Mid-air collision between Ka 4 and Piper J3C-65 at Sion Airport

On August 26, 1966, a mid-air collision occurred at Sion Airport involving a Piper J3C-65 and an Alexander Schleicher Ka 4 Rhönlerche II. The incident happened when the Ka 4, piloted by a student, was returning to land after an unsuccessful flight. Simultaneously, the Piper, with an instructor and student on board, was preparing for takeoff. The aircraft collided approximately 15 to 20 meters above the runway, resulting in both being destroyed. The instructor and one student were fatally injured, while the other student sustained serious injuries.

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.