AD 85-25-08

85-25-08 ALLISON GAS TURBINE DIVISION, GENERAL MOTORS CORP. (ALLISON, formerly DETROIT DIESEL ALLISON): Amendment 39-5189. Applies to Allison Model 250-C28 and -C30 Series engines, which incorporate compressor mount assembly P/N 6896021, 6898966, or 6898611 installed in rotorcraft certificated in any category. The following engine model and compressor serial numbers are affected:

ENGINE MODEL COMPRESSOR SERIAL NUMBER 250-C28B CAC 70011 thru 70793, 70795 250-C28C CAC 28001 thru 28021 250-C30, -C30P, -C30S CAC 90001 thru 90822

EXCEPT: Existing Model 250-C28 and -C30 Series engines which have incorporated Allison Commercial Engine Bulletin CEB 72-2085/3085, Revision 1, dated April 30, 1985, or FAA approved equivalent. Compliance is required as indicated unless already accomplished. To prevent possible failure of the compressor mount that can cause misalignment and subsequent failure of compressor to turbine shafting spline joints which may lead to an inflight loss of power or disconnect of the gas producer turbine rotor with a subsequent inflight shutdown/overspeed uncontained turbine wheel failure, accomplish the following: (a) Within the next 100 hours time-in-service after the effective date of this AD, unless already accomplished within the last 200 hours time-in-service, and thereafter at intervals not to exceed 300 hours tim-in- service from the last inspection, perform the following: Inspect P/Ns 6896021, 6898966, or 6898611 compressor mount assembly in accordance with the accomplishment instructions of Allison CEB-A-72-2080/3081 dated September 15, 1982, or FAA approved equivalent. The following continued service criteria apply for compressor mount assemblies found to have a crack(s) during the inspection: (1) If there is only one crack in the compressor mount assembly and that crack has not progressed to within 3/8 inch of the edge of the mount sheet metal, the mount assembly can continue in service provided thatinspection is made at intervals not exceeding 25 hours since the last inspection. (2) If the crack has progressed to within 3/8 inch of the edge of the mount sheet metal, or if there is more than one crack of any length, the compressor mount assembly must be removed from service before further flight. (b) At the next compressor assembly overhaul/repair event, but not later than November 30, 1986, perform the following: Replace P/N 6896021, 6898966, or 6898611 compressor mount assembly with P/N 23007217 in accordance with the Accomplishment Instructions of Allison CEB 72-2085/3085, Revision 1, dated April 30, 1985, or FAA approved equivalent. Aircraft may be ferried in accordance with the provisions of FAR 21.197 and 21.199 to a base where the AD can be accomplished. Upon request, an equivalent means of compliance with the requirements of this AD may be approved by the Manager, Chicago Aircraft Certification Office, FAA, 2300 East Devon Avenue, Des Plaines, Illinois 60018. Upon submission of substantiating data by an owner or operator through an FAA maintenance inspector, the Manager, Chicago Aircraft Certification Office may adjust the compliance time specified in this AD. The following Allison commercial engine bulletins are incorporated herein and made a part hereof pursuant to 5 U.S.C. 552(a)(1): CEB-A-72-2080/3081 dated September 15, 1982 CEB-72-2085/3085, Revision 1, dated April 30, 1985. All persons affected by this directive who have not already received these documents from the manufacturer may obtain copies upon request to Allison Gas Turbine Division, General Motors Corp., P.O. Box 420, Indianapolis, IN 46206-0420. These documents also may be examined at the Office of Regional Counsel, FAA, ATTN: Rules Docket No. 85-ANE-42, 12 New England Executive Park, Burlington, Massachusetts 01803, weekdays, except Federal holidays, between 8:00 a.m. and 4:30 p.m. This amendment becomes effective January 6, 1986.