AD 95-07-03

A proposal to amend part 39 of the Federal Aviation Regulations (14 CFR part 39) to include an airworthiness directive (AD) that is applicable to AlliedSignal Aerospace (formerly Garrett Auxiliary Power Division and Garrett Turbine Engine Co.) GTCP85 series auxiliary power units (APU) was published in the Federal Register on July 28, 1994 (59 FR 38384). That action proposed to require modifying the APU to install an exhaust centerbody to contain turbine wheel fragments from exiting the APU axially. Due to the increased risk associated with airborne failures, flight operable APU's would be required to be modified within 24 months after the effective date of the AD, and within 36 months after the effective date of this AD for APU's that are ground operable only. These actions would be performed in accordance with AlliedSignal Aerospace Alert Service Bulletin (ASB) No. GTCP85-49-A6831, dated March 17, 1994, applicable to APU's installed on McDonnell DouglasDC-9/MD-80 series aircraft, and AlliedSignal Aerospace Service Bulletin (SB) No. GTCP85-49-6919, dated May 17, 1994, applicable to APU's installed on several other aircraft makes and models.

Interested persons have been afforded an opportunity to participate in the making of this amendment. Due consideration has been given to the comments received.

One commenter states that the APU's installed on Boeing 737 series aircraft should not be affected by this AD because APU turbine rotor axial uncontainment does not pose a hazard to Boeing 737 series aircraft. The FAA concurs and has revised the AD accordingly.

One commenter states that the APU's installed on British Aerospace BAC 1-11 series aircraft should also not be affected by this AD because APU turbine rotor axial uncontainment does not pose a hazard to British Aerospace BAC 1-11 series aircraft. The FAA concurs and has revised the AD accordingly.

One commenter states that the AD should be applicable only to APU's with the cast material MAR-M-247 turbine wheel, as only these turbine wheels have experienced uncontained failures. The FAA concurs and the applicability paragraph of this final rule has been revised accordingly.

Two commenters state that the AD should clearly specify the APU model numbers affected and agree with the model numbers listed in the applicable service bulletins. The FAA concurs and the applicability paragraph of this final rule has been revised accordingly.

One commenter states that the AD should not be applicable to APU's installed on Boeing 727 aircraft, as the APU is ground operable only. The FAA does not concur. An APU turbine wheel axial uncontainment may pose an unsafe condition even with the aircraft on the ground.

One commenter states that the AlliedSignal Aerospace ASB No. GTCP85-49-A6707, mandated by AD 93-07-13, provides adequate containment capability, and that requiring implementation of AlliedSignal Aerospace SB No. GTCP85-49-6919 is unnecessary. The FAA does not concur. Airworthiness directive 93-07-13 mandates compliance with Garrett SB No. GTCP85-49-A6706, not AlliedSignal Aerospace ASB No. GTCP85-49-A6707 (Garrett has recently undergone a name change to AlliedSignal Aerospace). Even reading the comment as referring to AlliedSignal Aerospace ASB No. GTCP85-49-A6707, that SB only addresses radial, not axial, uncontainment. AlliedSignal Aerospace SB No. GTCP85-49-6919 addresses axial uncontainment.

One commenter states that the final rule should allow use of subsequent revisions to the SB's in order to avoid unnecessary alternate method of compliance requests. The FAA does not concur. If the SB's incorporated by reference in this AD are further revised, those revisions can be reviewed by the FAA in advance of publication and authorized as constituting alternate methods of compliance, thereby alleviating the need for each individual operator to obtain a separate approval to use the revised SB. Until those future revisions exist, however, the FAA cannot incorporate them into this AD.

One commenter states that the AD should not be applicable to APU's with the standard two-piece turbine wheel. The two-piece turbine wheel has not experienced the failure mode addressed in the AD. The FAA concurs and has revised the applicability paragraph to limit the AD to APU's equipped with one-piece cast turbine wheels.

Two commenters concur with the rule as proposed.

Since issuance of the NPRM, the FAA has increased its labor estimate to $60 per work hour. The economic analysis of this AD has been revised accordingly.

In addition, AlliedSignal Aerospace has issued Revision 1 to SB No. GTCP85-49-6919, and ASB No. GTCP85-49-A6831, both dated January 15, 1995. This final rule now references these revised service documents.

After careful review of the available data, including the comments noted above, the FAA has determined that air safety and the public interest require the adoption of therule with the changes described previously. The FAA has determined that these changes will neither increase the economic burden on any operator nor increase the scope of the AD.

There are approximately 3,000 APU's of the affected design in the worldwide fleet. The FAA estimates that 1,500 APU's installed on aircraft of U.S. registry will be affected by this AD, that it will take approximately 5 work hours per APU to accomplish the proposed actions, and that the average labor rate is $60 per work hour. Required parts will cost approximately $7,055 per APU if the exhaust duct is not reworkable, $3,254 per APU if the exhaust duct is reworkable, and the FAA estimates that 1,050 domestic APU's are reworkable. Based on these figures, the total cost impact of the AD on U.S. operators is estimated to be $7,041,450.

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.

For the reasons discussed above, I certify that this action (1) is not a "significant regulatory action" under Executive Order 12866; (2) is not a "significant rule" under DOT Regulatory Policies and Procedures (44 FR 11034, February 26, 1979); and (3) 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 final evaluation has been prepared for this action and it is contained in the Rules Docket. A copy of it 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 U.S.C. App. 1354(a), 1421 and 1423; 49 U.S.C. 106(g); and 14 CFR 11.89.

§39.13 - (AMENDED) 2. Section 39.13 is amended by adding the following new airworthiness directive: