Airworthiness Directives; Bell Helicopter Textron, Inc. Model 214B, 214B-1, and 214ST Helicopters

This amendment supersedes an existing airworthiness directive (AD), applicable to Bell Helicopter Textron, Inc. (BHTI) Model 214B, 214B-1, and 214ST helicopters, that currently establishes a mandatory retirement life of 60,000 high-power events for the main transmission upper planetary carrier (carrier). This amendment requires changing the method of calculating retirement life for the carrier from high-power events to a maximum accumulated Retirement Index Number (RIN) of 120,000. This amendment is prompted by fatigue analyses and tests that show certain carriers fail sooner than originally anticipated because of the unanticipated high number of lifts or takeoffs (torque events) performed with those carriers in addition to the time-in-service (TIS) accrued under other operating conditions. The actions specified by this AD are intended to prevent fatigue failure of the carrier, which could result in failure of the main transmission and subsequent loss of control of the helicopter.