Collision en vol entre Ka 4 et Piper J3C-65 à l'aéroport de Sion

Le 26 août 1966, une collision en vol s'est produite à l'aéroport de Sion impliquant un Piper J3C-65 et un Alexander Schleicher Ka 4 Rhönlerche II. L'incident s'est produit lorsque le Ka 4, piloté par un élève, revenait pour atterrir après un vol infructueux. Simultanément, le Piper, avec un instructeur et un élève à bord, se préparait au décollage. Les appareils sont entrés en collision à environ 15 à 20 mètres au-dessus de la piste, entraînant la destruction des deux. L'instructeur et un élève ont été mortellement blessés, tandis que l'autre élève a subi de graves blessures.

1. Aerotow — local soaring: In late afternoon the student in Greif I HB-579 launched on aerotow from Sion for a planned duration flight but was unable to find sufficient lift and eventually returned toward the airfield to land.
2. Mixed traffic operations: At Sion the grass runway 26 was being used simultaneously by gliders and powered aircraft under a complex mixed-traffic arrangement where glider circuits could intersect powered aircraft approaches and departures.
3. Piper preparing departure: While the glider was returning to land, the instructor took the front seat of Piper J-3C HB-OAV after his student’s previous flight and taxied to the threshold of the grass runway 26 to depart again with the student on board.
4. Piper initiates takeoff: The instructor in HB-OAV commenced a takeoff run on the grass runway 26 at the same time that glider HB-579 was on short final to land, placing both aircraft on converging, vertically overlapping flight paths.
5. Priority not yielded: Contrary to rules giving landing aircraft and gliders priority, the Piper instructor continued the takeoff instead of holding clear of the approach path of the landing glider.
6. Converging flight paths: The glider on final and the Piper climbing after liftoff reached the same area about 400 m beyond the runway 26 grass threshold at roughly 15–20 m above ground with insufficient separation to avoid each other.
7. Mid-air collision: The glider HB-579 and Piper HB-OAV collided about 15–20 m above the grass runway 26 at Sion, then crashed between the two parallel runways, destroying both aircraft and causing serious injuries to all three occupants, two of whom later died.