Airworthiness Directives; Schweizer Aircraft Corporation and Hughes Helicopters, Inc. Model 269A, 269A-1, 269B, 269C, and TH-55A Helicopters

This amendment supersedes an existing airworthiness directive (AD), applicable to Schweizer Aircraft Corporation and Hughes Helicopters, Inc. Model 269A, 269A-1, 269B, 269C, and TH-55A helicopters with certain main rotor (M/R) drive shafts installed, that currently requires a one-time radiographic inspection or other non- destructive inspection of certain M/R drive shafts for cracks, distortion, corrosion, or other surface damage, at specified time intervals or upon the occurrence of specified conditions. This amendment requires the same inspections as the previous AD, but expands the applicability of certain inspections to additional models of the affected helicopters, and excludes certain M/R drive shafts from certain inspections. This amendment is prompted by a reevaluation as a result of a comment to the previous AD suggesting the need to expand the applicability of certain inspections to additional models of the affected helicopters and to exclude certain M/R drive shafts from certain inspections. The actions specified by this AD are intended to prevent structural failure of the M/R drive shaft, separation of the M/ R from the helicopter, and subsequent loss of control of the helicopter.