The pilot was briefed by the client's agent immediately before the flight which involved spraying four paddocks. After spraying two paddocks the pilot decided to check the wind drift by activating a smoke generator before spraying the third paddock. He had sprayed this paddock on two prior occasions at ten day intervals. He aimed the aircraft at the centre of the paddock with the intention of being at spray height halfway down the paddock. While crossing the paddock boundary at about 30 feet above the ground on descent, there was a loud bang. The aircraft began to display a tendency to roll to the right. The pilot controlled the aircraft, jettisoned the hopper load and flew to the airport without further incident. After inspecting the aircraft, the pilot realized that it had collided with wires. He drove to the client's property and was informed for the first time that the Hydro Electricity Commission had installed a new powerline across the paddock to a dam the previous day. The dam was outside the area to be sprayed. There were no poles in the area to be sprayed; the wires spanned the paddock.
