A320 weight change in flight through FMGC

[DEE-DUCK]

We have a new procedure, on the A320, that has been introduced, from airbus.
It involves the changing of the aircrafts weight through the FMGC in flight........ It is as follows:


Select MCDU, DATA, then AIDS, then PARAM, then PARAM ALPHA label, and then input GWFK
into any of the empty line. Read the aircraft weight from the FAC and then update the weight on the Fuel Prediction page.

Does anyone else follow this procedure on the A320??????

[idg]

Very Interesting! When did this come about?

We have had the Vls and Vapp less than 5 knots apart on approach on our 321s for some time. Up to now this has not materialised on the 320s, but just recently this too has been happening.

Some of our guys think it's to do with incorrect FMGS weight due to overweight pax! Thus the FAC providing the Vls is giving the speed aerodynamically but the FMGS is giving the Vapp from the inserted weight. By doing your procedure you will fix this problem I think.

Do you have a reference from Airbus for this?

[DBate]

Interesting!

We don't have this procedure yet, but as you say that it's coming directly from airbus, that might change.

The sometimes occuring difference of less than 5 kts between the FAC-calculated Vls and the FMGC calculated Vapp is a well known 'problem'.

During approach we simply check, wether the Vapp is 5 kts higher than Vls. If it is not, than we overwrite the Vapp on the MCDU PERF APPR Page.

So long,
DBate

[Hand Solo]

Sounds a bit complex! I'd certainly agree with the problem of Vls and Vapp <5kts being due to overweight passengers. I once carried a very large sports team and on final approach discovered Vls was actually above Vapp! Still its not exactly a major problem, just change the Vapp in the MCDU or select Vls+5 manually.

[Belowclouds]

By selecting speed manually you go to SELECTED mode. This precludes GSmini to work besides adds additional problem in case of GA. So I guess adding several knots to Vapp in MCDU is enough

[Wingswinger]

This precludes G/S mini to work...

My preference would always be to use selected. G/S mini is, imho, one of the dafter ideas ever incorporated into aircraft automatics. In strong gusty conditions all it does is leave you with unwanted excess speed in the flare which alters the visual attitude, delaying the touchdown, leaves you open to overflaring and puts runway behind you. Fine if you're on a 4000m runway such as at LHR. However, on a short runway with a downsloping threshold such as ABZ 34 it is a curse.

[Dream Land]

At my company we don't have such a procedure, we are lucky enough to have accurate load sheets, having such a SOP on the books seems to miss the real problem

Dream Land

[mcdhu]

mmmmmmm................. Although the assumption must be that if this procedure comes from Airbus, then they must have tested it, I would urge caution here. Have a good read of FCOM Bulletin 819/1 on the CD ROM or 46/2 in the paper manuals titled ''Characteristic and protection Speeds'' - especially re the accuracy required from the 3 AOA sources.

Cheers all,
mcdhu

[mcdhu]

...............lots of clues in the QRH 2.15 and onwards ''Unreliable Airspeed''.

Cheers
mcdhu

[Engine overtemp]

Dream Land says

At my company we don't have such a procedure, we are lucky enough to have accurate load sheets, having such a SOP on the books seems to miss the real problem

I'm sorry but you must be really naive to believe that any load sheet is that accurate! I for one weigh considerably more than the "average" allowed by my regulatory authorities so what makes your load sheet more accurate? (Or are you living in a "Dream Land?")