00-29940. Airworthiness Directives; General Electric Company (GE) CF6-50 Turbofan Engines

AGENCY:

Federal Aviation Administration, DOT.

ACTION:

Notice of proposed rulemaking (NPRM).

SUMMARY:

This amendment proposes the adoption of a new airworthiness directive (AD) that applies to GE CF6-50 turbofan engines. This proposal would require removal of old high pressure compressor (HPC) air ducts and mating hardware and replacement with newly designed air ducts and reworked mating hardware. This proposal is prompted by reports of an uncontained low pressure turbine (LPT) disk failure that resulted from an air duct failure that caused a fan mid shaft (FMS) separation. The actions specified by the proposed AD are intended to prevent HPC air duct failures that could result in FMS failures, that in turn could result in rejected takeoffs or uncontained LPT events.

DATES:

The FAA must receive comments on this proposal by January 23, 2001.

ADDRESSES:

Submit comments to Docket No. 2000-NE-30-AD in one of the following ways:

Mail comments to the Federal Aviation Administration (FAA), Office of the Regional Counsel, New England Region, Attention: Rules Docket No. 2000-NE-30-AD, 12 New England Executive Park, Burlington, MA 01803-5299. You may also send a request for a copy of the proposal or regulatory evaluation from that address. If you want us to acknowledge receipt of your comments, you must include a self-addressed, stamped postcard on which the Docket No. is written. We will date-stamp your postcard and mail it back to you. OR

E-mail comments to [e-mail]. You must include Docket No. 2000-NE-30-AD in the subject line.

You can get the service information referenced in this proposal from General Electric Company via Lockheed Martin Technology Services, 10525 Chester Road, Suite C, Cincinnati, Ohio 45215, telephone: [phone]; fax: [phone]. You may examine the AD docket (including any comments and service information) at the FAA, New England Region, Office of the Regional Counsel, 12 New England Executive Park, Burlington, MA between 8:00 a.m. and 4:30 p.m., Monday through Friday, except Federal holidays. You may also examine the service information at the Office of the Federal Register, 800 North Capitol Street, NW., suite 700, Washington, DC.

FOR FURTHER INFORMATION CONTACT:

Karen Curtis, Aerospace Engineer, Engine Certification Office, FAA, Engine and Propeller Directorate, 12 New England Executive Park, Burlington, MA 01803-5299; telephone: [phone], fax: [phone].

SUPPLEMENTARY INFORMATION:

Comments Invited

You are invited to participate in the proposed rule making by submitting written data, views, or arguments as you may desire. Your communications should identify the Rules Docket number and be sent to the address specified above. All communications received on or before the closing date for comments, specified above, will be considered before we take action on the proposed rule. The proposals contained in this action 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 sent 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 action must send a self-addressed, stamped postcard on which the following statement is made: “Comments to Docket Number 2000-NE-30-AD.” The postcard will be date stamped and returned to the commenter.

Availability of NPRM's

Any person may obtain a copy of this NPRM by submitting a request to the FAA, New England Region, Office of the Regional Counsel, Attention: Rules Docket No. 2000-NE-30-AD, 12 New England Executive Park, Burlington, MA 01803-5299.

Discussion

The FAA was recently made aware of a CF6-50 engine installed on a Boeing 747 airplane that experienced an uncontained LPT disk failure caused by an HPC air duct failure, which resulted in a FMS separation. This was the first documented air duct failure that has resulted in a disk separation. There have been 51 occurrences of air duct cracking, six of which have resulted in fan mid shaft (FMS) separation, and two of which have resulted in partial rupture of the HPC stage 14-bolted joint. All six FMS separations have also resulted in uncontained LPT blade failures. Although air duct failures were first documented in 1976, two subsequent redesigns have failed to correct the cracking problem.

The FAA has reviewed General Electric Aircraft Engines Service Bulletin (SB) CF6-50 72-1200, dated May 8, 2000; General Electric Aircraft Engines Alert Service Bulletin (ASB) CF6-50 72-A1200, Revision 1, dated July 20, 2000; and Revision 2, dated November 2, 2000 which describe procedures for removal of the HPC air duct assembly part number 99128M36G03/G04/G05/G06/G08/G20/G21 or 1644M16G03 and mating hardware (rear shaft or 11-14 spool shaft) and replace with the new design air duct and reworked mating hardware.

Proposed Actions

Since an unsafe condition has been identified that is likely to exist or develop on other products of this same type design, the proposed AD would require removal of old HPC air ducts and mating hardware and replacement with newly designed air ducts and reworked mating hardware. This proposal is prompted by reports of an uncontained LPT disk failure that resulted from an air duct failure that caused a FMS separation. The FAA is proposing this AD to prevent HPC air duct failures that could result in FMS failures that in turn could result in rejected takeoffs or uncontained LPT events.

Economic Impact

There are about 1730 engines of the affected design in the worldwide fleet. The FAA estimates that 469 engines installed on aircraft of U.S. registry would be affected by this proposed AD, that it would take about 70 work hours per engine to disassemble and reassemble the HPC module, that it would take 19 hours to rework the mating hardware and that the average labor rate is $60 per work hour. Each new air duct assembly will cost $32,985. Based on these figures, the total proposed AD cost impact on U.S. operators is estimated to be $17,974,425.

Regulatory Impact

This proposal does not have federalism implications, as defined in Executive Order 13132, because it would not have a substantial direct effect 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. Accordingly, the FAA has not consulted with state authorities prior to publication of this proposal.

For the reasons discussed above, I certify that this proposed regulation (1) is not a “significant regulatory action” under Executive Order 12866; (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 part 39 of the Federal Aviation Regulations (14 CFR part 39) as follows:

PART 39—AIRWORTHINESS DIRECTIVES

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

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

§ 39.13

[Amended]

2. Section 39.13 is amended by adding the following new airworthiness directive:

General Electric Company: Docket No. 2000-NE-30-AD.

Applicability: This airworthiness directive (AD) is applicable to CF6-50 turbofan engines with high pressure compressor (HPC) rotor air duct assemblies P/N's 9128M36G03/G04/G05/G06/G08/G20/G21, or 1644M16G03 installed. These engines are installed on but not limited to Boeing 747, Airbus A300, and McDonnell Douglas DC10 airplanes.

Note 1:

This AD applies to each engine identified in the preceding applicability provision, regardless of whether it has been modified, altered, or repaired in the area subject to the requirements of this AD. For engines that have been modified, altered, or repaired so that the performance of the requirements of this AD is affected, the owner/operator must request approval for an alternative method of compliance in accordance with paragraph (c) of this AD. The request should include an assessment of the effect of the modification, alteration, or repair on the unsafe condition addressed by this AD; and, if the unsafe condition has not been eliminated, the request should include specific proposed actions to address it.

Compliance: Required as indicated, unless accomplished previously.

To prevent HPC air duct failures that could result in fan mid shaft (FMS) failures and uncontained LPT events, accomplish the following:

(a) At next HPC rotor exposure, remove the HPC air duct assembly part number 99128M36G03/G04/G05/G06/G08/G20/G21 or 1644M16G03 and mating hardware (rear shaft or 11-14 spool shaft) and replace with the new design air duct and reworked mating hardware in accordance with the accomplishment instructions of General Electric Aircraft Engines Service Bulletin (SB) CF6-50 72-1200, dated May 8, 2000; General Electric Aircraft Engines Alert Service Bulletin (ASB) CF6-50 72-A1200, Revision 1, dated July 20, 2000; or General Electric Aircraft Engines Alert Service Bulletin (ASB) CF6-50 72-A1200, Revision 2, dated November 2, 2000.

(b) For the purposes of this proposal, HPC rotor exposure is defined as disassembly of the HPC stage 2 disk flange or removal of the HPC stage 1 disk.

Alternative Methods of Compliance

(c) 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 (ECO). Operators shall submit their request through an appropriate Federal Aviation Administration (FAA) Principal Maintenance Inspector, who may add comments and then send it to the Manager, ECO.

Note 2:

Information concerning the existence of approved alternative methods of compliance with this airworthiness directive, if any, may be obtained from the ECO.

Issued in Burlington, Massachusetts, November 15, 2000.

Robert Mann,

Acting Manager, Engine and Propeller Directorate, Aircraft Certification Service.