AAIB report: Eurocopter EC135, serious incident during maintenance flight
Eurocopter EC135 (G-POLA) incident during maintenance flight, Northumberland.
![G-POLA](https://assets.publishing.service.gov.uk/government/uploads/system/uploads/image_data/file/92687/s300_G-POLA_Fig_1.jpg)
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.