The pilot was conducting aerial observation of his pipeline head gate to check for debris. The pilot overflew the area at 150 feet above ground level (agl) and "observed a light tailwind and no downdraft." The pilot performed a left 360 degree turn and flew over the area a second time between 50 and 60 feet agl. The airplane encountered a "severe downdraft" and settled into terrain. The right wing spar was broken in the impact, as was the right main landing gear and nosewheel. The propeller was destroyed. The pilot reported no mechanical anomalies with the airplane.