The highest vibration level dropped from 24 mm/s pk at the gearbox horizontal measurement locationnear the input shaft to 7.8 mm/s pk after change to a flexible coupling. Analysis of the flexible coupling failure established that fatigue cracking in the flexplate arm at the bolted joint between the flexplate and main rotor gearbox yoke Tail Rotor Drive Shaft Coupling Failure - Rotorcraft Engineering - Eng-tips The shaft couplings will also need to be undone for the same reason. Drive shaft coupling failure . The drive shaft to be displaced laterally and the flexible coupling to flail against the surrounding structure. In such a case, the vehicle can no longer be propelled, and the. The most likely cause of the failure is due to the interaction between torsional vibration and the operation of the governor. The drive shaft was implemented. An early and common symptom of a failing drive shaft is an intense vibration coming from underneath the vehicle. If the drive shaft’s uni...