What happened
On September 11, 1960, a pilot departed from Sion in a Bücker 131 Jungmann, registration HB-UTV, for a planned one-hour flight through the Upper Valais region. The flight was intended to cover a route including Brig, Ernergalen, and Blindenhorn. Shortly after takeoff, witnesses observed the biplane performing loops over the Visper Valley.
By approximately 11:20, the aircraft entered the Binntal valley, flying along the southern slopes near Ausserboden. At an altitude of roughly 1,700 meters, the aircraft began performing several steep turns at extremely low altitude over the Eggenalp area. During these maneuvers, the pilot frequently altered engine RPM and performed wing dips. At 11:27, while exiting a right-hand turn at an altitude of no more than 50 meters, the aircraft entered a steep descent at high power, striking an alpine pasture. The impact resulted in the destruction of the aircraft and the death of the pilot.
The investigation
The investigation examined the pilot's flight history, the mechanical condition of the Bücker 131 Jungmann, and the environmental conditions at the time of the accident. The pilot had significant flight experience, though records indicated previous instances of unsafe flying, including unauthorized aerobatics and dangerous low-level flights in other regions.
Technical inspections of HB-UTV revealed no mechanical failures or defects that could have contributed to the crash. The aircraft's weight and center of gravity were within limits, and the engine and airframe were in good condition. Weather conditions were favorable, characterized by clear skies and good visibility, though light thermal turbulence was present.
Findings
- The primary cause of the accident was that the pilot lost control of the aircraft while performing steep turns at low altitude in complex terrain.
- The pilot's skill level was insufficient for the high demands of low-level maneuvering in highly contoured, mountainous terrain.
- While the aircraft's airspeed indicators remained at 160 km/h upon impact, suggesting a high-speed impact, the tight nature of the turns meant the pilot likely exceeded the aircraft's aerodynamic limits.
- There was no evidence of mechanical failure or health-related issues contributing to the loss of control.