AD 85-25-09

85-25-09 ALLISON GAS TURBINE DIVISION, GENERAL MOTORS CORP. (ALLISON, formerly DETROIT DIESEL ALLISON): Amendment 39-5190. Applies to Allison Model 250-C28B and -C28C engines installed in rotorcraft certificated in any category with the following engine and turbine serial numbers:

MODEL ENGINE SERIAL NUMBER TURBINE SERIAL NUMBER 250-C28B CAE 860011 thru 860787CAT 70011 thru 70804 250-C28C CAE 280001 thru 280039CAT 28001 thru 28039

EXCEPT: Existing Model 250-C28B and -C28C engines which have incorporated all of the following Allison Commercial Engine Bulletins (CEB):

SUBJECT CEB-A-72-2127, Rev. 1 dated Sept. 15, 1985, or FAA approved equivalents; and Engine, Turbine Assembly, Turbine-to-Compressor Coupling Shaft-Replace CEB-72-2101, Rev. 1 dated Sept. 15, 1985, or FAA approved equivalent; and Engine, Compressor Assembly, Spur Adapter Gearshaft - modified by adding Three Slots in Bore & Plugging Oil Feed Hole CEB-72-2063, Rev. 4 dated Sept. 15, 1985, or FAA approved equivalent; and Engine, Compressor and Gearbox Assemblies - modify to Roller Number 2 1/2 Bearing Configuration CEB-72-2099, Rev. 1 dated Sept. 15, 1985, or FAA approved equivalent. Engine, Turbine-Exhaust Collector Modifications

Compliance is required as indicated unless already accomplished. To prevent carbon buildup on turbine shafts and couplings that can cause shaft rub and subsequent shaft or coupling failures leading to possible overspeed and/or uncontained turbine wheel failures accomplish the following: (a) Within the next 50 hours time-in-service after the effective date of this AD, unless already accomplished within the last 250 hours time-in-service, and thereafter at intervals not to exceed 300 hours time- in-service from the last inspection, perform the following: Clean and inspect turbine shafting/couplings, and replace the P/N AS 3085-018 O-ring (two for P/N 23032345 and one for P/N 6896895 or P/N 6889071 turbine-to-compressor-coupling) on the aft end of the spur adapter gearshaft in accordance with CEB-A-72-2122 dated September 15, 1985, or FAA approved equivalent. (b) At the next engine or module repair/overhaul shop visit, when both the compressor and gearbox are disassembled to permit access, but not later than November 30, 1987, perform the following: (i) Modify spur adapter gearshaft assembly P/N 23005276 in accordance with Allison CEB 72- 2101, Revision 1 dated September 15, 1985, or FAA approved equivalent. (ii) Modify engine compressor and gearbox assemblies to include the roller bearing configuration at the 2 1/2 bearing location in accordance with Allison CEB 72-2063, Revision 4 dated September 15, 1985, or FAA approved equivalent. (iii) Replace turbine-to-compressor-coupling P/N 6896895, or P/N 6889071, 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 CEB-A-72-2127, Revision 1 dated September 15, 1985, or FAA approved equivalent. (c) At the next turbine repair/overhaul shop visit, but not later than November 30, 1987, modify the turbine-exhaust-collector in accordance with Allison CEB 72-2099, 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. 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-72-2127, Revision 1, dated September 15, 1985 CEB-72-2101, Revision 1, dated September 15, 1985 CEB-72-2063, Revision 4, dated September 15, 1985 CEB-72-2099, Revision 1, dated September 15, 1985 CEB-A-72-2122 dated September 15, 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-41, 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.