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

This amendment adopts a new airworthiness directive (AD), applicable to Sikorsky Aircraft Corporation Model S-61A, D, E, L, N, NM, R, and V helicopters, that requires a nondestructive inspection (NDI) for cracks in the main rotor shaft (shaft), and requires removal of any shaft with a crack and replacement with an airworthy shaft. This AD also requires appropriate marking of shafts and log book entries by the operator to determine the shaft retirement life, and establishes a new retirement life for the shaft. This amendment is prompted by four reports of cracks occurring in helicopters that were utilized in repetitive external lift (REL) operations. The actions specified by this AD are intended to detect a fatigue crack in the shaft that could result in shaft structural failure, loss of power to the main rotor, and subsequent loss of control of the helicopter.