Summary
This document proposes the adoption of a new airworthiness directive (AD) that is applicable to Eurocopter Deutschland Model MBB- BK 117 helicopters. This proposal would change the retirement life for the tail rotor (output) drive bevel gear (bevel gear). This proposal is prompted by a fatigue analysis of the bevel gear conducted by the manufacturer due to installation of different tail rotor blades. The actions specified by the proposed AD are intended to prevent fatigue failure of the bevel gear, loss of tail rotor drive, and subsequent loss of control of the helicopter.