Incidente del Cirrus 18 cerca de Löhningen durante un intento de térmica
El 1 de septiembre de 1985, un Schempp-Hirth Cirrus 18 experimentó un incidente cerca de Löhningen, Suiza. El piloto, que tenía la intención de aterrizar en el aeródromo de Schaffhausen, encontró térmicas débiles y comenzó a espiralear a aproximadamente 1000 metros de altitud. El planeador entró repentinamente en una barrena, y a pesar de los esfuerzos del piloto, no se pudo detener la rotación. La aeronave descendió casi verticalmente en un bosque, resultando en la destrucción del planeador y heridas graves para el piloto. El informe confirmó que el accidente fue causado por la velocidad del planeador cayendo por debajo del mínimo durante el vuelo térmico en condiciones turbulentas.
- Aerotow local soaring: The pilot aerotowed from Bohlhof for a local soaring flight toward the Randen area, reaching a maximum altitude of about 1350 m MSL.
- Marginal weak thermals: In the Chornberg area the thermals were weak to moderate, poorly usable, and accompanied by gusty winds up to 20 kt, leading to a gradual loss of height.
- Limited height margin: Near Chornberg the pilot realized he no longer had sufficient altitude to return to Bohlhof and instead planned to land at Schaffhausen airfield, with only about 540 m height above it.
- Slow circling in lift: At about 1000 m MSL the pilot began thermaling turns in weak, gusty lift at an indicated airspeed of roughly 90–100 km/h, close to minimum speed.
- Stall and spin entry: While circling in the weak, turbulent thermal the glider suddenly rolled left, stalled, and entered a spin.
- Failed spin recovery: The pilot attempted to stop the rotation but was unable to recover fully, with witnesses observing several turns, a brief cessation of spinning, and a roll-like motion to the right.
- Crash - serious injury: The glider descended almost vertically into a forest near Chornberg, destroying the aircraft and seriously injuring the pilot.