Accident Sequence
The certified flight instructor (CFI) and student pilot were on an instructional flight. When the CFI reduced throttle to demonstrate a power-off stall, the engine experienced a loss of power, though the propeller continued to windmill. Attempts to restore engine power were unsuccessful. The CFI maneuvered the airplane towards a nearby field, where it was landed before a row of trees. During the landing roll, the airplane collided with the trees.
Previous Maintenance
Two weeks before the accident, the engine had "...cut out on round out at Fernandina Airport." Maintenance personnel performed corrective action that included adjusting the idle speed and the idle mixture. The CFI reported that on several previous occasions when flying the accident airplane, the engine had lost power when the throttle was reduced.
Postaccident Examination
Postaccident examination of the airplane revealed a sufficient quantity of fuel. During an engine run in a test cell at the manufacturer's facility, the engine lost power when the throttle was reduced below 1,500 rpm. The engine was only able to sustain operation at low power settings by manually leaning the fuel-to-air ratio. Examination of the servo fuel injector (servo) at the manufacturer's facility following the engine run revealed that a plastic sleeve was missing or separated from the idle stop. Bench testing of the servo showed that with the throttle at the idle stop and the mixture control in the full rich position, the airflow was 6.0 pounds per hour instead of the specified 100.0, and the fuel flow was 1.2 pounds per hour instead of the specified 6.0 to 7.0. Further bench testing revealed that the fuel flow at 4 of the test points exceeded specified limits, while the fuel flow was within limits at 2 of the test points. No determination could be made as to when the plastic sleeve separated from the idle stop.