AD 89-23-12

89-23-12 ALLISON GAS TURBINE DIVISION, GENERAL MOTORS CORPORATION (Allison, formerly Detroit Diesel Allison): Amendment 39-6345. Applicability: Allison Model 250-C28B and -C28C engines, with P/N 6898952 second stage turbine nozzle assembly, installed in aircraft certificated in any category except those with the following turbine assembly serial numbers:

Engine Model Turbine Serial Number 250-C28B CAT 70498, CAT 70499

CAT 70502, CAT 70513 and subsequent 250-C28C CAT 28010 and subsequent

Compliance: Required as indicated, unless already accomplished. To prevent failure of the second stage turbine nozzle which can lead to rubbing contact between the nozzle diaphragm and the second stage turbine wheel possibly resulting in an uncontained turbine wheel failure, accomplish the following: (a) Within the next 100 hours time-in-service after the effective date of this AD, or at the next turbine repair or overhaul, whichever occurs first, but not later thanNovember 30, 1989, perform the following: Modify and reidentify second stage turbine nozzle, P/N 6898952, into P/N 23001942, in accordance with Allison Commercial Engine Alert Bulletin CEB-A-72-2044, Revision 4, dated May 1, 1989. NOTE: Existing Model 250-C28B and -28C engines which have incorporated Allison Commercial Engine Alert Bulletin CEB-A-72-2044, Revision 4, dated May 1, 1989, or prior issues of CEB-72-2044, or engines which have incorporated P/N 23001942 are already in compliance with this AD. (b) 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. (c) Upon submission of substantiating data by an owner or operator through an FAA Airworthiness Inspector, an alternate method of compliance with the requirements of this AD or adjustments to the compliance schedule specified in this AD may be approved by the Manager, Chicago Aircraft Certification Office, Federal Aviation Administration, 2300 East Devon Avenue, Des Plaines, Illinois 60018. The second stage turbine nozzle modification shall be done in accordance with Allison Commercial Engine Alert Bulletin CEB-A-72-2044, Revision 4, dated May 1, 1989. This incorporation by reference was approved by the Director of the Federal Register in accordance with 5 U.S.C. 552(a) and 1 CFR Part 51. Copies may be obtained from Allison Gas Turbine Division, General Motors Corporation, P.O. Box 420, Indianapolis, Indiana 46206-0420. Copies may be inspected at the Regional Rules Docket, Office of the Assistant Chief Counsel, Federal Aviation Administration, New England Region, 12 New England Executive Park, Room 311, Burlington, Massachusetts 01803, or at the Office of the Federal Register, 1100 L Street, N.W., Room 8301, Washington, D.C. 20591. This amendment (39-6345, AD 89-23-12) becomes effective on October 29, 1989.