L-13 Blanik crash at Unterer Schafberg results in fatality and injury
On July 28, 1975, a LET L-13 Blanik crashed at the Unterer Schafberg in Switzerland. The aircraft, piloted by an experienced glider pilot with his daughter as a passenger, stalled and impacted the west slope of the mountain. The pilot was killed, and the passenger sustained injuries. The investigation found that the crash was likely due to the aircraft stalling near the ridge, with possible contributing factors including inappropriate flight tactics and mismanagement of the Fowler flaps. The glider was destroyed in the accident.
- Ridge soaring flight: After winch launch and thermaling near Muottas Muragl, the pilot flew the Blanik along the Schafberg ridge in weak lift with his daughter in the rear seat.
- Low speed near terrain: In weak ridge lift the pilot likely flew close to minimum sink speed, with limited speed margin despite being in close proximity to the slope.
- Fowler flaps extended: The aircraft was being flown along the Schafberg with the Fowler flaps approximately half extended, altering stall behaviour at low speed near the ridge.
- Stall onset near slope: While flying close to the west slope of the Unterer Schafberg, the glider suddenly dropped its right wing, indicating a stall at or below minimum safe speed.
- Flaps retracted in stall: As the right wing dropped, the pilot retracted the Fowler flaps, a control input later shown in tests to commonly precipitate a spin from this condition.
- Spin and height loss: The Blanik entered a steep right-hand spin or steep turning descent, completing roughly one to two rotations and losing substantial height with very limited clearance from the slope.
- Crash - fatal: Unable to recover or turn away in the remaining space, the glider impacted the west slope of the Unterer Schafberg at a steep angle, killing the pilot and seriously injuring the passenger.