On November 4, 1999, a Kaman K-1200 (registration N164KA) operated by Mountain West Helicopters, Llc was involved in an aviation accident near Emida, ID. Investigators recorded the probable cause as: Failure of the splined engine adaptor as a result of torsional overstress. Factors include a worn freewheeling clutch assembly. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
A helicopter experienced a sudden power loss shortly after departure during initial climb, prompting a forced landing. Post-accident inspection revealed a fractured engine adaptor due to torsional overstress, linked to wear in the freewheeling sprag clutch assembly.
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.