During a flying training sortie the instructor simulated an engine failure by moving the mixture control to the idle cut off position. The student closed the throttle and pulled the carburettor heat on, the instructor then moved the mixture control to rich. During the descent the throttle was opened twice. Prior to commencing a go-around, at about 100 feet above ground level, the student moved the carburettor heat control to cold. At about 200 feet, on climb, the instructor simulated another engine failure by again moving the mixture control to idle cut off. As soon as the student lowered the nose of the aircraft the instructor moved the mixture control to rich, with the throttle open. However, there was no response from the engine and the aircraft was subsequently landed in swampy terrain. No mechanical engine defect was found and tests carried out revealed that the engine should have been capable of operating normally. Atmospheric conditions at the time of the accident were conducive to moderate carburettor icing at cruise power and severe icing at descent power. The carburettor heat control was not operated in accordance with the manufacturer's instructions.
