Airworthiness Directive · Amendment 39-17830 · Main rotor head
Sikorsky Aircraft Corporation Helicopters
This AD applies to Model S-76A, B, and C helicopters with a main rotor hub (MRH) pilot, part number (P/N) 76103-08003-101, installed, certificated in any category.
We are superseding Airworthiness Directive (AD) 2005-22-01 for Sikorsky Aircraft Corporation (Sikorsky) Model S-76A, B, and C helicopters. AD 5002-22-01 required inspecting the main rotor lower bifilar arm assembly (bifilar arm assembly) for a crack, and if there is a crack, replacing the bifilar arm assembly. AD 2005-22-01 also required a one-time test for the correct torque on the lug nuts, and if necessary, conducting torque stabilization tests. This new AD retains the requirements of AD 2005-22-01 and also requires replacing the main rotor hub (MRH) pilot with a different part-numbered MRH pilot, which is terminating action for the requirements of the AD. This AD was prompted by the development of a terminating procedure for the inspections required by AD 2005-22-01. We are issuing this AD to prevent failure of a bifilar lug, damage to the main rotor system, and subsequent loss of control of the helicopter.
You are responsible for performing each action required by this AD within the specified compliance time unless it has already been accomplished prior to that time.
(1) For MRH pilots with 1,500 or more hours time-in-service (TIS), within 50 hours TIS, and thereafter at intervals not to exceed 50 hours TIS, inspect the lower bifilar arm assembly for a crack in the lug attachment area. Conduct the inspection of the lower bifilar arm assembly by following the Accomplishment Instructions, paragraphs 3.A.(1) through 3.A.(6), of Sikorsky Alert Service Bulletin No. 76-65-62, dated December 14, 2004 (ASB 76-65-62).
(i) If there is a crack on any bifilar assembly arm lug, before further flight, replace the bifilar arm assembly with an airworthy bifilar arm assembly.
(ii) If no crack is found at the initial inspection, perform a one-time torque test. Perform the torque test and the additional torque procedures as stated in the Accomplishment Instructions, paragraphs 3.B.(1) through 3.B.(3), of ASB 76-65-62. The torque test is not required at the recurring inspection intervals of the lower bifilar arm assembly.
(iii) Within 600 hours TIS, replace the MRH pilot, P/N 76103-08003-101, with an MRH pilot, P/N 76103-08003-102.
(2) For MRH pilots with less than 900 hours TIS, prior to accumulating 1,500 hours TIS, replace the MRH pilot, P/N 76103-08003-101, with a MRH pilot, P/N 76103-08003-102.
(3) After the effective date of this AD, do not install an MRH pilot, P/N 76103-08003-101, on any helicopter.
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
