Accident Sequence
The helicopter was on a flight to a site near Guadalupe Pass, an area known for erratic and gusty winds. The pilot was on an approach to a high meadow with an elevation of approximately 5,460 feet when the helicopter entered a descent and crashed well short of the intended landing area. A witness reported that the main rotor RPM slowed and the rotor blades coned prior to impact.
Investigation Findings
Evidence indicated that the helicopter impacted in a level attitude and at a high rate of descent. An investigation revealed that a coupling on the engine-to-main transmission drive shaft had become disconnected. There was evidence that the male driveshaft coupling was not properly secured to the flange on the main rotor driveshaft's engine end.
Maintenance Background
Eight days prior to the accident, an air conditioning system was installed on the helicopter. This installation would have required that a drive shaft coupling be disconnected. There was evidence that the self-locking nuts were reused when the coupling was reconnected.