AD 91-04-02

EMERGENCY AIRWORTHINESS DIRECTIVE AVIATION STANDARDS NATIONAL FIELD OFFICE U.S. Department of Transportation P.O. BOX 26460 OKLAHOMA CITY, OKLAHOMA 7: 125 Federal Aviation Administration February 8, 1991 Priority Letter Airworthiness Directive (AD) prompted by Subsequent to issuing AD 90-21-01, failures of third in-service failures of the stage turbine stage turbine stators have occurred at cyclic times in-service lower than predicted by the initial failure analysis upon which compliance schedule of AD 90-21-01 must be further reduced to the AD was based. The FAA has therefore determined, based on service experience, that the stator replacement prevent additional failures. fracture. stage turbine to stator contact and subsequent Stator failure may result in third Amendment 39-6749. additional failures. Since this condition is likely to exist or develop on other engines of this same type design, this AD requires replacement of the third stage turbine stator assembly within certain schedules. Priority Division, Allied-Signal Incorporated, Model TPE331 turboprop and TSE331-3U immediately upon receipt. Pursuant to the authority of the Federal Aviation Act of delegated to me Letter turboshaft 91-04-02, applicable to engines, is by the Administrator, the following issued and is effective Garrett Engine Manufacturing Company of Arizona): February 8, 1991. 91-04-02 Garrett Turbine GARRETT ENGINE DIVISION, ALLIED-SIGNAL, INC, (formerly Engine Priority letter AD issued on _formerly Airesearch Applicability: Model TPE331-1, -2, -2UA, -30, -3UW, -5, -6, -6A turboprop and TSE331-3U turboshaft engines equipped Part Number (P/N) 868379-5 third stage stator assemblies, certificated in any category. accomplished. Compliance: Required as indicated, unless already accomplish the following: To prevent uncontained third stage turbine rotor failures, Replace the third stage turbine stator assembly, P/N 868379-5, in accordance with the following initial schedule: EMERGENCY AIRWORTHINESS DIRECTIVE

2 91-04-02 3rd Stage Stator Time in Service Since New or Since Rework to P/N 868379-5 Configuration Less than 1050 cycles. Replacement Schedule Prior to accumulating 1100 cycles. 1050 or more cycles. Within the next 50 cycles in service after receipt of this AD. If cycles are unknown Within the next 50 cycles in service after receipt of this AD - Thereafter, replace at intervals not to exceed service since new or since rework to P/N 868379-5 configuration. Note: Guidance and information regarding the replacement of the stator assembly can be obtained from Garrett Service Bulletin TPE331-A72-0699, Revision 3, dated February 4, 1991. Refer to Garrett Service Bulletin TPE/TSE331-72-0019, Revision 15, dated February 4, 1991, for definition of critical component service definitions, and stator serviceability' in limits, including the required life limit, cycle provisions of FAR 21.197 and 21.199 to a base where the AD can be Aircraft accordance accomplished. D. Upon submission of substantiating data by an owner or operator through an FAA Airworthiness Inspector, the Manager, Los Angeles Aircraft Certification Office, Transport Airplane Directorate, Aircraft Certification Service, _ FAA, 3229 East Spring Street, Long Beach, California 90806-2425, may approve an equivalent means of compliance or an adjustment of the compliance schedule which provides an equivalent level of safety. Priority Letter 91-04-02 supersedes AD 90-21-01, Amendment 39-6749. This Priority Letter 91-04-02, issued February 8, 1991, becomes effective immediately upon receipt. FOR FURTHER INFORMATION CONTACT: Mr • Joseph Costa, Aerospace Engineer, Propulsion Branch, ANM-140L, Los Angeles Aircraft Certification Office, Transport Airplane Directorate, Aircraft Certification Service, 3229 East Spring Street, Long Beach, California 90806-2425; telephone (213) 988-5246.