[Federal Register Volume 76, Number 142 (Monday, July 25, 2011)]
[Rules and Regulations]
[Pages 44245-44246]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 2011-18654]





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 Rules and Regulations

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  Federal Register / Vol. 76, No. 142 / Monday, July 25, 2011 / Rules 

and Regulations  



[[Page 44245]]







DEPARTMENT OF TRANSPORTATION



Federal Aviation Administration



14 CFR Part 25



[Docket No. NM454 Special Conditions No. 25-441-SC]




Special Conditions: Gulfstream Model GVI Airplane; Limit Engine 

Torque Loads for Sudden Engine Stoppage



AGENCY: Federal Aviation Administration (FAA), DOT.



ACTION: Final special conditions.



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SUMMARY: These special conditions are for the Gulfstream GVI airplane. 

This airplane has novel or unusual design features when compared to the 

state of technology envisioned in the airworthiness standards for 

transport category airplanes. These design features include engine size 

and the potential torque load imposed by sudden engine stoppage. These 

special conditions pertain to their effects on the structural 

performance of the airplane. The applicable airworthiness regulations 

do not contain adequate or appropriate safety standards for these 

design features. 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: August 24, 2011.



FOR FURTHER INFORMATION CONTACT: Carl Niedermeyer, FAA, Airframe/Cabin 

Safety Branch, ANM-115, Transport Standards Staff, Transport Airplane 

Directorate, Aircraft Certification Service, 1601 Lind Avenue, SW., 

Renton, Washington 98057-3356; telephone (425) 227-2279; electronic 

mail [email protected].



SUPPLEMENTARY INFORMATION:



Background



    On March 29, 2005, Gulfstream Aerospace Corporation (hereafter 

referred to as ``Gulfstream'') applied for an FAA type certificate for 

its new Gulfstream Model GVI passenger airplane. Gulfstream later 

applied for, and was granted, an extension of time for the type 

certificate, which changed the effective application date to September 

28, 2006. The Gulfstream Model GVI airplane will be an all-new, two-

engine jet transport airplane with an executive cabin interior. The 

maximum takeoff weight will be 99,600 pounds, with a maximum passenger 

count of 19 passengers.



Type Certification Basis



    Under provisions of Title 14, Code of Federal Regulations (14 CFR) 

21.17, Gulfstream must show that the Gulfstream Model GVI airplane 

(hereafter referred to as ``the GVI'') meets the applicable provisions 

of 14 CFR part 25, as amended by Amendments 25-1 through 25-119, 25-

122, and 25-124. 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 GVI because of a novel 

or unusual design feature, special conditions are prescribed under the 

provisions of 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 novel or 

unusual design features, the special conditions would also apply to the 

other model under provisions of Sec.  21.101.

    In addition to complying with the applicable airworthiness 

regulations and special conditions, the GVI 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 also issue a 

finding of regulatory adequacy pursuant to 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, in 

accordance with Sec.  11.38, and they become part of the type 

certification basis under Sec.  21.17(a)(2).



Novel or Unusual Design Features



    The GVI will have high bypass engines. Engines of this size, 

configuration, and failure modes were not envisioned when Sec.  25.361, 

which addresses loads imposed by engine seizure, was adopted in 1965. 

Worst case engine seizure events have become increasingly more severe 

with increasing engine size because of the higher inertia of the 

rotating components. The GVI engines are sufficiently different and 

novel to justify issuance of a special condition to establish 

appropriate design standards.



Discussion of Special Conditions



    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 

supporting structures should remain serviceable after a limit load 

event.

    Since 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) has proposed a design standard for today's large engines. For 

the commonly-occurring deceleration events, the proposed standard would 

require engine mounts and structures to support maximum torques without 

detrimental permanent deformation. For the rare-but-severe engine 

seizure events such as loss of any fan, compressor, or



[[Page 44246]]



turbine blade, the proposed standard would require engine mounts and 

structures to support maximum torques without failure, but allows for 

some deformation in the structure.

    The FAA concludes that modern large engines, including those on the 

GVI, 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 recommended by ARAC. The 

special conditions also clarify the design criteria that apply to 

auxiliary power units.



Discussion of Comments



    Notice of proposed special conditions No. 25-11-11-SC for 

Gulfstream GVI airplanes was published in the Federal Register on May 

5, 2011 (76 FR 25648). One supportive comment was received and the 

special conditions are adopted as proposed.



Applicability



    As discussed above, these special conditions are applicable to the 

GVI. Should Gulfstream apply at a later date for a change to the type 

certificate to include another model incorporating the same novel or 

unusual design features, these special conditions would apply to that 

model as well.



Conclusion



    This action affects only certain novel or unusual design features 

of the GVI. 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



    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 Gulfstream GVI airplanes.

    The following special conditions are in lieu of Sec.  25.361(b):

    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 which 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

    (b) Separately, 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 

paragraphs 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. Any permanent deformation that results from the conditions 

specified in paragraph 3 must not prevent continued safe flight and 

landing.



    Issued in Renton, Washington, on July 18, 2011.

Ali Bahrami,

Manager, Transport Airplane Directorate, Aircraft Certification 

Service.

[FR Doc. 2011-18654 Filed 7-22-11; 8:45 am]

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