The pilot had refuelled the aircraft to capacity with mogas, and then carried out two flights of about 20 minutes duration each. Takeoff for the third flight was into wind, and towards a rain shower. At about 20 feet above the ground the aircraft began to sink. The pilot lowered the nose and applied full power, but no change in engine note was detected and it appeared that full power was not being delivered. The sink continued, and the pilot commenced a gentle turn to the left to avoid a power line beyond the end of the strip. When ground contact was imminent the pilot closed the throttle and landed straight ahead into an open grass paddock. During the landing roll the aircraft collided with a mound of earth. The pilot later advised that he had not had time to dump the load before the aircraft was almost in ground contact, and he then anticipated that a safe landing was possible. He also stated that prior to this flight he had considered ceasing operations, but was influenced to continue because the weather at the treatment area was favourable, and because a further load of chemical had already been mixed. No defects were discovered with the engine, and a test carried out using mogas revealed that the engine was capable of developing full power. The quality of the fuel being used at the time of the accident could not be determined as the fuel tank was ruptured and the entire contents were lost. The engine is not approved for operation on mogas. It was possible the rain shower near the end of the strip may have generated a wind effect sufficient to degrade the climb performance of the aircraft.
