What happened
A commercial air taxi pilot was conducting a flight inspection of a runway at Russian Mission, Alaska, when the aircraft experienced a significant loss of power. While flying on the downwind leg, the engine of the Cessna 207 lost most of its power, and the pilot was unable to restore enough thrust to maintain flight.
To avoid a more serious accident, the pilot elected to perform a forced landing on the nearby, frozen Yukon River. During the approach, the pilot misjudged the aircraft's altitude because the all-white, featureless surface of the river made depth perception difficult. The aircraft struck the surface while the pilot was still executing a slight right turn. Both the pilot and his passenger were uninjured.
The investigation
An inspection of the crash site conducted two days after the accident revealed the presence of numerous ice crystals in the left fuel tank sump. Aside from these crystals, no other obvious abnormalities were identified during the examination. Due to the time elapsed between the collection of the sample and the accident, it could not be determined if the ice crystals contributed to the engine power loss.