AD 93-25-16

Effective January 18, 1994.

The incorporation by reference of Allied-Signal Propulsion Engines ASB No. TFE731-A72-3504, Revision 1, dated July 2, 1993, is approved by the Director of the Federal Register as of January 18, 1994.

The incorporation by reference of Allied-Signal Aerospace Company, Garrett Engine Division, ASB No. TFE731-A72-3504, dated November 25, 1992, was approved previously by the Director of the Federal Register as of April 9, 1993 (58 FR 16113, March 25, 1993).

Comments for inclusion in the Rules Docket must be received on or before March 4, 1994.

Submit comments in triplicate to the Federal Aviation Administration (FAA), New England Region, Office of the Assistant Chief Counsel, Attention: Rules Docket No. 93-ANE-71, 12 New England Executive Park, Burlington, MA 01803-5299.

The service information referenced in this AD may be obtained from AlliedSignal Engines, Aviation Services Division, Data Distribution, Dept. 64-3/2102-1M, P.O. Box 29003, Phoenix, AZ 85038-9003; telephone (602) 365-2548. This information may be examined at the FAA, New England Region, Office of the Assistant Chief Counsel, Burlington, MA; or at the Office of the Federal Register, 800 North Capitol Street, NW., suite 700, Washington, DC.

Joseph Costa, Aerospace Engineer, Los Angeles Aircraft Certification Office, FAA, Transport Airplane Directorate, 3229 East Spring Street, Long Beach, CA 90806-2425; telephone (310) 988-5246, fax (310) 988-5210.

On February 19, 1993, the Federal Aviation Administration (FAA) issued AD 92-26-09, Amendment 39-8503 (58 FR 16113, March 25, 1993), to require an improved, more definitive eddy current inspection of certain fan disks for cracks, and replacement, if necessary, of these fan disks. That action was prompted by reports of an uncontained failure of a fan disk on an Allied-Signal Aerospace Company, Garrett Engine Division, Model TFE731-3 turbofan engine. The FAA investigation determined that a fatigue crack originated in the aft acute corner of the dovetail slot. The fan disk had accumulated a total of 5291 cycles in service (CIS) at the time of the failure, and had been eddy current inspected in 1990 when the disk had accumulated 4055 CIS. The fan disk displayed evidence of broaching grooves produced during the manufacture of the blade dovetail slots. These machining grooves may have contributed to the disk failure. From a metallurgical analysis, the FAA has determined that the failed fan disk had dovetail cracks which were not detected at the time of the eddy current inspection. A review of the eddy current inspection process used to inspect this disk and all disks inspected prior to May 1991 revealed that the process will not reliably detect this type of crack on these disks. Fan disk cracks, if not detected, could result in an uncontained fan disk failure.

Since the issuance of that AD, the FAA has determined that an additional 30 fan disks will require inspection, or replacement, if necessary. In addition, the Applicability Section of AD 92-26-09 identified the Learjet 55 series as one aircraft that might have an affected engine installed. The FAA has since learned that no Learjet 55 series aircraft has an affected engine, and therefore, deletes the Learjet 55 series from that list of aircraft. Finally, AlliedSignal Propulsion Engines has issued Revision 1 to AlliedSignal Propulsion Engines Alert Service Bulletin (ASB) No. TFE731-A72-3504. This AD incorporates this revision.

The FAA has reviewed and approved the technical contents of Allied-Signal Aerospace Company, Garrett Engine Division, ASB No. TFE731-A72-3504, dated November 25, 1992, and AlliedSignal Propulsion Engines ASB No. TFE731-A72-3504, Revision 1, dated July 2, 1993, that describe procedures for an improved, more definitive eddy current inspection of these fan disks for cracks.

Since an unsafe condition has been identified that is likely to exist or develop on other engines of this same type design, this AD supersedes AD 92-26-09 to require inspection of an additional 30 fan disks. Fan disks inspected in accordance with the existing AD, 92-26-09, need not be inspected again. The inspection schedule for fan disks not yet inspected in accordance with the existing AD, however, remains the same, using April 9, 1993, the effective date of AD 92-26-09 as the starting point. The actions are required to be accomplished in accordance with the service bulletins described previously.

Since a situation exists that requires the immediate adoption of this regulation, it is found that notice and opportunity for prior public comment hereon are impracticable, and that good cause exists for making this amendment effective in less than 30 days.

Although this action is in the form of a final rule that involves requirements affecting flight safety and, thus, was not preceded by notice and an opportunity for public comment, comments are invited on this rule. Interested persons are invited to comment on this 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 under the caption ``ADDRESSES.'' All communications received on or before the closing date for comments will be considered, and this rule may be amended in light of the comments received. Factual information that supports the commenter's ideas and suggestions is extremely helpful in evaluating the effectiveness of the AD action and determining whether additional rulemaking action would be needed.

Comments are specifically invited on the overall regulatory, economic, environmental, and energy aspects of the rule that might suggest a need to modify the 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 that summarizes each FAA-public contact concerned with the substance of this AD 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 Number 93-ANE-71.'' The postcard will be date stamped and returned to the commenter.

The regulations adopted herein will 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 final rule does not have sufficient federalism implications to warrant the preparation of a Federalism Assessment.

The FAA has determined that this regulation is an emergency regulation that must be issued immediately to correct an unsafe condition in aircraft, and is not a ``significant regulatory action'' under Executive Order 12866. It has been determined further that this action involves an emergency regulation under DOT Regulatory Policies and Procedures (44 FR 11034, February 26, 1979). If it is determined that this emergency regulation otherwise would be significant under DOT Regulatory Policies and Procedures, a final regulatory evaluation will be prepared and placed in the Rules Docket. A copy of it, if filed, may be obtained from the Rules Docket at the location provided under the caption ``ADDRESSES.''

Air transportation, Aircraft, Aviation safety, Incorporation by reference, Safety.

Accordingly, pursuant to the authority delegated to me by the Administrator, the Federal Aviation Administration amends 14 CFR part 39 of the Federal Aviation Regulations as follows:

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.