Airworthiness Directives; MD Helicopters, Inc. Model 369D, 369E, 369F, and 369FF Helicopters

This amendment revises an airworthiness directive (AD) for the specified MD Helicopters, Inc. (MDHI) helicopters that currently requires identifying the part number (P/N) of the bolts that attach the tail rotor gearbox to the tailboom and replacing any bolt of inadequate grip length with an airworthy bolt. That AD also requires adding an additional washer if more than four threads protrude from the nutplate. This amendment requires the same actions as the existing AD but reduces the applicability to only certain tailboom serial numbers and parts modified in accordance with either Supplemental Type Certificate (STC) SH5055NM or SH4801NM. This amendment also corrects a typographical error and clarifies that a slippage mark needs to be reapplied to each bolt regardless of the outcome of the required torque test. This amendment is prompted by the need to correct and clarify the applicability and other portions of the existing AD. The actions specified by this AD are intended to prevent loss of a tail rotor gearbox due to bolts of inadequate grip length and subsequent loss of control of the helicopter.