AD 96-25-12

The Federal Aviation Administration (FAA) has received three reports of compressor wheels, installed on Sundstrand T-62T-40C series auxiliary power units (APUs), that ruptured prior to the published cyclic life limit. Of the three ruptures, two were uncontained. The investigation revealed that the compressor wheels ruptured due to low cycle fatigue. This condition, if not corrected, could result in compressor wheel rupture, which could result in an uncontained APU failure and damage to the aircraft.

The FAA has reviewed and approved the technical contents of Sundstrand Aerospace Service Bulletin (SB) No. SB-T-62T-49-120, Revision 2, dated November 5, 1996, Revision 1, dated September 9, 1996, and Original, dated July 22, 1996, that describe procedures for removal from service of certain compressor wheels in accordance with a drawdown schedule, and replacement with new design serviceable parts, and establishes a new cyclic life limit for existing compressor wheels.

Since an unsafe condition has been identified that is likely to exist or develop on other APUs of the same type design, this AD is being issued to prevent compressor wheel rupture. This AD requires removal from service of certain compressor wheels in accordance with a drawdown schedule, and replacement with serviceable parts, and establishes a new cyclic life limit for existing compressor wheels. The actions are required to be accomplished in accordance with the SB 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 invitedon 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 96-ANE-27." 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."

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 adding the following new airworthiness directive: