Accident Summary
On the day of the accident, the pilot departed San Jose, California, and climbed to 4,600 feet mean sea level (msl) en route to Novato. Radar data indicated the aircraft leveled off at 4,600 feet on a heading of 330° at a ground speed of 180 knots true airspeed. At 1528 Pacific Standard Time, the aircraft began a descent. Within 24 seconds, it descended to 4,100 feet msl and its heading changed 10° to the right. The last radar return, 12 seconds later, showed a further heading change of 150° to the right and a descent to 2,300 feet msl.
Witness Observations
Witnesses observed the aircraft descending at high speed in a right turn with the engines operating at high power. Just before impact, the right bank angle and nose-low attitude increased. The aircraft struck the ground in a steep nose-down, right-wing-low attitude.
Investigation Findings
No preimpact mechanical malfunctions or failures were found during the examination of the wreckage. No autopsy was performed; only a gross external examination of the pilot's fragmented body was possible. Before departure, the pilot had remarked that he was bothered by a bad cold.
Probable Cause
The official probable cause was loss of control in flight for undetermined reasons. A contributing finding was physical impairment (other organic problem) on the part of the pilot-in-command.