What happened
On June 15, 1966, a pilot was conducting aerobatic training maneuvers near Beromünster, Switzerland, in preparation for the upcoming national motor flying championships. The flight took place under favorable weather conditions with good visibility. While performing a series of high-G maneuvers, the pilot began to drift away from the intended north-to-south flight axis toward a forested ridge located approximately 1.5 km east of the airfield.
During the execution of a sequence of maneuvers, including a loop and a vertical eight, the aircraft lost significant altitude. While performing an inverted roll-reversal, the Bücker-Lerche HB-URN struck a line of fir trees on the ridge, which rises about 150 meters above the airfield. The impact resulted in the fatal destruction of the aircraft and the death of the pilot.
The investigation
The investigation examined the aircraft's condition, the pilot's medical fitness, and the flight sequence. Technical inspection of the Bücker-Lerche revealed no evidence of mechanical failure or control malfunctions. The engine, fuel system, and flight controls were found to be in working order, and the aircraft's weight and balance were within limits. The fuel selector was set to the aerobatic position, and the throttle was found at full power.
Medical examinations of the pilot confirmed that there were no signs of health issues or impairment immediately preceding the accident. Witnesses at the scene observed the flight and noted that the pilot appeared to be flying a sequence of maneuvers that eventually led to the impact.
Findings
- The pilot failed to maintain the required minimum flight altitude of 500 meters.
- There was a failure in spatial and altitude awareness, as the pilot drifted toward the terrain without realizing the proximity of the ridge.
- The pilot's focus on executing specific maneuvers for the upcoming competition likely led to a lack of attention regarding position and height.
- The flight path during the final maneuver was too shallow, contributing to the loss of altitude.