What is HMU on Airbus A320? (Hydromechanical Unit)

The HydroMechanical Unit (HMU) is an essential component of the Airbus A320 aircraft. It plays a crucial role in the operation and control of the aircraft’s fuel system. The HMU is responsible for regulating the flow of fuel from the aircraft’s fuel tanks to the engines, ensuring that the engines receive an adequate and consistent fuel supply for optimal performance.

The HMU consists of various mechanical and hydraulic components that work together to control the fuel flow. It incorporates advanced technology and precision engineering to meet the demanding requirements of modern aircraft.

How Does the HydroMechanical Unit Work?

The HydroMechanical Unit operates through a series of interconnected systems and components. To better understand its functionality, let’s take a closer look at the key components of the HMU:

Flow Divider

The flow divider is an integral part of the HMU that splits the fuel flow into two separate streams, one for each engine. It ensures that both engines receive an equal amount of fuel, which is crucial for maintaining balanced engine performance and preventing engine surging or flameouts.

The flow divider operates by mechanically dividing the fuel flow based on the pressure and flow rate. It is designed to provide precise and accurate fuel distribution between the engines, even under varying operating conditions.

Fuel Metering Valve

The fuel metering valve is another critical component of the HMU. It controls the amount of fuel flowing to the engines based on the inputs from the engine control system. The valve adjusts the fuel flow to maintain the desired engine power and optimize fuel efficiency.

The fuel metering valve operates by modulating the fuel pressure and flow rate according to the engine’s demands. It ensures that the engines receive the correct fuel-to-air ratio for efficient combustion and power generation.

Maintenance and Troubleshooting of the HydroMechanical Unit

To ensure the proper functioning of the HMU and avoid any potential issues, regular maintenance and troubleshooting procedures must be followed. Here are some essential aspects to consider:

Periodic Inspections

Periodic inspections of the HMU should be conducted as per the manufacturer’s recommendations. These inspections involve checking various components, such as the flow divider, fuel metering valve, and associated hydraulic lines, for any signs of wear, damage, or leaks.

The inspections also include testing the HMU’s performance, such as verifying the fuel flow and pressure regulation within the specified limits. Any deviations or abnormalities found during the inspections should be addressed promptly to ensure the HMU’s proper functioning.


If the HMU exhibits any issues or malfunctions, troubleshooting procedures should be followed to identify and rectify the problem. This typically involves diagnosing the system using specialized tools and equipment, such as pressure gauges and diagnostic software.

Common troubleshooting steps may include checking for fuel leaks, verifying the fuel pressure and flow rate, and inspecting the electrical connections and wiring associated with the HMU. Once the issue is identified, the necessary repairs or component replacements can be performed.

The Importance of the HydroMechanical Unit

The HydroMechanical Unit is a critical component of the Airbus A320 aircraft, ensuring efficient fuel flow and engine performance. Its precise control and regulation of fuel distribution between the engines contribute to the overall safety, reliability, and fuel efficiency of the aircraft.

By maintaining the correct fuel-to-air ratio and preventing engine surging or flameouts, the HMU plays a vital role in ensuring smooth and uninterrupted flight operations. It is designed to withstand the demanding conditions of commercial aviation and undergoes rigorous testing and certification to ensure its reliability and performance.


The HydroMechanical Unit (HMU) is an integral part of the fuel system on the Airbus A320 aircraft. It regulates the flow of fuel to the engines and ensures optimal engine performance. Through its components such as the flow divider and fuel metering valve, the HMU provides precise fuel distribution and control.

Maintenance and troubleshooting procedures are essential to keep the HMU in optimal condition. Periodic inspections and timely repairs help identify and rectify any issues that may arise. By functioning effectively, the HMU contributes to the overall safety, reliability, and performance of the Airbus A320 aircraft.

For More: What is EFOB on Airbus A320? (Estimated Fuel On Board)