Airworthiness Directive · Amendment 39-16514 · Sikorsky Aircraft Corporation (Sikorsky) Model S-70A and S-70C Helicopters
Sikorsky Aircraft Corporation (Sikorsky) Model S-70A and S-70C Helicopters
Model S-70A and S-70C helicopters with a tail gearbox output bevel gear (gear), part number 70358-06620, certificated in any category.
This amendment adopts a new airworthiness directive (AD) for the Sikorsky Model S-70A and S-70C helicopters. This AD requires an ultrasonic test (UT) inspection of the tail gearbox output bevel gear (gear) for a crack. If you find a crack, replacing the gear with an airworthy gear is required before further flight. This AD is prompted by three gear cracking incidents, one of which resulted in the tail rotor separating from the helicopter. The actions specified by this AD are intended to detect a crack in the gear to prevent a tail rotor separating, loss of tail rotor control, and subsequent loss of control of the helicopter.
To prevent a tail rotor separating, loss of tail rotor control, and subsequent loss of control of the helicopter, do the following:
(a) Within 500 hours time-in-service (TIS), unless accomplished previously, and thereafter at intervals not to exceed 500 hours TIS, remove the tail rotor servo control and pitch beam shaft, and using a Level II Ultrasonic Testing Technician or equivalent, ultransonic inspect the gear for a crack. Ultrasonic inspect the gear by following paragraphs A.(5)a. through A(5)n. of Special Service Instructions No. 70-121A, Revision A, dated May 21, 2009. If you find a crack, before further flight, replace the gear with an airworthy gear.
(b) To request a different method of compliance or a different compliance time for this AD, follow the procedures in 14 CFR 39.19. Contact the Manager, Boston Aircraft Certification Office, FAA, Attn: Michael Schwetz, Aviation Safety Engineer, Boston Aircraft Certification Office, 12 New England Executive Park, Burlington, MA 01803, telephone (781) 238-7761, fax (781) 238-7170, for information about previously approved alternative methods of compliance.
(c) The Joint Aircraft System/Component (JASC) Code is 6520: Tail rotor gearbox.
