Thanks for replies so far.
I used to enter both GWFK and AOA in PARAM ALPHA call up. This gives an indication of FAC weight, as compared to the calculated FMC GW with preflight-entered ZFW and FOB. I check AOA for reasonableness, so that I can have some faith in the FAC computed GW.
I also would like to know what that Alpha code is Mr Elite. I'm buggered if I can find any ref to FAC weight anywhere in the box or FCOM in these latest MSNs.