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bsmonroe

Chasing Fuel Numbers

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I apologize if this has been posted before - I couldn't find anything quite like this using the search function.This is regarding the 747-400:A trip from EGLL to FAJS should only take roughly 108,000 lbs of fuel - or so says FS Navigator. So I specified that amount in the Load Planner and started up the simulator with 120,000 lbs of fuel.But when I run this through the FMC, it says, no, you need 120,000 lbs of fuel. Unless I leave the reserves at "blank" - the flight plan will not take.So I close out and adjust the amount on the load planner to 130,000 lbs of fuel.Same scenario, same location, same airport - but now the FMC says it wants 130,000 lbs of fuel! It is as though the FMC is using the total available fuel as the planning number.So the next step is to "max out" the load planner, load up the maximum fuel without going over the MTOW.But now the simulator says that the plane is over MTOW - and worse, the numbers showing in the "fuel" configuration screen are not the same as those entered in the planner.Anyone have any idea why this is happening? You can't make any adjustments using the simulator fuel menu (which is how it is supposed to work as I understand it) but it doesn't seem like you can adjust it using the planner either.

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Don't really understand. Where is the FMC saying you need 120,000lbs of fuel? ie. what page?When you say the 'planner', is that the load editor? If so, the fuel option there does not actually load fuel into the aircraft - it's just so you can keep tabs on the aircrafts gross weight while loading pax and cargo.You have to use the PMDG options menu to load fuel. Wierd things can happen if you use the default FS fuel editor.


Phil Brown

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It is the FMC Perf-Init page under "Fuel Calc" that keeps setting itself to whatever the reading is in the FS fuel menu.Yes, I do not use the FS Fuel menu to change the fuel.

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"Fuel calc" does not mean the amount of fuel the FMC has calculated for the journey. Rather, it means the amount of fuel that has been calculated to be on board -- i.e. this will always tell you the total amount of fuel in the tanks (and thus it's no wonder you're getting the behaviour you're describing).To see the amount of fuel the FMC is calculating for the journey, go the PROG page. There, you'll see how much fuel the FMC is projecting you'll have on board when you land. The difference between this and the fuel on board is the amount you'll burn during the trip.Martin

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""Fuel calc" does not mean the amount of fuel the FMC has calculated for the journey. Rather, it means the amount of fuel that has been calculated to be on board -- i.e. this will always tell you the total amount of fuel in the tanks"Unless you have a fuel leak ;)The CALC value will only show the FQIS sensed total amount in the tanks at the following times"1) when the engines are not running2) during fuel jettison.The FQIS uses fuel tank sensors (probes, densitometers, compensators).At all other times, the CALC value represents the Fuel Quantity Indicating System tank value at engine start minus the quantity used by the engines (according to fuel flow sensors on the engine).Cheers.Q>

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Just a note re the load manager - while it does not actually load fuel, it does preset the saved fuel load figure. After that you will see this figure in the PMDG/options/fuel menu, ready to be 'applied'.I note however this only works if you retain the default panel state - if I select some other panel state (as I normally do) this preset figure is 'lost', replaced by whatever figure was there when the state was saved.regards,Markhttp://www.precisionmanuals.com/images/forum/747400.jpgXPHomeSP2/FS9.1/3.2HT/1024mb/X700pro256


Regards,

Mark

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Guest Buck Bolduc

>""Fuel calc" does not mean the amount of fuel the FMC has>calculated for the journey. Rather, it means the amount of>fuel that has been calculated to be on board -- i.e. this will>always tell you the total amount of fuel in the tanks">>Unless you have a fuel leak ;)>>The CALC value will only show the FQIS sensed total amount in>the tanks at the following times">>1) when the engines are not running>2) during fuel jettison.>>The FQIS uses fuel tank sensors (probes, densitometers,>compensators).>>At all other times, the CALC value represents the Fuel>Quantity Indicating System tank value at engine start minus>the quantity used by the engines (according to fuel flow>sensors on the engine).>>Cheers.>Q>>>"Fuel Leak":)Maybe thats it. I forget the specific numbers, but on a flight to EGLL-KBOS the prog page told me I would have plenty of fuel, forget exactly how much but I think it was in the order of 12,000lb's.I landed on fumes. I neglected to figure in headwinds I think.I found if I'm going East, no problem. Going West, better add in another 15-20 for headwinds.Noticed this on other flights also.

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