@ JimGreen
update of ZFW in flight with the value received by GWFK in my opinion and according my experiences I did on this nice aircraft is not really recommended. Although we all know very well the discrepancies which may occur if StandardPaxWeight and StandardBaggageWeight are used for loadsheet computation and the "real loads" boarding our aircraft.
The GWFK value received via AIDS is obviously a kind of an "aerodynamical weight" value only and basically coming from the AOA and computed by the FACs. (as far as I know.)
Resons for not recommending to adjust the GW on the FUEL PRED acc the GWFK value (found by own observations and by "playing" with the AIDS machine):
This GWFK weight figure may change by tons !! during the flight.
Example:
during climb out I checked GWFK: 2.x tons more than on the loadsheet - I adjusted GW on the FUEL PRED page
after hours in cruise I checked GWFK: again 1.x tons more than the already adjusted GW
- now in total an increase to the loadsheet mass by more than 3 tons.
on final approach last check of the GWFK value (to the wiseacres: Yes I know we should have some other pages open on the FMCs during final approach
but: by surprise and not expected now nearly 3 tons less than the cruise value, which means: finally the GWFK value stayed quite close to the expected LW according loadsheet.
Hope this helps a bit.