Accident Overview
While attempting a takeoff from a gravel bar, the aircraft crashed. The pilot had estimated the usable area for the takeoff to be between 400 and 500 feet.
Investigation
After the accident, investigators recovered the aircraft and performed an engine run test. They determined that the density altitude at the time of the accident was at least 3,400 feet above mean sea level.
During the engine test, the carburetor heat butterfly valve was evaluated. The valve operated normally when set to the "ON" position. However, when the valve was placed in the "OFF" position, it opened only partially. This partial opening resulted in the engine being unable to deliver full static power during the test.
Findings
The source does not provide an explicit probable cause for the accident. The factors identified include the limited takeoff area on the gravel bar, the elevated density altitude, and a malfunctioning carburetor heat butterfly valve that did not fully open when set to OFF, as observed during post-accident testing.