Looks like this is a simulation of fuel sloshing away from pumps during climb, then flowing back to pumps after level off. Pretty cool!

 

This is how it works, center tanks below a specified level are off during climb.  The logic senses when pitch is less than a 5 deg NU for a specified amount of time and then goes into cruise mode and asks the pilot to kindly turn the pumps on.  I've seen the message appear before I leveled off and had this explained to me by one of the team...., RSR I believe.

This is how it works

Dan

I had been at cruise for awhile when this occurred. However, there could have been a step climb involved in the sequence of events. I don't remember. Does this make any sense?

Robert,

 

No Knives? So what do you use with the cheese tray?

 

Bertie G

You will notice on the fuel panel that above Main Tank Overrides 2 and 3 there is a graphic of an upside down funnel with multiple dots in it. This is to signify that the Override pumps have higher output pressure than the main tank pumps (2X), but more importantly it helps crews identify which are the override pumps when configuring tank to engine, so you don't turn off the main tank pumps 2 and 3 inadvertently in a darkened environment. We always reference the fuel synoptic to verify it truly is tank to engine, along with verifying the 2 and 3 overrides are turned off, cross feeds 1 and 4 being closed, and last that the message blanks.

I was under the impression that was the fuel dump schematic. The funnel does match the dump display on the fuel page on the lower DU.

5 hours ago, Ralgh said:

I was under the impression that was the fuel dump schematic. The funnel does match the dump display on the fuel page on the lower DU.

Yes, your right Ralgh, the symbol does match the jettison nozzle symbol at the tips of the dump manifold, but the schematic on the fuel panel is a normal fuel schematic that does not show the transfer valves, dump manifold, or nozzle valves (only on the synoptic).

Another description the funnel can represent is that each override pump can power up to 2 engines for takeoff and cruise conditions, whereas a single main pump can provide sufficient thrust for takeoff on 1 engine only and up to engines at cruise. Again, it goes back to the higher output pressure (2X). Of course, if the CWT pumps are on, then the overrides are inhibited by the FSMC's. 

The practical pilot application of this is that the funnel really helps visually see at a glance where the overrides are, because if a pilot can push a wrong switch in the dark, someone , somewhere usually will, like intending to turn on a battery switch, but instead dropping oxygen masks on the ground in a dark airplane...

Quote

Once tank to engine is established, tanks 1 and 4 are isolated, but there crossfeed between left and right, 2/3, is still open. Why are tank 2/3 crossfeed switches guarded, and why don't they get closed to prevent transfer? It's almost like flying a twin with the crossfeed left open.

What are the disadvantages of this on a twin?

Note that the 747-400 crossfeed manifold has a "crossflow compensator". It will only allow fuel flow if one side of the manifold has more than 3psi than the other. This should take care of small differences in fuel pump output power.  

Cheers

JHW

I'm glad someone has started a thread on fuel configuration.  I'm finding that I'm usually landing with about 30,000 lbs of fuel remaining.  However, none of the fuel is left in the tank that supplies the APU.  So, I land with adequate fuel but can't start the APU.  I just have to wait for ground power before engine shutdown.

Is there a way to manage the fuel config in flight, so there's enough fuel in the tank for the APU?

Thanks!

Rob Olson 

When you get the FUEL TANK/ENG EICAS message, you would close the unguarded crossfeed valves. Believe those are 1 and 4. Once you do that, each engine will burn fuel from their respective tanks.

On ‎3‎/‎4‎/‎2017 at 11:28 AM, RobertO1035 said:

Is there a way to manage the fuel config in flight, so there's enough fuel in the tank for the APU?

Comply with the procedure in the video in the first post of this thread. This is precisely the reason I made it.

Thank you!

Why not just disable all of the crossfeeds, then each engine draws from its own dedicated tank.

14 hours ago, Boomer said:

Why not just disable all of the crossfeeds, then each engine draws from its own dedicated tank.

Instead of turning off the OVERRIDE pumps in addition to closing the crossfeeds? Why run the pumps the whole time if you don't need to? Same reason you turn the landing lights off when you get out of the terminal area (or per whatever SOP you follow): save having to buy parts more often.

There's some background logic to the guarded switches too. They're guarded for a reason, though I can't recall off the top of my head at the moment.

No I meant follow the procedure you outlined but also disable the guarded crossfeeds.

24 minutes ago, Boomer said:

No I meant follow the procedure you outlined but also disable the guarded crossfeeds.

Yeah, definitely don't mess with those unless a checklist calls for it. That goes for anything guarded.