Airworthiness Directives; General Electric Company CF6 Series Turbofan Engines

DEPARTMENT OF TRANSPORTATION

14 CFR Part 39

[Docket No. 93-ANE-04]

Airworthiness Directives; General Electric Company CF6 Series

Turbofan Engines

AGENCY: Federal Aviation Administration, DOT.

ACTION: Notice of proposed rulemaking (NPRM).

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SUMMARY: This document proposes the adoption of a new airworthiness

directive (AD) that is applicable to General Electric Company (GE) CF6-

45/-50 series turbofan engines. This proposal would require

installation of a fan stator case stiffening ring assembly, and a new

stage one fan shroud. This proposal is prompted by a report of an

uncontained stage one fan blade failure, which resulted in an inflight

engine shutdown, and damage to the aircraft. The actions specified by

the proposed AD are intended to prevent an uncontained stage one fan

blade failure, which can result in an inflight engine shutdown, and

damage to the aircraft.

DATES: Comments must be received by February 10, 1994.

ADDRESSES: Submit comments in triplicate to the Federal Aviation

Administration (FAA), New England Region, Office of the Assistant Chief

Counsel, Attn: Rules Docket No. 93-ANE-04, 12 New England Executive

Park, Burlington, MA 01803-5299. Comments may be inspected at this

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

Federal holidays.

The service information referenced in the proposed rule may be

obtained from General Electric Aircraft Engines, CF6 Distribution

Clerk, room 132, 111 Merchant Street, Cincinnati, OH 45246. This

information may be examined at the FAA, New England Region, Office of

the Assistant Chief Counsel, 12 New England Executive Park, Burlington,

MA.

FOR FURTHER INFORMATION CONTACT: Robert J. Ganley, Aerospace Engineer,

Engine Certification Office, ANE-142, Engine and Propeller Directorate,

Aircraft Certification Service, FAA, New England Region, 12 New England

Executive Park, Burlington, MA 01803-5299, telephone (617) 238-7138;

fax (617) 238-7199.

SUPPLEMENTARY INFORMATION:

Comments Invited

Interested persons are invited to participate in the making of the

proposed rule 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 above. All

communications received on or before the closing date for comments,

specified above, will be considered by the Administrator before taking

action on the proposed rule. The proposals 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 rule. All

comments submitted will be available, both before and after the closing

date for comments in the Rules Docket for examination by interested

persons. A report summarizing each FAA-public contact concerned with

the substance of this proposal will be filed in the Rules Docket.

Commenters wishing the FAA to acknowledge receipt of their comments

submitted in response to this notice must submit a self-addressed,

stamped postcard on which the following statement is made: ``Comments

to Docket No. 93-ANE-04.'' The postcard will be date stamped and

returned to the commenter.

Availability of NPRMs

Any person may obtain a copy of this NPRM by submitting a request

to the FAA, New England Region, Office of the Assistant Chief Counsel,

Attn: Rules Docket No. 93-ANE-04, 12 New England Executive Park,

Burlington, MA 01803-5299.

Discussion

The Federal Aviation Administration (FAA) has received a report of

an uncontained stage one fan blade failure, attributed to excessive fan

blade tip clearance. Engines without a fan stator case stiffening ring

assembly, and a new stage one fan shroud, operate with relatively open

stage one fan blade tip clearances. Increased fan rotor vibration

occurs when the average tip clearance exceeds the maximum allowable

clearance tolerances. This increased vibration increases stresses in

the fan blade shank, which leads to cracking and subsequent blade

failure. This condition, if not corrected, could result in an

uncontained stage one fan blade failure, which can result in an

inflight engine shutdown, and damage to the aircraft.

The FAA has reviewed and approved the technical contents of GE CF6-

50 Service Bulletin (SB) No. 72-573, Revision 5, dated September 15,

1981, that describes procedures for the installation of the stiffening

ring assembly and new stage one fan shroud.

Since an unsafe condition has been identified that is likely to

exist, or develop, on other engines of this same type design, the

proposed AD would require installation of a fan stator case stiffening

ring assembly and a new stage one fan shroud, which will result in

reduced running clearances, and lower fan blade stresses. The

compliance end date of August 31, 1995, ensures timely compliance

without forced engine removals based on hardware availability. The

actions would be required to be accomplished, in accordance with the

service bulletin described previously.

There are approximately 67 GE CF6-45/-50 series turbofan engines of

the affected design in the worldwide fleet. The FAA has been advised by

the manufacturer that there are no engines on U.S. registered aircraft

that would be affected by this AD. However, should an affected engine

be imported on an aircraft and placed on the U.S. registry in the

future, it would take approximately 48 work hours to accomplish the

proposed actions, and that the average labor rate is $55 per work hour.

Required parts would cost approximately $9,360 per engine. Based on

these figures, the total cost impact of the proposed AD is estimated to

be $12,000 per engine.

The regulations proposed herein would not have substantial direct

effects on the States, on the relationship between the national

government and the States, or on the distribution of power and

responsibilities among the various levels of government. Therefore, in

accordance with Executive Order 12612, it is determined that this

proposal would not have sufficient federalism implications to warrant

the preparation of a Federalism Assessment.

For the reasons discussed above, I certify that this proposed

regulation (1) is not a ``significant regulatory action'' under

Executive Order 12886; (2) is not a ``significant rule'' under the DOT

Regulatory Policies and Procedures (44 FR 11034, February 26, 1979);

and (3) if promulgated, will not have a significant economic impact,

positive or negative, on a substantial number of small entities under

the criteria of the Regulatory Flexibility Act. A copy of the draft

regulatory evaluation prepared for this action is contained in the

Rules Docket. A copy of it may be obtained by contacting the Rules

Docket at the location provided under the caption ADDRESSES.

List of Subjects in 14 CFR Part 39

Air transportation, Aircraft, Aviation safety, Safety.

The Proposed Amendment

Accordingly, pursuant to the authority delegated to me by the

Administrator, the Federal Aviation Administration proposes to amend 14

CFR part 39 of the Federal Aviation Regulations as follows:

PART 39--AIRWORTHINESS DIRECTIVES

1. The authority citation for part 39 continues to read as follows:

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

106(g); and 14 CFR 11.89.

Sec. 39.13 [Amended]

2. Section 39.13 is amended by adding the following new

airworthiness directive:

General Electric Company: Docket No. 93-ANE-04.

Applicability: General Electric Company (GE) CF6-45/-50 series

turbofan engines installed on, but not limited to, Airbus A300

series, Boeing 747 series, and McDonnell Douglas DC-10 series

aircraft.

Compliance: Required as indicated, unless accomplished

previously.

To prevent an uncontained stage one fan blade failure, which can

result in inflight engine shutdown, and damage to the aircraft,

accomplish the following:

(a) For engines that have not been modified in accordance with

any revision level of GE CF6-50 Service Bulletin (SB) No. 72-573,

prior to the effective date of this AD, install a fan stator case

stiffening ring assembly and stage one fan shroud, in accordance

with GE CF6-50 SB No. 72-573, Revision 5, dated September 15, 1981,

by August 31, 1995.

(b) An alternative method of compliance or adjustment of the

compliance time that provides an acceptable level of safety may be

used if approved by the Manager, Engine Certification Office. The

request should be forwarded through an appropriate FAA Maintenance

Inspector, who may add comments and then send it to the Manager,

Engine Certification Office.

Note: Information concerning the existence of approved

alternative methods of compliance with this airworthiness directive,

if any, may be obtained from the Engine Certification Office.

(c) Special flight permits may be issued, in accordance with FAR

21.197 and 21.199, to operate the aircraft to a location where the

requirements of this AD can be accomplished.

Issued in Burlington, Massachusetts, on December 21, 1993.

Jay J. Pardee,

Acting Manager, Engine and Propeller Directorate, Aircraft

Certification Service.

[FR Doc. 94-589 Filed 1-10-94; 8:45 am]

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