Incident Overview
Shortly after departure, while climbing initially, the helicopter experienced an abrupt loss of power. The pilot executed a forced landing to a nearby road.
Post-Accident Inspection
Examination of the transmission assembly found the splined engine adaptor fractured. The fracture resulted from a torsional overstress imposed on the transmission by the engine. Investigators determined that the adaptor fracture was secondary to another failure further along in the drive train or transmission.
Transmission Component Wear
Further inspection revealed that the freewheeling sprag clutch assembly, located at the drive shaft input to the main transmission, exhibited significant wear. This wear included smearing, non-uniform surface wear, and cam deformation. Damage or dragging in this assembly could account for the overstress fracture of the engine adaptor.