What happened
On June 7, 1975, a pilot initiated a cross-country flight from Bex, Switzerland, towing a Foka SZD-24C glider, registration HB-776. The flight plan involved a 500 km route with a turnaround point in Landeck, Austria, alongside a second glider. After releasing from the tow at 2,500 meters, the pilot proceeded through the Alps, passing over the Furka and Oberalp passes.
Upon reaching the vicinity of Sedrun at an altitude of approximately 400 to 500 meters, the pilot identified a suitable plateau south of the village for an off-field landing and notified a companion via radio. While attempting to maneuver for the final approach, the pilot reported encountering significant turbulence and downdrafts, prompting an increase in airspeed to maintain control. In a final attempt to avoid the steep terrain, the pilot pulled up the aircraft just before impact. At 12:50, the HB-776 struck the ground approximately 29 meters below the ridge line. The impact caused the wreckage to slide 5 meters uphill before sliding down the slope. The pilot sustained serious injuries, and the aircraft was destroyed.
The investigation
The investigation examined the pilot's credentials, the aircraft's technical condition, and flight data. The pilot was a qualified flight instructor with extensive experience on this specific model. The Foka SZD-24C was found to be airworthy, with its weight and center of gravity within legal limits at the time of the accident.
Investigators analyzed barogram data to verify the pilot's claims regarding atmospheric conditions. While the pilot reported encountering strong downdrafts, the barogram showed a continuous descent during the final 13 minutes of flight, with a sink rate of less as low as 1 m/s in the final minute. Meteorological reports confirmed moderate turbulence in the area but did not support the presence of severe downdrafts capable of causing the observed descent profile.
Findings
- The pilot's flight speed was approximately 100 km/h during the final approach, which aligns with his decision to fly at an increased speed.
- The barogram data contradicts the pilot's claim of encountering strong downdrafts that would have caused significant altitude loss.
- The improper approach planning and insufficient altitude prior to beginning the final descent were the primary factors leading to the crash.