Airworthiness Directive · Amendment 39-18107 · Tail rotor drive shaft
Sikorsky Aircraft Corporation (Sikorsky) Helicopters
This AD applies to Model S-76A, S-76B, S-76C, and S-76D helicopters, serial numbers (S/N) up to and including 761050, certificated in any category, with a tail drive shaft (TDS) part number (P/N) and S/N as follows:
(a) P/N 76361-04004 (all dash numbers) with an S/N up to and including A127-01092; or
(b) P/N 76361-04604 (all dash numbers) with an S/N with a prefix A240 or B240, or with an S/N C240-00001 through C240-00880.
We are adopting a new airworthiness directive (AD) for certain Sikorsky Model S-76A, B, C, and D helicopters. This AD requires inspecting the tail rotor drive shaft (TDS) flange-to-shaft attachment hardware for correct assembly and correct torque of the fasteners. If there is a discrepancy, this AD requires, before further flight, applying an index mark to the flange and TDS, inspecting the flange and shaft for a crack, fracture, wear, and certain measurements, and replacing any part that does not meet the approved criteria before further flight. This AD is prompted by a partial loss of tail rotor drive resulting in a forced landing. The actions specified by this AD are intended to prevent failure at the flange-to-shaft attachment, loss of a tail rotor drive, 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.
Within 30 hours time-in-service:
(1) Inspect each TDS flange attachment hardware at all four locations for looseness and torque stripe misalignment as depicted in Figure 1 and shown in Figure 2 of Sikorsky Aircraft Corporation Alert Service Bulletin ASB 76-66-52, Basic Issue, dated April 1, 2014 (ASB). Inspect each nut to determine whether it can be rotated by hand. Determine whether the hardware is assembled correctly by following the Accomplishment Instructions, paragraph B.(3)(a) through B.(3)(b) of the ASB. Determine the torque of each nut.
(2) If there is no looseness, torque stripe misalignment, incorrect hardware assembly, and if no nut can be rotated by hand and the torque of any nut is not less than 105 inch-pounds, no further action is required by this AD.
(3) If there is looseness, torque stripe misalignment, incorrect hardware assembly, a nut rotated by hand, or the torque of any nut is less than 105 inch-pounds, do the following:
(i) Apply an index mark to the flange and shaft to make sure the flange is reinstalled in the same position and to maintain shaft balance, unbolt and remove the flange from the shaft, and visually inspect each radius washer for wear or fretting. Replace any washer with wear or fretting.
(ii) Inspect the flange and shaft for a crack, fracture, wear on the mounting hole, and diameter by following the Accomplishment Instructions, paragraph 3.D.(5)(a) through 3.D.(5)(e), of the ASB. If the flange and shaft fail any of the inspection criteria, before further flight, replace the TDS with an airworthy TDS.
(iii) Align index marks, install the flange on the shaft, and coat the grip length of each bolt and the contact surfaces on each radius washer and washer with epoxy polyamide primer.
(iv) Torque each nut by following either paragraph D.(9) or D.(10) of the Accomplishment Instructions of the ASB.
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.
