What happened
On July 18, 2006, a single-seat Rolladen Schneider LS-4 glider, registration HB-1832, was engaged in a long-distance VFR cross-country flight. The pilot had departed from Bad Ragaz with the intention of completing a 580 km triangle flight. As the flight progressed, weather conditions deteriorated; following a thunderstorm near the Oberalp Pass, thermal activity weakened significantly.
While flying near Disentis, the pilot noted the declining lift and considered an outlanding. Seeking to find remaining thermals, the pilot entered Val Plattas, following the western slope. Upon detecting a brief upward movement of 1.8 m/s, the pilot executed a sharp left turn toward the slope to capitalize on the lift. During this maneuver, the aircraft experienced a sudden and rapid descent of 51 meters within just four seconds, accompanied by a loss of control effectiveness.
The glider struck treetops and subsequently struck the ground, before sliding 34 meters down a steep slope. The pilot sustained serious injuries, while the aircraft was destroyed.
The investigation
The investigation utilized pilot statements, eyewitness accounts, and flight logger data to reconstruct the flight path. Investigators examined the aircraft's maintenance history, noting it was airworthy and within weight and balance limits. The investigation also reviewed meteorological data, which indicated that following a thunderstorm at the Oberalp Pass, variable and gusty wind conditions were present in the area.
Findings
- The pilot was highly experienced and properly trained.
- The aircraft was in a valid state of airworthiness.
- At the time of the accident, thermal activity had diminished, and local wind conditions were unstable due to recent convective activity.
- The pilot turned toward the terrain, a maneuver that violates fundamental soaring principles and prevented the necessary recovery maneuvers to regain airspeed and altitude.