What happened
On the afternoon of April 29, 1979, a Cessna 150 L, registration HB-CEF, departed from the Bad Ragaz airfield for a private recreational flight. The aircraft was carrying a pilot and one passenger. While flying near the Ilanz area and turning toward Laalx, the aircraft began flying noticeably slow. Witnesses observed the plane banking sideways and entering a spin. During the maneuver, the engine appeared to cut out. After several rotations, the aircraft struck a slope northwest of Laax with a steep nose-down attitude. Both occupants sustained fatal injuries upon impact, and the aircraft was destroyed.
The investigation
Investigators examined the wreckage and the flight conditions at the time of the accident. The aircraft's weight and center of gravity were found to be within permissible limits. Technical inspections of the wreckage confirmed that all flight controls were properly connected and functional, and the landing flaps were retracted. No structural damage or mechanical failures were identified that could have caused the loss of control. The weather was suitable for VFR flight, though investigators noted that local turbulence in the mountainous terrain could have contributed to the loss of airspeed. The pilot's medical records showed no health issues, and there was no evidence of alcohol consumption.
Findings
- The aircraft entered a spin due to the speed dropping below the minimum stall speed for reasons that could not be determined.
- The pilot was not trained in aerobatic maneuvers and was unable to recover the aircraft from the spin, despite having sufficient altitude to do so.
- The pilot did not immediately reduce engine power during the initial loss of control, a step recommended in the manufacturer's manual for recovering from unintended spins.
- The engine cutout observed during the spin may have been caused by centrifugal forces interrupting the fuel supply to the carburetor or manual adjustments to the throttle.