NTSB investigators either traveled in support of this investigation or conducted a significant amount of investigative work without any travel, and used data obtained from various sources to prepare this aircraft accident report.
The pilot was conducting a local aerobatic flight with a pilot-rated passenger occupying the rear seat (which was equipped with flight controls). The pilot's son was flying another airplane, returning to the home airport after a local sightseeing flight. The airport was at the southeast corner of a reservoir, which surrounded the airport on three sides (all but the east side). The accident site was located on flat, featureless, snow-covered terrain northwest of the airport. The son reported that, as he was flying north away from the airport over the west side of the reservoir, it was frozen over, and covered with snow. He stated that the surface was flat with no cracks, and the lighting was flat as well so that he had difficulty judging his height above the ground. As he continued north, the surface showed some cracks, which helped him with height visualization. About 7 miles north of the airport, he transitioned to the east side of the reservoir, and headed south toward the airport. The son's airplane was about 200 ft above ground level and several miles from the runway on final approach, when an exchange of radio transmissions led the son to believe that his father was going to pass by him. He never saw his father's airplane. An airplane witness had just taken off from the airport in another airplane; he saw the son's airplane on a 2-mile final approach and then saw a debris field forming as the accident airplane impacted the ground behind the son's airplane.
Examination of the accident site and the wreckage indicated that the airplane impacted the ground at high speed in a near level attitude, consistent with controlled flight into terrain. No evidence of any preimpact mechanical malfunctions or anomalies was found. It is likely that, as a result of the flat light conditions described by the pilot's son, the pilot did not realize he was descending over the featureless, snow-covered terrain.
The pilot had undiagnosed heart disease, which placed him at significant risk for sudden severe impairment/incapacitation from an acute cardiovascular event such as a heart attack, arrhythmia, or stroke. However, the operational evidence indicated that this crash was controlled flight into terrain with a pilot rated passenger in the rear seat who could have taken over in the event the pilot became severely impaired or incapacitated. As a result, it is unlikely the pilot's heart disease contributed to the accident.