I waited and waited to post this but i'm really stuck on this . My FMC is always showing- using res fuel. Now i'm using the real flight plans right out of the real 737-700 cockpit that the pilot gives me after his done with it and i know that this bird is major accurate so i'm not using a flight sim fuel planner -it's the real deal. So here we go as an example , it says FOB- 018800 so i punch in 18800 in total fuel- FS Actions at it fiqueres it out by itself to the proper tanks, and in this case i have 1539 in the center tank.Now my ALTN wants 001700 and my res wants 003254 so i add the 2 together which is 4954 but i punch in 5.0 in the res slot of the FMC and the gross when i punch it in it's very close to the flight plan cause i usually put some weight for cargo which of course drives the gross up. Any one see why the heck on every flight it keeps saying ---using res fuel? cause i'm beat on this on .But i leave the centre fuel tank off a lot if there's not much in it so would that do it ?

Are you using the same cost index?

Yes i am, right from the actual flight plan.

Different WX maybe? I've checked the NGX with different LIDO generated flightplans and it's very accurate when it comes to fuel consumption (+/- 2% all the time). As long as the trip fuel is caclulated using the same mean wind component as the one you get in FS you should get very similar results. If you want, send me one of your FPs so I can have a look what the problem may be.

well maybe u would get the same message from a fmc of a real 737? if u set ur res to 4.5 the message will probebly go away. but i think its not unusal to use the res because 5 tonnes are quite some fuel.

Weather, maybe? You inputting the exact weather from the same day? If the winds aloft are changing (and/or they aren't input right into the FMC), then you might get different numbers.

Pan and Willi, both of your comments make sense and i will ask the pilots about it and you know what ,now that you mentioned it i use REX weather and i've noticed that i've had some major headwinds happening at cruise so yes that could very well be it .Be very clear that i am in no way implying that PMDG is off on this cause i know it's me but just don't know what it is.