What happened
On September 4, 2013, an Alisport Silent 2 Targa, registration HB-5506, departed from Mollis airfield for a private visual flight rules (VFR) flight. After an initial climb using its retractable engine, the pilot proceeded to fly through various valleys in the Grisons region, performing several circles near the Crap Ner and Crap Tgina areas.
During the final phase of the flight, the aircraft was flying at a low altitude, between 110 and 150 meters above the ground, heading toward the Vorab Glacier. While performing a clockwise turn, the aircraft entered a steep descent of approximately 70 to 80 degrees. Witnesses observed the glider pitching downward in a spinning motion near a high-voltage power line. Although the pilot managed to stop the rotation and attempted to recover the aircraft before impact, the low altitude made a successful recovery impossible. The aircraft struck the terrain at an angle of approximately 60 degrees, resulting in the death of the pilot and the total destruction of the aircraft.
The investigation
SUST investigators analyzed flight data from the aircraft's Flarm collision warning system, which recorded the flight path and engine status. The investigation also utilized eyewitness accounts from a helicopter pilot and local residents, as well as technical inspections of the wreckage.
Investigators examined the pilot's background, noting his extensive experience in both motor gliding and his previous history as a highly successful champion in delta wing (hang gliding) competition. The investigation also looked into meteorological conditions, which included moderate thermals and gusty winds, and the technical state of the Alisport Silent 2 Targa, finding no evidence of mechanical failure or pre-existing technical defects.
Findings
- The pilot lost control of the glider at a low altitude, preventing an effective avoidance of the terrain.
- The pilot was flying at a very low height above the ground with insufficient speed reserves.
- During the final maneuvers, the pilot performed clockwise turns even when the terrain was rising on the right side of the flight path.
- The pilot was under the influence of alcohol at the time of the accident.
- The pilot's previous intensive training in delta wing flying may have caused him to rely on automated cognitive patterns—such as different distance and speed estimations—that were less appropriate for the specific requirements of gliding in such terrain.
- The pilot suffered from an eye condition that could have caused visual impairment.