What happened
On April 24, 1976, a Cessna 177, registration HB-CDV, was conducting a VFR flight from Ajaccio, Corsica, to Geneva, Switzerland. Despite being warned by meteorologists in Ajaccio about severe turbulence, icing, and the risk of thunderstorms with snow in the Alps, the pilot proceeded with the flight.
During the descent near Chambéry, the aircraft's radio communications became intermittent and eventually failed. The last transmission, received at 16:48 UTC, indicated the aircraft was descending near level 65 near the Passery crossing. The aircraft subsequently struck the snowy terrain at the Tête du Parmelan in the Haute-Sought region of France at an altitude of approximately 1,600 meters. The impact resulted in 3 deaths (the pilot and two passengers). The wreckage was not located until May 17, 1976, by a pilot from the Annecy Aero Club.
The investigation
Investigators examined the wreckage and the flight's technical history. The aircraft was found in a heavily fragmented state, with the fuselage folded at a 70-degree angle. The propeller blades were bent, but traces indicated the engine was not turning at the moment of impact.
Technical analysis of the radio equipment suggested that the sudden loss of signal strength during the final communication was likely caused by the antenna being torn from the airframe. This was attributed to the significant aerodynamic forces exerted by heavy ice accumulation on the antenna. The investigation also noted that the pilot had been using a personal navigation procedure to penetrate IMC conditions over Lake Geneva, despite lacking IFR qualifications.
Findings
- The primary cause of the accident was intense icing, which likely led to engine failure and disrupted communications.
- The pilot proceeded with the flight despite explicit warnings regarding severe icing, turbulence, and thunderstorms.
- The aircraft was not equipped with any de-icing devices for the airframe or propeller.
- The antenna was likely stripped from the aircraft due to the weight and drag of accumulated ice.
- The wreckage was extremely difficult to locate because the aircraft's color blended with the snowy terrain and the site was obscured by trees.