What happened
On June 25, 1961, a Piper Cub J3C, registration HB-OXG, was performing a return flight from Kägiswil to Sion. While flying at approximately 3,000 meters near the Gemmi Pass, the aircraft encountered several rain showers. During the descent toward the Rhone Valley, the engine suddenly lost power at an altitude of about 1,700 meters.
Unable to reach Sion, the pilot identified a suitable landing area near Chippis. As the pilot approached the site, they realized a strong mountain wind was creating a significant headwind/tailwind situation. To avoid landing with a heavy tailwind—which risked overshooting the field into a drainage ditch—the pilot attempted a late turning maneuver to land into the wind. However, due to insufficient altitude, the aircraft could not complete the turn, resulting in a broken landing that heavily damaged the wings, engine, and landing gear. The pilot sustained only a minor injury.
The investigation
The investigation examined the aircraft's mechanical condition and the pilot's decision-making during the emergency. Investigators found that sufficient fuel remained in both wing tanks, ruling out fuel exhaustion. A technical inspection of the carburetor by Transair AG revealed no blockages, debris, or water contamination. The investigation also reviewed the weather conditions, noting a humid and unstable atmosphere typical of summer thunderstorms in the Alps.
Findings
- The primary cause of the accident was an engine failure, likely resulting from carburetor icing. Although the pilot had been using the carburetor heat, the icing may have developed during the descent while the throttle was at idle.
- The pilot failed to account for changing wind directions, assuming the wind conditions were the same as during the earlier departure from Sion.
- The attempt to execute a late course correction at low altitude significantly increased the risk of the accident.