Airworthiness Directives; MD Helicopters, Inc., Model 600N Helicopters

This amendment adopts a new airworthiness directive (AD) for the specified MD Helicopters, Inc. (MDHI) model helicopters that requires reducing the life limit of the main rotor drive shaft (drive shaft) and changing the life limit on the component history card or equivalent record. This amendment is prompted by the review of final fatigue test data, which indicates that the life limit of the drive shaft should be reduced by 2000 hours time-in-service (TIS). The actions specified by this AD are intended to prevent failure of the drive shaft, loss of drive of the main rotor system, and subsequent loss of control of the helicopter.