Airworthiness Directives; Boeing Defense and Space Group Model 234 Helicopters

This document publishes in the Federal Register an amendment adopting Airworthiness Directive (AD) 2004-06-51, which was sent previously to all known U.S. owners and operators of Boeing Defense and Space Group (Boeing) Model 234 helicopters by individual letters. This AD requires, before further flight, inspecting the upper shaft extension for a crack and modifying the aft vertical shaft assembly (assembly). Thereafter, this AD requires, before the first flight of each day, inspecting the upper shaft extension for any crack. If any crack is found during any of the inspections, replacing the assembly with an airworthy assembly is required before further flight. This amendment is prompted by the discovery of a crack in the upper shaft extension of an assembly. The actions specified by this AD are intended to detect a crack in the upper shaft extension, which could result in catastrophic failure of the assembly and subsequent loss of control of the helicopter.