What happened
On June 27, 1997, at approximately 14:45 local time, a Pilatus B4 glider, registration HB-1319, crashed into a slope in the municipality of Schönried (Rellerli), Switzerland. The aircraft was participating in a private gliding event, and the pilot was performing maneuvers within a thermal updraft. Witnesses observing the scene from a nearby mountain restaurant reported seeing three gliders circling at an altitude of roughly 100 to 150 meters; they observed the lowest aircraft suddenly enter a vertical descent. The glider struck the mountainside approximately 50 meters below the restaurant, resulting in the fatal injury of the pilot and the total destruction of the aircraft.
The investigation
Investigators examined the wreckage and the flight conditions at the time of the accident. The aircraft had been properly maintained, with its most recent periodic inspection completed in May 1997. Technical analysis of the wreckage showed that the wing bolts and control surfaces were intact, with all observed damage being a direct result of the high-impact force. The aircraft's weight and balance were within approved limits, and the pilot was properly restrained in his seat.
Meteorological data indicated a weather pattern characterized by a stationary front and turbulent, gusty winds. While the flight instruments were too damaged to provide a precise flight path, the impact angle was estimated at approximately 60 degrees downward. An autopsy of the pilot was conducted to determine if any physiological factors contributed to the loss of control.
Findings
Evidence from the scene and witness accounts strongly suggest that the accident was caused by a stall occurring in gusty air conditions. The investigation considered two primary contributing factors:
- The pilot may have inadvertently allowed the airspeed to drop below the minimum required speed (approximately 61 km/h) while distracted by the proximity of two other circling gliders.
- Medical findings revealed an acute inflammation in the pilot's brainstem. This condition could have caused significant disturbances in circulatory or respiratory functions, potentially leading to a sudden period of physical impairment or loss of consciousness.
Safety action
No specific safety recommendations were issued in this report.