What happened
On June 7, 1978, an ASW 20 glider, registration OE-5163, was participating in a gliding competition in Switzerland. The pilot, flying as a guest participant, had departed from Grenchen airfield to compete in a designated circuit involving several waypoints. The flight proceeded normally until the final stages near Sumiswald.
During the approach for an outlanding, the aircraft was observed by a fellow competitor circling at low altitude, appearing to search for thermals. Shortly thereafter, a witness on the ground observed the glider flying low near a farmstead before it entered a steep, descending turn. The aircraft struck the ground at Chleinegg with a high angle of attack, resulting in the destruction of the glider and the death of the pilot, who succumbed to his injuries shortly after arriving at a local hospital.
The investigation
Investigators analyzed barograph recordings, which revealed that the aircraft had been in a continuous descent for approximately 17.5 minutes prior to impact, losing about 770 meters. Physical examination of the wreckage showed that the aircraft's flaps were in position 5, and the longitudinal trim was set in a tail-heavy configuration. The investigation also confirmed that the aircraft's weight and center of gravity were within permissible limits and that there were no pre-existing mechanical defects in the flight controls.
Findings
- The primary cause of the accident was the undershooting of the minimum flying speed.
- A late decision to land prevented the pilot from executing an adequate landing pattern and preparation.
- Incorrect longitudinal trim (set tail-heavy) likely contributed to the loss of airspeed and the subsequent stall.
- The pilot had relatively limited experience with this specific aircraft model, having completed only 19 flights in the ASW 20 prior to the accident.