On September 23, 2000, about 1330 Pacific daylight time, a Cessna 172, N8315L, sustained substantial damage after colliding with a vehicle while the airplane was on final approach to Chehalem Airpark, Newberg, Oregon. The airplane is owned and operated by Blue Max Flying Club, Incorporated, of Lake Oswego, Oregon, and was being operated as a visual flight rules (VFR) instructional flight under the provisions of Title 14, CFR Part 91. The certified flight instructor, and student pilot both sustained serious injuries. Visual meteorological conditions prevailed and no flight plan was filed for the local flight. In a written statement, the certified flight instructor reported that the airplane was on final approach to runway 07. Shortly before touchdown, with the flight instructor flying the airplane, the airplane encountered a downdraft and subsequently collided with a dump truck traveling southbound on an adjacent county road that runs perpendicular to the runway. After colliding with the truck, the airplane impacted the runway and slid to a stop. The airplane sustained substantial damage to the fuselage. Both main gear legs and the nose wheel strut separated from their respective attach points when the airplane collided with the truck. According to the United States Government Airport/Facility Director, runway 07 at Chehalem Airpark is 2,285 feet in length, with a 300-foot displaced threshold. The displaced threshold is approximately 318 feet from the center of the county road.