An exercise in emergency procedures was being carried out in the circuit area. A number of landings were completed, with the instructor simulating a jammed tail rotor pedal. On the last landing, a jammed right pedal was being simulated. After a standard approach for the circumstances, the student flared at about 45 centimetres above the ground and at a speed of about 15 knots. As he then began to reduce power, the engine apparently suffered a substantial loss of power and the aircraft landed heavily. The left landing skid dug in, and the helicopter somersaulted before coming to rest on its right side. No fault or defect was subsequently found with the engine or its systems which might have explained the reported power loss. Atmospheric conditions at the time of the accident were conducive to the formation of carburettor icing, particularly during descents with reduced power. The pilots had not used carburettor heat during the approach, possibly because the carburettor air temperature gauge was indicating a temperature just above the caution range. This instrument was later found to be reading in error by 9 degrees. The pilots had not checked the reading of the gauge against the ambient temperature prior to engine start, and were therefore unaware of the malfunction. When the power loss occurred, the helicopter was in such a position that it had contacted the ground before the instructor could initiate any corrective action.