Aux Pump Running on Battery Question

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    I’m new here and bought a 320E. What a fun plane! I’m curious about the aux fuel pump. When I turn the battery master switch on I can hear the pump running in each main fuel tank even though the aux pump switch is centered in the off position. Is this normal?

    BTW, I read about the differences pre and post MEB88-3 at this link:




    Hi, David. IIRC, from my 320C ownership, the pumps in the tips run with the battery switch on. Just like my 310Q. They’re connected to the L & R landing light circuit breakers. Not boost pumps, but they keep the tip tank fuel where it needs to be.


    Rich is right, they are the main transfer pumps within the tip tanks, not to the engines. The service bulletin is about the aux pumps.

    Pull the landing light breakers and they will stop.



    Hi David
    Welcome to TCF. You only turn those pumps off while work is being performed on the plane and you want silence. Never fly with them off! They port fuel in the tank to the area of the tank with the fuel lines.

    Congrats on the 320E. I had one many years ago and they are great performers. If you fly them 12k and up they will scoot.


    I make a point of pulling the landing light breaker when the master is on during maintenance. I’d recommend the same.


    Thanks for the info!

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