During a maintenance flight to adjust engine speed, main rotor rpm varied between its maximum and minimum continuous limits. A mechanical stop within the adjusting potentiometer had failed in such a way that main rotor speed could not be controlled accurately, putting the helicopter at a significant risk. The pilot had not been specially trained to carry out the flight test but his actions in flight 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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Published 24 October 2019