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V Alpha prot highlevel A320

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V Alpha prot highlevel A320

Old 10th Jul 2023, 10:55
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V Alpha prot highlevel A320

Hi,

scenario: you enter a holding in 18000ft. The fmgc says: set hld speed. So you push the button and he flies managed. Reaching the turn in the holding the va prot band comes up. So what speed would the airbus fly and what would happen if he flies the speed? Protections coming on?

thanks!

sw
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Old 10th Jul 2023, 11:31
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With autopilot engaged, the aircraft will command pitch down as a last resort to remain above VLS.

Someone can correct me but this is what I have observed and read in the FCOM, but this was during descent.
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Old 10th Jul 2023, 12:03
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For managed speed/Mach, the lowest target is VLS, and the highest target is: ‐ VMAX in the case VMAX is equal to VFE, or ‐ VMAX - 5 kt in the case VMAX is equal to VMO/MMO.
During turn VLS would go up, so Managed speed target would go up to be at least VLS. But in case of high bank turn and turbulence could definitely trigger Alpha floor before the aircraft has time to process it. I have done it once in sim, won’t do it again; steep turn ahead and turbulence just go to selected and give you some margin.
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Old 10th Jul 2023, 17:57
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VLS doesn't change with G i e. in turn. It's the alpha prot moves up. If holding speed is correct for the altitude there should be no problem. AP bank has limit. If speed drop below alpha prot AP will trip and aircraft will maintain alpha prot unless stick is pushed to unlatch the speed. Beyond •63M there's no alpha floor.
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Old 11th Jul 2023, 00:02
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Originally Posted by vilas
VLS doesn't change with G i e. in turn. It's the alpha prot moves up. If holding speed is correct for the altitude there should be no problem. AP bank has limit. If speed drop below alpha prot AP will trip and aircraft will maintain alpha prot unless stick is pushed to unlatch the speed. Beyond •63M there's no alpha floor.
My bad I was wrong. After checking FCOM again if I understood correctly Vls being based on VS (actually vs1g so non g dependant) it won't change with the load factor.
In clean configuration Vls=1.28VS so you should be fine with up to 52° of bank, alpha prot coming in before that anyway.

Though during my type rating the instructor definitely managed (one way or another) to make us trigger alpha floor after starting a turn for an approach with speed managed at green dot.
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Old 11th Jul 2023, 06:45
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Autopilot should limit load factor by reducing bank angle before ending up in alpha protection. You have a surprisingly small margin at green dot and I’ve triggered a stall warning in the simulator during a level turn with 30 degrees angle of bank (alternate law obviously). “New underwear, please”.
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Old 11th Jul 2023, 14:20
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Originally Posted by snl13
My bad I was wrong. After checking FCOM again if I understood correctly Vls being based on VS (actually vs1g so non g dependant) it won't change with the load factor.
In clean configuration Vls=1.28VS so you should be fine with up to 52° of bank, alpha prot coming in before that anyway.

Though during my type rating the instructor definitely managed (one way or another) to make us trigger alpha floor after starting a turn for an approach with speed managed at green dot.
During type rating we give a demo of low energy warning on approach "Speed Speed". That is done by doing level turn and reducing thrust. If continued in this state can trigger alpha floor. No surprise.
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Old 12th Jul 2023, 06:37
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Well the AC didn’t reduce the bank angle. And managed speed was the target which was green dot. So we agree: A320 in a high alt pattern can’t fly managed speed?

Last edited by Speedwinner; 14th Jul 2023 at 05:21.
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