You see ZFW value is needed for the following things and these values will be incorrect if in wrong ZFW entry is entered.
- GW displayed on ECAM and Fuel Prediction page
- CG displayed on Fuel prediction page
- FM predictions
- Speeds displayed on MCDU (F, S, O, Vls, Vapp) as GW and C of G is required for computation of these speeds.
Note if values are taken from FMGC, these values if wrong may lead to wrong V1, V2, and Vr computation.
So is it right to say if no ZFW entry all the above 4 entries wont be displayed?
But in air except for Vapp all the values are calculated by FAC and displayed on PFD will be correct and will not match with FM but on ground these values on PFD are displayed by FM as FAC does not work on ground.
Rather notice apart from ZFW we also need Fuel qty form FQI and Fuel Flow from FADEC so if any of these are not working fine then also these values will be wrong. But I think not too much impact as these are generally correct but it is the ZFW which is entered by pilot and an error is likely.
Also note Vsw, V alpha prot and V alpha max are not affected as these are based on aerodynamic data.
So we can say protection speeds are not impacted by ZFW/ZFWCG as they are on PFD.
Now where do we actually need CG value inflight..i know it is needed for 2 kts decrease in Vapp speed if forward C.G may be in some failures we need this CG value i am not sure of..