What is FMU on Boeing 737? (Fuel Metering Unit)

The Fuel Metering Unit (FMU) is a crucial component of the Boeing 737 aircraft’s fuel system. It plays a significant role in managing the flow and distribution of fuel to the engines to optimize performance and ensure safe operations. The FMU regulates the fuel supply by controlling the fuel pump and monitoring various parameters to maintain the desired fuel-air mixture ratio, essential for efficient combustion and engine power output. This article will delve into the functions and importance of the Fuel Metering Unit on the Boeing 737, shedding light on its critical role in flight operations.

How Does the Fuel Metering Unit Work?

The Fuel Metering Unit on the Boeing 737 operates based on inputs from multiple sensors and systems. Its primary function is to regulate the fuel flow and pressure while maintaining the correct air-to-fuel ratio for combustion in the engines. To achieve this, the FMU monitors several parameters, including engine speed, engine pressure ratio, and ambient conditions, to calculate and adjust the appropriate fuel flow rate.

The FMU receives signals from the Engine Control Unit (ECU), which continuously monitors engine parameters and sends commands to optimize performance. The ECU provides the FMU with real-time data, such as engine speed and pressure ratio, allowing the FMU to make accurate adjustments to fuel flow.

The Fuel Metering Unit also incorporates a pressure regulator, which ensures that the fuel pressure remains within the specified limits. By maintaining the proper pressure, the FMU facilitates efficient fuel atomization and distribution, promoting optimal combustion and reducing the risk of potential engine malfunctions or damage.

The Significance of the Fuel Metering Unit on the Boeing 737

The Fuel Metering Unit is integral to the safe and efficient operation of the Boeing 737 aircraft for several reasons:

1. Fuel Efficiency: The FMU plays a crucial role in optimizing fuel consumption by regulating the air-to-fuel mixture. By maintaining the correct ratio, the FMU ensures efficient combustion, reducing fuel wastage and enhancing overall fuel efficiency.

2. Engine Performance: The fuel-air mixture ratio directly impacts engine performance and power output. The FMU continuously adjusts the fuel flow rate based on real-time engine parameters to maintain the ideal mixture, allowing the engines to operate at their maximum potential.

3. Flight Safety: The FMU is designed to prevent fuel starvation, which can lead to engine flameout or loss of power. By ensuring a consistent and appropriate fuel supply, the FMU safeguards against potential engine failures, reducing the risk of in-flight emergencies.

4. Reliability and Redundancy: The Boeing 737 is equipped with redundant systems to ensure continued operation in case of component failure. The FMU is no exception, featuring a backup unit known as the Standby Fuel Metering Unit (SFMU). In the event of an FMU malfunction, the SFMU seamlessly takes over the fuel control function, maintaining the aircraft’s reliability and safety.

The Fuel Metering Unit is a critical component that directly impacts the performance, efficiency, and safety of the Boeing 737. Its precise control over fuel flow and air-to-fuel ratio enables the aircraft to operate optimally, delivering a smooth and reliable flying experience for passengers and crew.


The Fuel Metering Unit (FMU) on the Boeing 737 aircraft is responsible for regulating fuel flow, pressure, and air-to-fuel ratio to ensure efficient combustion, optimal engine performance, and flight safety. Through continuous monitoring of engine parameters and timely adjustments, the FMU plays a vital role in optimizing fuel consumption and preventing potential engine failures. Its reliability and redundancy, backed by the Standby Fuel Metering Unit (SFMU), enhance the overall safety and reliability of the Boeing 737. Understanding the functions and significance of the FMU helps us appreciate the intricate systems and engineering behind one of the world’s most popular aircraft.

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