What happened
On April 5, 2018, an Agusta-Bell 47G2 helicopter, registration F-GGLB, was conducting instructional flight maneuvers at the Libourne Artigues-de-Lussac aerodrome in France. The flight was part of a type-rating program for a pilot-in-training, accompanied by an instructor.
While performing a circuit on runway 04, the aircraft was on its downwind leg at a low altitude. Witnesses reported hearing the engine spluttering, followed by the helicopter adopting a nose-down attitude. The aircraft subsequently turned and collided with the ground in a nearby vineyard, where it immediately caught fire. The accident resulted in two fatalities, claiming the lives of both the instructor and the student.
The investigation
The BEA examined the wreckage and the engine components to determine the cause of the power loss. Investigators found that the helicopter had struck the ground with a high vertical speed and a significant bank angle, with the main rotor rotating slowly at the moment of impact. The engine was found to be delivering little to no power prior to the collision.
Upon inspection of the Marvel-type Volare carburetor, investigators identified a quality defect in the weld of one of the two floats. This defect allowed fuel to gradually leak into the float, unbalancing the fuel level within the float bowl. This imbalance caused erratic engine performance and a subsequent reduction in power.
Maintenance records showed that while the engine was operating under an extended time-between-overhaul (TBO) program, the carburetor itself was not specifically listed as an accessory requiring periodic inspection. Furthermore, the investigation noted that a manufacturer service bulletin recommending the replacement of these specific floats with newer foam versions had not been implemented on this aircraft.
Findings
- The primary cause of the accident was a reduction in engine power resulting from a fuel supply fault caused by a leaking carburetor float.
- The instructor likely attempted an emergency descent or autorotation to manage the power loss, but the maneuver became uncontrollable during the turn to align with the wind.
- The low altitude of the flight left insufficient margin to recover from the engine failure.
- The lack of a specific inspection requirement for the carburetor allowed the manufacturing defect to remain undetected despite the engine's extended service life.