The pilot was engaged in the chemical spraying of several properties in the general vicinity of his own property near Gatton. After completing the spraying of two properties, the pilot began positioning the aircraft in order to spray his own crop. A witness observed the aircraft as it turned to the right and flew at low level beneath power lines across a highway. The aircraft was then seen to bank slightly to the right and strike another set of power lines on the opposite side of the highway. Two of the wires were broken and the third remained entangled with the aircraft. The aircraft struck the ground in an inverted attitude. The power lines struck by the aircraft had been erected about three weeks before the accident. They had been erected at the request of the pilot to service a portion of his property. He had flown under the wires on several occasions in the preceding three weeks.