After completing the flight from Lausanne to Neuchâtel, the crew, composed of a student pilot and his instructor, took off facing the lake, for the return flight. During the initial climb, the aeroplane turned left, then the turn became steeper. The aeroplane entered a nose-down spin and crashed into a small wood bordering the lake, at around 600 m from the aerodrome.
During the initial climb, there was a substantial power loss at low height. This power loss was probably due to the failure of the right carburetor. The non-compliance with the recommended interval between two complete inspections of the carburetors may have contributed to the singularity on the right carburetor not being detected. The disconnection of one of the electronic modules of the ignition system may have occurred in flight and thus may have played a part in the decrease in engine power.
The crew started a left turn. The presence of obstacles on the lake, for example water sports, or the concern about having to land on water may have influenced the crew in this choice. Holding the aeroplane nose-up after the decrease in power combined with a roll action probably led to the aeroplane entering a spin. Given the low height when the crew lost control, they were unable to regain control of the aeroplane. The strong vibrations caused by the loss of the right carburetor may have been a contributing factor to the loss of control.