Accident du Pilatus B4-PC 11AF lors d'un examen de voltige à Zweisimmen

Le 19 juillet 1986, un Pilatus B4-PC 11AF a été impliqué dans un accident à Zweisimmen, Suisse, lors d'un examen de voltige. Après avoir largué le câble de remorquage à environ 700 mètres, le pilote a effectué une série de manœuvres acrobatiques. Les manœuvres ont été initialement bien exécutées, mais les spirales étaient trop serrées, entraînant une perte d'altitude significative. Lors de l'approche finale, le planeur a décroché et s'est écrasé dans la rivière Simme. Le pilote a subi de graves blessures et une hypothermie, mais a survécu. L'appareil a été détruit.

1. 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.
2. 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.
3. 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.
4. 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.
5. 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.
6. 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.