In a helicopter having a main rotor, a tail boom and a circulation control slot along one side of the tail boom, and a thruster which is selectively directable at either side or both sides of the rear end of the tail boom, anti-torque and yaw control are effected by generating separate air flow streams of different pressures by means of separate pressure means and conducting said separate air flow streams at said different pressures in separate passages to respectively the circulation control slot and to the thruster.