How Fly By Wire Has Made Flying Easier

The first time I heard the term “Fly By Wire” was when I was watching a documentary about fighter jets, specifically the F-16. This fighter jet was the first to use a fly-by-wire system, making it easier for the pilot to control the aircraft. So, I thought fly-by-wire was only for fighter jets. I had no idea this cool system would also be used in commercial airplanes like the Airbus A320.

That’s why you often hear the term “Fly By Wire” when talking about Airbus planes, especially the A320 and up. Other planes use this system too, which I’ll get into later.

Fly By Wire, or FBW, is a term that refers to flight control systems where computers process the inputs from the pilot or autopilot. These computers then send electrical signals to actuators that move the flight control surfaces. This is different from older systems that used mechanical linkage, meaning the pilot’s inputs don’t directly move the control surfaces. Instead, the computer reads the inputs and decides how to move the control surfaces based on active Flight Control Laws.

The Advantages of Using Fly By Wire

FBW systems offer reduced weight, improved reliability, and better damage tolerance. These benefits were first recognized in military aircraft design. The F-16, introduced in 1973, was the first aircraft to use FBW for all its flight controls.

FBW is particularly useful in military aircraft that need to be agile. It helps detect and automatically correct unintended increases in angle of attack or sideslip by slightly moving the control surfaces in the opposite direction. FBW also includes highly reliable flight envelope protection systems that enhance safety when the system is functioning at its normal level.

How Fly By Wire Systems Work

In an FBW system, the Flight Control Computer (FCC) uses the principle of error control. It continually senses the position of a control surface and compares it with the pilot’s or autopilot’s command input. The computer then sends an appropriate corrective signal to the control surface. This is known as feedback compensation. The FCC regulates the system by comparing output signals to input signals, and any error between the two becomes a command to the flight control surface until output equals input.

FBW systems have a forward path and a feedback loop. The forward path is the signal route from the FCC to the control surface, and the feedback loop is the signal route from the control surface back to the FCC. The system can also use a filter to block feedback of signals or motion that occur too frequently.

Additional Features and Control Laws

The FCCs in FBW systems are programmed with control laws that govern the feedback control system. These laws are usually named after the primary feedback parameter, like ‘pitch rate’ or ‘g command.’ Engineers have to tune the integrator gain setting to prevent excessive lag in the aircraft’s response. Most FBW designs, including those from Boeing and Airbus, use an arrangement called “proportional plus integral” control to avoid excessive lag.

FBW allows for different effective dynamics during specific phases of flight by introducing modes like an approach mode or a flare mode. In both Airbus A320 series and Boeing 777, the control laws are not fully active until after the aircraft is airborne due to sensor limitations.

Redundancy and Safety Measures

Instead of having a conventional backup, commercial aircraft with FBW systems usually have redundancy for the FCCs and sensors. For example, the Boeing 777 and Airbus A340 employ triplex FCSs and also have limited mechanical backup.

When all components are working, the system is said to be operating in normal law. Limited failures usually cause the system to revert to a degraded but still computed FCS mode.

Can Fly By Wire Systems Fail?

Yes, FBW systems can fail due to various reasons like electronic malfunctions, software glitches, power failures, component failures, environmental factors, and human error. To mitigate these risks, modern aircraft with FBW systems incorporate redundancy, backup systems, and extensive testing.

Fly By Wire in Commercial Planes

Every commercial aircraft built by Airbus since the introduction of the A320 family in 1987 has had FBW incorporated into its design. Boeing, Airbus’s main competitor, has also incorporated FBW technology in their new models, including the 777 and 787. However, the Boeing 737 and cargo 767s do not have FBW mainly because of the high cost associated with redesign and recertification.