What happened
The pilot reported for duty at 0200 hours to operate a cargo flight from Burbank, CA, to Phoenix, AZ. Following the first leg of the trip, the pilot arrived at a company apartment for crew rest between 0600 and 0630 hours. After approximately five hours of sleep, the pilot awoke at about 1200 hours.
The return leg of the operation commenced with a takeoff at 2055 hours. At 2230 hours, while maintaining a constant airspeed, heading, and altitude, the aircraft collided with a mountain. The impact occurred approximately 10 nautical miles south of the pilot's usual flight course. There was no evidence found to suggest that any attempt was made by the pilot to avoid the terrain.
The investigation
The aircraft and all of its components were examined during the investigation, and no mechanical deficiencies were noted. During the inquiry, another pilot at the company apartment reported observing a box of 'Dimetapp' decongestant pills on the pilot's shaving kit, noting that two pills were missing.