What happened
On May 15, 1980, a K 8 B glider, registration HB-809, departed from Birrfeld aerodrome for a local training flight. The aircraft was initially operated via aero-tow. At approximately 17:30 local time, while returning to Birrfeld from the direction of Aarau, the glider entered the lee side of the Chestenberg mountain, resulting in a rapid loss of altitude.
In an attempt to recover height, the pilot maneuvered toward Brunegg, reaching an altitude of approximately 543 meters. Noticing a slight updraft, the pilot turned left to follow the northern flank of the mountain toward the west-northwest. However, the aircraft encountered severe turbulence and downdors. While attempting to avoid a high-voltage power line, the pilot executed a left turn toward the slope, causing the left wing to strike the top of a tree. The impact tore the wing from the aircraft, leading to a crash that resulted in one serious injury.
The investigation
The investigation established that the pilot held a valid glider license and there was no evidence of medical impairment during the flight. The HB-809 was airworthy, with its weight and center of gravity within permissible limits, and no technical malfunctions were identified. Meteorological data indicated a high-pressure system with Bise winds following a cold front, characterized by moderate to strong gusts.
Findings
- The primary cause of the accident was the collision with obstacles resulting from continuing the flight at an insufficient altitude and too close to the hillside.
- The pilot's decision to seek thermals at such a low altitude contradicted established aviation safety principles.
- A safer alternative would have been to initiate an immediate approach to Birrfeld or perform an outlanding in a known suitable field near Brunegg.
- Contributing factors included a lack of decisive action, insufficient flight experience, and poor flight tactics.