Airworthiness Directives; Bell Helicopter Textron Canada Model 407 Helicopters

This amendment supersedes an existing airworthiness directive (AD) for Bell Helicopter Textron Canada (BHTC) Model 407 helicopters which requires a one-time replacement of certain oil cooler blower bearings. Also, the existing AD requires adding a limitation and caution to the rotorcraft flight manual (RFM) and inspecting, replacing, and lubricating certain bearings at specified intervals. This amendment adds certain segmented drive shaft bearings to the applicability and requires modifying the oil cooler blower inlet ducts and airflow shields and replacing certain bearings. Thereafter, this amendment requires removing the current temporary limitations and inserting revised limitations into the RFM. This amendment also requires revising the inspection and lubrication requirements. This amendment is prompted by several cases of bearing failure. The addition of certain segmented drive shaft bearings is due to two recent failures. The actions specified by this AD are intended to prevent failure of a bearing, loss of tail rotor drive, and a subsequent loss of directional control of the helicopter.