On September 11, 1998, about 1530 Alaska daylight time, a float equipped Taylorcraft airplane, N43140, sustained substantial damage while landing on a lake, about 6 miles southeast of Big Lake, Alaska. The airplane was being operated as a visual flight rules (VFR) local area personal flight when the accident occurred. The airplane was operated by the pilot. The certificated private pilot, and the sole passenger, were not injured. Visual meteorological conditions prevailed. The flight originated from an adjacent lake about 1526. During a telephone conversation with the National Transportation Safety Board (NTSB) investigator-in-charge (IIC), on September 12, 1998, at 1300, the pilot said he departed Papoose Lake, and was performing touch and go landings on Crooked Lake. During the landing touchdown, the tip of the right float dug into the water. The right float assembly was torn off the fuselage, and the right wing struck the water. The airplane then sank. In the pilot/operator report (NTSB form 6120.1/2) submitted by the pilot, he indicated that during the landing approach, the airplane developed a sink rate that "felt mushy." The pilot reported he added engine power and aligned the airplane with the water. The right wing dropped, and the right float dug into the water.