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Hello can someone explain the difference between the fcu and fuel flow transmitter and how they work together alongside the fuel pump?

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    $\begingroup$ If you illustrate your question with a diagram of the fuel system you are talking about, it will clarify and focus the question. This will help people answer it. The terms you are using are so vague (and so varied across manufacturers) that they are unhelpful out of context. $\endgroup$
    – Mark Jones Jr.
    Aug 21, 2019 at 17:10

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The Fuel Control Unit controls the flow of fuel to a turbine, it is in effect the mechanism by which the throttle works.

A fuel flow meter is simply a device that measures fluid flow (in this case the flow of fuel) through a line. The location, quantity and operation of flow meters varies by aircraft and configuration. Broadly speaking they are used to calculate actual fuel burn as well as to make sure the proper amount of fuel is flowing to an engine.

The fuel pump is the device that drives fuel to the engine/FCU from the tank. Again systems vary heavily but broadly pumps are used to move fuel from the lowest point in the tanks to an engine that may be above that point as well as to build sufficient fuel pressure to allow injectors/delivery systems to work.

In the simplest of systems a fuel pump sends fuel over a fuel line to an FCU. Somewhere on that line is a flow meter so that you can measure fuel flow out of the tank, into the engine.

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  • $\begingroup$ This is right. One thing that I might add to differentiate the FCU from the FFD is that the Full Authority Digital Engine Controller (FADEC) only communicates with the FCU, not the FFD. FCU takes orders from the FADEC and reports back its flowrate. FFD reports directly and exclusively to the cockpit for flowrate indication to the pilots. Part of the start procedure on many FADEC controlled engines is to wait for the FFD to indicate positive flow before moving throttle or condition lever from "fuel shutoff". $\endgroup$
    – LStrom
    Aug 22, 2019 at 17:27

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