On March 7, 1999, about 1540 Alaska standard time, a wheel equipped, Piper PA-12, N4040M, sustained substantial damage while landing on the frozen surface of Flathorn Lake, approximately 20 miles southwest of Big Lake, Alaska. The airline transport pilot and the two passengers on board were not injured. The airplane was being operated as a local, personal flight under 14 CFR Part 91. The flight departed Anderson Lake, Palmer, Alaska, about 1500. Visual meteorological conditions prevailed at the time of the accident, and no flight plan was filed. The pilot told the NTSB investigator-in-charge (IIC) during a telephone interview on March 8, and wrote in his NTSB Pilot / Operator report, that he saw other airplanes landing on the frozen surface of Flathorn Lake, and decided to land as well. During landing the snow was initially hard packed as it had appeared from the air. During the landing roll, the airplane's tires sank into soft snow, and the airplane nosed over.