Summary
This document proposes the adoption of a new airworthiness directive (AD) that is applicable to Sikorsky Aircraft Corporation (Sikorsky) Model S-61 A, D, E, L, N, NM, R, and V helicopters. This proposal would require a nondestructive inspection (NDI) for cracks in the main rotor shaft (shaft), and require removal of any shaft with a crack and replacement with an airworthy shaft. This proposal would also require appropriate marking of shafts and log book entries by the operator to determine the shaft retirement life, and would establish a new retirement life for the shaft. This proposal is prompted by four reports of cracks occurring in helicopters that were utilized in repetitive external lift (REL) operations. The actions specified by the proposed 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.