The Boeing 777 has 14 spoilers. The left wing has seven: five outboard and two inboard spoilers. Likewise, the right wing has seven: two inboard and five outboard spoilers. Spoilers serve two purposes on the aircraft. They assist the flaperons and ailerons during roll control, and they also act as speed brakes.

Each spoiler is connected to a power control unit (PCU). The PCUs are hydraulic actuators and use different hydraulic systems of the aircraft for redundancy. For the PCUs to actuate, they need input signals, and there are four possible sources. The roll signal can be given by using the control wheels or by the autopilot computer. The speed brake signal can be manual or automatic. The auto speed brake system will not be covered in the flight control series.

Let's start with the control wheels. As we saw in the previous chapter, when the control wheels are rotated to give a roll command, the position transducers send the wheel position signal to the flight computers. The control wheel rotation also sends a mechanical signal through cables. The mechanical signal will directly control numbers four and eleven spoilers. The electrical signal is processed by the actuator control electronics (ACE) and transferred to the primary flight computer (PFC). The PFC informs the ACE to deflect the flaperons and the ailerons. It also informs the ACE to operate the spoilers.

The ACE will now electrically open the control valves on the spoiler PCUs. On the left wing, as the flaperon and aileron deflect upwards, the spoilers move up. On the right wing, as the flaperon and aileron deflect downwards, no control input is given to the spoilers on the right side during a roll command. The number four spoiler on the left wing is not fly-by-wire controlled. It is operated by the mechanical cable connected directly to the control wheels. The cable movement opens the PCU hydraulic valve, and the spoiler moves up.

When a right roll command is given, the fly-by-wire controlled spoilers on the right wing deflect up, and the left-wing spoilers are not controlled. The number eleven spoiler will move with the mechanical input from the control wheels.

Next, the autopilot input resulting in spoiler deflection. The autopilot computer requests a roll command to the primary flight computer (PFC). The PFC will send two calculated signals: one for the ACE to move the control surfaces and the other for the autopilot computer to back drive the control wheels. As the ACE moves the fly-by-wire controlled spoilers and other surfaces, the autopilot computer back drives the control wheels. Control wheel rotation will move the mechanically controlled number four spoiler. Once the autopilot command is over, the surfaces and the control wheels will return to neutral position.

Finally, let's see the speed brake control. The speed brake lever is used to deflect the spoilers. The lever has three positions: spoilers down, armed for auto speed brake, and up for manual control. Selecting the lever to the up position will move a clutch assembly. The change in position is picked up by the transducer. The position transducer sends a signal to the flight computer through the ACE. The PFC commands the ACE to move all 14 spoilers to their maximum deflection. During an aircraft roll command, the control wheels give the mechanical signal to the number four and eleven spoilers, which is not possible when using the speed brake lever. Therefore, during speed brake extension, all spoilers are fly-by-wire controlled, including numbers four and eleven.