Airworthiness Directive · Amendment 39-16281 · Sikorsky Aircraft Corporation Model S-76A, B, and C Helicopters
Sikorsky Aircraft Corporation Model S-76A, B, and C Helicopters
Model S-76A, B, and C helicopters, with a main rotor servo actuator (servo actuator), Sikorsky Aircraft Corporation (Sikorsky) part number (P/N) 76650-09805-109 or -110 (also marked as HR Textron or Woodward HRT P/N 3006760-109 or -110), installed, certificated in any category.
This amendment adopts a new airworthiness directive (AD) for Sikorsky Aircraft Corporation (Sikorsky) Model S-76A, B, and C helicopters that requires inspecting each installed Woodward HRT (formerly HR Textron) main rotor servo actuator (servo actuator) for a high rate of leakage and replacing each affected servo actuator with a servo actuator containing a newly re-designed servo actuator piston. This amendment is prompted by a National Transportation Safety Board (NTSB) Safety Recommendation issued in response to an accident involving a Model S-76C helicopter. In the NTSB Safety Recommendation, the performance of a servo actuator piston upon reaching 3,000 hours time-in-service (TIS) was questioned as a result of piston head seal leakage and piston head plasma spray flaking. The actions specified by this AD are intended to prevent degraded servo actuator performance as a result of piston head seal leaking and plasma spray flaking, which could result in subsequent loss of control of the helicopter.
To detect leaking in a servo actuator, which could lead to degraded servo actuator performance and subsequent loss of control of the helicopter, do the following:
(a) For a servo actuator with 1,500 or less hours time since new (TSN) or time since overhaul (TSO), determine the leakage rate on or before reaching 1,500 hours TSN or TSO. This 1,500 hour TSN or TSO inspection revises the airworthiness limitations section of the applicable maintenance manual.
(b) For a servo actuator with 2,250 or less hours TSN or TSO, but more than 1,500 hours TSN or TSO, determine the leakage rate on or before reaching 2,250 hours TSN or TSO.
(c) If the leakage rate in any servo actuator exceeds 700 cc per minute when performing the leakage rate inspection specified in paragraph (a) or (b) of this AD, then:
(1) Replace that servo actuator piston, HR Textron or Woodward HRT P/N 41004321 or P/N RW41004321, with a servo actuator piston, P/N 41012001 or P/N 41012001-001, and re-identify the servo actuator on the servo actuator data plate as Sikorsky P/N “76650-09805-111” and Woodward HRT P/N “3006760-111” using a metal stamp method; or
(2) Replace the servo actuator with an airworthy servo actuator, Sikorsky P/N 76650-09805-111, Woodward HRT P/N 3006760-111.
(d) On or before 3,000 hours TSN or TSO, whichever occurs first, replace each servo actuator piston and re-identify the servo actuator as specified in paragraph (c)(1) of this AD or replace each servo actuator as specified in paragraph (c)(2) of this AD.
(e) Modifying and re-identifying each servo actuator as specified in paragraph (c)(1) of this AD or replacing each servo actuator as specified in paragraph (c)(2) of this AD is terminating action for the requirements of this AD for the modified and re-identified or replaced servo actuator.
(f) 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: Terry Fahr, Aviation Safety Engineer, 12 New England Executive Park, Burlington, MA 01803, telephone (781) 238-7155, fax (781) 238-7170, for information about previously approved alternative methods of compliance.
(g) The Joint Aircraft System/Component (JASC) Code is 6730: Rotorcraft Servo System.
The aircraft, engines and makers this AD names, by the model designations in its text. A model listed here may still be outside the AD's serial ranges.
Aircraft
