Summary
This document proposes the adoption of a new airworthiness directive (AD) that is applicable to Bell Helicopter Textron, A Division of Textron Canada Ltd. (BHTC) Model 206L, L-1, L-3, and L-4 helicopters. This proposal would require creation of a component history card using a Retirement Index Number (RIN) system, establishing a system for tracking increases to the accumulated RIN, and a maximum accumulated RIN for certain main rotor masts (masts) and main rotor trunnions (trunnions). This proposal is prompted by fatigue analyses and tests that show certain masts and trunnions fail sooner than originally anticipated because of the unanticipated higher number of external load lifts and takeoffs (torque events) performed with those masts and trunnions in addition to the time-in-service (TIS) accrued under other operating conditions. The actions specified by the proposed AD are intended to prevent fatigue failure of the mast or trunnion, which could result in loss of the main rotor system and subsequent loss of control of the helicopter.