Accident Overview
The aircraft was on a day visual flight rules (VFR) flight from Ontario, California, to Las Vegas, Nevada, when it collided with mountainous terrain near the top of a 6,500-foot peak. Radar data indicated that approximately 20 minutes before the accident, the aircraft began a gradual descent from about 10,000 feet.
Mechanical and Pilot Factors
Investigation found no preimpact part failure or malfunction of the aircraft, engine, or autopilot. The pilot had a rest period on the previous day, but it could not be determined whether he obtained any sleep before a 1700 Pacific Standard Time (PST) flight. After that flight, he voluntarily flew on a late-night flight with another company. That flight was delayed in returning and did not land at Ontario until about 0500 PST the next morning. Approximately 41 minutes later, the pilot took off on the accident flight.
Official Findings
The probable cause as determined by the investigation includes an altitude deviation (uncontrolled) during cruise-normal phase, with findings that the pilot in command did not maintain altitude, the descent was inadvertent, and fatigue (lack of sleep) was a factor. The second occurrence was an in-flight collision with terrain/water during an uncontrolled descent, with mountainous/hilly terrain as a contributing finding.