Arming of Auto-brake - A-320 aircraft

[sharpshooter41]

FCOM says that after start, Auto brake should be armed after checking of the flight controls.

Why is this???

[vilas]

FROM OPERATIONAL LIAISON MEETING FBW


7

Safety Precautions ...

��The Flight Control check to be done priorto

autobrake arming:

��If the spoilers are left in the extendedposition after

landing...

��…the aircraft willsuddenly brake at autobrake MAX

arming!!!

��Recommendationintroduced in the SOP.

[Jonty]

Spoiler extension during the flight control check MAY activate max auto brake.

[vilas]

Spoiler extension will not activate auto brake as the speed has to be greater than 72kt.

[gcc_]

Backtrack runway at super high speed maybe?(over 72 knots)

[Brotti]

Your ground speed must be at or above 40 kts besides spoiler extension for the max mode activation

From FCOM DSC-32-30-10 P 7/14
SYSTEM ACTIVATION
Automatic braking is activated:
‐ at the command for ground spoilers extension (Refer to DSC-27-10-20-C Speed Brakes and
Ground Spoilers - Speed Brake Control), for LO and MED mode.
‐ at the command for ground spoilers extension and the aircraft speed is above 40 kt, for MAX
mode.

[Natstrackalpha]

Well, it may be because, if you have armed autobrake, then the spoilers won`t deploy if autobrake is armed, when doing the ground flying control check, but then that does not make sense, but your mains are compressing the oleos, so thats it then. Its weird, this one, I lack so much knowledge as a student.

Here`s one, Spoilers, armed and autobrake set . . . line up for takeoff, thrust back to idle, spoilers deploy?

Wait, wait, wait, max autobrake starts as soon as wheels rotate and do NOT wait until 72kts, its LO braking that kicks in at 72kts, max starts at wheel rotation, straight away, thats what max is all about, it does not brake harder, it brakes . . sooner. Max,= immed..... Med= 40 kts........., Lo =72kts.
because, because, if you RTO you want it to stop you - not have a debate with itself as to what speed you are doing,

"well, let him wait deary, av been max braking all day, my discs are killin me and over heating, what the heck does he think this is 72 knots . . ? I should co-co . . .

[vilas]

brotti
If you read further on the same para you have quoted you will see

"Therefore, if the aircraft makes an acceleration stop and begins to decelerate when its speed is
under 72 kt, the automatic braking will not activate because the ground spoilers will not extend."
It is confusing but possibly above 40kts you need to extend spoilers to activate MAX autobrake.while above 72kts they extend autmatically and trigger MAX breaking.
Operational liason meeting FBW is Airbus explanation why max AB is to be armed after flt ctl check..

[SloppyJoe]

Natstrackalpha

72 Kts is only a command to the ground spoilers not the autobrake. The autobrake LO, MED or MAX will not engage if GROUND spoilers do not deploy.

On landing the 72kts is not relevant as spoilers deploy on main wheel compression LO and MED.

For RTO the spoilers only deploy above 72kts.

The 40kts you are getting confused about is irrelevant and I honestly do not understand it as it states that for MAX to engage must have spoiler activation and be above 40kts and nose wheel compressed. Maybe it is GS and the 72kts for spoiler activation is IAS.

if you RTO you want it to stop you - not have a debate with itself as to what speed you are doing

This is incorrect, cleared for immediate take off due aircraft on 5 nm final, after setting thrust and reaching 50kts you have an ECAM relating to a door or similar. The first exit is 3000ft away. Do you really want to stop in 1000ft and then spend a minute figuring out you need to disarm the spoilers whilst the guy behind you has to go around. Its probably due to dirt in the door but as your brakes are now hot you have to wait at the gate for an hour before you can go again.

thats what max is all about, it does not brake harder, it brakes . . sooner.

This is also incorrect. MED and LOW is a deceleration rate target that the computer aims for. If you use max reverse it will apply less braking as can meet its deceleration rate with less. MAX is just as the button says, it supplies maximum braking to the wheels. At MAX autobrake the aircraft for a given speeds stopping distance varies with its weight. For MED and LO as long as the target deceleration can be met the stopping distance for a specific speed remains the same regardless of aircraft weight.

[Natstrackalpha]

Thanks Sloppy, time to revise autobraking system.

[sharpshooter41]

Thanks for the inputs. So, we still do not have a clear-cut reason for this action.

I suppose will just have to follow the recommendation of the Ops Liaison Meeting. However, it is quite unlikely that spoilers are left in the out position after ldg; aircraft is taxiied in and switched off; then it is started up ( with the spoilers still in the out position) and taxiied out and now when the Auto brake is armed the aircraft comes to a screeching halt.

[sierra_sotiropoulos]

From the A320 FCOM:

Autobrake activates:
- When the ground spoilers extend, for LO and MED mode.
- When the ground spoilers extend and the aircraft speed is greater than 40 knots, for MAX mode.
Therefore, if the aircraft makes an acceleration stop and begins to decelerate when its speed is under 72 knots, the automatic braking will not activate because the ground spoilers will not extend.

Moreover:
- Autobrake "LOW" activates with 4 seconds delay and decelerates at 1.7 meters/second2
- "MEDIUM" activates with 2 seconds delay and decelerates at 3 meters/second2
- "MAX" activates with zero delay.

[Natstrackalpha]

So, am half right!

Lo Med Hi

Brakes, soon, sooner and sooner and hard, harder and harder.

Spoilers retract after landing when Throttle at FWD idle?
Autobrake disengages with auto brake selected pb pushed or momentary (careful) application of the toe brakes - there then follows the dis-arming of the spoilers. Clamshells close, spoilers retracted at selection of fwd idle.

With ref to RTO - it makes sense, thank you. But, if, if the case were that auto brakes apply at throttle idle then to cancel same, in order to make that turn off for the one on final Sloppy, Sir, then it would simply be a case of touch the toe brakes and thus cancel the autobraking system. . . . (setting.) So, effectively, no big deal, or is everyone saying that the autobraking (process) and the spoilers are inextricably linked - I think not, I think you can cancel autobrake whatever way you want. Toe or pb. you can retract spoliers by fwd idle and/or disarm spoilers, all actions of which would be instinctive and not require time for pre-thought unless landing heavy on wet - and still, it would be a case of simply gently but firmly plant it down and apply Full rev with med or low depending on conditions and let mother nature do its work, like, spoilers, autobrake etc. If you don`t like what you get then de-select autobrakeing and watch out for the 1,000 psi, no?

Or am I totally wrong here . .?

[sierra_sotiropoulos]

From A320 FCOM

Ground Spoiler Retraction:
The ground spoilers retract:
-After landing, or after rejected takeoff, when the ground spoilers are disarmed.

Note: if ground spoilers are not armed, they extend at the reverse selection and retract when idle is selected.

- During a touch & go, when at least one thrust lever is advanced above 20.

Note: After an aircraft bounce, the ground spoilers remain extended with the thrust levers at idle.

Comment:
The disarming of the spoilers from the captain upon runway vacation "triggers" the after landing flow performed by the FO.

[sierra_sotiropoulos]

There are some airlines that do not allow the FO to taxi the aircraft.
In this case, during landing rollout the captain always assumes control at 70 knots.