Summary
This document proposes the adoption of a new airworthiness directive (AD) that is applicable to Bell Helicopter Textron Canada (BHTC) Model 407 helicopters. This proposal would require shimming the tail rotor drive system bearing supports (bearing supports). This proposal is prompted by reports of cracked bearing hangar support arms in the area of the fillet radius. The actions specified by the proposed AD are intended to prevent failure of the bearing supports, which could result in excessive tail rotor drive system vibration, loss of tail rotor drive, and subsequent loss of control of the helicopter.