Event Summary
During flight, the engine of an amphibious plane began to run rough. The pilot attempted to correct the situation, but the engine continued to operate at reduced power. He elected to land the aircraft in a field and extended the landing gear. However, the pilot saw that the aircraft would not clear trees, so he decided to land on a nearby lake. There was not enough time to retract the gear; therefore, during the landing, the plane flipped over. It continued to float, and later, it was turned to an upright position and towed out of the lake on its gear.
Post-Accident Findings
The pilot stated that he had drained the sumps before the flight. After the accident, he drained about 5 ounces of fluid from the upper drain, and about half of it was water. However, the water was found after the aircraft had floated upside down in the lake overnight.