Summary
This document proposes adopting a new airworthiness directive (AD) for Bell Helicopter Textron, Inc. (BHTI) Model 204B helicopters. The AD would require replacing any main rotor mast assembly (mast), part number (P/N) 204-011-450-001, within 25 hours time-in-service (TIS). This proposal is prompted by the crash of a restricted category Model UH-1B helicopter due to failure of a mast, P/N 204-011-450-001. The same mast P/N is used on the Model 204B helicopters. The actions specified by the proposed AD are intended to prevent failure of the mast and subsequent loss of control of the helicopter.