What happened
On April 25, 1970, a pilot conducting a training flight near Hausen am Albis entered a downdraft while flying on the leeward side of the Albiskette ridge. After initially utilizing rising air to navigate toward the Sihltal and Üetliberg, the pilot encountered sinking air on the return leg, which prevented the aircraft from returning to the windward side of the ridge.
Unable to maintain sufficient altitude, the pilot decided to terminate the flight and attempted an outlanding on a meadow near Langnau am Albis. During the final approach, a sudden wind gust caused a rapid loss of altitude. The K 8 B aircraft, registration HB-7lag, struck the outer branch of an apple tree with its left wing before hitting a wire fence. The impact caused the aircraft to rotate approximately 100 degrees and come to a stop on the field with a broken left wing and a compressed fuselage. The pilot sustained no injuries.
The investigation
Investigators examined the aircraft and the site of the accident, which occurred on the eastern slope of the Albiskette. The investigation confirmed that the pilot held a valid glider license and showed no signs of medical impairment at the time of the event. The K 8 B was found to be in an airworthy condition, with its weight and center of gravity within permissible limits. The terrain was noted to have a 1.2-meter high wire fence and fruit trees bordering the landing area.
Findings
- The primary cause of the accident was improper flight tactics.
- The pilot entered a downdraft with insufficient altitude reserves, making it impossible to regain the windward side of the ridge.
- The chosen landing site was suitable for an outlanding, but the remaining altitude was inadequate to execute a steep approach necessary to compensate for the prevailing wind conditions.