The helicopter was heading in a westerly direction following takeoff from the pilot's property. The track was to take the aircraft directly over Mount Gayndah so the pilot decided to track to the south of the mountain to provide better terrain clearance. When the helicopter was abeam the mountain, at about 500 feet above ground level, it struck two power lines suspended between a pole on top of the mountain and a pole 1100 metres to the south in the foothills. The pilot was unaware the aircraft had struck the wires, but immediately lowered the collective and turned the aircraft towards the only available cleared area. Approaching the area it became obvious to the pilot that the aircraft would not clear trees on the approach path and he increased the collective. The helicopter cleared the trees and turned right through 180 degrees before touching down in a level attitude while travelling rearward. The landing skids collapsed and the aircraft slewed to the right before coming to rest. The two 90 tonne breaking strain wires had been broken when they were struck by the main rotor blades of the helicopter. The wires then severed the tail rotor drive shaft, a substantial portion of one tail rotor blade and almost severed the tail boom just in front of the vertical stabilisers.