You have probably heard the term “fly by wire” but do you understand what it is and have some idea of how it works?
Understanding fly by wire is a complex topic however here we try to give you a basic understanding of what it is.
Fly by wire is a term used to explain how the control surfaces of an aeroplane are moved (by control surfaces we are referring to the ailerons, rudder and elevators. i.e the movable parts of the aircraft that are used to control it).
Before fly by wire, the method of moving control surfaces was by cable. When the pilot moves the yoke (or stick) and rudder pedals, this directly manipulates cables that displace the control surfaces. This is still used effectively on many smaller aircraft.
The larger an aeroplane gets, the bigger the control surfaces must be, and the more force must be exerted by pilots to move them. So hydraulic controls became popular. The amount of force on the cables is amplified by hydraulic actuators that move the control surfaces. This is the most-utilised method used in airliners today.
Fly-by-wire aeroplanes operate differently. In a fly by wire aircraft, the pilot inputs commands via a sidestick or yoke to a computer and any deflection of the yoke or rudder pedals by the pilots is detected by computer sensors. The sensors then determine the amount of deflection, or movement, needed in the control surfaces (using data such as aircraft altitude and airspeed) and send this information to hydraulic actuators which then move the ailerons, elevators and rudder.
There are numerous advantages to fly by wire systems, including weight savings and safety features that can incorporated into the computer software. Each system has a number of back up systems meaning to protect the integrity of the whole system.
To give you some idea of the system configuration, the A320 has 7 flight control computers:
2 ELACs: Elevator Aileron Computer (normal elevator and horizontal stabilizer control, as well as aileron control)
3 SECs: Spoilers Elevator Computer (spoiler control as well as standby elevator and stabilizer control)
2 FACs: Flight Augmentation Computer (electrical rudder control)
So from this, you can see that there are multiple levels of control for most of the control surfaces. If one set of computers was to fail you would still have some control over the aeroplane.