Tank to Engine

[744 driver 14]

Guys,I was recently watching the ITVV Virgin 744 video and noticed something that caught my eye. Early in the flight the Captain goes over the process of configuring the fuel system for tank to engine. The process is done as normal but after the system is configured the EICAS shot shows that main tanks 2 & 3 boost pumps are shown as active (green, with no band) but the lines of fuel flow don't indicate that fuel is flowing to engines 2 & 3 from these pumps. Crossfeed valves 1 & 4 are closed and 2 & 3 are open as they should be. However, the green flow lines seem to indicate that fuel is flowing from main tank 2 override/jettison pump to engines 2 & 3 but that pump is white, indicating off.Somebody take a look at this and let me know what's really going on here because whenever I've done this in the sim, as soon as I turn off the override pumps the boost pumps come on immediately thereafter and the lines of flow indicate that fuel is being supplied to each respective engine with crossfeed valves 2 & 3 open and 1 & 4 closed.Sorry for the long-winded explanation but I'm missing something here.Thanks guys.Mark

[744 driver 14]

Anybody have any explanation yet?

[Jet Tech 31]

Mark,I think (and I may be wrong) that when the aircraft is configured for Take off, that the fuel system is set up for Tank to Engine Fuel Feed to ensure that each engine has its own fuel supply from its own tank for redundancy. Once you enter the climb phase and clean up the aircraft (flaps up) you should go back to the normal fuel feed operation in which the center/stabilizer or 2 & 3 mains supply fuel for all 4 engines. As long as the 2/3 overrride pumps are selected ON, they will always supply fuel instead of the main boost pumps (due to much higher output pressure) so what you are seeing on the Eicas would be a normal inication for that configuration. The #2 and #3 main pumps will show green because they are on and producing pressure but the override pumps provide more pressure and force the boost pump check valve closed. When you go Tank to Engine toward the end of the flight, you would likely deselect the Override pumps and use the main pumps to provide fuel to the #2 and #3 engines thus changing the look on the Eicas. Hope that makes sense.RegardsPaul Gollnick :-cool Technical Operations/Customer Operational SupportPrecision Manuals Development Groupwww.precisionmanuals.comhttp://www.precisionmanuals.com/images/forum/devteam.jpg

[Qavion 19]

Haven't got the video, but perhaps the resolution/clarity of the image isn't showing the green lines?The expression "Tank to Engine" is kind of a misnomer... Tanks 2&3 feed BOTH #2 and #3 engines (only 1&4 are truly tank to engine in this config). Were there green lines looping over the #2/#3 engine symbols showing this?Of course, there could have been a problem with the aircraft. If the EICAS cannot ascertain the positions of the relevant valves and pump pressures, it cannot draw the lines.Cheers.Q>

[744 driver 14]

Thanks guys for your replies. After the first officer configures the x-feed valves and fuel pumps per normal procedure for tank to engine ops. the EICAS fuel synoptic display clearly shows as I've described:Main tanks 2&3 boost pumps are shown as active (green with NO band) but the lines of flow don't indicate that fuel is flowing to engines 2&3 from these pumps.The main tanks 2&3 override/jett pumps are shown as off (white).The green lines of flow actually show fuel is (supposedly) flowing from ovd/jett pump in #2 tank to engines 2&3 eventhough the pump is white(off).Tha x-feed valves 2&3 are open of course and 1&4 are closed.As you say Q, there may be something wrong in the logic or valve poitioning whereby it is not able to show the true flow of fuel on this particular aircraft.Very odd to say the least. Anyway guys, thanks again for your replies.