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A320 Characteristic Speeds

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A320 Characteristic Speeds

Old 2nd Apr 2021, 11:43
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A320 Characteristic Speeds

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.
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Old 2nd Apr 2021, 12:47
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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.
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Old 2nd Apr 2021, 13:56
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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.
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Old 2nd Apr 2021, 18:24
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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.
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Old 2nd Apr 2021, 20:24
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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.
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Old 3rd Apr 2021, 00:40
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Thanks. Where do the unfamiliar find ISI 34.11.00028?
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Old 3rd Apr 2021, 03:17
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Thank you everyone for their inputs. Things seem quite clear now.
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Old 3rd Apr 2021, 08:07
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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
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Old 3rd Apr 2021, 14:56
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Thanks. Appreciate it.
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Old 13th Apr 2021, 11:40
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Originally Posted by B737NG_Pilot View Post
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.
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Old 17th Apr 2021, 20:07
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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.
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