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FAC weights and Vls

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FAC weights and Vls

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Old 6th Dec 2018, 16:22
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FAC weights and Vls

Any ideas as to why Airbus would use FAC weights (which can be off by as much as 5-10k pounds) to determine Vls?

Our procedure has always been to bump Vapp by at least +5 above Vls.

What is the FAC weight even used for?
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Old 6th Dec 2018, 17:13
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What is the FAC weight even used for?
​​​​​​​As a cross check against rubbish speeds generated by inserting a rubbish ZFW during INIT.
See this OEB from 2004.
http://www.blackholes.org.uk/PP/oeb-819-1.pdf
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Old 6th Dec 2018, 18:02
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Yes, I have that. But we’ve been told by Airbus that FAC weights can be off by as much as 10000 lb.

Not that great of a cross check.
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Old 6th Dec 2018, 19:05
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Have to regularly adjust Vapp on the 319's but for whatever reason the 320's are always fine. No idea why there is a difference between the two bar different software.
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Old 6th Dec 2018, 22:02
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I have more confidence in the FAC weight than the weight from our load closeout, which uses ludicrously low average weights.
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Old 6th Dec 2018, 22:36
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Originally Posted by halfofrho View Post
Have to regularly adjust Vapp on the 319's but for whatever reason the 320's are always fine. No idea why there is a difference between the two bar different software.
The A320 display the speeds derived from the FMGC weights (as opposed to aerodynamic data) so you’ll always get a 5kt split but it doesn’t necessarily mean it’s more accurate.
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Old 6th Dec 2018, 23:29
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Originally Posted by EGPFlyer View Post


The A320 display the speeds derived from the FMGC weights (as opposed to aerodynamic data) so you’ll always get a 5kt split but it doesn’t necessarily mean it’s more accurate.
Not all airplanes do that. It's been a relatively recent modification to the planes in my fleet.
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Old 7th Dec 2018, 02:14
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The old birds use the FAC to determine the characteristics speeds and the MCDU to compute the VAPP. On the newer models, all the speed displayed are from the data inserted in the MCDU. And the FAC are only there as a back up. In case of major discrepancy, a « CHECK GW » message will be triggered after airbone.

Last edited by pineteam; 7th Dec 2018 at 06:11. Reason: Typo
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Old 7th Dec 2018, 02:34
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Originally Posted by Check Airman View Post
I have more confidence in the FAC weight than the weight from our load closeout, which uses ludicrously low average weights.
i wouldn’t and Airbus says you shouldn’t.
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Old 7th Dec 2018, 04:07
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Originally Posted by Altcrznav View Post


i wouldn’t and Airbus says you shouldn’t.
I step in here and am interested.

do you have a reference for that ?
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Old 7th Dec 2018, 09:44
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@ Altcrznav
Have a read in this excellent document from Airbus : ISI 22.00.00061 "FMGC & FAC - Gross weights and associated characteristic speed computations on Single Aisle"

@ Goldenrivett
Your attachment is not an OEB, it is an outdated FCOM BULLETIN
Attached Files
File Type: pdf
ISI%2022.00.00061.pdf (847.8 KB, 83 views)
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Old 7th Dec 2018, 10:26
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Originally Posted by pineteam View Post
The old birds use the FAC to determine the characteristics speeds and the MCDU to compute the VAPP. On the newer models, all the speed displayed are from the data inserted in the MCDU. And the FAC are only there as a back up. In case of major discrepancy, a « CHECK GW » message will be triggered after airbone.
I was reading this on FCOM recently and there is no explanation why airbus did that.
Effectively what we see in PFD below 14600 and 240 is still dummy and what we entered in MCDU? Unless there is a 7 ton error? Where in this case it will show what in PFD...
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Old 7th Dec 2018, 16:44
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Hi Lantirn,

Try to have a look in the FCTM-Aircraft Systems-Flight Management- ZFW-ZFWCG entry errors.
You will see that for the newer models the speed displayed on the PFD are always from the data inserted from the MCDU even with the « Check GW »message
But like in the older models, V&Prot, V&Max and Vsw are still based on aerodynamic data.
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Old 8th Dec 2018, 11:21
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The A320 display the speeds derived from the FMGC weights (as opposed to aerodynamic data) so you’ll always get a 5kt split but it doesn’t necessarily mean it’s more accurate.
Good to know, thanks!
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