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Fuel System Bugs?

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    Fuel System Bugs?

    I ended up with a fuel imbalance this morning. As I rebalanced the tanks (fuel pumps on the low side off, cross-feed open), the imbalance message on the upper MFD did not show a reduction of imbalance. After completing the rebalance, recall correctly no longer brings up the fuel caution, but the imbalance message remains on the upper MFD with the original 7.42 (x1000) pounds of imbalance. Additionally, with the pumps back on for the left side and cross-feed closed, the upper MFD fuel quantity for the left side is not decreasing. Hopefully, this is just an issue with the MFD. BTW, failures are disabled at the moment.

    Also, how do I determine how much fuel is in the center tanks? The upper MFD is showing 8.79 and 7.73 (x1000) pounds of fuel on the left and right (with the left side being stuck) and 23.9 (x1000) total pounds of fuel. I'm assuming the total excludes the center tanks, but I'm not seeing anything in the FCOM that would show me how to find the fuel quantity of the center tanks.
    Last edited by geoffda; 14May2022, 21:48.
    Geoff Darst

    #2
    It would tell you, the indication should be right between the indication for the left and right tanks. Screenshots of what you're seeing would help.
    Captain Kevin

    Kevin Yang

    Comment


      #3
      Here is a screenshot. The left-side fuel quantity on the upper MFD is frozen and the unbalanced error is still there. Meanwhile, the total fuel is 19.2 so it is unclear where the fuel quantity numbers are coming from as 3.00 * 2 = 6.00. Perhaps what is being displayed is the center tank quantity? If so, how do I get the MFD to show me what is in the main tanks?
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      Last edited by geoffda; 14May2022, 21:21.
      Geoff Darst

      Comment


        #4
        Hi, I have ended up with this bug as well. No failure, NOTHING to indicate any reason for that fuel imbalance.

        Attached Files
        Jan Podlipsky

        Comment


          #5
          In your screenshot left fuel quantity is 8.79, center is 3.00, and right is 7.42. 8.79+3.00+7.42=19.2
          David Sigmon

          Comment


            #6
            From your last screenshot, you have 8.79 on the left tank, 3.0 on the center tank and 7.42 on the right tank, for a total of 19.2 (Lbs x 1000). You should be using your center tank fuel at this point, (all fuel pumps on). While center tank is being used, you will most likely be unable to reduce the imbalance, and you should not have an imbalance if properly selected the fuel pumps, again, all of them should be on.
            Cristian Caicedo A.

            Comment


              #7
              Originally posted by davidsigmon View Post
              In your screenshot left fuel quantity is 8.79, center is 3.00, and right is 7.42. 8.79+3.00+7.42=19.2
              Face-palm! Thanks David. The imbalance warning was messing me up. Ok, so the issue is that after rebalancing, *only* the center tank quantities are decrementing on the upper MFD display (with the out of balance side still showing yellow and the warning).
              Geoff Darst

              Comment


                #8
                Originally posted by ccapilot View Post
                From your last screenshot, you have 8.79 on the left tank, 3.0 on the center tank and 7.42 on the right tank, for a total of 19.2 (Lbs x 1000). You should be using your center tank fuel at this point, (all fuel pumps on). While center tank is being used, you will most likely be unable to reduce the imbalance, and you should not have an imbalance if properly selected the fuel pumps, again, all of them should be on.
                Thanks. Ok, so maybe once the center tanks run out, the left and right will start decrementing and I can rebalance. All pumps are on at the moment. I'll revisit and report back once the center tanks are dry. The imbalance was pilot error on my part. I missed turning on the right center during before-start.
                Geoff Darst

                Comment


                  #9
                  Originally posted by geoffda View Post

                  Thanks. Ok, so maybe once the center tanks run out, the left and right will start decrementing and I can rebalance. All pumps are on at the moment. I'll revisit and report back once the center tanks are dry. The imbalance was pilot error on my part. I missed turning on the right center during before-start.
                  Yes correct, or if you really want to rebalance your tanks without waiting for the fuel in center tank to finish, you can turn your center tank fuel pumps off until the fuel rebalance is complete and then turn the center fuel pumps back on
                  Cristian Caicedo A.

                  Comment


                    #10
                    Thanks for the help everyone. I shut down the center pumps and the left and right tank quantities started decrementing again. With the center tanks shut down, I also shut down the low-side pumps, opened the cross-feed and was able to rebalance. At that point the imbalance warning disappeared and I'm back burning the remaining fuel from my center tanks. In short, everything is now working as expected.
                    Geoff Darst

                    Comment


                      #11
                      Unfortunately, in my case, the fuel imbalance is true.
                      Jan Podlipsky

                      Comment


                        #12
                        What do your fuel pump switches look like?
                        Geoff Darst

                        Comment


                          #13
                          Originally posted by geoffda View Post
                          Thanks for the help everyone. I shut down the center pumps and the left and right tank quantities started decrementing again. With the center tanks shut down, I also shut down the low-side pumps, opened the cross-feed and was able to rebalance. At that point the imbalance warning disappeared and I'm back burning the remaining fuel from my center tanks. In short, everything is now working as expected.
                          Always use fuel from the center fuel tank before using wing tanks EXCEPT when for takeoff the center tank fuel quantity is less than 5000 lbs / 2300 kg, where in this case you will take off with center tank pumps off until above 10,000 ft and/or pitch decreases to accelerate to a climb speed greater than 250 kts.

                          In general, wing tanks fill before fuel is put in the center tank. Center tank is used until empty (run pumps until you get a FUEL annunciation) then wing tanks are used with exception above noted.
                          Dan Downs KCRP
                          i7-10700K 32GB 3600MHz 3080Ti

                          Comment


                            #14
                            Thanks Dan. I just ran the center tanks dry, got my fuel warning and shut them down. Now that I have a better understanding of the fuel system behavior, disabling the center tank fuel pumps for <5,000 lbs makes total sense.
                            Geoff Darst

                            Comment


                              #15
                              Geoff, I know you mentioned that you have failures turned off. I did want to point out though for anyone who is wanting to use failures at some point (or is currently using them). Never attempt to transfer fuel into a tank that has an unexpectedly low quantity unless you are absolutely sure that the tank isn't leaking. If there is a leak in that tank and you start trying to move fuel into the tank to rebalance, you'll just end up pumping even more fuel overboard.
                              Tim Lincoln
                              My YouTube Channel

                              Comment


                                #16
                                Originally posted by Want2BFlyin View Post
                                Geoff, I know you mentioned that you have failures turned off. I did want to point out though for anyone who is wanting to use failures at some point (or is currently using them). Never attempt to transfer fuel into a tank that has an unexpectedly low quantity unless you are absolutely sure that the tank isn't leaking. If there is a leak in that tank and you start trying to move fuel into the tank to rebalance, you'll just end up pumping even more fuel overboard.
                                Just like Air Transat 236.
                                Captain Kevin

                                Kevin Yang

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