What happened
On July 23, 1969, at approximately 14:40, an ASK 13 glider, registration D-6048, was conducting a training flight near Muottas Muragl in the Engadin region. The flight, which was part of a summer training camp, was being conducted by a flight instructor and a student. After a delayed start due to a tow rope failure, the aircraft was launched via winch.
While flying along the western slope of the mountain at an altitude of approximately 2,420 meters, the aircraft encountered complex wind conditions. Witnesses observed the glider banking and then entering a steep left-hand spiral. The aircraft descended rapidly behind a ridge and struck the mountainside approximately 5/8ths of a turn from its last visible heading. The impact, occurring only about 30 meters above the ground, resulted in the fatal deaths of both occupants and the total destruction of the aircraft.
The investigation
Investigators examined the wreckage and the meteorological conditions present at the time of the accident. The aircraft was found in an inverted position, having struck the ground with a left-wing tilt. Technical inspections of the ASK 13 revealed no mechanical failures; all control surfaces, including the elevators, rudder, and ailerons, were properly connected and functional. The aircraft's center of gravity was within the permissible range, though positioned toward the forward limit.
Meteorological analysis focused on the presence of the Maloj Wind, a characteristic regional wind. Investigators identified that at the altitude of the accident, the aircraft was near the upper limit of this wind zone, where significant vertical wind shear and turbulence are common. Witnesses also noted that the aircraft was flying at a low speed, estimated at roughly 80 km/h, which was near the aircraft's minimum operating speed.
Findings
- The aircraft encountered a sudden wind gust or drop in airspeed while flying at a low altitude in turbulent air.
- The pilot likely experienced a loss of airspeed that dropped the aircraft below its minimum flying speed.
- In an attempt to maneuver away from the slope, the pilot's reaction likely induced a left-wing drop and subsequent stall.
- The pilot's subsequent control inputs likely triggered a spin or a spiral dive, which could not be recovered due to the extremely low altitude.
- The flight instructor had only received mountain flying orientation just nine days prior to the accident.