Airworthiness Directives; Agusta Model A109A, A109AII, and A109C Helicopters

This amendment adopts a new airworthiness directive (AD) applicable to Agusta Model A109A, A109AII, and A109C helicopters. This action requires inspecting the main transmission to determine if certain Gleason crowns are installed and replacing any unairworthy Gleason crown with an airworthy Gleason crown. This amendment is prompted by the discovery of a cracked Gleason crown during an unscheduled transmission inspection prompted by abnormal noises coming from the transmission during main rotor deceleration. The actions specified in this AD are intended to prevent failure of the main transmission, loss of rotor drive, and subsequent loss of control of the helicopter.