Accidente de un ASK 23B durante la aproximación final cerca del aeródromo de Buttwil

El 11 de agosto de 2001, un planeador Alexander Schleicher ASK 23B se estrelló aproximadamente a 1,7 km al este-noreste del aeródromo de Buttwil en Suiza. El piloto, un estudiante en su 16º vuelo en solitario, perdió el control de la aeronave poco antes de la aproximación final, resultando en un accidente fatal. El planeador entró en una barrena invertida e impactó en un campo, lo que llevó a la destrucción de la aeronave y la muerte del piloto. La investigación sugirió que el fenómeno de 'sensaciones de subgravedad' pudo haber contribuido a la pérdida de control.

1. Aerotow — local soaring: The student pilot launched by aerotow from Buttwil for a planned two-hour solo soaring flight and later returned to the vicinity of the airfield after completing the task time.
2. Unusual attitude onset: At about 500–600 m AGL near the airfield, shortly before entering the landing circuit, the glider transitioned from normal flight into a left sideslip-like attitude with the left wing dropping.
3. Low solo experience: The pilot was on his 16th solo flight with only about 16 hours of total flight time, limiting his experience in recognizing and managing unusual attitudes and low‑g sensations.
4. Possible low-g sensations: The investigators considered that sub‑gravity (low‑g) sensations during the developing maneuver may have led the pilot to inappropriately push and hold the control stick forward.
5. Nose-down pitch input: After the left-wing-low slip, the pilot allowed or commanded the nose to drop rapidly, with the glider pitching forward over the nose and left wing while losing only 50–100 m of height and with little speed increase.
6. Inverted spin developed: The forward pitching motion progressed into a fully developed inverted spin with several turns at nearly constant pitch attitude, rotation rate, and sink, with no visible signs of recovery control inputs.
7. Crash - fatal: Still in an inverted spin attitude, the glider impacted a field and was destroyed, fatally injuring the pilot.