AD 98-12-22 Amendment 39-10576

This amendment adopts a new airworthiness directive (AD), applicable to Bell Helicopter Textron Canada (BHTC) Model 407 helicopters that requires shimming the tail rotor drive system bearing supports (bearing supports). This amendment is prompted by reports of cracked bearing hangar support arms in the area of the fillet radius. The actions specified by this 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.