Originally Posted by
MD83FO
...
id like to know, which one is correct, the airplane computer or the weight and balance estimate.
None, probably. They are both estimates, calculated with standard mass assumptions or aerodynamic measurements.
It used to be GWFK (in kg), but on our FMGS, that doesn’t work either. So either Airbus had it removed on newer versions, or it depends on the manufacturer (Thales or Honeywell).
Speeds on the PFD used to be calculated by the FAC, and speeds displayed on the MCDU came from the FMGS. So sometimes VLS was as high as VAPP is the FAC calculated a higher weight.
However, Airbus had this modified so that the speeds on the PFD now come from the FMGS. So from the data of the load sheet. This is to prevent discrepancy. Probably because the weight calculated by the FAC is not that accurate.
Correction: Speeds on the PFD are still calculated by the FAC, but with data from the FMS. Aerodynamic data is used as backup.