A320 Characteristic Speeds

[B737NG_Pilot]

On few A320 CEO's The characteristic speeds displayed on the PFD are computed by the Flight Augmentation Computer (FAC), according to the FMS weight data (for PFD/MCDU display consistency and accuracy purposes), and aerodynamic data as a backup.

While on some A320 CEO's
The characteristic speeds displayed on the PFD are computed by the Flight Augmentation Computer (FAC), according to aerodynamic data.

However for the A320 NEO's

The characteristic speeds displayed on the PFD are computed by the Flight Augmentation Computer (FAC), according to the FMS weight data (for PFD/MCDU display consistency and accuracy purposes). Why No Aerodynamic Data here ?

What aerodynamic data are they referring to?

Also why on the A320 NEO

In landing configurations (CONF 3 and FULL) VLS is always equal to, or greater than,VMCL.

[Fursty Ferret]

By "aerodynamic data" Airbus means AoA.

Using FMGC computed weight instead of AoA means that the data is consistent between both sides of the flight deck and more accurate as well - I'm sure someone told me that the GW can only be estimated to within about 3 tonnes from AoA data, but is probably within a couple of hundred kilograms from the loadsheet.

Second point - dunno. There are some failure conditions that ask for the aircraft to be landed at VLS (which is acceptable anyway) and perhaps there's an issue with control authority given the size and relative positions of the bigger engines. Just a guess though.

[vilas]

The usual calculation is FAC calculates GW and from that the Vs1g. VLs and other speeds are multiples like 1.23 of Vs1g etc. As A320 Neo, XLR is rapidly evolving Air bus makes some changes but they may not find it necessary to explain or share.

[Check Airman]

Fursty Ferret

I’m tempted to have a bit more faith in the FAC weights. Whenever I check, the FAC weights are invariably higher than the load sheet. If it were truly random, I’d expect the FAC to be lower on some days.

That said, if I recall, the FAC is accurate to within +/-3500lb, and most times, the load sheet value is within that range.

[320busboy]

simple answer is read ISI 34.11.00028

longer answer is.

Based on FAC standard. A318 and sharklets are the same standard. Airlines can also choose to activate the fms characteristic speeds from FMS Gross weight.

[Check Airman]

Thanks. Where do the unfamiliar find ISI 34.11.00028?

[B737NG_Pilot]

Thank you everyone for their inputs. Things seem quite clear now.

[320busboy]

Check Airman

you can find in service information from Airbus world if you have access. If not. Ask your engineer or training department. They should be able to help you

[Check Airman]

Thanks. Appreciate it.

[SavedByTheTCAS]

Also why on the A320 NEO

In landing configurations (CONF 3 and FULL) VLS is always equal to, or greater than,VMCL.

Vmcl is the minimum control speed in landing config at which it is possible to maintain control with a ma 5 degree bank when full power is applied. The speed is important because it relates to asymmetric overload.
As was said before, some failure, i.e. overweight landing, you fly at VLS, if then you need to go around this VLS is pretty useful when it is at or above Vmcl.
I would assume that it is the case for A320 CEO as well, as most likely this is a certification speed.

[LW20]

Airbus realized, that the FAC GW is too inaccurate. Although the AoA Probes are correctly installed, there can be differences up to +- 5 tons. At the first flight, were the exact weight is known, + - 2,5 tons are accepted by Airbus.