FLIGHT CONTROL SYSTEM AND METHOD FOR A ROTARY WING AIRCRAFT, ENABLING IT TO MAINTAIN EITHER TRACK OR HEADING DEPENDING ON ITS FORWARD SPEED

A flight control method and system for a rotary wing aircraft. When the longitudinal speed UX of the aircraft is greater than a first threshold speed Vthresh1, a first mode of operation of the method enables flight to be performed while maintaining track relative to the ground, the flight setpoints of an autopilot being a ground course angle TKsol, a forward speed Va, a flight path angle P, and a heading Ψ. When the longitudinal speed UX is less than a second threshold speed Vthresh2, a second mode of operation enables flight to be performed while maintaining heading, the flight setpoints being the longitudinal speed UX, a lateral speed VY, a vertical speed WZ, and the heading Ψ.