Accident Summary
A training flight ended with the airplane nosed over after a forced landing. The airplane had departed with full fuel in both wing tanks. Approximately 45 minutes into the flight, the certified flight instructor (CFI) began demonstrating a simulated emergency landing approach. The CFI configured the airplane for the maneuver while the student read the engine troubleshooting checklist aloud. During the maneuver, the CFI pushed the throttle control knob forward every 500 feet of altitude loss in an attempt to temporarily increase revolutions per minute (rpm) and "clear" the throttle. The CFI stated that the carburetor heat control was in the full on position during the entire maneuver, but it was found in the off position after the accident.
While the airplane was about 1,500 feet mean sea level and on the simulated base leg of a traffic pattern, the CFI pushed the throttle forward. The engine did not respond normally and sounded as though it was winding up. After several seconds, the engine quit and the propeller stopped. The CFI attempted to restart the engine using the engine troubleshooting checklist, but it failed to respond. The airplane touched down in a soft dirt field and nosed over, coming to rest inverted.
Examination and Findings
Personnel who recovered the wreckage shortly after the accident stated that they found 15 to 20 gallons of fuel in the wing tanks and the carburetor heat control in the off position. The outside air temperature and dew point temperature around the time of the accident were applied to an industry Carburetor Icing Probability Chart. Both recorded temperatures were within the "serious icing at glide power" portion of the chart. With the engine still mounted in the airframe, investigators ran the engine for several minutes at various rpm settings and noted no anomalies. No evidence of pre-accident mechanical malfunctions was found during the examination of the engine and airframe.