AD 96-04-01

This amendment supersedes an existing airworthiness directive (AD), applicable to AlliedSignal Inc. (formerly Garrett Engine Division) TFE731 series turbofan engines, that currently requires eddy current inspection of certain fan rotor disks for cracks, and replacement, if necessary, with serviceable parts. This amendment requires reinspection of 33 additional fan rotor disks, beyond the quantity of reinspections required by AD 93-25-16. This amendment is prompted by discrepancies in several magnetic tape records discovered as a result of recent improvements in the inspection tape review process. The actions specified by this AD are intended to prevent an uncontained failure of the fan rotor disk due to fatigue cracking in the dovetail slots, which can result in inflight engine shutdowns, severe secondary damage, and fan rotor assembly separation from the engine.

Final rule; request for comments.

96-04-01 AlliedSignal Inc.: Amendment 39-9512. Docket 95-ANE-54. Supersedes AD 93-25-16, Amendment 39-8780.

Applicability: AlliedSignal Inc. (formerly Garrett Engine Division) TFE731-2, -2A, -3, -3R series turbofan engines with fan rotor disks, part numbers (P/N's) 3072162-1 through -4, 3073436-1 through -4, 3073539-2, and 3074529-2, installed on, but not limited to: Avions Marcel Dassault Falcon 10, 50, 100 series; Learjet 31, 35, 36 series; Lockheed-Georgia 1329-23, -25 series; Israel Aircraft Industries 1124 series; Raytheon British Aerospace HS125 series; and Sabreliner NA-265-65 aircraft. NOTE: This airworthiness directive (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 use the authority provided in paragraph (e) to request approval from the Federal Aviation Administration (FAA). This approval may address either no action, if the current configuration eliminates the unsafe condition, or different actions necessary to address the unsafe condition described in this AD. Such a request should include an assessment of the effect of the changed configuration on the unsafe condition addressed by this AD. In no case does the presence of any modification, alteration, or repair remove any engine from the applicability of this AD.

Compliance: Required as indicated, unless accomplished previously.

To prevent an uncontained failure of the fan rotor disk due to fatigue cracking in the dovetail slots, which can result in inflight engine shutdowns, severe secondary damage, and fan rotor assembly separation from the engine, accomplish the following:

(a) No further action is required for fan rotor disks previously eddy current inspected in accordancewith the requirements of AD 92-26-09 and AD 93-25-16.

(b) Remove prior to further flight fan rotor disk, P/N 3073539-2 or 3072162-2, with Serial Number (S/N) 8-18040-6300, in accordance with Allied-Signal Inc. Alert Service Bulletin (ASB) No. TFE731-A72-3504, dated November 25, 1992, or AlliedSignal Inc. ASB No. TFE731-A72-3504, Revision 1, dated July 2, 1993, and replace with a serviceable fan rotor disk.

(c) Incorporate new eddy current inspection procedures in accordance with ASB No. TFE731-A72-3578, dated May 31, 1995, within 30 days after the effective date of this AD. Fan rotor disks requiring eddy current inspection, prior to the incorporation of the new eddy current procedure previously mentioned, may be inspected in accordance with AlliedSignal Inc. ASB No TFE731-A72-3504 dated November 25, 1992, or TFE731-A72-3504, Revision 1, dated July 2, 1993.

(d) Eddy current inspect fan rotor disks, P/N 3072162-1 through -4, 3073436-1 through -4, 3073539-2, and 3074529-2,in accordance with the Accomplishment Instructions of AlliedSignal Inc. ASB No. TFE731-A72-3578, dated May 31, 1995, and if necessary, replace with a serviceable disk, as follows:

(1) For fan rotor disks listed by S/N in Table 2 of Allied-Signal Inc. ASB No. TFE731-A72-3504, dated November 25, 1992, or AlliedSignal Inc. ASB No. TFE731-A72-3504, Revision 1, dated July 2, 1993, inspect, and if necessary, replace with a serviceable fan rotor disk within 50 cycles in service (CIS) after April 9, 1993 (effective date of AD 92-26-09).

(2) For the 10 added fan rotor disks listed by S/N in Table 3 of AlliedSignal Inc. ASB No. TFE731-A72-3504, Revision 1, dated July 2, 1993, with 5,000 or more CIS since new on January 18, 1994 (effective date of AD 93-25-16), inspect, and if necessary, replace with a serviceable fan rotor disk, within the next 50 CIS after January 18, 1994 (effective date of AD 93-25-16).

(3) For fan rotor disks listed by S/N in Table 3 of AlliedSignal Inc. ASB No. TFE731-A72-3504, Revision 1, dated July 2, 1993, other than the 10 added fan rotor disks, with 5,000 or more CIS since new on April 9, 1993, (effective date of AD 92-26-09), inspect, and if necessary, replace with a serviceable fan rotor disk, within the next 50 CIS after April 9, 1993 (effective date of AD 92-26-09).

(4) For the 10 added fan rotor disks listed by S/N in Table 3 of AlliedSignal Inc. ASB No. TFE731-A72-3504, Revision 1, dated July 2, 1993, with less than 5,000 CIS since new on January 18, 1994, (effective date of AD 93-25-16), inspect, and if necessary, replace with a serviceable fan rotor disk within the next 100 CIS after January 18, 1994, (effective date of AD 93-25-16) or prior to accumulating 5,050 CIS since new, whichever occurs first.

(5) For fan rotor disks listed by S/N in Table 3 of AlliedSignal Inc. ASB No. TFE731-A72-3504, Revision 1, dated July 2, 1993, other than the 10 added fan rotor disks, with less than 5,000 CIS since new on April 9, 1993 (effective date of AD 92-26-09), inspect, and if necessary, replace with a serviceable fan rotor disk, within the next 100 CIS after April 9, 1993 (effective date of AD 92-26-09), or prior to accumulating 5,050 CIS since new, whichever occurs first.

(6) For fan rotor disks listed by S/N in Table 4 of AlliedSignal Inc. ASB No. TFE731-A72-3504, Revision 1, dated July 2, 1993, inspect, and if necessary, replace with a serviceable fan rotor disk, within the next 100 CIS after January 18, 1994, (effective date of AD 93-25-16).

(7) For fan rotor disks listed by S/N in Table 1 of AlliedSignal Inc. ASB No. TFE731-A72-3578, dated May 31, 1995, inspect, and if necessary, replace with a serviceable disk, within 50 CIS after the effective date of this AD.

(e) 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, Los Angeles Aircraft Certification Office. The request should be forwarded through an appropriate FAA Principal Maintenance Inspector, who may add comments and then send it to the Manager, Los Angeles Aircraft Certification Office. NOTE: Information concerning the existence of approved alternative methods of compliance with this airworthiness directive, if any, may be obtained from the Los Angeles Aircraft Certification Office.

(f) Special flight permits may be issued in accordance with sections 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.

(g) The actions required by this AD shall be done in accordance with the following service documents:

Document No.
Pages
Revision
Date
AlliedSignal Inc. ASB No. TFE731-A72-3578
1-12
Original
May 31, 1995
Total pages: 12.

Allied-Signal Inc. ASB No. TFE731-A72-3504
1-24
Original
November 25, 1992
Total pages: 24.

Allied-Signal Inc. ASBNo. TFE731-A72-3504
1-28
Revision 1
July 2, 1993
Total pages: 28.

This incorporation by reference was approved by the Director of the Federal Register in accordance with 5 U.S.C. 552(a) and 1 CFR part 51. Copies may be obtained from AlliedSignal Aerospace, Attn: Data Distribution, M/S 64-03/2101-201, P.O. Box 29003, Phoenix, AZ 85038-9003; telephone (602) 365-2493, fax (602) 365-5577. Copies may be inspected at the FAA, New England Region, Office of the Assistant Chief Counsel, 12 New England Executive Park, Burlington, MA; or at the Office of the Federal Register, 800 North Capitol Street, NW., suite 700, Washington, DC.

(h) This amendment becomes effective on March 15, 1996.

On December 21, 1993, the Federal Aviation Administration (FAA) issued airworthiness directive (AD) 93-25-16, Amendment 39-8780 (59 FR 4, January 3, 1994), applicable to AlliedSignal Inc. (formerly Garrett Engine Division) TFE731-2, -3, and -3R series turbofan engines. That AD requires eddy current inspection of certain fan rotor disks for cracks, and replacement, if necessary, of these fan rotor disks. That action was prompted by reports of an uncontained failure of a fan rotor disk on an AlliedSignal Inc. 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 rotor disk had accumulated a total of 5,291 cycles in service (CIS) at the time of the failure, and had been eddy current inspected in 1990 when the disk had accumulated 4,055 CIS. The fan rotor disk displayed evidence of broaching grooves produced during the manufacture of the blade dovetail slots.These machining grooves may have contributed to the fan rotor disk failure. From a metallurgical analysis, the FAA determined that the failed fan rotor 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 fan rotor disk and all fan rotor disks inspected prior to May 1991 determined that the inspection process was not acceptable. Those fan rotor disk cracks, if not corrected, could result in an uncontained failure of the fan rotor disk due to fatigue cracking in the dovetail slots, which can result in inflight engine shutdowns, severe secondary damage, and fan rotor assembly separation from the engine.

After 1991, the eddy current inspection process required magnetic tape records (henceforth referred to as tapes) of the eddy current inspection results for the fan rotor disk dovetail slots. These tapes can be reviewed at any time following the initial inspection without inconveniencing the operator. Since the issuance of that AD, through recent improvements in the inspection tape review process, and continued review of the tapes, the FAA has identified several tape records as having discrepancies. A discrepancy does not always indicate that a crack exists. This superseding AD requires a re-inspection of 33 additional fan rotor disks, beyond the quantity of re-inspections required by AD 93-25-16, to ensure that cracked fan rotor disks are removed from service. To date, eddy current inspections have detected fatigue cracks in the dovetail slots in approximately 176 (or 4%) TFE731-2, -2A, -3, and -3R fan rotor disks, and those fan rotor disks have been removed from service.

The FAA has reviewed and approved the technical contents of AlliedSignal Alert Service Bulletin (ASB) No. TFE731-A72-3578, dated May 31, 1995, that describes procedures for an improved, more definitive eddy current inspection for fan rotor disk dovetail slot cracks.

Sincean unsafe condition has been identified that is likely to exist or develop on other engines of this same type design, this AD supersedes AD 93-25-16 to require reinspection of 33 additional fan rotor disks, beyond the quantity of reinspections required by AD 93-25-16, to ensure that cracked fan rotor disks are removed from service. This action is required to be accomplished in accordance with the ASB 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. Comments Invited

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 95-ANE-54." 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. Ithas 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."

List of Subjects in 14 CFR Part 39
Air transportation, Aircraft, Aviation safety, Incorporation by reference, Safety.

Adoption of the Amendment
Accordingly, pursuant to the authority delegated to me by the Administrator, the Federal Aviation Administration amends 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 USC 106(g), 40113, 44701.

39.13- [AMENDED]
2. Section 39.13 is amended by removing Amendment 39-8780, (59 FR 4, January 3, 1994), and by adding a new airworthiness directive, Amendment 39-9512, to read as follows: