AD 85-25-12

85-25-12 ALLISON GAS TURBINE DIVISION, GENERAL MOTORS CORP. (ALLISON, formerly DETROIT DIESEL ALLISON): Amendment 39-5191. Applies to Allison Model 250-C28B and -C28C engines, which incorporate P/N 23008080 turbine-to-compressor-coupling, installed in rotorcraft certificated in any category. Compliance is required as indicated unless already accomplished. To prevent possible cracks in turbine-to-compressor coupling P/N 23008080 from progressing to where a disconnect failure could occur and subsequently could result in an overspeed uncontained failure of the gas producer turbine rotor, accomplish the following: Within the next 100 hours time-in-service after the effective date of this AD, or at the next turbine repair/inspection when access to P/N 23008080 coupling is gained, whichever occurs first, but not later than March 6, 1986, perform the following: Replace P/N 23008080 turbine-to-compressor-coupling with P/N 23032345 and install two P/N AS 3085- 018 O-rings on the aft end of the spur adapter gearshaft in accordance with Allison Commercial Engine Alert Bulletin CEB-A-72-2127, Revision 1, dated September 15, 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. Allison CEB-A-72-2127, Revision 1, dated September 15, 1985, is incorporated herein and made a part hereof pursuant to 5 U.S.C. 552(a)(1). 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-40, 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.