Pilatus B4 stall and crash during thermaling near Schönried, Switzerland
On June 27, 1997, a Pilatus B4 glider crashed near Schönried, Switzerland, resulting in the fatality of the pilot. The incident occurred while the pilot was thermaling with two other gliders in moderate thermal conditions and strong west winds. Witnesses observed the glider suddenly enter a steep dive and crash. The investigation suggested a stall in turbulent air as the primary event, with a potential medical condition of the pilot as a contributing factor. The glider was destroyed upon impact.
- Thermaling in gaggle: While on a local soaring flight, the pilot was circling in a thermal with two other gliders above the Rellerli area in turbulent, gusty conditions.
- Böiger Westwind: A relatively strong, gusty westerly wind and moderate thermals created turbulent conditions that could promote an inadvertent stall.
- Possible medical issue: The pilot had an acute inflammatory lesion in the brainstem which, according to the autopsy, could have caused circulatory or respiratory disturbances and impaired his ability to control the glider.
- Speed decays in turn: While circling as the lowest of the three gliders, the accident glider’s airspeed decreased below the minimum safe speed for the bank angle, leading to an aerodynamic stall.
- Abrupt stall and dive: The glider experienced a stall with a near-vertical nose-down departure, entering a steep dive from which no recovery was observed by witnesses.
- Crash - fatal: The glider impacted the downhill slope about 50 meters below the Rellerli mountain restaurant in a roughly 60° nose-down attitude, destroying the aircraft and fatally injuring the pilot.