On April 1, 1997, about 1145 Alaska standard time, a wheel-ski equipped Piper PA-18 airplane, N4500W, registered to the U.S. Department of the Interior and operated by the National Park Service (NPS), received substantial damage while landing at the Noatak Airport, Noatak, Alaska. The solo commercial pilot, a NPS employee, was not injured. The U.S. Government operated flight was initiated for the purpose of maintaining pilot flight proficiency, and operated in visual meteorological conditions under 14 CFR Part 91. The flight last departed Kotzebue, Alaska, and the immediate destination was the Noatak Airport. During a telephone conversation with the NTSB investigator-in-charge on April 3, the pilot related he was returning to work with the NPS as a Park Ranger/Pilot, after a three month furlough. Since he had not flown during the time he was furloughed, he felt a need to practice his flying skills prior to a mission flight planned for the next day. The pilot was making a series of full stop landings at the Noatak Airport on wheel/ski equipped landing gear with the skis retracted. On the fourth landing on runway 36, the pilot said the airplane porpoised and bounced, and then went to the left during the landing roll. He said he overcorrected to the right, and then to the left. The airplane ground looped to the left, and came to rest facing in a westerly direction. Postaccident inspection disclosed damage to a longeron and the horizontal stabilizer. The written report submitted to the NTSB by the pilot indicated his total flight experience in a Piper PA-18 airplane was approximately five hours at the time of the accident.