A helicopter mast is driven by a transmission with a swashplate individually linked to pitch horns on each rotor blade. At least four actuators are coupled to the swashplate, three of which normally control the attitude and position of the swashplate. A separate power unit is provided for each actuator, each power unit being independently driven from the transmission. Means are then provided to shift control of the swashplate from one of the three actuators to a fourth actuator upon any one becoming disabled.