On April 21, 1999, about 2210 Alaska daylight time, a tundra tire, tailwheel equipped Piper PA-18 airplane, N1389A, received substantial damage while landing on runway 29 at the King Salmon Airport, King Salmon, Alaska. The certificated private pilot, and the one passenger aboard were not injured. The airplane was being operated as a visual flight rules (VFR) cross-country flight under Title 14, CFR Part 91, when the accident occurred. Visual meteorological conditions prevailed, and a VFR flight plan was filed. The flight last departed Merrill Field, Anchorage, Alaska, about 1900, and the destination was the King Salmon Airport. During a telephone conversation with the National Transportation Safety Board investigator-in-charge on April 22, the pilot stated that the touchdown and the landing roll were uneventful, until the airplane's nose veered slightly to the left. He said he compensated by applying right rudder, but the airplane suddenly ground looped to the left. He stated that the right main landing gear collapsed, and the right wing collided with the runway during the ground loop. The airplane sustained substantial damage to the right wing, and right wing struts. The pilot noted that there were no preaccident mechanical anomalies with the airplane.