Airworthiness Directives; Boeing Defense and Space Group Helicopter Division Model 234 Series Helicopters

This amendment supersedes an existing airworthiness directive (AD), applicable to Boeing Defense and Space Group Helicopter Division (Boeing) Model 234 series helicopters, that currently requires inspections of the forward and aft transmission first stage sun and spiral bevel ring gear bolted connection (bolted connection). This amendment requires a revision to the inspection intervals and criteria used during these inspections, as well as adds a visual inspection of the pinion and spiral bevel ring gear. This amendment is prompted by reports that certain of the affected helicopters have been discovered with loose nuts on the bolted connection more frequently than was anticipated in the previous AD. The actions specified by this AD are intended to prevent wear of the spiral bevel ring gear flange surface, failure of the bolted connection, transmission failure, and subsequent loss of control of the helicopter.