Home Airbus Airbus A320 What is MSU on Airbus A320? (Mode Selector Unit)

What is MSU on Airbus A320? (Mode Selector Unit)

The Mode Selector Unit (MSU) is a crucial component of the Airbus A320 aircraft. It plays a vital role in the flight control system, allowing pilots to select various airplane modes and engage specific functions during different phases of flight. The MSU is responsible for managing autopilot functions, autothrust, flight control laws, and many other essential features.

The MSU is located on the center pedestal between the pilot and co-pilot seats. It consists of a multifunctional rotary control knob, buttons, and indicator lights that provide pilots with control over the aircraft’s various systems and modes. Let’s delve deeper into the functionality and importance of the Mode Selector Unit on the Airbus A320.

The Functions of the Mode Selector Unit (MSU)

The Mode Selector Unit (MSU) on the Airbus A320 aircraft offers a wide range of functions that contribute to the safe and efficient operation of the aircraft. Here are some of the key functions provided by the MSU:

1. Autopilot Control

One of the primary functions of the Mode Selector Unit (MSU) is to control the autopilot system. The MSU allows pilots to engage and disengage the autopilot, making it an essential tool for reducing workload during flight. Pilots can use the MSU to select and engage autopilot modes such as heading hold, flight level change, vertical speed, and altitude hold.

Additionally, the MSU enables pilots to navigate through different flight phases seamlessly. For example, during the climb phase, pilots can engage the climb mode on the MSU, allowing the autopilot to control the aircraft’s climb rate and maintain a predetermined speed until reaching the desired altitude. This significantly reduces the pilot’s workload and enhances the safety and efficiency of the aircraft’s ascent.

2. Autothrust Management

The MSU is also responsible for managing the autothrust system on the Airbus A320 aircraft. Autothrust is an automated system that controls the aircraft’s thrust setting to maintain a selected speed, often in conjunction with the autopilot system. It helps pilots in controlling the aircraft’s speed during different phases of flight, such as climb, cruise, and descent.

With the MSU, pilots can select various autothrust modes, such as manual thrust, speed control, or Mach hold. These modes enable the aircraft’s engines to automatically adjust their power output to maintain the desired speed or Mach number set by the pilot. The MSU provides pilots with the ability to manage the autothrust system effectively, ensuring precise speed control and fuel efficiency.

3. Flight Control Law Selection

The Mode Selector Unit (MSU) plays a crucial role in selecting different flight control laws on the Airbus A320 aircraft. Flight control laws are sets of rules and logic implemented in the aircraft’s fly-by-wire system that govern its behavior and response to pilot inputs. These laws ensure the aircraft’s stability, performance, and protection.

Using the MSU, pilots can select flight control laws such as Normal Law, Alternate Law, and Direct Law. Normal Law is the primary flight control law that provides full flight envelope protection and enables various flight control features. If a fault or abnormal condition occurs, the system may transition to Alternate Law, which limits some protections but maintains basic stability and control functions. In case of further system degradation, pilots can manually select Direct Law, which provides direct control surface deflection corresponding to their inputs.

The MSU’s role in flight control law selection is crucial, as different flight control laws offer varying degrees of protection, control authority, and system redundancy. The ability to manually select these laws through the Mode Selector Unit enhances the pilots’ situational awareness and allows them to adapt to different scenarios effectively.

The Importance of the Mode Selector Unit (MSU)

The Mode Selector Unit (MSU) plays a critical role in ensuring the safe and efficient operation of the Airbus A320 aircraft. Its functionality and importance can be summarized as follows:

1. Enhanced Pilot Workload Management

The MSU significantly reduces the pilot’s workload by providing centralized control over various flight systems and modes. By allowing pilots to engage autopilot, select autothrust modes, and manage flight control laws, the MSU simplifies the flying experience and enables pilots to focus on monitoring the aircraft’s systems and overall flight situation.

By reducing pilot workload, the MSU enhances crew efficiency and decision-making capabilities. This is especially crucial during critical phases of flight, such as takeoff, climb, descent, and landing, where pilots need to monitor multiple systems simultaneously while maintaining precise control over the aircraft.

2. Precise Flight Control and Performance

The MSU’s ability to engage different modes and manage flight control laws enables precise control and performance of the Airbus A320 aircraft. By selecting appropriate autopilot modes and autothrust settings, pilots can achieve the desired flight parameters, such as climb rate, speed, and altitude, with precision and accuracy.

Moreover, the MSU’s role in selecting flight control laws ensures the aircraft’s stability, responsiveness, and protection in different flight conditions. This enhances the overall flight safety and provides pilots with the necessary tools to handle various abnormal situations and emergencies effectively.

3. Integration with Advanced Avionics Systems

The Mode Selector Unit (MSU) is an essential component of the Airbus A320’s advanced avionics systems. It interfaces with other flight management, navigation, and display systems, allowing seamless integration and interaction between these systems. This integration enhances the pilots’ situational awareness, making it easier to manage and navigate through various flight phases.

Furthermore, the MSU’s integration with advanced avionics systems enables automatic flight guidance, precision navigation, and fuel-saving features. These capabilities contribute to efficient and economical flight operations, benefiting airlines and passengers alike.


The Mode Selector Unit (MSU) is a critical component of the Airbus A320 aircraft, providing pilots with control over autopilot functions, autothrust management, and flight control law selection. It enhances pilot workload management, enables precise flight control and performance, and seamlessly integrates with advanced avionics systems to enhance situational awareness and efficiency.

The MSU’s multifunctional control knob, buttons, and indicator lights serve as the primary interface between the pilots and the aircraft’s various systems and modes. It is an indispensable tool that contributes to the safe and efficient operation of the Airbus A320, ensuring a smooth and enjoyable flying experience for both pilots and passengers.

For More: What is EEC on Airbus A320? (Electronic Engine Computer)

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