What happened
On February 8, 2011, a Piper PA-28-161, registration OO-TMI, was conducting a pilot license examination flight at EBZH airfield. During the flight, a flight examiner initiated a simulation of a Practiced Forced Landing (PFL). As part of the exercise, the throttle was retarded to idle and the carburetor heat was activated.
While on final approach, the student pilot realized the aircraft was too low and attempted to abort the landing by applying more throttle. However, the engine failed to respond and remained at a low RPM. The flight examiner took control to prevent a stall, but the aircraft could not reach the runway. The plane touched down in a field adjacent to the airfield, crossed a road, and struck concrete pillars and barbed wire before coming to a halt. Both occupants escaped the wreckage without injury, though the aircraft sustained heavy damage to the landing gear, propeller, and wings.
The investigation
Investigators examined the engine, fuel systems, and meteorological data to determine why the engine failed to respond to throttle input. Analysis of the fuel flow transmitter revealed that the fuel flow dropped significantly, even reaching zero for a 12-second period, shortly after the power reduction. This indicated a total obstruction of the airflow or fuel flow.
Environmental data from nearby stations showed temperatures around 4°C to 6°C with a dew point of 3°C, which are conditions highly conducive to ice formation in a carburetor. The investigation also noted that the pilot's decision to extend the descent due to traffic on the circuit resulted in the aircraft being too low for a successful landing attempt.
Findings
- The engine ceased functioning approximately two minutes before the impact.
- Carburetor icing caused the engine failure by obstructing the venturi.
- The carburetor heat was only applied at the moment of power reduction, which was insufficient to prevent ice formation in the existing conditions.
- The flight was a simulated exercise, but the actual engine failure turned the simulation into a real emergency.
- The aircraft was in an airworthy condition prior to the event.