Airworthiness Directives; Bell Helicopter Textron, Inc. Model 412 and 412EP Helicopters

This amendment adopts a new airworthiness directive (AD), applicable to Bell Helicopter Textron, Inc. (BHTI) Model 412 and 412EP helicopters, that requires creation of a component history card or equivalent record using a Retirement Index Number (RIN) system; establishes a system for tracking increases to the accumulated RIN; and establishes a maximum accumulated RIN for certain main rotor masts (masts) and main rotor spline plates (spline plates). This amendment is prompted by fatigue analyses and tests that show certain masts and spline plates fail earlier than originally anticipated because of an unanticipated high number of takeoffs and external load lifts utilizing high power settings, in addition to the time-in-service (TIS) accrued under normal operating conditions. The actions specified by this AD are intended to prevent fatigue failure of the mast or spline plate, which could result in failure of the main rotor system and subsequent loss of control of the helicopter.