What happened
On June 9, 1964, a Bücker 131 Jungmann, registration HB-URS, was conducting an alpine orientation flight near Piz Borel, Switzerland. The flight, part of a training course for the Swiss Air Traffic School, was operated by a flight instructor accompanied by a student pilot.
While navigating the terrain near the Piz Borel massif, the instructor attempted to utilize rising air currents to clear a mountain ridge. During the maneuver, the aircraft entered a sequence of events that led to a loss of control. The aircraft struck the ground in a steep, nose-down attitude following a right-hand turn, resulting in the destruction of the aircraft and two serious injuries to the occupants.
The investigation
Investigators examined the wreckage and the flight profiles provided by both occupants. The investigation focused on the aircraft's performance and the environmental conditions at the time of the accident. The engine was recovered and tested, showing normal performance during a test run, and no evidence of mechanical failure, fuel starvation, or icing was found.
Discrepancies between the instructor's and the student's accounts were noted. While the instructor suggested a gradual loss of engine power, the student reported no such engine issues but noted a lack of acceleration and a descending trend. The investigation prioritized the student's account due to his direct observation of the flight instruments and his lack of involvement in the controls during the critical phase.
Findings
- The aircraft was flying in a high-altitude environment near 2800 meters.
- The pilot initiated a turning maneuver to avoid the ridge after realizing the planned crossing was no longer feasible.
- The investigation concluded that the pilot entered a speed loss (stall) during the maneuver.
- A lack of visual reference due to the transition from bright light to shadow likely hindered accurate altitude estimation.
- The pilot may have failed to maintain sufficient altitude and airspeed reserves, a critical principle of mountain flying, which left no margin for error when encountering local downdrafts or terrain.