The helicopter was being used as an airborne filming platform. It was being flown at about 30 feet above ground level along the side of a roadway, while the film crew filmed a bus that was travelling along the road. The helicopter was observed to gain altitude and pass over a power line then descend again to 30 feet above ground level. After travelling a further 500 metres the helicopter struck a spur line running from the main power line, pitched nose up before descending out of control and colliding with the ground. The wreckage slid 50 metres before coming to rest on the road. The positon of both the sun and the support poles of the spur line would have made detection of the line difficult unless the pilot had prior knowledge of its position. The pilot was not seen to conduct a survey of the area for obstacles prior to commencing low level operations. The task required the pilot to concentrate on the bus to the right of the helicopter as well as the flight path ahead. Examination of the wreakage did not reveal any malfunction which may have contributed to the occurrence. It appeared that on impact with the spur line one cable contacted the bottom of the windscreen pillar and the other became entangled in the rotor blades. All significant damage to the aircraft appeared to have resulted from ground impact.