01-10889. Airworthiness Directives; GE Aircraft Engines CT7 Series Turboprop 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 GE Aircraft Engines (GE) CT7 series turboprop engines. This proposal would require removal of stage 2 turbine aft cooling plates of a certain part number (P/N) and installation of cooling plates of a new design. This proposal is prompted by a report of a stage 2 turbine aft cooling plate cracking, resulting in an uncontained engine failure. The actions specified by the proposed AD are intended to prevent stage 2 turbine aft cooling plate cracking, which could result in uncontained engine failure, and damage to the airplane.

DATES:

Comments must be received by July 2, 2001.

ADDRESSES:

Submit comments in triplicate to the Federal Aviation Administration (FAA), New England Region, Office of the Regional Counsel, Attention: Rules Docket No. 2000-NE-61-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 a.m. and 4:30 p.m., Monday through Friday, except Federal holidays. 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:

Barbara Caufield, 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

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 2000-NE-61-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-61-AD, 12 New England Executive Park, Burlington, MA 01803-5299.

Discussion

In July 1999, the FAA was made aware of an uncontained failure of a GE CT7-5 turboprop engine, caused by a cracked stage 2 turbine aft cooling plate. In February 2000, GE identified and reported the root cause of the cooling plate failure to the FAA. The failure was due to micro-cracking at the cooling air holes and a reduction in material properties, caused during manufacture by an excessive electro-discharge machining (EDM) recast layer in the air holes followed by inadequate abrasive flow. GE has identified those cooling plates manufactured by this method, as P/N 6064T07P02, having the serial number (SN) prefix of GFF. GE also has reported that a few unaffected stage 2 turbine aft cooling plates, P/N 6064T07P02 having a SN prefix other than GFF, are installed mainly on engines in foreign military service. This condition, if not corrected, could cause cracking of the stage 2 turbine aft cooling plate, resulting in an 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 GE CT7 series turboprop engines of the same type design, the proposed AD would require replacing affected stage 2 turbine aft cooling plates with new design aft cooling plates, P/N 6064T07P05, having cooling holes made by conventional drilling methods.

Economic Impact

There are approximately 564 engines of the affected design in the worldwide fleet. The FAA estimates that 180 engines installed on airplanes of U.S. registry would be affected by this proposed AD, that it would take approximately 0.5 work hour per engine to accomplish the proposed actions, and that the average labor rate is $60 per work hour. Required aft cooling plates would cost approximately $15,282 per engine. Based on these figures, the total cost impact of the proposed AD on U.S. operators is estimated to be $2,756,160. The manufacturer has stated that it may provide the new design aft cooling plate at no cost to operators, and that if the aft cooling plate is replaced at the next engine or hot section module overhaul shop visit, no additional labor costs will be incurred.

Regulatory Impact

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:

GE Aircraft Engines: Docket No. 2000-NE-61-AD.

Applicability: This airworthiness directive (AD) is applicable to GE Aircraft Engines (GE) CT7 Models CT7-5A2, -5A3, -7A, and -7A1 turboprop engines, installed on but not limited to Construcciones Aeronauticas, SA CN-235 series and SAAB Aircraft AB SF340 series 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

Compliance is required at the next overall of the engine or hot section module, or within 8,000 cycles after the effective date of this AD, whichever occurs first, unless already done.

To prevent stage 2 turbine aft cooling plate cracking, which could result in an uncontained engine failure and damage to the airplane, do the following:

(a) Replace stage 2 aft cooling plate P/N 6064T07P02 with stage 2 aft cooling plate P/N 6064T07P05.

(b) After the effective date of this AD, do not install any stage 2 aft cooling plate P/N 6064T07P02.

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 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

(d) 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 airplane to a location where the requirements of this AD can be accomplished.

Issued in Burlington, Massachusetts, on April 24, 2001.

Donald E. Plouffe,

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