1966 Sion Aerodrome Collision Between Piper Cub and Glider (HB-OAV)

Incident Overview and Casualties On the afternoon of August 26, 1966, a mid-air collision occurred at Sion aerodrome involving a Piper Cub, registration HB-OAV, and a Greif I glider, registration HB-579. The two aircraft struck each other approximately 15 to 20 meters above the grass runway, roughly 400 meters from its threshold, before crashing to the ground at 17:05. Both aircraft were destroyed. The three occupants sustained severe injuries; the Piper instructor died during transfer to a hospital, and the glider student pilot died eight days later. ## Aircraft and Operational Context The Piper Cub HB-OAV was a high-wing, tandem two-seater operated by the Valais section of the Aéro-Club de Suisse. It was powered by a 90-horsepower Continental C90-8F engine. The glider HB-579 was a single-seat Greif I operated by the Sion gliding group. At the time of the accident, the Piper was being flown by an instructor who had taken over from a student pilot to provide dual instruction. The glider was being flown by a student pilot attempting one of the required timed glider flights for a license, under the formal supervision of a powered and glider flight instructor because the regular glider instructor was absent. ## Investigation Findings The Federal Commission for Aircraft Accident Investigations opened its preliminary inquiry 1.5 hours after the crash and concluded it on December 13, 1966. A flight reconstruction was conducted on February 17, 1967, at Sion aerodrome. The investigation determined that the direct cause of the collision was that the pilot responsible for the Piper HB-OAV cut off the priority of the glider HB-579, which was preparing to land. The Piper pilot had been dissatisfied with a student's solo spiral exercises and decided to take over the aircraft for dual instruction. After landing, he took the front seat, taxied to the threshold of the grass runway, and prepared for takeoff at the moment the glider presented itself for landing. ## Aerodrome and Weather Conditions Sion aerodrome features two parallel runways: a 1,100-meter grass runway located 20 meters north of a 2,000-meter paved runway. The collision occurred between the two runways. The aerodrome's operating regulations, approved by the Federal Air Office, prohibited simultaneous movements on the paved and grass runways and required pilots to check that the approach channel was clear before taxiing for takeoff. Weather conditions at the time included light cumulus clouds at 2,700 meters, visibility of 15 to 20 kilometers, wind from 250 degrees at 10 to 15 knots, a temperature of 19 degrees Celsius, and light turbulence near the ground.