Summary
This document proposes the adoption of a new airworthiness directive (AD) that is applicable to McDonnell Douglas Helicopter Systems (MDHS) Model 600N helicopters. This proposal would require applying serial numbers to several life-limited components related to pitch control and removing and replacing the components according to new life-limits. This proposal is prompted by fatigue tests that indicate a need for shorter service lives for these components. The actions specified by the proposed 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.