What happened
On May 19, 2012, an LS 1-0 glider, registration D-0251, was engaged in a VFR private flight in the Swiss Alps. The pilot, an experienced aviator with over 3,000 total flight hours, had departed from the Schänis airfield earlier that morning. After a long flight spanning several hours and traversing various alpine regions including Piz Linard and the Churfirsten, the aircraft was maneuvering near the Klausen Pass.
At approximately 16:22 local time, while flying along the ridge of the Glatten, the aircraft collided with the terrain at an altitude of roughly 2,400 meters. The impact and subsequent falls against rocky outcrops caused the total destruction of the aircraft. The pilot sustained fatal injuries. Due to the difficult terrain and the scattered nature of the debris, the wreckage was not located until 46 days later.
The investigation
The SUST investigation utilized eyewitness accounts, document reviews, and data from the aircraft's onboard FLARM collision warning device. Technical inspections of the wreckage were not possible due to the extent of the destruction, but investigators ruled out mechanical failure, as there were no signs of technical issues during the preceding five hours of flight. The aircraft's weight and center of gravity were also confirmed to be within permissible limits.
Investigators analyzed the flight path recorded by the FLARM device, which showed the aircraft following the mountain edge. Meteorological data indicated moderate Föhn winds from the south-southeast, with visibility exceeding 10 km. The investigation also looked into the pilot's extensive experience, noting that he was a seasoned mountain glider pilot.
Findings
- The primary cause of the accident was a collision with the terrain because the pilot was flying at a low airspeed too close to the ground.
- The pilot's speed was significantly below the recommended safety margin, which suggests a flight speed of at least 1.45 times the stall speed should have been maintained when flying near terrain.
- The pilot likely misjudged the required margin of error, potentially due to the narrow safety margins inherent in mountain soaring or fatigue after nearly five hours of flight.
- No technical malfunctions or health issues contributed to the event.