Special Conditions; General Electric Aircraft Engines Model(s) GE90-75B/-85B/-76B Turbofan Engines

DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 33

[Docket No. 94-ANE-18; Notice No. 33-08]

Special Conditions; General Electric Aircraft Engines Model(s)

GE90-75B/-85B/-76B Turbofan Engines

AGENCY: Federal Aviation Administration, DOT.

ACTION: Notice of proposed special conditions.

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SUMMARY: This document proposes special conditions for the General

Electric (GE) Aircraft Engines Model(s) GE90-75B/-85B/-76B turbofan

engines. The Federal Aviation Administration (FAA) has determined that

the requirements of Federal Aviation Regulation (FAR) 14 CFR part 33,

including the requirements of Sec. 33.94, Blade Containment and Rotor

Unbalance Test, relative to the location of fan blade fracture for the

containment test, do not contain adequate or appropriate safety

standards for the certification of the GE90-75B/-85B/-76B turbofan

engines. This finding is based on a novel or unusual design feature of

the GE90 fan blade. Therefore, this document proposes special

conditions which the Administrator finds necessary to establish a level

of safety equivalent to that established by the airworthiness standards

of part 33 of the FAR.

DATES: Comments must be submitted on or before August 25, 1994.

ADDRESSES: Comments on this proposal may be submitted in triplicate to:

Federal Aviation Administration (FAA), New England Region, Office of

the Assistant Chief Counsel, Attn: Rules Docket No. 94-ANE-18, 12 New

England Executive Park, Burlington, Massachusetts 01803-5299. Comments

must be marked: Docket No. 94-ANE-18. Comments may be inspected at this

location between 8 a.m. and 4:30 p.m., Monday through Friday, except

Federal holidays.

FOR FURTHER INFORMATION CONTACT:

Tim Mouzakis, Engine and Propeller Standards Staff, ANE-110, Engine and

Propeller Directorate, Aircraft Certification Service, FAA, New England

Region, 12 New England Executive Park, Burlington, MA 01803-5229;

telephone (617) 238-7114; fax (617) 238-7199.

SUPPLEMENTARY INFORMATION:

Comments Invited

Interested persons are invited to participate in the making of the

proposed special conditions by submitting such written data, views, or

arguments as they may desire. Communications should identify the Rules

Docket number and be submitted in triplicate to the address specified

under ADDRESSES. All communications received on or before the closing

date for comments, specified under DATES, will be considered by the

Administrator before taking action on the proposal. The proposal

contained in this notice may be changed in light of the comments

received.

Comments are specifically invited on the overall regulatory,

economic, environmental, and energy aspects of the proposed special

conditions. All comments submitted will be available in the Rules

Docket for examination by interested persons, both before and after the

closing date for comments. A report summarizing each substantive public

contact with FAA personnel concerning this proposal will be filed in

the docket.

Commenters wishing the FAA to acknowledge receipt of their comments

submitted in response to this notice must submit with those comments a

self-addressed, stamped postcard on which the following statement is

made: ``Comments to Docket No. 94-ANE-18.'' The postcard will be date

stamped and returned to the commenter.

Background

On December 16, 1991, General Electric Aircraft Engines applied for

type certification of Model(s) GE90-75B/-85B/-76B turbofan engines.

These engines incorporate a first stage fan blade manufactured using

carbon graphite composite material. This unusual design feature results

in the GE90 fan blade having significant difference in material

property characteristics when compared to conventionally designed fan

blades using non-composite materials. For example, the probability that

a composite fan blade will fail below the inner flowpath diameter is

highly improbable, making inappropriate the requirement contained in

Sec. 33.94 paragraph (a) subparagraph (1) to show blade containment

after a failure of the blade at the outermost retention feature.

The current requirements of Sec. 33.94 are based on metallic blade

characteristics and service history and are not appropriate for the

unusual design features of the composite fan blade found on the GE90

series turbofan engines. The FAA has determined that a more realistic

blade retention test will be achieved with a fan blade failure at the

inner flowpath diameter (complete airfoil) instead of the outermost

retention feature as is currently required by Sec. 33.94 paragraph (a)

subparagraph (1).

The FAA has also determined that the composite fan blade

construction presents other factors that must be considered. Tests and

analyses must account for the effects of in-service deterioration of,

manufacturing and materials variations in, and environmental effects on

the composite material. Further, tests and analyses must show that a

lightning strike on the composite fan blade will not result in a

hazardous condition to the aircraft and that the engine will meet the

requirements of Sec. 33.75. Therefore, these Special Conditions are

proposed which define the additional requirements which the

Administrator considers necessary to establish a level of safety

equivalent to that established by the Airworthiness Standards of part

33.

Type Certification Basis

Under the provisions of Sec. 21.101, General Electric Aircraft

Engines must show that the GE Model(s) GE90-75B/-85B/-76B turbofan

engines met the requirements of the applicable regulations in effect on

the date of the application. Those Federal Aviation Regulations are

Sec. 21.21, as amended through Amendment 21-68, August 10, 1990, and

part 33, as amended through Amendment 33-14, August 10, 1990.

The Administrator finds that the applicable airworthiness

regulations in part 33, as amended, do not contain adequate or

appropriate safety standards for the GE90 series turbofan engine

because of its novel or unusual design feature. Therefore, the

Administrator proposes these special conditions under the provisions of

Sec. 21.16 to establish a level of safety equivalent to that

established in the regulations.

Special conditions, as appropriate, are issued in accordance with

Sec. 11.49 of the FAR after public notice and opportunity for comment,

as required by Sec. 11.28 and Sec. 11.29(b), and become part of the

type certification basis in accordance with Sec. 21.101 paragraph (b)

subparagraph (2).

Conclusion

This action affects only GE Model(s) GE90-75B/-85B/-76B turbofan

engines. It is not a rule of general applicability and affects only the

manufacturer who applied to the FAA for approval of these engines

containing this novel or unusual design feature.

List of Subjects in 14 CFR Part 33

Air transportation, Aircraft, Aviation safety, safety.

The authority citation for these special conditions continues to

read as follows:

Authority: 49 U.S.C. App. 1354(a), 1421, 1423; 49 U.S.C. 106(g);

14 CFR 21.16, and 14 CFR 11.28.

The Proposed Special Conditions

Accordingly, the Federal Aviation Administration (FAA) proposes the

following special conditions as part of the type certification basis

for the General Electric Aircraft Engines GE90 series turbofan engines.

(a) The following must be shown by tests and analyses, or other

methods acceptable to the Administrator, that, in lieu of the fan blade

containment test with the fan blade failing at the point specified in

Sec. 33.94 paragraph (a) subparagraph (1), a fan blade containment test

with the fan blade failing at the inner flowpart diameter demonstrates:

(1) That the disk and fan blade retention system can withstand

without failure a centrifugal load equal to two times the maximum load

which the engine could experience within approved operating

limitations, and

(2) That by a procedure approved by the Administrator an operating

limitation must be established which specifies the maximum allowable

number of start-stop stress cycles for the fan blade retention system.

The fan blade retention system includes the portion of the fan blade

from the inner flowpath diameter inward to the blade dovetail, the

blade retention components, and the fan disk and fan blade attachment

features.

(b) It must be shown that the probability of fan blade retention

system failure, for any cause, during the service life of the engine to

be extremely improbable.

(c) It must be shown by test or analysis that a lightning strike on

the composite fan blade structure will not result in a hazardous

condition, and that the engine will meet the requirements of

Sec. 33.75.

(d) The tests and analyses required by (a)(1) and (a)(2) of these

special conditions must account for the effects of in-service

deterioration, manufacturing and materials variations, and

environmental effects.

Issued in Burlington, Massachusetts, on June 28, 1994.

Ronald L. Vavruska,

Acting Manager, Engine and Propeller Directorate, Aircraft

Certification Service.

[FR Doc. 94-16678 Filed 7-8-94; 8:45 am]

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