Airbus requested, and the FAA 
approved, an extension to the application for FAA type certification to 
November 15, 2009. The Model A350-900 airplane has a conventional 
layout with twin wing-mounted Rolls-Royce Trent XWB engines. It 
features a twin-aisle, 9-abreast, economy-class layout, and 
accommodates side-by-side placement of LD-3 containers in the cargo 
compartment. The basic Model A350-900 airplane configuration 
accommodates 315 passengers in a standard two-class arrangement. The 
design cruise speed is Mach 0.85 with a maximum take-off weight of 
602,000 lbs.
    The existing regulations are inadequate because the new, large-
bypass fan engines of the Model A350-900 airplanes can cause more 
damage in a failure event than could the previous engines. To maintain 
the level of safety envisioned by Title 14, Code of Federal Regulations 
(14 CFR) 25.61(b), more comprehensive criteria are needed for the new 
generation of high-bypass engines. The more severe events resulting 
from extreme engine-failure conditions would be treated as dynamic-load 
conditions. The special conditions would distinguish between the more 
common engine-failure events and those rare events resulting from 
structural failures. The more common events would continue to be 
treated as static torque-limit load conditions. The severe events would 
be considered ultimate loads, and include all transient loads 
associated with the event. An additional safety factor would be applied 
to the more critical airframe supporting structure.

Type Certification Basis

    Under 14 CFR 21.17, Airbus must show that the Model A350-900 
airplane meets the applicable provisions of 14 CFR part 25, as amended 
by Amendments 25-1 through 25-129.
    If the Administrator finds that the applicable airworthiness 
regulations (i.e., 14 CFR part 25) do not contain adequate or 
appropriate safety standards for the Model A350-900 airplane airplane 
because of a novel or unusual design feature, special conditions are 
prescribed under Sec.  21.16.
    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 or similar 
novel or unusual design feature, the special conditions would also 
apply to the other model under Sec.  21.101.
    In addition to the applicable airworthiness regulations and special 
conditions, the Model A350-900 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. The FAA must issue a 
finding of regulatory adequacy under section 611 of Public Law 92-574, 
the ``Noise Control Act of 1972.''
    The FAA issues special conditions, as defined in 14 CFR 11.19, 
under Sec.  11.38, and they become part of the type-certification basis 
under Sec.  21.17(a)(2).

Novel or Unusual Design Features

    The Model A350-900 airplane will incorporate the following novel or 
unusual design features: engines with large-bypass fans capable of 
producing much higher failure loads than previous engines. The Model 
A350-900 airplane will therefore require additional dynamic-load 
analyses to assess the most severe engine-failure events. The loads 
resulting from these conditions would be considered as ultimate loads, 
with an additional safety factor applied to the airframe supporting 
structure.

Discussion

    The size, configuration, and failure modes of jet engines has 
changed considerably from those envisioned by 14 CFR 25.361(b) when the 
engine-seizure requirement was first adopted. Engines have become 
larger and are now designed with large-bypass fans capable of producing 
much higher failure loads. Relative to the engine configurations that 
existed when the rule was developed in 1957, the present generation of 
engines are sufficiently different and novel to justify special 
conditions for Model A350-900 airplanes. Service history has shown that 
the engine-failure events that tend to cause the most severe loads are 
fan-blade failures, and these events occur much less frequently than 
the typical ``limit'' load condition.
    The regulatory authorities and industry developed a standardized 
requirement in the Aviation Rulemaking Advisory Committee (ARAC) forum. 
The technical aspects of this requirement have been agreed upon and 
have been accepted by the ARAC Loads and Dynamics Harmonization Working 
Group. These special conditions reflect the ARAC recommendation and are 
essentially harmonized with the corresponding European Aviation Safety 
Agency (EASA) Certification Specifications (CS) 25. In addition, the 
ARAC recommendation includes corresponding advisory material that is 
incorporated in CS-25. This advisory material is considered an 
acceptable means of compliance to the special conditions.
    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.

Discussion of Comments

    Notice of proposed special conditions no. 25-13-29-SC for Airbus 
Model A350-900 airplanes was published in the Federal Register on 
November 12, 2013 (78 FR 67323). No substantive comments were received, 
and the special conditions are adopted as proposed.

[[Page 46170]]

Applicability

    As discussed above, these special conditions apply to the Airbus 
Model A350-900 airplanes. Should Airbus apply later for a change to the 
type certificate to include another model incorporating the same novel 
or unusual design feature, the special conditions would apply to that 
model as well.

Conclusion

    This action affects only certain novel or unusual design features 
on the Model A350-900 airplanes. 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 Airbus Model A350-900 airplanes.
    In lieu of Sec.  25.361(b), the following special conditions apply:
    1. 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:
    a. Sudden engine deceleration due to a malfunction that 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 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:
    a. Sudden auxiliary power-unit deceleration due to malfunction or 
structural failure, and
    b. the maximum acceleration of the power unit.
    3. For engine-supporting structure, an ultimate loading condition 
must be considered that combines 1g flight loads with the transient 
dynamic loads resulting from:
    a. 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 
special conditions 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 adjacent supporting airframe structure.
    5. 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 
special condition 3.

    Issued in Renton, Washington, on July 15, 2014.
John P. Piccola, Jr.,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 2014-18657 Filed 8-6-14; 8:45 am]
BILLING CODE 4910-13-P


