On July 18, 1998, about 1400 Alaska daylight time, a Piper PA-14 float equipped airplane, N5133H, sustained substantial damage when it collided with water during initial takeoff from Big Lake, Alaska. The private pilot and the sole passenger sustained minor injuries. The flight was conducted under 14 CFR Part 91, as a personal flight returning to Wasilla Lake Seaplane Base, Wasilla, Alaska. Visual meteorological conditions prevailed at the time of the accident, and no flight plan was filed. The pilot told the NTSB investigator on July 18, that during takeoff, his seat was not locked and slipped aft. He said he lost hold of the flight controls, pulled the throttle to idle, and crashed into the water. The airplane was equipped with Cessna 170 seats, and new Cessna 170 seat tracks. Photographs of the pilot's seat tracks show no visible wear or elongation of the retaining pin holes. The pilot had received dual seaplane instruction, and was scheduled the following week for a seaplane check flight. He did not hold a seaplane rating.