What happened
On May 8, 1974, a Mooney M20E, registration HB-DER, departed from Lausanne-Blécherette airport for a flight involving engine failure and stall training. The flight was part of a transition program for a pilot with limited experience, supervised by a more experienced pilot acting as an instructor.
During the flight, the aircraft performed a series of highly aggressive maneuvers over the Eclépens-La Sarraz region. Witnesses observed the aircraft performing vertical climbs, rolls, and steep dives. During one of the final maneuvers, the aircraft entered a steep dive and subsequently a right-hand spin. The aircraft struck a field at the 'Les Trois Noyers' site near Eclépens, resulting in the two fatalities of the occupants and the total destruction of the aircraft.
The investigation
Investigators examined the flight sequence, the aircraft's technical condition, and the backgrounds of both occupants. The investigation established that the aircraft was in a proper state of airworthiness, with weight and balance within permissible limits. The engine and propeller were found to have functioned normally until the impact.
Evidence from witnesses, though none were aeronautically trained, described a series of maneuvers that exceeded standard flight envelopes. The investigation also reviewed the professional history of the pilot acting as instructor, noting a prior suspension for unauthorized maneuvers. Furthermore, toxicological analysis revealed that the instructor was under the influence of alcohol at the time of the accident.