What happened
On August 8, 1962, a student pilot initiated a soaring flight near Zweisimmen, Switzerland, in a Grunau Baby II, registration HB-565. After being towed into the air at 14:20 CEST, the pilot successfully engaged with a thermal, eventually reaching an altitude of approximately 3,300 meters. The flight lasted nearly four hours.
As evening approached, the thermal strength diminished. While attempting to gain additional altitude near the forested western slope of the Girshubel, the pilot performed several maneuvers. During a right-hand turn away from the slope at a speed of 65 km/h, the pilot applied excessive bank. This resulted in the aircraft flying toward the terrain at an angle of 35 to 45 degrees. In an attempt to initiate a left-hand turn away from the slope, the pilot encountered difficulty with the rudder controls. With the terrain approaching rapidly, the pilot pulled back on the elevator, leading the aircraft to impact the trees at 18:12.
The investigation
The investigation examined the aircraft's mechanical condition and the pilot's flight profile. While a defect was discovered in the rudder hinge mechanism—specifically, a missing locking screw that allowed the hinge part to rotate—testing revealed that this defect did not significantly impair the aircraft's controllability. The rudder could still move fully in both directions without visible deformation.
The investigation also reviewed the pilot's experience and the flight duration. The pilot was a student with approximately eight hours of total flight time. Furthermore, the investigation noted that the flight had lasted nearly four hours, significantly exceeding the recommended flight duration limits for students, which are intended to prevent fatigue.
Findings
- The primary cause of the accident was likely the stalling of the aircraft while flying near the slope in weakening upward currents.
- The pilot's limited flight experience and potential fatigue from a flight lasting nearly four hours likely contributed to the loss of control.
- Any perceived loss of rudder effectiveness was likely a result of the aircraft entering a stalled state rather than the identified mechanical hinge defect.