What happened
At 14:45 MDT, the pilot departed on a routine visual flight rules repositioning flight, a route he had flown frequently before. After takeoff, he leveled the aircraft at 9,500 feet and proceeded on a direct course toward his destination. Approximately 30 minutes later, at about 15:15, the aircraft began a shallow oscillatory descent while it was roughly 28 miles from the Black Mountain Range.
Subsequently, the aircraft collided with a ridge located approximately one mile from Black Mountain Peak. The impact occurred while the aircraft was in a wings-level attitude at an elevation of about 8,500 feet. Weather conditions at the time were VFR with scattered clouds and 15 miles visibility.
The investigation
An examination of the wreckage revealed no evidence of a preimpact part failure or malfunction. The aircraft was equipped with an Arnav-20 LORAN unit and a Century IIB autopilot. The autopilot did not have an altitude hold function, but its mode selector was found positioned to the 'HDG' position. Additionally, the elevator trim was found near the neutral position.
Pathological and toxicological examinations revealed no indication of a physiological problem. However, the possibility of the pilot falling asleep or becoming incapacitated could not be determined.