NTSB investigators either traveled in support of this investigation or conducted a significant amount of investigative work without any travel, and used data obtained from various sources to prepare this aircraft accident report.
The sport pilot of the experimental, amateur-built, amphibious airplane flew to meet a friend to camp for the night along a river. He landed on the river to the north, flying over power lines during the landing approach, and pulled the airplane onto the shore. The pilot offered to help his friend search for a life vest that had floated downstream after he finished unloading the gear from the airplane. Multiple witnesses watched as the pilot departed northbound on the river, made a 180° turn southbound, then flew over the river, beneath treetop level, and out of sight. They reported hearing a loud "boom" and the engine noise stop just before a power outage occurred. One witness reported seeing the airplane flying 30-40 ft above the river when it "suddenly flipped backwards and then hit the water." One witness reported that the sky was grey and overcast, and that the sun was setting about the time of the accident, making the power lines difficult to see. The powerlines directly overhead of the accident site displayed striations consistent with the airplane impacting the powerlines.
Examination of the wreckage revealed no evidence of a preexisting anomaly or malfunction that would have precluded normal operation. Toxicology testing on the pilot detected two medications, which were unlikely to have caused impairment, and the autopsy revealed an enlarged heart; however, there was no evidence of a heart attack or any other incapacitating event. It is likely that, while flying along the river at low altitude, the pilot failed to see the powerlines, which resulted in an in-flight collision with the powerlines and impact with the river.