What happened
On the afternoon of October 16, 1966, a Mooney Mark 21, registration HB-DEB, departed from Kloten on a private VFR flight intended for Morocco, with a planned intermediate stop in France. The aircraft was carrying the pilot and three passengers.
Shortly after departure, the aircraft encountered deteriorating weather conditions characterized by low cloud bases and fog. While navigating through hilly terrain south of Herzogenbuchsee, the aircraft entered a cloud layer. In an attempt to regain visual contact with the ground, the pilot performed several course changes. During a steep turn, the aircraft exceeded its critical bank angle and entered an inverted position. The aircraft subsequently struck the ground at a high speed and a shallow angle, resulting in the four fatalities on board and the total destruction of the aircraft.
The investigation
Investigators examined the wreckage and analyzed the weather patterns in the region. The investigation confirmed that the aircraft was flying in a zone affected by a weather disturbance moving from southwest to northeast, which brought low visibility and heavy cloud cover.
Technical examination of the Mooney Mark 21's engine, propeller, flight controls, and structural components revealed no mechanical failures or pre-impact irregularities. The investigation found that the aircraft's instruments, including an artificial horizon and navigation equipment, were present but the aircraft was not certified or equipped for instrument flight rules (IFR). The investigation also reviewed the pilot's training records and the weather briefings received prior to departure.
Findings
- The pilot was not trained for instrument flight.
- The aircraft was not certified or approved for flight under instrument flight rules.
- The aircraft entered weather conditions that made it impossible to continue flying under visual flight rules (VFR).
- The pilot lost spatial orientation while attempting to maneuver out of the clouds to regain visual reference.