What happened
On August 14, 1971, a K 8 B glider, registration HB-764, departed from Zweisimmen airfield for a local flight. While flying at an altitude of approximately 1,800 meters near the Niderhorn, the pilot encountered strong northwesterly winds. These conditions caused the aircraft to drift across the ridge into the rear Diemtoge Valley, where it encountered severe downdrafts.
In an attempt to regain altitude, the pilot flew eastward, but the weather conditions deteriorated as rain showers and thunderstorms moved into the area. Faced with increasing instability, the pilot decided to perform an outlanding on a south-facing slope northeast of Enetchirel. The approach was made on a 1:10 downward slope under heavy turbulence. Approximately 150 meters after passing a telephone line, the glider touched down on the descending terrain. After a ground roll of about 150 meters, the left wing struck the ground, causing the aircraft to veer left and ultimately strike a barbed-wire fence. The pilot escaped without injury, though the aircraft sustained heavy damage.
The investigation
Investigators examined the meteorological conditions, the pilot's experience, and the aircraft's mechanical state. At the time of the accident, the area was experiencing significant convective activity, with cloud bases between 2,000 and 2,500 meters and potential gusts reaching up to 30 knots. The pilot, who held a valid glider license and had 280 hours of flight experience, was found to be in good health. The investigation confirmed that the HB-764 was airworthy and showed no signs of technical malfunction prior to the impact.
Findings
- The pilot allowed the aircraft to drift into a high-risk area of the valley due to unfavorable northwesterly winds.
- The decision to attempt a landing on a significant downward slope was improper flight tactics.
- The pilot became overwhelmed by the complex flying and tactical requirements presented by the severe weather and difficult terrain.