You enter your ZFW and ZFW CG from the load sheet. This tells the FMS how much the airplane weights and where is the center of gravity WITHOUT THE FUEL.
The FMS will know how much fuel are there in the tanks and with that data will compute and show you the GW (gross weight) and GW CG in the FUEL PRED page of the FMS. The center of gravity of the airplane will be the one of the ZFW corrected by the CG of the fuel (ZFW CG plus or minus a certain amount, the data is in the FMS memory).
After start you should check that the GW CG shown in the FUEL PRED page of the FMS is similar to the one of the load sheet.
After airborne the FMS constantly updates de GW CG after the fuel gets burned, the info is always shown in the FUEL PRED page.
Taxi fuel: the taxi fuel figure is in the INIT B page and it is for planning purposes. After engine start the INIT B page is no longer there, and if you press INIT and then lateral arrow the FMS will take you to FUEL PRED page. The FOB gets updated with the actual amount in the tanks. If in the INIT B page the taxi is 0.2 (200 kgs) but the taxi time is short and the fuel burned during taxi is just 100 kgs, the GW figure shown at the bottom of the System Display and the FUEL PRED page will be 100 kgs higher than then one showed in the INIT B before engine start up.
Last edited by iggy; 28th January 2020 at 10:58.
Reason: Taxi fuel