Summary
This document proposes adopting a new airworthiness directive (AD) for MD Helicopters Inc. Model 600N helicopters. The AD would require reducing the life limit of the main rotor drive shaft (drive shaft) and changing the life limit shown on the component history card or equivalent record. This proposal 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 the proposed AD are intended to prevent failure of the drive shaft, loss of drive to the main rotor system, and subsequent loss of control of the helicopter.