Airworthiness Directives; MD Helicopters Inc. Model MD900 Helicopters

This amendment adopts a new airworthiness directive (AD) for MD Helicopters Inc. (MDHI) Model MD900 helicopters. This action requires visually inspecting the drive shaft to determine the assembly part number (P/N) and marking the drive shaft assembly P/N and serial number (S/N) on any unmarked drive shaft. This AD also requires creating a component history card or equivalent record for certain drive shaft assemblies and replacing any drive shaft assembly that has reached its life limit. This amendment is prompted by the discovery of several drive shafts with no assembly P/N marked on the part, which could result in a drive shaft remaining in service past its life limit. The actions specified in this AD are intended to prevent failure of the drive shaft due to fatigue, which could result in total loss of drive to the main rotor hub and subsequent loss of control of the helicopter.