What happened
A flight instructor was conducting a Biennial Flight Review (BFR) for the owner of a tailwheel equipped airplane. Prior to the flight, the aircraft's annual inspection had lapsed, and the pilot's BFR was not current.
The pilot had replenished the aircraft's fuel using a personally owned container that held a mixture of 25 percent aviation fuel and 75 percent automotive fuel. Although the pilot reported draining the tanks before takeoff and observed no signs of contamination, the engine began to lose power and run rough approximately 400 feet above the ground after takeoff.
The pilot attempted an emergency landing in an area consisting of brush and small trees. The tailwheel equipped airplane collided with several trees, resulting in damage to the wings and fuselage. There were no injuries reported.
The investigation
Postaccident examination of the aircraft revealed the presence of water within both the carburetor and the left wing fuel tank. Laboratory analysis performed on the fuel from the pilot's personal fuel container determined that the liquid failed to meet the required specifications for aviation gasoline.