What happened
On July 28, 2004, a Bell 206 B helicopter, registration F-GEQE, was conducting an aerial photography mission near Lille, France. The flight, operated by Proteus Hélicoptube, was performing maneuvers at approximately 1,500 feet altitude. At 16:14 UTC, the pilot notified air traffic control that the engine had failed and that he intended to perform an emergency landing via autorotation.
Witnesses reported hearing a loud cracking sound and seeing white smoke emanating from the engine. During the descent, the pilot attempted to navigate toward a suitable landing site, likely seeking to avoid urban areas and high-voltage power lines. However, while performing a sharp left turn at a low altitude, the rotor RPM decreased significantly. This led to a loss of control, causing the aircraft to strike a lamppost and a roadside safety barrier before crashing into a wheat field. The impact resulted in two fatalities.
The investigation
The investigation focused on the mechanical failure of the Rolls-Royce Allison 250-C20B turboshaft engine. Investigators examined the wreckage and found that the engine had ceased producing power prior to impact. A detailed inspection of the engine revealed that the destruction of bearing number 5 was the primary driver of the engine failure. This failure caused axial thrust imbalances that subsequently damaged bearing number 3 and led to the complete shutdown of the gas generator.
Investigators also analyzed the lubrication system, discovering that the nozzle responsible for lubricating bearing number 5 was partially obstructed by metallic particles. The investigation also reviewed the pilot's flight path using radar data and witness accounts to reconstruct the final moments of the flight.
Findings
- The engine failure was caused by the failure of bearing number 5, potentially due to inadequate lubrication caused by a partially blocked nozzle.
- The pilot successfully identified the engine failure and initiated an autorotation procedure.
- Improper management of the autorotation maneuver was the primary cause of the accident, specifically the decision to extend the descent path and execute a sharp, low-altitude turn.
- The high-G maneuver during the turn caused the rotor RPM to drop below safe limits, resulting in the loss of aircraft control.