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When to Use OVRD Pumps (748)

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    When to Use OVRD Pumps (748)

    A question that's been driving me up the wall for awhile now. When the heck do I use these things? It does not seem so clear cut to me. I seem to have a primitive understanding that system logic helps determine when they are used when on. Should I simply use them and continue to if there isn't an EICAS message that would otherwise suggest leaving them off? Is there something in the SP to help with this? Reading up on the fuel section of the FCOM is... not the easiest task, to put it simply, but if someone is willing to sell me on reading a specific section, by all means please do. Thanks.

    Emerson Wells
    Emerson Wells

    #2
    Emerson, best way to put it is before you have the fuel tanks in TANK/ENG configuration, you want to have them on, but also if you want to jettison fuel, you want to have them on. TANK/ENG configuration on the 747-8 is when you have the fuel in main tanks 2 and 3 equal to that of main AND RESERVE tanks 1 and 4. The idea is you want all the tanks at the same level in TANK/ENG configuration. Once you reach that level, you turn the crossfeeds for 2 and 3 off along with the override pumps. That way each engine burns fuel from their respective tanks.
    Captain Kevin

    Kevin Yang

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    • Kevin Hall
      Kevin Hall commented
      Editing a comment
      I know you know what you mean, I guess it's a typo, but it's actually crossfeeds 1 and 4 that you should close to go tank to engine. Crossfeeds 2 and 3 are normally automatically controlled.
      Last edited by Kevin Hall; 23Nov2021, 23:53.

    #3
    Originally posted by Captain Kevin View Post
    Emerson, best way to put it is before you have the fuel tanks in TANK/ENG configuration, you want to have them on, but also if you want to jettison fuel, you want to have them on. TANK/ENG configuration on the 747-8 is when you have the fuel in main tanks 2 and 3 equal to that of main AND RESERVE tanks 1 and 4. The idea is you want all the tanks at the same level in TANK/ENG configuration. Once you reach that level, you turn the crossfeeds for 2 and 3 off along with the override pumps. That way each engine burns fuel from their respective tanks.
    Nice explanation, Kevin
    Rudy Fidao

    Comment


      #4
      Further to what Kevin has said and to be entirely accurate, when you are in flight the EICAS message FUEL TANK/ENG will display when main tank 2 quantity is equal to or less than the sum of main tank 1 plus reserve tank 1 quantity, OR when main tank 3 quantity is equal or less than the sum of main tank 4 plus reserve tank 4 quantity. In the tank-to-engine configuration the main pumps will then provide fuel under pressure to their respective engine until engine shutdown.

      The fuel system management cards (FSMCs) command fuel valves open or closed and the fuel pumps on or off according to fuel management logic, so when switching to TANK/ ENG configuration you should activate the OVRD switches to agree with the EICAS messages you see. If you get it wrong then the system’s logic should sense this and tell you. They will also automatically open the reserve transfer valves when main tank 1 or 4 fuel quantity decreases to approximately 6,100 kgs. Fuel will then transfer from reserve tanks 1 and 4 to the respective main tank. Incidentally, on the ground the FUEL TANK/ENG message will sometimes display when the inboard tank quantity is less than or equal to the sum of the adjacent outboard tank plus reserve tank plus 500 kgs in both wings.
      Michael Codd

      Comment


        #5
        Originally posted by Michael Codd View Post
        Further to what Kevin has said and to be entirely accurate, when you are in flight the EICAS message FUEL TANK/ENG will display when main tank 2 quantity is equal to or less than the sum of main tank 1 plus reserve tank 1 quantity, OR when main tank 3 quantity is equal or less than the sum of main tank 4 plus reserve tank 4 quantity. In the tank-to-engine configuration the main pumps will then provide fuel under pressure to their respective engine until engine shutdown.

        The fuel system management cards (FSMCs) command fuel valves open or closed and the fuel pumps on or off according to fuel management logic, so when switching to TANK/ ENG configuration you should activate the OVRD switches to agree with the EICAS messages you see. If you get it wrong then the system’s logic should sense this and tell you. They will also automatically open the reserve transfer valves when main tank 1 or 4 fuel quantity decreases to approximately 6,100 kgs. Fuel will then transfer from reserve tanks 1 and 4 to the respective main tank. Incidentally, on the ground the FUEL TANK/ENG message will sometimes display when the inboard tank quantity is less than or equal to the sum of the adjacent outboard tank plus reserve tank plus 500 kgs in both wings.
        Thank you Michael and Kevin both for your clear and easy to follow responses. It's been quite enjoyable learning more about this and the 744. I'll need to make better use of the forum in the future, it seems like quite a fruitful source to be sure.

        Emerson Wells
        Emerson Wells

        Comment


          #6
          Emerson, in your initial post, you mentioned the Boeing 747-8, so my response was based off of that. The Boeing 747-400 is largely the same, except that the reserve tanks are tied to tanks 2 and 3 rather than 1 and 4 as on the 747-8. Therefore, in the case of the Boeing 747-400, TANK/ENG configuration would take place when the quantity of tanks 2 and 3 are equal to that of tanks 1 and 4 respectively. By the time you reach this point, the reserve tanks will have been empty, and therefore not relevant for the calculation.
          Captain Kevin

          Kevin Yang

          Comment


            #7
            Originally posted by Captain Kevin View Post
            Emerson, in your initial post, you mentioned the Boeing 747-8, so my response was based off of that. The Boeing 747-400 is largely the same, except that the reserve tanks are tied to tanks 2 and 3 rather than 1 and 4 as on the 747-8. Therefore, in the case of the Boeing 747-400, TANK/ENG configuration would take place when the quantity of tanks 2 and 3 are equal to that of tanks 1 and 4 respectively. By the time you reach this point, the reserve tanks will have been empty, and therefore not relevant for the calculation.
            Much appreciated on the additional 744 advice. I believe I did notice this change on my first switch-over to the 747-8, but the understanding of the difference in procedure is very helpful and interesting! Many thanks, and a happy Thanksgiving (unless I'm being foolish and you do not celebrate the holiday)!
            Emerson Wells

            Comment


              #8
              Whilst you would be correct that Thanksgiving is an American holiday, I did have to work today, so nothing too spectacular.

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              Captain Kevin

              Kevin Yang

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              • PopsBellNC
                PopsBellNC commented
                Editing a comment
                Kenworth,,,SWEET!
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