Helicopter Control Lost After Mechanical Failure During Climbout (N102HT)

Incident Overview

Approximately two minutes after beginning a climbout, the pilots of a helicopter detected a vibration in the airframe followed by a loud bang. In response, they entered an autorotation and selected a field for a forced landing. As the pilots attempted to control the helicopter, the flight controls did not respond to inputs. Control was subsequently lost, and the helicopter impacted the ground in an inverted attitude.

Wreckage Examination

Examination of the helicopter revealed that the main drive clutch and engine gimble ring with the torsional coupling had failed. Debris from the failed components was not recovered for examination. A review of maintenance logs showed that the drive coupling assembly had accumulated 511 hours of total service since new. Additionally, wreckage examination disclosed that the entire transmission assembly had rotated from its normally installed position, and the flight control rods were displaced from their normal positions.