Flying Controls
The Harrier has two integrated flying control systems - one for wing-borne flight and one for jet-borne flight- with only one conventional set of cockpit controls.

For wing-borne flight the Harrier uses conventional aerodynamic control surfaces, with the ailerons on the outer wings and the all-moving slab tailplane being driven by hydraulic jacks. The rudder is manual in first generation aircraft and powered in the Harrier II. The surfaces are linked to the pilot's control stick and rudder pedals by a system of rods and cables - the latter being used to reduce weight. As the rudder was unpowered on earlier generation aircraft simple auto-stabilisation was provided for pitch and roll only. The Harrier II features a comprehensive automatic flight control system, with stability augmentation active in both jet-borne and conventional flight..

To cater for jet-borne flight, where the aerodynamic forces on the conventional surfaces are reduced or eliminated, a system of air jet reaction control valves are utilised. These are placed in the extreme nose, tail and at the wingtips to provide pitch, roll and yaw control. The system uses air bled from the high-pressure compressor of the engine and the valves are opened using pilot commands from his normal controls. Indeed, the valves at the wingtips and in the tail are directly linked to the aileron, tailplane and rudder so that when each of these surfaces moves its corresponding valve also opens. This occurs during both wing and jet-borne flight, but as the engine bleed is only operative when the main engine nozzles are vectored below 20 degrees no jet reaction force is produced unless the aircraft is partially jet-borne. The interlinking of the aerodynamic and reaction controls, allied to the progressive increase in the amount of air bled from the engine with increasing nozzle vectoring above 20 degrees, ensures that the aircraft is fully controllable at all airspeeds and during transition.