An unintended yaw is a persistent accident characterised by an unexpected helicopter rotation around the yaw axis without the pilot’s intention and any technical malfunctions. Unintended yaw accidents are one of the top operational causes of helicopter accidents, causing serious damages and fatalities each year. This thesis in collaboration with Airbus Helicopters and the FAA does a numerical investigation of unintended yaw to provide a characterisation of the phenomena for different helicopter configurations with an open tail rotor and find an optimal recovery method. The simulations include trimmed flights and time domain flights to assess the yaw trim capabilities of the helicopter. Specific attention is placed on the tail rotor aerodynamics and demands. An uncontrollable unintended yaw did not appear for any of the evaluated flight cases and helicopter configurations, showing that the pilot always could trim the helicopter with sufficient pedal margin. In case of unintended yaw, applying immediate and maximum opposite pedal to the rotation of the helicopter could always recover the yaw rate to zero.