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

This amendment adopts a new airworthiness directive (AD), applicable to MD Helicopters, Inc. (MDHI) Model 600N helicopters, that requires applying serial numbers to several life-limited components related to pitch control and removing and replacing the components according to new life-limits. This amendment is prompted by fatigue tests that indicate a need for shorter service lives for these components. The actions specified by this AD are intended to prevent failure of the collective pitch control tubes, collective stick housings, and collective pitch tube assemblies, which can cause loss of collective pitch control, and subsequent loss of control of the helicopter.