A320 auto-brake selection

[FullyFullyReady]

Hi All,

Wondering what the reason is for the difference in the timing of auto-brake selection between some sets of SOPs. On departure consensus seems to be after the flight control check (presumably due to spoilers being part of that check?) and on approach some manuals state it is selected during the descent whereas some others state it be selected with gear down. As I alluded I presume this is due to some kind of system logic or trigger which I haven't yet read about; is anyone able to shed any light on the specific reason?

[vilas]

I had answered this a long time ago:
FROM OPERATIONAL LIAISON MEETING FBW
7Safety Precautions ...

The Flight Control check to be done prior to autobrake arming:

If the spoilers are left in the extended position after landing...

the aircraft will suddenly brake at autobrake MAX arming!!!

Recommendation introduced in the SOP.


For Approach and landing it can be selected in approach preparation and briefing and the selection is confirmed at gear down. Also at flap3 selection.

[sonicbum]

Hi vilas,

Hopefully somebody should have done the preliminary cockpit preparation and the walkaround, but it could happen indeed. What about doing the flight controls check with the autobrake max above 40 kt during taxi ? Upon extension of the ground spoilers the system will trigger the autobrake max as well. We shouldn't be taxing at 40 kt but I can see it as a realistic scenario hence the need to arm the autobrake only after the flt controls check.

By the way this has nothing to do with legality :ok::E

[vilas]

sonicbum
I myself do not see the possibility of Spoilers being in extended position during taxiing. Airbus may have just covered their backside. However taxing above 40kts. during controls check only one side spoilers will extend that may not trigger MAX braking because Airbus would have added that in their presentation.

[Meikleour]

Vilas: Surely the GRD SPLS are not activated by the Flight control check?

Therefore no risk of MAX Autobrake.

[Goldenrivett]

Hi Meikleour,
Surely the GRD SPLS are not activated by the Flight control check?
Agreed.
But suppose you forgot to stow the ground spoilers after landing, and shut the engines down. The spoilers would gradually stow themselves with the loss of Hyd Pressure, so there is a chance you'd miss the clue on the walk around. After the next engines start and taxi out, if the spoiler handle was still in the armed position - then Airbus think there is a chance of Max Auto Brake being applied when the MAX switch is selected.

If you do the flight control checks first, then you should notice the ground spoilers are up, stow the handle, then arm it.

[Meikleour]

Goldenrivett: I like your train of thought! If its possible, then I suppose someone someday will do it!

To be realistic with 20 years on Airbus types, the only time it was a serious risk was during Base Training whilst taxying around for another go after a full stop landing.

[Goldenrivett]

Meikleour: I wonder if someone will invent active feed back through the speed brake handle?

[Meikleour]

Goldenrivett: Unlikely! That would make it like a Boeing!!!!

[Gryphon]

- Spoilers are armed in the after start check list everytime, so they are always armed for taxi (you don't need so many errors to be performed before).
- Flight control check never activate the ground spoilers, but only the flight spoilers (roll function)
- Ground spoilers activation happen only with speed above 72kts, that means you have to taxi faster than 72kts
- There is indeed an active feedback through the speedbrake handle for armed position as in the Boeing (you have to pull it up). There isn't for deployed position but it's not relevant for the case.
- I have no idea why it should be done after the flight control check, but maybe because with this check your are checking the computers (ELAC, SEC) which control and monitor these conditions.

[Goldenrivett]

Hi Gryphon
I have no idea why it should be done after the flight control check,
Villas explained it with his OPERATIONAL LIAISON MEETING FBW quote in post #2.
"If the spoilers are left in the extended position after landing..."

It's only a stupid computer. If you don't cancel the signal (i.e. stow the speed brake handle) then the computer is still latched into Ground Spoiler activation.
If you restart the engines in the same condition (handle still armed), then the computer still thinks you want ground spoilers and gives you them. If you Arm Max Auto brakes, the logic will then apply max auto brakes.

There isn't for deployed position but it's not relevant for the case.
It is more obvious in a Boeing because the speed brake handle will be fully deployed. On the Airbus you have to view the flight controls systems page (during the controls check)

that means you have to taxi faster than 72kts
No - that is only to deploy Automatic Ground Spoilers when you select idle power.

[sonicbum]

- Spoilers are armed in the after start check list everytime, so they are always armed for taxi (you don't need so many errors to be performed before).
- Flight control check never activate the ground spoilers, but only the flight spoilers (roll function)
- Ground spoilers activation happen only with speed above 72kts, that means you have to taxi faster than 72kts
- There is indeed an active feedback through the speedbrake handle for armed position as in the Boeing (you have to pull it up). There isn't for deployed position but it's not relevant for the case.
- I have no idea why it should be done after the flight control check, but maybe because with this check your are checking the computers (ELAC, SEC) which control and monitor these conditions.

Hi Gryphon,

- So the flight controls check does not check the ground spoilers but I have always seen 5 spoilers coming up during the flight controls check... :hmm:

- check the autobrake arming conditions for max :rolleyes:

Cheers

[Goldenrivett]

Hi sonicbum,
but I have always seen 5 spoilers coming up during the flight controls check...
I suggest you learn to count or return to stand.
See DSC-27-10-20 Architecture, Roll Control,
"One aileron and four spoilers on each wing control the aircraft about the roll axis."

[Meikleour]

sonicbum: oh dear!!!!!!...........

[vilas]

I think Goldenrivett has it right because otherwise the precaution appears meaningless to be put in FCOM.

[sonicbum]

My bad sorry gents I had the 330 in mind, which has nothing to do with the ground spoilers either, but it gets messy sometimes (on the 330 you have 5 roll spoilers).

P.s meikleour breathe

[Gryphon]

Hi Goldenrivett,

Now I see your point: you think that the Spoiler will be latched in deployed condition because the computer. I don't, and that's why I'm talking about 72 kts, flight control check nothing to do with ground spoilers, and handle feed back irrelevant.

I think that computers will be reset when engine shut down. But the real problem is you and me "thinking" instead of providing references to docs.

In the other hand I cannot find anything in FCOM, but only in FCTM SOP,s. Maybe it is just a flow pattern and nothing else. Maybe not...

[Goldenrivett]

Hi Gryphon,
But the real problem is you and me "thinking" instead of providing references to docs.
http://www.blackholes.org.uk/PP/AGS.jpeg
I think that computers will be reset when engine shut down.
Please point out the "ENG MASTER" switch logic gate on the diagram.

Why do you think "GND Spoiler .... Disarm" is performed during After Landing Checks?
Why not simply keep them Armed ready for the next take off?
Maybe it is just a flow pattern and nothing else. Maybe not...
Do you really think Airbus just want to give us things to do and look busy during Flow Patterns?

[Gryphon]

Hi Goldenrivett,

Firstly I'll try to answer you:

Please point out the "ENG MASTER" switch logic gate on the diagram

The diagram explain the Spoiler extension condition, not retraction. And only in "Normal standard" operations (what if all computers have been switched Off....this is not in the diagram...then?)

Why do you think "GND Spoiler .... Disarm" is performed during After Landing Checks?
Why not simply keep them Armed ready for the next take off?

Maybe not to taxi-in and enter the apron to your parking position with the Spoiler deployed? Maybe because perhaps after low Hyd press at engines shut down, the spoiler will not totally retract due to the absence of airflow, and you don't want the spoiler partially extended during the turn around?

Do you really think Airbus just want to give us things to do and look busy during Flow Patterns?

No, I don't think so. But there are actions to be completed in a given order or moment, as per SOP,s, with no connection to any system logic. We can talk about PF disarming Spoiler before PNF switching Off the Radar or retracting the flaps. The 10000 ft flow patterns ask you to select EFIS option to constrain and LS (if applicable) ON, and it doesn't mean something will happen if you do the selection at a different altitude, and a long etc.

But again, I don't have the answer and perhaps you and Vilas are totally correct. what I'm trying to complain about is that you cannot find the explanation in the FCOM SOP,s (not even is stated there) and only a sentence in the FCTM with no more emphasis than in any other flow pattern. If they want to keep the secret to be able to share it only in the "OPERATIONAL LIAISON MEETING FBW", at least I expect something similar to a "CAUTION: Do not select Auto Brake to Max until after Flight Control Check to avoid any unwanted brake activation."

Furthermore if waiting until performing the flight control check is for you to realize that the spoiler are deployed, I think is easier to check the SD in the ECAM: In phase 2 (after engines start) Wheel page is displayed automatically and is very noticeable there the spoiler position, indicated in the same way it is in the Flight Control page.

But again, I'm not saying you are not right, only that I don't know.

[Goldenrivett]

Hi Gryphon,
If they want to keep the secret to be able to share it only in the "OPERATIONAL LIAISON MEETING FBW", at least I expect something similar to a "CAUTION: Do not select Auto Brake to Max until after Flight Control Check to avoid any unwanted brake activation."
It's not secret - I found it easily with a Google search, or try Taxi_Procedures.pdf (http://www.blackholes.org.uk/PP/Taxi_Procedures.pdf) slide 7.

It's only a problem if you forget to disarm the ground spoilers after landing, miss all the clues, restart the engines, fail to notice the Spoilers are still in the armed position, miss the GND Spoilers on the wheel page, then select MAX Auto Brake on taxi out. I know it's sad - but there are pilots out there capable of missing all those clues - and it's happened.
The SOP is the last "belt & braces" error trap during the flight controls check - nothing more complicated.

[Gryphon]

OK, thanks! Finally I got it!

FCOM, FCTM, MEL, etc. Then Google search if needed. Hopefully I will find some slides from Blackholes.org :)

Ciao :ok: