Summary
This document proposes adopting a new airworthiness directive (AD) for the specified Sikorsky Aircraft Corporation (Sikorsky) model helicopters. The AD would require, within a specified time, creating a component history card or equivalent record. The AD would also require 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 would require calculating a moving average of lift cycles per hour TIS at specified intervals on each IFWU assembly. The moving average would be 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 would require a repetitive inspection, which requires a visual and dimensional inspection of the IFWU assembly at specified intervals. This AD would also require recording certain information and replacing each part that is beyondthe wear limits or that exhibits visual surface distress with an airworthy part. In addition, this AD would require permanently marking the REL IFWU camshafts and gear housings with the letters "REL" on the surface of these parts. This proposal is prompted by an accident in which the left and right IFWU assembly on a helicopter slipped or disengaged resulting in both engines overspeeding, engine shutdowns, and loss of engine power to the transmissions. The actions specified by the proposed 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.