Accidente del Pilatus B4-PC 11AF durante examen de acrobacia en Zweisimmen
El 19 de julio de 1986, un Pilatus B4-PC 11AF estuvo involucrado en un accidente en Zweisimmen, Suiza, durante un examen de acrobacia. Después de soltar el cable de remolque a aproximadamente 700 metros, el piloto realizó una serie de maniobras acrobáticas. Las maniobras se ejecutaron correctamente al principio, pero las espirales fueron demasiado cerradas, lo que llevó a una pérdida significativa de altitud. Durante la aproximación final, el planeador entró en pérdida y se estrelló en el río Simme. El piloto sufrió heridas graves e hipotermia, pero sobrevivió. La aeronave fue destruida.
- Aerotow aerobatics flight: The pilot aerotowed from Zweisimmen runway 35 to about 700 m AGL and began the planned aerobatic exam sequence overhead the airfield.
- Overly steep spirals: During the three right spirals, the bank angle was about 80°, causing an abnormally high sink rate and greater than expected loss of altitude.
- Low exit altitude: Despite the examiner’s relayed request to stop the program, which the pilot did not acknowledge, he completed the third spiral and exited into downwind at only about 80 m AGL and 85 km/h, well below the recommended spiral exit height.
- Low-speed turn to final: From this low downwind, the pilot initiated a 180° left turn toward final for runway 35 at a speed near minimum flying speed and with possible sideslip and tailwind gust influence.
- Stall and wing drop: After turning about 150° and as the nose was raised toward the runway heading, the pilot felt a jolt and tail lift, and the glider abruptly rolled steeply left into a stall from which recovery was not possible at the low height.
- Crash - serious injury: The glider impacted nose-down in the Simme river near the airfield, was destroyed, and the pilot sustained serious injuries and severe hypothermia while trapped for about 90 minutes in cold water.