AAIB report Eurocopter EC135, serious incident during maintenance flight

G-POLA

During a maintenance flight to adjust speed, main rotor rpm varied between its maximum and minimum continuous limits. A mechanical stop within the speed control system had failed in such a way that main rotor speed could not be controlled accurately, putting the helicopter at significant risk. The pilot’s actions prevented rotor speed exceeding its limits and a more serious outcome. The manufacturer and operator have taken safety action regarding the conduct of airborne engine speed adjustments.

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