A320 flight control protections

[Maverick2167]

Hello,
looking for insight on the following flight control protection/Laws on the A320

1. with the auto thrust active and during cruise ,if we bring back the thrust lever all the way to IDLE, at some point of time will the HIGH AOA protection kick in- including alpha floor ?
2. Same scenario as 01, but with Autothrust Inoperative (disconnected) will the High AOA protection kick in, and will the speed remain at Alpha prot?
3. Autopilot limitation is 160ft AGL for ILS CAT 1 and 250ft AGL for the NON-precision approach, I understand that if we do not deactivate the pilot at the mentioned threshold, the FMA will display "Disconnect AP for Landing" will the vertical and lateral mode also revert to basic mode i.e. HDG & VS ?

Thanks

[321XLR]

Originally Posted by Maverick2167

Hello,
looking for insight on the following flight control protection/Laws on the A320

1. with the auto thrust active and during cruise ,if we bring back the thrust lever all the way to IDLE, at some point of time will the HIGH AOA protection kick in- including alpha floor ?
2. Same scenario as 01, but with Autothrust Inoperative (disconnected) will the High AOA protection kick in, and will the speed remain at Alpha prot?
3. Autopilot limitation is 160ft AGL for ILS CAT 1 and 250ft AGL for the NON-precision approach, I understand that if we do not deactivate the pilot at the mentioned threshold, the FMA will display "Disconnect AP for Landing" will the vertical and lateral mode also revert to basic mode i.e. HDG & VS ?

Thanks

1, 2: My understanding is Alpha Protection is available if Auto Thrust is in a functional/operative state (not "broken" due to maintenance issue). Auto Thrust does not need to be ACTIVE or ENGAGED at the time

3: I have not seen that FMA, I always get AP off by 500 radar altitude at the latest.

Other folks could probably elaborate better than me.

[vilas]

Alpha floor is not available beyond M.6. Alpha prot is a latching Condition. Once activated it will maintain alpha prot unless stick is pushed forward to unlatch it, then speed will increase.

[Maverick2167]

Thanks for the reply, just to understand. Once AP disengages at or below Alpha PROT, the aircraft will descend(naturally) and since HIGH AOA protection is active, the aircraft will maintain speed at Alpha PROT regardless of the descend V/S?

[vilas]

Originally Posted by Maverick2167

Thanks for the reply, just to understand. Once AP disengages at or below Alpha PROT, the aircraft will descend(naturally) and since HIGH AOA protection is active, the aircraft will maintain speed at Alpha PROT regardless of the descend V/S?

Yes! It maintains alpha prot AoA. It may even climb to maintain it if required.

[OPEN DES]

The AP will trip off at alpha prot + 1 deg (a320 ceo) some phase advance for pitch rate considered for a318/319/319 ceo and all neos.
Alpha floor activation by fac (alpha) or elac (alpha/pitch plus sidestick nose up demand) is indeed inhibited above M0.6 for all variants.

Once alpha prot is activated it is nominally a latched condition whereby sidestick controls alpha directly. Sidestick neutral=alpha prot, full sidestick=alpha max.
However phase-out will happen when certain specific conditions are met, mostly when High Lift devices are out and/or close to the ground. (I.e no latching) Otherwise nominally alpha prot is phased out when forward sidestick is applied (function sidestick deflection and time).

Alpha prot value depends on variant and starts to decrease beyond M0.3 (due Mach compressibility effect).

Alpha floor activation (< M0.6) normally occurs after Alpha prot threshold however can be phase advanced by ground speed/head wind gradient in landing config.
Alpha floor activation can also be independent of filtered alpha purely, when high pitch (25deg) and/or high aoa prot is active and sidestick deflection > 14deg.

So in your scenario expect the AP to trip first, and then the aircraft to reach and maintain alpha prot without alpha floor activation.

[FlightDetent]

#3 will depend on the installation. There have been subtle upgrades all along.

The 160' for CAT I is a regulatory value of 80% (no less than) from the lowest MNM value. Same for CAT II manual landing (even on another type) where AP is mandatory but takeover to manual needs to be done before 80'.

So I was told.

[Flyit Pointit Sortit]

I think the above has been answered but can anyone enlighten on me on Flare mode?

In flare mode, the THS is frozen, yet the "system" trims the aircraft to 2 degrees nose down over 8 seconds. Where does this trim input come from. Is it from the elevators?? Im very confused

Cheers

[OPEN DES]

Hello,

The flare law is a pitch attitude demand control law with direct and integrated lines, whereby THS is declutched below 50ft RA: i.e. only the elevators are actuated.

θc=pitch commanded at zero sidestick
-between 50ft and 30ft: θc is equal to pitch that was existing at 50ft RA
-below 30ft: θc is reduced to -2deg over 8 seconds to restore conventional aircraft behaviour upon entry into ground effect

hope this helps

[Flyit Pointit Sortit]

Thanks for the reply, unfortunately I don t really understand the answer. I understand that the pitch attitude is taken at 50 ft and then used as the basis of the trim down notion.

But this trim can’t be from the THS as it’s is frozen. So where does the “trim” come from? I can only assume that it’s from the Elevators. In which case, do the ELACS/ SECs command the pitch down motion that then requires a counter active pitch up input on the side stick so that the sum movement of the aircraft remains at zero. (Much as in the same way that the side stick inputs are summed in a “DUAL INPUT” scenario but in FLARE mode, the ELACs/SECs are behaving as if they are a second side stick pitching down)

I hope that explains my confusion

[OPEN DES]

Yes the elevators provide the pitch down below 30 ft. THS is declutched, so it’s elevators only.

[Flyit Pointit Sortit]

Thanks Open Des

[Fursty Ferret]

3. Autopilot limitation is 160ft AGL for ILS CAT 1 and 250ft AGL for the NON-precision approach, I understand that if we do not deactivate the pilot at the mentioned threshold, the FMA will display "Disconnect AP for Landing" will the vertical and lateral mode also revert to basic mode i.e. HDG & VS ?

Been a while since I was on the A320 but I would expect that it'll attempt an autoland off any ILS approach unless the topography / beam shape is so wild that it triggers the autoland warning via rad alt discrepancies or excessive deviation.

[Denti]

Originally Posted by Fursty Ferret

Been a while since I was on the A320 but I would expect that it'll attempt an autoland off any ILS approach unless the topography / beam shape is so wild that it triggers the autoland warning via rad alt discrepancies or excessive deviation.

Indeed, the system doesn’t know the airports ILS status and always treats it as the highest available aircraft capability, so usually CAT 3 DUAl/SINGLE.

For the NPA it depends how it is coded. If the approach is in the database with a runway point, it will usually revert to basic modes during flare (triple click), which mens that one gets flight director guidance well below the 250 ft, haven’t tried the autopilot, but i expect it to be a regulatory limit rather than an aircraft enforced one. In the end it does also depend on equipment status, with FLS it is 200ft, LPV it is 160 ft and GLS it is either 160 ft or 0 ft if AUTOLAND is displayed.

[hikoushi]

If you choose to leave the FD on to touchdown, FLS deflections remain displayed down to the ground on many (most? All?) approaches. You will still see “F-LOC F-G/S” in green on the FMA as you taxi in, too. I wouldn’t try flying that all the way down, will be a memorable landing for sure!

[vilas]

If the NPA is programmed to threshold (not to MAP) and inbound track is runway track you can keep FDs on but do manual landing. New mods allow this.