What happened
On May 24, 1969, at approximately 17:03, a Jodel D 11 aircraft, registration HB-SOW, crashed while attempting to land at the Gruyères airfield. The flight originated from Porrentruy as part of a multi-leg journey. During the final approach to runway 36, the pilot attempted to correct a perceived high approach by initiating a second glide (glissade). During this maneuver, the aircraft's nose pitched up, leading to a sudden loss of lift on the right wing. The aircraft struck the ground approximately 120 meters before the runway threshold, resulting in the destruction of the aircraft and two light injuries to the occupants.
The investigation
The investigation examined the aircraft's technical condition, the pilot's performance, and the environmental factors at the time of the accident. Investigators reviewed the aircraft's maintenance history, noting that HB-SOW had been well-maintained and was within weight and balance limits. Meteorological data was analyzed to evaluate the pilot's claim regarding updrafts, which was ultimately refuted by official records. Furthermore, the investigation scrutinized the pilot's physiological state, as blood tests revealed alcohol concentrations of 0.5 to 0.6 per mille in the pilot and 0.8 to 0.9 per mille in the passenger.
Findings
- The primary cause of the accident was that the pilot exceeded the allowable angle of attack while initiating a glide at a low altitude.
- The pilot's ability to perform fine control inputs was likely impaired by alcohol consumption, which can lead to overconfidence and reduced self-control.
- It is highly probable that the pilot attempted a sudden correction to avoid a go-around, causing a sharp change in the angle of attack.
- While the pilot reported speeds of 110–120 km/h, witnesses suggested the airspeed was likely too low for the maneuver.
- There were no evidence of pre-existing technical defects in the aircraft's mechanical systems.