01-24274. Airworthiness Directives; General Electric Company GE90 Series Turbofan Engines

AGENCY:

Federal Aviation Administration, DOT.

ACTION:

Notice of proposed rulemaking (NPRM).

SUMMARY:

The Federal Aviation Administration (FAA) proposes to adopt a new airworthiness directive (AD) that is applicable to General Electric Company (GE) GE90 series turbofan engines. This proposal would require removing from service high pressure turbine (HPT) interstage seals, identified by GE as the pre-life-improved rotor (pre-LIR) configuration, and installing a new design, identified by GE as the life improved rotor (LIR) configuration seal. This proposal would also require a new lower life limit for the LIR configuration seal. This proposal is prompted by an uncontained engine failure which occured during a factory development engine ground test. The actions specified by the proposed AD are intended to prevent failure of the HPT interstage seal that could result in an uncontained engine failure and damage to the airplane.

DATES:

Comments must be received by November 26, 2001.

ADDRESSES:

Submit comments in triplicate to the Federal Aviation Administration (FAA), New England Region, Office of the Regional Counsel, Attention: Rules Docket No.2001-NE-32-AD, 12 New England Executive Park, Burlington, MA 01803-5299. Comments may also be sent via the Internet using the following address: [e-mail] Comments sent via the Internet must contain the docket number in the subject line. Comments may be inspected at this location between 8:00 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 Company via Lockheed Martin Technology Services, 10525 Chester Road, Suite C, Cincinnati, OH 45215; telephone: [phone], fax: [phone]. This information may be examined at the FAA, New England Region, Office of the Regional Counsel, 12 New England Executive Park, Burlington, MA.

FOR FURTHER INFORMATION CONTACT:

John E. Golinski, Aerospace Engineer, Engine Certification Office, FAA, Engine and PropellerDirectorate, 12 New England Executive Park, Burlington, MA 01803-5299; telephone: [phone]; fax: [phone].

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 before taking 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 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 action must submit a self-addressed, stamped postcard on which the following statement is made: “Comments to Docket Number 2001-NE-32-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. 2001-NE-32-AD, 12 New England Executive Park, Burlington, MA 01803-5299.

Discussion

In September, 2000 a GE90 factory development engine experienced an uncontained failure of the HPT interstage seal during an engineering ground test. The failure occurred on the current configuration HPT interstage seal, identified as the LIR configuration. The LIR configuration HPT interstage seal was introduced as part of an HPT product improvement package. The earlier production configuration HPT interstage seal, identified as the pre-LIR interstage seal, part numbers (P/N's) are 1711M20P08, 1711M20P14, 1711M20P16, and 1711M20P17. The LIR HPT interstage seal P/N is 1847M96P02.

GE initiated an investigation to understand the root cause of the failure and to define the necessary field containment and corrective actions. As part of the investigation GE initiated inspections on pre-LIR and LIR HPT interstage seals that would provide additional data to support the failure investigation and assist in the determination of the necessary field containment actions. These inspections identified four pre-LIR interstage seals and one LIR interstage seal that had confirmed cracks.

The failure investigation consisted of analysis and testing to identify the failure modes of the pre-LIR and LIR HPT interstage seals. In addition, GE instituted an on-wing inspection program of pre-LIR seals to acquire additional data to support the investigation. To prevent pre-LIR HPT interstage seal failures, GE issued a service bulletin that removes pre-LIR HPT interstage seals from service and replaces them with improved LIR HPT interstage seals that are not susceptible to the same failure modes. This AD proposes scheduled replacement of pre-LIR HPT interstage seals.

As a result of the root cause investigation into the failure of the LIR HPT interstage seal and the investigation of the cracked HPT seals identified by the inspection program, GE determined the root cause of the cracks in the forward retainer tip area of the LIR HPT interstage seal were attributed to exposure to higher than anticipated operating temperatures. This causes a reduction of the low cycle fatigue properties of the material in this local area, which results in crack initiation. Analysis concludes that a reduction of the life limit for the LIR HPT interstage seal P/N 1847M96P02 is required. GE is in the process of incorporating design enhancements that will provide improved cooling in the forward retainer tip area that may allow for a life limit increase at some future date. This condition, if not corrected, could result in failure of the HPT interstage seal, uncontained engine failure, and damage to the airplane.

FAA's Determination of an Unsafe Condition and Proposed Actions

Since an unsafe condition has been identified that is likely to exist or develop on other GE90 series turbofan engines of the same type design, the proposed AD would require scheduled replacement of HPT interstage seal P/N's 1711M20P08, 1711M20P14, 1711M20P16, and 1711M20P17 with a serviceable HPT interstage seal. This proposed AD would also establish a new, lower life limit of 3,500 cycles-since-new for HPT interstage seal P/N 1847M96P02. The actions would be required to be accomplished in accordance with the service bulletin described previously.

Economic Analysis

There are approximately 232 GE90-76B, -77B, -85B, -90B, and -94B series turbofan engines of the affected design in the worldwide fleet. The FAA estimates that 36 engines installed on airplanes of U.S. registry, with one domestic operator would be affected by this proposed AD. The FAA estimates that the cost for replacing the pre-LIR HPT interstage seals is $536,340, based on an assumption of how many seals will be replaced prior to reaching the full retirement life. The FAA also estimates that the LIR HPT interstage seal life reduction cost will be $3,396,820, and is based on the pro-rated costs of HPT interstage seals that will be removed due to the reduced life limit. Based on these figures, the total cost of the proposed AD on U.S. operators is estimated to be $3,933,160.

Regulatory Analysis

This proposed rule 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 proposed rule.

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. 2001-NE-32-AD

Applicability

This airworthiness directive (AD) is applicable to General Electric Company (GE) GE90-76B, -77B, -85B, -90B, and -94B turbofan engines with high pressure turbine (HPT) interstage seals part numbers (P/N's) 1711M20P08, 1711M20P14, 1711M20P16, 1711M20P17, and 1847M96P02 installed. These engines are installed on, but not limited to Boeing 777 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 (g) 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

Compliance with this AD is required as indicated, unless already done.

To prevent failure of the HPT interstage seal that could result in an uncontained engine failure, and damage to the airplane, do the following:

Replacement of HPT Interstage Seals P/N's 1711M20P08, 1711M20P14, 1711M20P16, and 1711M20P17

(a) For GE90-76B, -77B, -85B, -90B engines with HPT interstage seals P/N's 1711M20P08, 1711M20P16, and 1711M20P17 installed, and GE90-76B and -77B engines with interstage seal P/N 1711M20P14 installed, replace seals at next shop visit piece-part exposure with a serviceable HPT interstage seal, after the effective date of this AD, but not to exceed 4,800 cycles-since-new (CSN), or before December 31, 2006, whichever occurs earlier.

(b) For GE90-85B and -90B engines with HPT interstage seal P/N 1711M20P14 installed, replace seal at next shop visit piece-part exposure with a serviceable HPT interstage seal, after the effective date of this AD, but not to exceed 2,800 CSN, or before December 31, 2006, whichever occurs earlier.

(c) After the effective date of this AD, do not install any HPT interstage seal P/N's 1711M20P08, 1711M20P14, 1711M20P16, and 1711M20P17 into an engine.

Reduced Life Limit

(d) For engines with HPT interstage seals P/N 1847M96P02 installed, remove engine from service before exceeding the reduced cyclic life limit of 3,500 CSN.

(e) This AD establishes a new cyclic life limit for HPT interstage seal, P/N 1847M96P02. Except as provided in paragraph (g) of this AD, no alternate life limits for this part may be approved.

Definition

(f) For the purpose of this AD, a shop visit piece-part exposure is defined as an engine removal, for maintenance that cannot be performed while installed on the airplane, and that the HPT interstage seal is completely disassembled when accomplished in accordance with the disassembly instructions of the engine manual.

Alternative Methods of Compliance

(g) 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 must submit their request through an appropriate 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.

Special Flight Permits

(h) Special flight permits may be issued in accordance §§ 21.197 and 21.199 of the Federal Aviation Regulations (14 CFR 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 September 20, 2001.

Jay J. Pardee,

Manager, Engine and Propeller Directorate, Aircraft Certification Service.