On March 5, 2006, approximately 1130 Pacific standard time, a single-engine Piper PA-18-135 airplane, N1991A, sustained substantial damage after landing short of a gravel bar runway near Saint Paul, Oregon. The airplane was registered to and operated by a private individual. The commercial pilot and his sole passenger were not injured. Visual meteorological conditions prevailed for the local flight, which was operated in accordance with 14 CFR Part 91, and a flight plan was not filed. The flight departed the Flying M Airport, Yamhill, Oregon, at 1100. According to a written report submitted to the NTSB investigator-in-charge, dated March 12, 2006, the pilot stated that while landing on a gravel bar the airplane's wheels contacted the water and soft sand just short of the gravel bar, which caused the airplane to nose over and come to rest in an inverted position. The pilot reported that the rudder was substantially damaged and that the accident could have been prevented if he had extended his touchdown zone far enough ahead to ensure solid footing for his tires.