What happened
On the morning of August 12, 1965, a flight student from the Swiss Air Traffic School departed Hausen for a scheduled cross-country flight toward Pontarlier. Shortly after takeoff, the pilot deviated from the assigned route, heading toward the city of Zug to perform low-altitude maneuvers over his former workplace.
While flying at an altitude estimated between 150 and 200 meters, the pilot began performing irregular circles over the Gutsch hill. During these maneuvers, which included banking at angles of 45 to 60 degrees, the pilot attempted to increase the bank angle and pull back on the elevator to compensate for a perceived loss of visibility caused by the left wing. This action caused the Bücker 131 Jungmann, registration HB-URL, to stall. The aircraft entered a near-inverted position and could not be recovered, ultimately striking the crest of a hill with its left wing before impacting the ground heavily.
The investigation
The investigation examined the pilot's flight history, the aircraft's mechanical state, and the circumstances leading to the deviation from the flight plan. Investigators found that the pilot had a significant amount of flight experience, including approximately 50 hours on this specific aircraft type. The investigation also looked into the pilot's intent, noting that he had expressed a desire to fly over his former colleagues during their break. Evidence suggested that the pilot had performed similar low-level maneuvers in the same area just days prior to the accident.
Findings
- The primary cause of the accident was the pilot losing control of the aircraft due to an aerodynamic stall during a low-altitude display flight.
- The pilot intentionally deviated from the prescribed flight path to perform maneuvers for the purpose of impressing onlookers.
- The pilot's decision to increase the bank angle and pull back on the controls at a low altitude left insufficient altitude margin to recover from the resulting stall.
- The pilot had a pre-existing intention to perform these maneuvers, as evidenced by his comments to others and similar flights conducted earlier in the week.