Page "Fly-by-wire" Paragraph 5

Fly-by wire systems are quite complex, but their operation can be explained in simple terms.

When a pilot moves the control column ( or sidestick ), a signal is sent to a computer ( analogous to moving a game controller ) the signal is sent through multiple wires ( channels ) to ensure that the signal reaches the computer.

A ' Triplex ' is when there are three channels being used.

The computer receives the signals, performs a calculation ( adds the signal voltages and divides by the number of signals received to find the mean average voltage ) and adds another channel.

These four ' Quadruplex ' signals are then sent to the control surface actuator, and the surface begins to move.

Potentiometers in the actuator send a signal back to the computer ( usually a negative voltage ) reporting the position of the actuator.

When the actuator reaches the desired position, the two signals ( incoming and outgoing ) cancel each other out and the actuator stops moving ( completing a feedback loop ).