At 1445 MDT, the 60 year old pilot departed on a routine, VFR, repositioning flight which he had frequently flown before. After takeoff, he leveled the aircraft at 9500 ft on a direct course toward the destination. While en route at about 1515, the aircraft began a shallow oscillatory descent when it was about 28 miles from the Black Mountain range. Subsequently, the aircraft collided with a ridge about 1 mile from Black Mountain Peak while in a wings level attitude at an elevation of about 8500 ft. The weather at that time was VFR with only scattered clouds and 15 miles visibility. An exam 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 had no altitude hold function, but its mode selector was found positioned to the 'HDG' position. Also, the elevator trim was found near the neutral position. Pathological and toxicological exams revealed no indication of a physiological problem. The possibility of the pilot falling asleep or becoming incapacitated could not be determined.