Summary
This document proposes the adoption of a new airworthiness directive (AD) that is applicable to Bell Helicopter Textron, Inc. (BHTI) Model 412 and 412EP helicopters. This proposal would require creation of a component history card using a Retirement Index Number (RIN) system; would establish a system for tracking increases to the accumulated RIN; and would establish a maximum accumulated RIN for certain main rotor masts (masts) and main rotor spline plates (spline plates). This proposal 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 the proposed 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.