Ka 4 Rhönlerche II collision with trees during training flight at Bettlachstock, Switzerland
On June 26, 1964, a Ka 4 Rhönlerche II glider, piloted by a student, collided with trees during a training flight near Bettlachstock, Switzerland. The flight, originating from Granges airfield, aimed to practice ridge soaring along the Jura mountains. The student pilot, while executing a turn, failed to maintain adequate distance from the slope, resulting in an unavoidable collision. The glider was significantly damaged, but the pilot escaped without injuries. The incident was attributed to the pilot's inattention during the maneuver.
- Ridge soaring flight: The student pilot departed Granges airfield in a Rhönlerche II for a ridge-soaring training flight along the Jura with a planned maximum duration of 75 minutes and specified speed and altitude constraints.
- Low experience level: The pilot was a student with only 9 hours 38 minutes and 83 flights of total glider experience, all on the Rhönlerche II, and was still completing the altitude-gain flights required for his license.
- Weak, irregular lift: While ridge soaring near Bettlachstock, the glider encountered weak and irregular lift averaging about 1 m/s, and had descended roughly 120 m in the preceding six minutes, likely keeping the pilot close to the slope.
- Prolonged right turn: At about 1305 while flying along the Jura with the ridge on his left, the pilot initiated a right turn at about 78 km/h and 45° bank to reverse direction along the slope but allowed the turn to continue too long toward the terrain.
- Late turn termination: The pilot, inattentive to his position relative to the slope, failed to stop the turn in time to re-establish safe separation from the hillside.
- Collision with trees: With insufficient lateral clearance remaining, the glider could no longer avoid terrain and struck the tops of trees on the steep, forested south face of the Bettlachstock.
- Crash - no injury: After contacting the trees the glider fell into the forest, was about 80% destroyed, and the pilot escaped uninjured.