Colisión del ASK 18 con un árbol durante vuelo de ladera cerca de Lommiswil, Suiza

El 15 de agosto de 1981, un Alexander Schleicher ASK 18 estuvo involucrado en un accidente cerca de Lommiswil, Suiza. El planeador, pilotado por un ciudadano suizo, se desenganchó del avión remolcador a 1600 metros pero luego experimentó un indicador de velocidad bloqueado. Durante un giro a la derecha alejándose de la ladera, el planeador descendió y colisionó con un árbol. El piloto sufrió heridas graves y la aeronave fue destruida. La investigación identificó volar por debajo de la velocidad mínima como una causa confirmada, con factores contribuyentes que incluyen los efectos del viento y la inexperiencia del piloto en este tipo de aeronave.

1. Ridge soaring flight: After aerotow release at about 1600 m MSL, the pilot conducted ridge-soaring 8-shaped patterns along the Hasenmatt south slope in generally sinking air.
2. Airspeed indication anomaly: Around 1440, the pilot noticed that the airspeed indicator needle was stuck at 95 km/h and did not respond even after tapping the instrument.
3. Lee and boundary layer: The right turn away from the ridge was flown at low height over the ground on the lee side of the Hasenmatt, likely within the ground boundary layer, reducing effective airspeed.
4. Pilot startled by noise: After completing a left turn west of Hasenmatt, the pilot heard an unexplained loud bang from the rear of the glider, which disturbed her concentration and may have led to unintentional aft stick input.
5. Low experience on type: The pilot had relatively little recent experience on the ASK 18 type, which likely reduced her ability to manage speed and attitude without reliable airspeed indication.
6. Stall and loss of control: At the end of the right turn away from the slope, the glider increasingly pitched nose-down and no longer responded effectively to elevator and aileron inputs, consistent with flight below minimum flying speed.
7. Crash - serious injury: The right wingtip struck the top of a fir tree and the glider fell down along the trunk to the ground, seriously injuring the pilot and destroying the aircraft.