What Is a Fly-by-Wire System in Aircraft and How it Works?

source: mediarenditions

Significant technological improvements have added to safety innovations in transportation systems – be it by air, water or plane. Regarding safety features of the aviation industry, technology has made a generous contribution over the last three decades. One such contribution is the fly-by-wire system.  

A fly-by-wire system in aircraft (FBW) is a flight control system which uses light electrical wires and computers instead of conventional mechanical connection between cockpit controls of the pilot and moving surfaces of the aircraft.

The pilot's inputs are converted into electronic signals and processed by the flight control system, which can apply control laws and safeguards to enhance aircraft performance and safety.

Here's the working of the FBW system in detail. 

• The pilot moves the control stick or yoke, which sends an electrical signal to the flight control computers.

• Flight control computers consider various factors, such as the aircraft's speed, altitude and attitude, and determine how to move the control surfaces.

• The flight control computers send electrical signals to the actuators, which move the control surfaces.

• The control surfaces move and the aircraft changes its attitude or direction.

The flight control computers can also take corrective action if the pilot makes a mistake. For example, if the pilot pulls back on the control stick too hard, the flight control computers can automatically reduce the amount of elevator deflection to prevent the aircraft from stalling.

There are so many advantages of this lightweight electric aircraft mechanism. Take a look at some of them below: 

• Increased safety: The fly-by-wire system can help prevent pilot errors and provide automatic protection against exceeding the aircraft's safe operating limits. 
• Enhanced performance: Fly-by-wire systems can make aircraft more manoeuvrable and efficient. This is because the flight control computers can optimise the control surfaces for different flight conditions.
• Reduced weight: Fly-by-wire systems are lighter than traditional mechanical systems, saving fuel and improving performance. This is because there is no need for heavy mechanical linkages between the cockpit controls and the control surfaces.
• More flexibility: These systems can be easily modified to accommodate new aircraft designs or features. This is because the control surfaces are not directly linked to the cockpit controls.
• Better handling: Fly-by-wire systems can enhance handling characteristics, such as improved roll control and pitch stability. This can make the aircraft easier to fly and more enjoyable to operate.
• Reduced maintenance: FBWs are less prone to wear and tear than traditional mechanical systems, which can reduce maintenance costs.
• Improved diagnostics: Fly-by-wire systems can provide better diagnostics, which can help to identify and troubleshoot problems more quickly.
• Increased situational awareness: Fly-by-wire systems can provide pilots with more information about the aircraft's status, improving situational awareness.

Like any other technology, this system also has some drawbacks. However, they are less significant and fewer in number than their advantages. Check them out below: 

• Increased complexity: FBW systems are more complex than traditional mechanical systems, making them more difficult to maintain and troubleshoot. This is because more components and linkages can fail.
• Higher reliance on electronics: FBW relies on electronic components, which can be vulnerable to damage or failure. If the flight control computers fail, the aircraft may become uncontrollable.
• Vulnerability to cyberattacks: As fly-by-wire systems are computer-based, they are susceptible to cyber threats. Malicious actors could gain unauthorised access to the flight control systems, compromising the aircraft's safety and control. 

Robust cybersecurity measures and protocols are essential to protect against such attacks, requiring continuous monitoring and updating to stay ahead of evolving threats.

The control laws dictate how the flight control computers instruct the flight control actuators in fly-by-wire systems. Typically, there are three control laws present, although the specific naming convention may vary among manufacturers. These laws operate similarly and are as follows:

1. Normal Law

This law is active under normal operating conditions without any system failures. In normal law, flight control computers operate fully, providing optimised control and handling characteristics.

2. Alternate Law

The alternate law is a reconfiguration law that occurs when system failures occur, preventing the flight control computers from accurately computing data for the control surface actuators. In alternate law, the flight control system adapts and provides limited control authority to maintain basic flight capabilities.

3. Direct Law

Similar to alternate law, direct law is another reconfiguration law activated in the presence of significant system failures. In direct law, the flight control computers are bypassed, and the control inputs from the pilot directly command the control surface actuators. This law provides a direct and immediate response to the pilot's inputs but with reduced automation and stability augmentation.

These control laws ensure that the fly-by-wire system maintains control and flight capabilities in various operating scenarios, ranging from normal conditions to degraded or emergencies.

Flight envelope protection is a critical feature of fly-by-wire systems (FBW) that enhances the safety and performance of aircraft. It refers to control laws and algorithms that prevent the aircraft from operating outside its safe flight protocols or exceeding its structural and aerodynamic limitations. 

• Operating beyond the flight envelope can lead to dangerous situations like stalls, spins, structural failure, or loss of control. 

• One aspect of flight envelope protection is angle of attack (AOA) protection. It ensures that the aircraft does not reach or exceed its critical angle of attack, the angle between the relative wind and the wing chord line where a stall occurs. 

• Another element is bank angle protection, which prevents excessive rolling or banking of the aircraft.  Additionally, flight envelope protection includes over-speed protection. It prevents the aircraft from exceeding its maximum allowed airspeed or Mach number.

• Flight envelope protection acts as an additional layer of safety, helping pilots avoid potentially hazardous situations and improving the overall safety of flight operations.

Fly-by-wire redundancies are nothing but added measures. This ensures that if one fails, the other takes over. Here's an exploration of the redundancies employed in FBW systems:

• Flight Control Computers (FCC): FBW systems typically consist of multiple FCCs that work in parallel. These computers receive and process control inputs from the pilot, implement control laws and command the actuators. 

  Redundancy is having multiple independent FCCs cross-check and monitor each other's outputs continuously. If a failure occurs in one FCC, the remaining computers take over seamlessly, ensuring uninterrupted control.

• Redundant Sensors: These systems rely on sensors to measure critical flight parameters and pilot inputs. Redundancy is implemented by using multiple sensors to measure the same parameters. Redundant sensor data are continuously compared, and any discrepancies or failures can be detected and mitigated.

• Redundant Actuators: Fly-by-wire systems employ redundant actuators responsible for moving the control surfaces. These actuators can be hydraulic, electric, or electromechanical. If one actuator fails, the remaining actuators can still provide control authority, maintaining the aircraft's manoeuvrability and control.

• Redundant Power Supplies: FBW requires a reliable and continuous power supply to operate effectively. Redundant power supplies, such as multiple generators or backup batteries, ensure uninterrupted power in case of power source failures.

• Fault Detection and Isolation: FBW systems incorporate sophisticated fault detection and isolation mechanisms. These systems continuously monitor the performance of critical components and systems, detecting any anomalies or failures. 

  Once FBW detects a fault, the system isolates the affected component or system, preventing its impact on the overall performance and ensuring that the remaining redundant components continue to function optimally.

The redundancies in FBW systems are designed to minimise the impact of failures, enhance system reliability, and provide multiple layers of protection. The Fly-by-wire system has almost no drawbacks, which is not the case with most technologies. The system makes flying operations smoother and ensures an extra level of security. Some aircraft, such as Boeing 777, have a Hydro mechanical control system as a backup against FBW.