AD 86-20-13

86-20-13 ALLISON GAS TURBINE DIVISION, GENERAL MOTORS CORP. (ALLISON, formerly DETROIT DIESEL ALLISON): Amendment 39-5465. Applies to Allison Model 250-C28 and -C30 Series engines installed in, but not limited to, Bell Model 206L-1, Messerschmitt-Bolkow-Blohm GmbH BO 105 LS A- 1, Sikorsky Model S-76A, Bell Model 206L-1, modified to incorporate the Allison 250-C30 engine, Bell Model 206L-3, and McDonnell Douglas Helicopter Company (Hughes) Model 369F and 369FF aircraft. The following engine models and turbine serial numbers are affected:

ENGINE MODEL TURBINE SERIAL NUMBER 250-C28B CAT 70001 thru 70802 and 70804 250-C28C CAT 28001 thru 28046 250-C30 Series CAT 90001 thru 95436 and 95438

EXCEPT existing Model 250-C28 and 250-C30 Series engines which have incorporated Allison Commercial Engine Alert Bulletin 250-C28/C30 CEB-A-72-2132/3146 dated October 1, 1985, or the following FAA approved equivalents:

Allison Message THO-2639W-RFR-85 dated February 7, 1985Allison C28 Overhaul Manual Temporary Revision 72-7, Page 12 dated January 22, 1986 Allison C30 Overhaul Manual Revision dated July 1, 1985, Section 72-50-00, Paragraph (7), page 524 Allison Commercial Service Letter 250-C28/C30 CSL-2071/3073 dated June 1, 1985

Compliance is required as indicated unless already accomplished. To prevent excessive wear and/or fretting damage on the external splines of the turbine spline adapter or the aft splines of the turbine-to-compressor coupling shaft, which can progress to a disconnect and subsequent overspeed gas generator turbine failure/uncontained failure, accomplish the following: (a) Within the next five hours time-in-service after the effective date of this AD, but not later than December 20, 1986, for inservice engines, inspect the gas generator turbine spline adapter locknut torque in accordance with Allison Commercial Engine Alert Bulletin 250-C28/C30 CEB-A-72-2132/3146 dated October 1, 1985, or FAA approved equivalent.(b) Before initial flight, for uninstalled affected turbine assemblies, inspect the gas generator turbine spline adapter locknut torque in accordance with Allison Commercial Engine Alert Bulletin 250-C28/C30 CEB- A-72-2132/3146 dated October 1, 1985, or FAA approved equivalent. NOTE: The compliance requirements of this AD were previously published in Allison Commercial Service Letter 250-C28/C30 CSL-A-2084/3087, Revision 1, dated September 29, 1986, FAA approved by the Manager, Chicago Aircraft Certification Office. 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. Allison Commercial Engine Alert Bulletin 250-C28/C30 CEB-A-72-2132/3146 dated October 1, 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 this document from the manufacturer may obtain copies upon request to Allison Gas Turbine Division, General Motors Corp., P.O. Box 420, Indianapolis, Indiana 46206-0420. This document also may be examined at the Office of Regional Counsel, FAA, ATTN: Rules Docket No. 86-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 December 3, 1986, as to all persons except those persons to whom it was made immediately effective by Priority Letter AD No. 86-20-13, issued October 8, 1986, which contained this amendment.