SEA06FA119 · Cessna 180

The airplane departed for a short flight between two private airstrips located less than 1 mile apart on opposite sides of a river in an area of rugged mountainous terrain. A witness at the departure airstrip reported the airplane's takeoff was uneventful. A witness at the destination airstrip reported hearing the airplane fly over heading downstream and stated that it was the pilot's routine before landing fly over. Witnesses, who were river rafting less than 1 mile downstream of the destination airstrip, observed the airplane over fly them heading downstream at an altitude of about 150 feet agl. They reported that the airplane entered a steep left turn, completed approximately 180 degrees of turn, collided with a tree and then impacted rocky terrain on the river bank. Examination of the airframe and engine revealed no evidence of any discrepancies that would have prevented normal operation of the airplane. The pilot had a history of allergies, and toxicological testing detected brompheniramine (a sedating antihistamine, available over the counter) in the pilot's blood at .223 ug/ml. The pilot also had a severe color vision deficiency. When the accident occurred, the skies were clear, and the sun was in the east at an altitude of 34.3 degrees above the horizon. As the pilot turned the airplane left from a downstream (southerly) heading to an upstream (northerly) heading, he would have been heading east directly toward the rising sun approximately midway through the turn.

Verbatim NTSB analysis and probable cause from the NTSB dataset