On May 3, 2003, about 1200 Alaska daylight time, a wheel-equipped Piper PA-18-160 airplane, N8240P, sustained substantial damage when it collided with the frozen surface of a river during a forced landing following a partial loss of engine power. The accident occurred about 80 miles northwest of Skwentna, Alaska. The airline transport certificated pilot and the sole passenger were not injured. The Title 14, CFR Part 91 personal flight operated in day visual meteorological conditions without a flight plan. The flight departed from an airstrip near Wasilla, Alaska, about 1030, and the destination was the area of the accident site. The pilot contacted the NTSB investigator-in-charge (IIC) on May 7. He related that he and a passenger were on a pleasure flight, and that he had been flying about 100 feet above the ground at a reduced power setting. He said he had initiated a 90 degree downwind turn, and hit a "sinker," which pushed the airplane towards the ground. He immediately applied full power, but the engine did not seem to respond with maximum power. The pilot indicated he did not have sufficient altitude to select a more desirable forced landing spot other than the frozen river nearby. He said he leveled the wings, and the airplane hit hard on the ice, damaging the fuselage, wings, and landing gear. When asked by the IIC if he was aware of why the engine did not seem to respond with maximum power, the pilot stated that he thought the engine had accumulated carburetor ice since he had been flying at a reduced power setting without the application of carburetor heat.