Accident
The pilot landed at the airport to refuel the airplane and pick up cargo. He spoke with three employees of the fixed base operator, who reported that he seemed alert and awake but wanted to make a "quick turn." After the airplane was fueled and the cargo loaded, the pilot departed. The airplane crashed one minute later. Night visual meteorological conditions prevailed at the time.
Aircraft and Flight
An aircraft performance GPS and simulation study indicated that the airplane entered a right bank almost immediately after takeoff and then made a 42-degree right turn. It was accelerating throughout the flight, from about 75 knots groundspeed shortly after liftoff to about 145 knots groundspeed at impact. The airplane climbed about 500 to 700 feet per minute to a peak altitude of about 260 feet above ground before descending. The simulation showed a gas generator speed of about 93 percent throughout the flight. The study indicated that the load factor vectors, which were the forces felt by the pilot, could have produced a somatogravic illusion of a climb, even while the airplane was descending.
Postaccident Examination
The postaccident examination of the airframe and engine revealed no evidence of mechanical malfunctions or failures that would have precluded normal operation.
Probable Cause
Based on the findings from the aircraft performance GPS and simulation study, the degraded visual reference conditions present about the time of the accident, and the forces felt by the pilot, it is likely that he experienced spatial disorientation, which led to his inadvertent controlled descent into terrain. The probable cause was determined to be the pilot's inadvertent controlled descent into terrain due to spatial disorientation, with the contributing factor being lack of visual reference due to night conditions.