Flight and Pressurization
During a night cross-country flight at Flight Level 250, the pilot left the cockpit and moved to the rear of the aircraft to attend to physiological needs. Supplemental oxygen was available in the cockpit but not in the rear section. The airplane was operated with a known pressurization system deficiency that limited flight to 17,000 feet mean sea level while maintaining a cabin altitude of 10,000 feet.
Communication Loss and Radar Tracking
After 2 hours and 10 minutes of flight, air traffic control declared the aircraft as 'no radio.' At 3 hours and 57 minutes after departure, radar plotted the airplane in a descending left turn until ground impact.
Engine Conditions and Pilot Location
Fuel starvation resulted in a loss of power to the left engine. Propeller signatures indicated that the right propeller was producing power at impact. The pilot's body was found in the aft cabin area against the aft cabin bulkhead.
Investigation Findings
The investigation determined a partial failure of the pressurization system. The pilot operated the aircraft with known equipment deficiencies. The pilot's poor judgment led to hypoxia, a physical impairment. The loss of engine power was nonmechanical and caused by fuel starvation. The collision with terrain occurred during the descent. Factors included the malfunctioning pressurization system and the pilot's decision to continue operation with that known discrepancy.
Probable Cause
The probable cause was the pilot's poor judgment and the resultant hypoxia sustained in the unpressurized airplane. Factors were the malfunctioning pressurization system and the pilot's decision to continue operation with that known discrepancy.