On January 14, 2010, about 1030 Alaska standard time, a wheel ski-equipped Piper PA-12 Airplane, N3233M, sustained substantial damage after landing on a snow-covered lake, about 15 miles southeast of Gulkana, Alaska. The airplane was being operated by Copper Valley Air Service Inc., Glennallen, Alaska, as a visual flight rules (VFR) passenger flight under Title 14, CFR Part 135, when the accident occurred. The commercial pilot and sole passenger were not injured. Visual meteorological conditions prevailed, and company flight following procedures were in effect. The flight departed the Gulkana Airport about 1030 for McCarthy, Alaska. During a telephone conversation with the National Transportation Safety Board (NTSB) investigator-in-charge (IIC) on January 15, the pilot said that due to the cold outside temperature, he departed Gulkana with the airplane's oil cooler cover in place. He said after departing, the engine temperature increased significantly, and he decided to land and remove the oil cooler cover. He reported that he chose a snow-covered lake for landing, and that after landing, he continued laying down tracks in the newly fallen snow to aid in his departure. The pilot said while laying down tracks the airplane's skis hit a ridge hidden under the snow. He said he examined the airplane and found a fuselage frame tube had broken near the right main landing gear attachment. He said he called for another airplane to pickup his passenger. The pilot said there were no mechanical problems with the airplane prior to the flight.