Incident Summary
A twin-engine airplane was conducting power-off stall maneuvers at an altitude of approximately 1,000 feet above ground level during a flight intended to demonstrate the aircraft to a prospective buyer. A witness observed the first stall maneuver and recovery, describing it as "good." During the second stall, the nose rose higher than the first, followed by the right wing dropping and a steep nose-down attitude. The airplane rotated approximately one and a half revolutions before disappearing behind trees. Prior to ground impact, the witness reported hearing the engines rev up.
Radar and Performance Analysis
A radar and aircraft performance study revealed that the accident airplane had departed the airport and subsequently executed a series of heading, speed, and altitude changes, ultimately crashing 14.6 nautical miles east of the departure airport. During several time periods, calculations of calibrated airspeed indicated a trend toward and below the published stall speeds of 63 knots with flaps extended and 71 knots with flaps retracted.
Examination Findings
An examination of the airplane and engines found no structural or mechanical anomalies.
Probable Cause
The probable cause, as determined by the official investigation, was the pilot-in-command's failure to maintain adequate airspeed resulting in an inadvertent stall/spin.