Airworthiness Directives; Various Helicopters

The FAA proposes to supersede Airworthiness Directive (AD) 2015-20-12, which applies to certain Sikorsky Aircraft Corporation Model S-61A, D, E, L, N, NM serial number (S/N) 61454, R, and V; Croman Corporation Model SH-3H; Carson Helicopters, Inc., Model S-61L and SH- 3H; Glacier Helicopter, Inc., Model CH-3E; Robinson Air Crane, Inc., Model CH-3E, CH-3C, HH-3C and HH-3E; and Siller Helicopters Model CH-3E and SH-3A helicopters. AD 2015-20-12 requires calculating or recalculating the hours time-in-service (TIS) of the main rotor shaft (MRS), determining whether the MRS is repetitive external lift (REL) or non-REL, performing a nondestructive inspection (NDI) for cracks, replacing any MRS that has cracks, replacing parts before their life limits and removing from service any parts that have exceeded their life limits. This proposed AD would also require establishing retirement lives for each REL MRS, including reducing life limits and allowing for modification of life limits based on service information, and removing any MRS with oversized dowel pin bores. Since the FAA issued AD 2015-20-12, a design re-evaluation shows that the MRS on certain helicopter models requires a lower life limit. This proposed AD would retain some of the requirements of AD 2015-20-12, and would also lower the retirement life for a certain MRS installed on certain helicopters and would update the type certificate holder name for some of the affected helicopter models. The FAA is proposing this AD to address the unsafe condition on these products.