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JSACKS

Fuel tank/mgmt confusion here...

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I loaded up the 744 at KSFO with 1/3 of a tank using the PMDG Options procedure. Shortly after takeoff, the upper EICAS displayed in amber " >Fuel Tank/Eng". I had no idea what was going on. Using the FUEL synoptic, I observed that Main 1 and Main 4 each had been autoloaded with 30K lbs while Main 2 and Main 3 had 33K lbs apiece. All seemed to be going fine. Engines 2 and 3 were in tank to engine mode while engines 1 and 4 were being crossfed from Main tank 2 and 3 (which I didn't understand or expect--why not? I don't really know...is this normal?).Can anybody help me understand what was happening with the fuel management here and why, and what was I supposed to do to extinguish the EICAS caution message?Appreciate any clarification, thanks!Jonathan


Jonathan Sacks

Dell XPS Gen 4, Pentium IV Northwood extreme 3.8Ghz, 3Ghz RAM, eVGA 7900 GTO,

12 GoFlight modules plus MCP-PRO AP and EFIS, GF pedestal, CH rudder pedals,

CH throttle quadrant, 42" LG LED, 24" DELL LCD, Windows XP, FS2004, FSUIPC 3.96

FS Autostart 1.1 (Build 11), FS Navigator 4.6, UT, FE, GE, REX, PMDG, Level-D, PSS, etc.

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Guest Peter Bowcut

Realistic feature of the 747-400 fuel management system. When you get the 'tank to engine' EICAS display, you must manually shut off the left and right crossfeed valves on the overhead panel. They are marked and are unguarded (no see-thru plastic flip cover over them). You don't need to mess with the crossfeed valves under the guarded covers - they work automatically as needed in normal flight operation. Then you must additonally shut off the left and right side wing tank Override fuel pumps (also marked on overhead panel). After this procedure, the fuel system is in tank to engine mode and the EICAS warning will exstinguish itself.The reason you see the warning in the configuration you describe is that the number 2 and 3 wing tanks have 3000 lbs more fuel in them than the 1 and 2 wing tanks at takeoff, respectively. At takeoff in your situation, the fuel system is going to intially be configured to crossfeed all engines from wing tanks 2 and 3 only. Very soon after you are airborne, tanks 2 and 3 will be burned off to 30,000 lbs and will be balanced with tanks 1 and 2 (everybody will have 30,000 lbs in each main wing tanks 1+2+3+4). Once the tanks are evened out in volume like this, the fuel system prompts you to configure for tank to engine mode, after which each individual engine will now feed directly from it's respective tank for the duration of the flight (engine 1 feeds from tank 1, engine 2 feeds from tank 2, etc). The idea is to keep the fuel supply balanced properly throughout the flight. When you are fully loaded with fuel, the engines intially all crossfeed from the center fuselage tank, then from the 2 and 3 main wing tanks, and finally crossfeeding is stopped and each engine burns fuel from it's 'resident' wing tank.

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Brilliant, mate. Got it and understood. Clear as a bell. Thanks mightily for posting. Really appreciated!Jonathan


Jonathan Sacks

Dell XPS Gen 4, Pentium IV Northwood extreme 3.8Ghz, 3Ghz RAM, eVGA 7900 GTO,

12 GoFlight modules plus MCP-PRO AP and EFIS, GF pedestal, CH rudder pedals,

CH throttle quadrant, 42" LG LED, 24" DELL LCD, Windows XP, FS2004, FSUIPC 3.96

FS Autostart 1.1 (Build 11), FS Navigator 4.6, UT, FE, GE, REX, PMDG, Level-D, PSS, etc.

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Guest Peter Bowcut

The Override wing tank pumps 'force' (by higher fuel pressure) all engines to cross-feed from tanks 2 and 3 only when the Override pumps are on and all crossfeed valves are open. This is the normal mode when tanks 2 and 3 have more fuel than tanks 1 and 4. Even though the fuel pumps for tanks 1 and 4 are turned on, the Override pumps 'make' engines 1 and 4 crossfeed from tanks 2 and 3 until the system is later configured for tank to engine mode.

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Simply put, the fuel quantities in all four wing tanks should be equal for landing. Because the inboard tanks (2&3) hold much more fuel than the outboards, you have to burn the fuel in the 2&3 tanks first. This means using the 2&3 tanks to feed all engines UNTIL the wing tank quantites are equal.Note: The powerful O/J (Jettison/Override) pumps in the 2&3 tanks allow you to feed all engines at once WITHOUT turning off your normal tank boost pumps). The pressure from the O/J pumps forces the check (one-way) valves on the low powered tank pumps to close. This stop the fuel in the #2 and #3 tanks being transferred into the outboard wing tanks (back through the boost pumps) and it stops the fuel coming out of the outboard tanks. If all the O/J pumps happened to fail, the check valves on the boost pumps would open, allowing an uninterrupted supply of fuel to the engines.Cheers.Q>

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Reminds me of the night I slept thru 'tank eng' - that was fun ;(I had to get creative and run all 4 engines from tanks 1 and 4 until balance was restored. I was a wreck the next day and never again did overnight flights in the queen :) - too much work waking up to step and manage fuel, even when I do time it right.edit - I guess the 747-8 fuel system will be full auto?regards,Markhttp://www.precisionmanuals.com/images/forum/747400.jpgXPHomeSP2/FS9.1/3.2HT/1024mb/X700pro256


Regards,

Mark

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