On July 1, 1998, at 1330 central daylight time, an American Yankee AA1-1TW, N5643L, impacted the terrain following a loss of directional control during a landing roll on runway 29 (3,539' x 100') at the Clark Airport, Point Lookout, Missouri. The ATP pilot and passenger were not injured and the airplane sustained substantial damage. The airplane was being operated as a personal flight under 14 CFR part 91 when the accident occurred. The flight originated Cape Girardeau, Missouri, at 1145. Visual meteorological conditions prevailed and no flight plan was filed. The pilot stated that during the landing roll, following a 3-point landing, the tailwheel began to vibrate. He reported the vibration increased and the airplane made a "sharp yaw to the left." After about 30 degrees of turn, the right landing gear attach bracket bolts sheared and the right wing contacted the runway. The airplane then skidded to the right side of the runway and exited the runway tail first. Inspection of the runway by the Clark Airport Operations Supervisor revealed tail wheel skid marks were present on the runway for a length in excess of 150 yards. Inspection of the airplane by an Inspector from the Kansas City Federal Aviation Administration Flight Standards District Office revealed the right arm of the tailwheel had failed approximately 1" from the center of the arm. Corrosion was present on the factured surface.