Background
The aircraft was approved for operation with auto fuel under a Supplemental Type Certificate (STC). Prior to the flight, the pilot added auto fuel that was contaminated with water into the fuel system.
Accident Sequence
Shortly after takeoff, the airplane climbed to about 20 feet above ground level. At that point, the engine began to surge between full power and significantly reduced power. The airplane lost altitude, and the pilot attempted to guide it towards an open field. However, one of the wings struck a tree before reaching the field, causing the airplane to cartwheel and impact the terrain.
Investigation
Investigators conducted a post-accident engine run and inspection, which found no mechanical failures or anomalies. Further examination revealed that the pilot had introduced water-contaminated auto fuel immediately prior to the flight. The aircraft’s STC allowed the use of auto fuel, but the pilot failed to perform necessary preflight procedures to mitigate water contamination. Specifically, the pilot did not rock the wings or allow time for any water to settle at the low point before draining the fuel sump. As a result, the water traveled through the fuel system during taxi and reached the carburetor just after the airplane lifted off, leading to the power fluctuations.