The student pilot had been authorised to carry out a one hour flight in the Bankstown Training Area for the purpose of practising steep turns and simulated forced landing approaches. The weather was fine and cool with light winds. Prior to DEPARTURE the student had been briefed by his instructor on the conduct of the flight. This had included specifying a minimum go-around height for forced landing approaches. The student was instructed to return to Bankstown by 1700 hours. The aircraft failed to return by the appointed time and, despite extensive efforts, was not located until the following morning. The wreckage was found in an open area and damage was consistent with the aircraft having struck the ground at a high rate of descent with a very low forward speed. Evidence was found to indicate that the engine was delivering little or no power at impact. Subsequent testing demonstrated the engine was capable of normal operation. A comparison of the actual weather conditions at the time of the accident and a carburettor icing probability chart, showed that serious carburettor icing was probable at descent power. The circumstances of the accident were consistent with the engine failing to respond to the opening of the throttle following a prolonged descent at idle power, following a practice forced landing approach. The student may have diverted his attention from flying the aircraft while attempting to restore power, resulting in a loss of control at low altitude. It was not possible to determine if the carburettor heat control had been operated in accordance with recommended procedures.