Following a period of circuit practice, the instructor was demonstrating some enroute emergency procedures. An autorotation was entered from 2000 feet, with the pilot aiming for a paddock on the side of a river. He advised that descent was continued to about 250 feet above the ground. Shortly after power was re-applied the helicopter collided with a set of power lines and dived to the ground. The pilot had noted two other sets of wires in the area, but had not sighted a set of three cables between the others until immediately before the collision. The helicopter was being operated outside the designated training area. The grey oxidised powerlines, which were estimated to be between 80 and 100 feet above ground level, were very difficult to see against the overcast sky conditions. The span between supporting poles was greater than those between the other sets of cables.
