The student pilot performed the preflight inspection, by the checklist, and under the supervision of the flight instructor, for the dual instructional flight. He checked the fuel gauges and looked in the tanks, but he did not "stick" the tanks and confirm the exact fuel quantity. He estimated that each tank was about "three-quarters" full. Fuel samples drained from the wings and the fuel strainer were absent of water and debris. The student pilot performed the engine start, run-up procedures, and before-takeoff checks, and all indications were normal. He then flew out to the local training area and performed steep turns. The flight instructor noted some minor deficiencies in the student's technique, and demonstrated the use of pitch and power to smooth the maneuver. They then transitioned to minimum-controllable-airspeed maneuvers, then to power-off stalls. During a stall recovery, the flight instructor noticed a reduction in engine power. He adjusted the throttle, mixture, and carburetor heat controls but the engine stopped producing power, and the propeller stopped completely. During the subsequent descent, the flight instructor contacted air traffic control, declared an emergency, and selected a field for the night forced landing. The airplane struck trees prior to the field, descended to the ground, nosed over, and came to rest inverted. There was only a faint odor of fuel and no evidence of fuel spillage at the scene. There was also no evidence of fuel in either fuel tank. Examination of the engine revealed no anomalies.

The National Transportation Safety Board determines the probable cause(s) of this accident as follows: