Airworthiness Directives; Sikorsky Aircraft Corporation Model S-61L, N, R, and NM Helicopters

This amendment adopts a new airworthiness directive (AD) for the specified Sikorsky Aircraft Corporation (Sikorsky) model helicopters that requires, within a specified time, creating a component history card or equivalent record. The AD also requires recording the hours time-in-service (TIS) and the external lift cycles (lift cycles) for each main gearbox input left and right freewheel unit (IFWU) assembly. Also, the AD requires calculating a moving average of lift cycles per hour TIS at specified intervals on each IFWU assembly. The moving average is used to determine if an IFWU assembly is used in repetitive external lift (REL) or non-REL helicopter operations. If an IFWU assembly is used in REL operations, this AD requires a visual and dimensional inspection of the IFWU assembly at specified intervals. This AD also requires recording certain information and replacing each part that is beyond the wear limits or that exhibits visual surface distress with an airworthy part. In addition, this AD requires permanently marking the REL IFWU camshafts and gear housings with the letters "REL" on the surface of these parts. This amendment is prompted by an accident in which the left and right IFWU assembly on a helicopter slipped or disengaged resulting in both engines over speeding, engine shutdowns, and loss of engine power to the transmissions. The actions specified by this AD are intended to prevent slipping in the IFWU assembly, loss of engine power to the transmissions, and subsequent loss of control of the helicopter.