93-17-13: Lower Coupling Drive Shaft

93-17-13 SCHWEIZER AIRCRAFT CORPORATION and HUGHES HELICOPTERS, INC.: Amendment 39-8684. Docket Number 93-SW-11-AD. Applicability: Model 269A, 269A-1, 269B, 269C, and TH55A helicopters, certificated in any category. Compliance: Required as indicated, unless accomplished previously. To prevent failure of the lower coupling drive shaft (shaft), loss of power to the rotor system, and subsequent loss of control of the helicopter, accomplish the following: (a) Within the next 30 days or 100 hours' time-in-service after the effective date of this AD, whichever occurs first-- (1) Install engine and rotor tachometer markings in accordance with Part II of Schweizer Aircraft Corporation Service Bulletin B-257.1, dated May 21, 1993 (SB). NOTE: Figure B-257.1-2 indicates the position of the white slippage mark on the lens and lens frame. (2) Visually inspect the shaft for cracks, machining steps, manufacturing tool marks, surface defects, and lack of cleanup during the production grinding operation in accordance with Part I of the SB. NOTE: Failure to accomplish proper cleanup of the shaft surface is evidenced by a non-uniform surface smoothness. The actual surface finish value may vary from shaft to shaft. (b) Repeat the visual inspection for cracks as described in paragraph (a)(2) of this AD at intervals not to exceed 300 hours' time-in-service from the last inspection. (c) Replace any shaft found to be unairworthy during the inspection required by this AD with an airworthy shaft, before further flight. (d) An alternative method of compliance or adjustment of the compliance time, which provides an acceptable level of safety, may be used when approved by the Manager, New York Aircraft Certification Office, FAA, New England Region, 181 South Franklin Avenue, Valley Stream, New York 11581. Operators shall submit their requests through an FAA Principal Maintenance Inspector, who may concur or comment and then send it to the Manager, New York Aircraft Certification Office. NOTE: Information concerning the existence of approved alternative methods of compliance with this AD, if any, may be obtained from the New York Aircraft Certification Office. (e) Special flight permits may be issued in accordance with FAR 21.197 and 21.199 to operate the helicopter to a location where the requirements of this AD can be accomplished. (f) The modification and inspections shall be done in accordance with Part I and II of Schweizer Aircraft Corporation Service Bulletin B-257.1, dated May 21, 1993. 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 Schweizer Aircraft Corporation, P.O. Box 147, Elmira, New York 14902. Copies may be inspected at the FAA, Office of the Assistant Chief Counsel, 4400 Blue Mound Road, bldg. 3B, room 158, Fort Worth, Texas 76106; or at the Office of the Federal Register, 800 North Capitol Street, NW., suite 700, Washington, DC. (g) This amendment becomes effective on October 20, 1993.