ALPHA CALL UP FAC GW

[MD83FO]

Hello, does anyone know how to check the airplane weight calculated by the FAC ?
it used to be GWFAC but the function seems disabled.

I’ve noticed huge differences from loadsheet on positioning flights (empty plane)
id like to know, which one is correct, the airplane computer or the weight and balance estimate.

[Check Airman]

I’ve never seen that entry. I know GWFL or GWFK.

[Bus Driver Man]

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.

[tubby linton]

Dsc 22_10-50-20 describes how to work out the aircraft mass from the displayed green dot.

[Check Airman]

Whether or not the call up works seems to be a company thing. Our old planes will allow it. The new planes won’t. On the very newest ones- they apparently forgot to disable it, so it works. I’m not going to tattle though.

[vilas]

Both are used but there's a switch over. The following Airbus document explains it but unable to post.
FMGC & FAC - Gross weights and associated characteristic speed computations on Single Aisle Reference: 22.00.00061 First Issue Date: 20-OCT-2010 Last Publication Date: 14-AUG-2015 ATA: 22-00

[Goldenrivett]

Originally Posted by MD83FO

id like to know, which one is correct, the airplane computer or the weight and balance estimate.

In 2004 Airbus said if there was a difference observed then to use the QRH values for computed speeds. (Load sheet ZFW + fuel remaining)
0.3 degrees error in mounting the AoA vanes = 3 Tons Gross weight.
Characteristic and Protection speeds