Hi John and others,

"my" 747-400 has a slightly different approach. When I wrote its fuelsystem, there were no priorities (at least not that I was aware of any). The idea came from the F-8E Crusader's system and I started documenting it at http://wiki.flightgear.org/Howto:Write_a_fuel_system_in_JSBSim

You may call it ugly (and I won't deny that), but it works :-) It's still not complete (two pumps are treated as one for example), but the basic stuff works (transfering fuel, crossfeed, jettison etc.). The system can be found in Aircraft/747-400/Systems/fuel.xml

Feel free to comment and/or use it. Improvements are also welcome of course :-)