The pilot had recently obtained a Commercial Helicopter Pilot Licence, and had been undergoing training for the issue of a cattle mustering endorsement. He had obtained permission from his employer to use the helicopter for a local flight. The approval was given on the understanding that operations were confined to normal procedures, and were not to include low flying. It was the pilot's intention to conduct two short flights, carrying two other persons on each occasion. The helicopter was given additional pre-flight inspections, following reports of vandalism to other helicopters in the area. No evidence of any vandalism was found and the pilot carried out a short solo flight to further verify the serviceability of the aircraft. The first two passengers then boarded the aircraft. About 30 minutes after DEPARTURE, the aircraft was observed operating, apparently normally, in a designated low flying area. It was then observed flying towards the south east at about 10 metres above the ground. The aircraft then entered a steep turn to the left, but after turning through some 200 degrees the main rotor blades struck the ground. The aircraft subsequently struck the ground heavily and cartwheeled around the rotor arc. A fierce fire broke out and engulfed the wreckage. A detailed technical investigation did not reveal any pre-impact defect or malfunction of the helicopter which might have contributed to the accident. There was also no evidence that the pilot had suffered any sudden illness or incapacity which might have affected his ability to control the aircraft. There was no known operational reason for the aircraft to be flown close to the ground, and it was possible that the pilot was demonstrating mustering techniques to his passengers. The wind at the time of the accident was from the south east at between 11 and 18 knots. The helicopter had been loaded near to the maximum allowable weight, and had not possessed sufficient performance to maintain level flight during the turn towards the downwind direction. The pilot had only limited experience in operations at high all-up-weight levels, and had evidently not realised the effect the increased weight had on the aircraft performance, particularly when turning downwind.