Mid-air collision involving Bonanza 35, Piper PA-18, and Mucha Standard at Zweisimmen airfield

On July 31, 1974, a mid-air collision occurred at Zweisimmen Airfield, Switzerland, involving a Beechcraft Bonanza 35, a Piper PA-18, and a Mucha Standard glider. The Bonanza 35, on a VFR flight from Zurich, collided with the Piper PA-18, which was towing the Mucha Standard glider shortly after takeoff. The Bonanza pilot was fatally injured, while the towplane pilot sustained severe injuries. The Mucha Standard glider pilot managed to release the towline and landed safely without damage. Both powered aircraft were destroyed in the incident.

1. Aerotow takeoff roll: The Mucha Standard glider HB-658, behind towplane HB-OUH, began its aerotow takeoff from the hard-surface runway with the start helper giving the launch signal.
2. Misjudged approaching Bonanza: Before authorizing the tow launch, the start helper saw the Bonanza west of Betelried but, based on its height and track, incorrectly assumed it was not intending to land and thus did not delay the launch.
3. Bonanza low over runway: While the tow combination was starting and climbing, the Bonanza HB-EBF flew along the runway centerline at about 80 m above ground with gear down and little or no flap, on what was effectively a landing approach.
4. Converging flight paths: As the towplane and glider climbed through about 15 m above ground, the Bonanza, slightly left of the towline and descending, closed rapidly from behind, with witnesses noting an increase in its engine power shortly before overtaking.
5. Glider releases towline: At the moment of collision, the glider pilot released the towline and continued independently to land on the remaining runway.
6. Mid-air collision: The Bonanza collided with the climbing towplane at about 15 m above ground, both powered aircraft crashed onto the runway with one fatal and one serious injury, while the glider landed safely without damage.