Anti Skid and Nose Wheel Steering Switch questions

[737Andi]

Hi,

I'm unfortunately not sure if I understood the full potential of this switch correctly. Hopefully someone can bring me nearer to this mystery.

From what I have read I understood the following.

If the switch is "on" the following applies:
- Anti Skid is activated
- Nose Wheel Steering is possible
- green hydraulic system is supplying the brake system (except parking brake which is always supplied by yellow system)

If the switch is "off" the following applies:
- Anti Skid is deactivated
- Nose Wheel Steering is deactivated (some airlines require this during pushback)
- yellow hydraulic system is supplying the brake system

I hope this is correct so far?

I have also understood that in a case of a failure in the green hydraulic system the normal braking system ceases to work and the yellow hydraulic system takes over.
When the pilot notices this on the yellow brake accu pressure indicator it is the correct procedure to let the brakes go, then flip the anti skid and nose wheel steering switch and then use the brakes again to stop the plane.

Is it correct that the plane looses its ability to steer the noseplane in this situtation?

Thanks for bringing some light into these things!

Best regards Andi

[AerocatS2A]

Are you talking about the A320?

I had thought that if you lose the brakes, the yellow system does not automatically take over which is why you need to turn the anti skid switch off. It is also my understanding that you would then have no nose wheel steering but you can still steer with differential braking and asymmetric thrust.

[737Andi]

Yes, I'm talking about the A320.

Ok..in this case it makes sense!

Thank you!

[Denti]

Hi,
If the switch is "on" the following applies:
- Anti Skid is activated
- Nose Wheel Steering is possible
- green hydraulic system is supplying the brake system (except parking brake which is always supplied by yellow system)

If the switch is "off" the following applies:
- Anti Skid is deactivated
- Nose Wheel Steering is deactivated (some airlines require this during pushback)
- yellow hydraulic system is supplying the brake system


Partly correct. If the switch is on, green usually supplies brake pressure, if green hydraulic system is lost the yellow hydraulic system supplies brake pressure, anti-skid and nose wheel steering remain available. And yes, the triple indicator shows brake pressure.

By the way, haven't seen any SOP that requires the switch to be off for push-back, that is what the pin on the nosewheel is there fore, and its status is shown as a line on the ECAM.

I have also understood that in a case of a failure in the green hydraulic system the normal braking system ceases to work and the yellow hydraulic system takes over.
When the pilot notices this on the yellow brake accu pressure indicator it is the correct procedure to let the brakes go, then flip the anti skid and nose wheel steering switch and then use the brakes again to stop the plane.

No. Normal brake failure is basically a non-issue. Alternate brake takes over, braking is a bit more sensitive and autobrake is lost. But that is about it. Had it on the line already during landing, really a non-issue, simply continue taxying as normal, no action line on the ECAM, no memory items, just a status that advises the pilots to use a landing distance procedure and that antiskid is still available.

For a complete loss of braking there is indeed a memory procedure that advises the pilot to release the brake pedals, order the PM to switch off the Antiskid-Nosewheel Steering switch, and once that is done use the brakes again, however check on the triple instrument to stay below 1000 psi brake pressures. Newer planes have an automatic brake pressure reducer, in that case the pilot can stomp as hard as he likes, he won't get more than 1000 psi. And yes, in that case nosewheel steering is lost, differential braking is available. But usually, come to a stop, get a tow truck.

[737Andi]

Hi Denti, thanks for your reply :)

Partly correct.

Reading your post I said exactly the same, or not?? :)

By the way, haven't seen any SOP that requires the switch to be off for push-back, that is what the pin on the nosewheel is there fore, and its status is shown as a line on the ECAM.

Mike Ray (former American Airlines Captain) mentioned this procedure in his A320 check ride book.

No. Normal brake failure is basically a non-issue. Alternate brake takes over, braking is a bit more sensitive and autobrake is lost. But that is about it.

Is alternate brake then still pressured by green or by yellow system?

[Uplinker]

By the way, haven't seen any SOP that requires the switch to be off for push-back, that is what the pin on the nosewheel is there fore, and its status is shown as a line on the ECAM.
.

We used to have this SOP for quite a long time, owing I think to an incident where something failed, leading to the NWS being pressurised and the tow bar swinging around once disconnected. A long time ago now and I cannot remember the details, but a modification was eventually made and the NWS switch could be left on for pushback.

[Denti]

Hi Denti, thanks for your reply :)
Reading your post I said exactly the same, or not?? :)

Not quite, the part about the yellow system taking over as long as the switch is on providing full service sans the autobrake wasn't in there.

Mike Ray (former American Airlines Captain) mentioned this procedure in his A320 check ride book.
Might be configured differently in the US, or a special configuration for a large customer. Haven't seen it in the airlines i have flown for, neither heard about that. Not saying that the SOP doesn't exist, many airlines do have their own set quite different from the airbus SOP set. And as Uplinker mentioned there might have been a reason at some point for that. I have never flown anything older than a 900 MSN retrofitted to the newest standard, and since im fairly new on the Bus, six years now, it certainly could have been a thing in the past.
Is alternate brake then still pressured by green or by yellow system?
Yellow.

[737Andi]

Not quite, the part about the yellow system taking over as long as the switch is on providing full service sans the autobrake wasn't in there.

Most likely I'm misunderstanding you :( but I wrote: "I have also understood that in a case of a failure in the green hydraulic system the normal braking system ceases to work and the yellow hydraulic system takes over."

One question regarding the following....

No. Normal brake failure is basically a non-issue. Alternate brake takes over, .........

For a complete loss of braking..........

If in both cases the yellow system jumps in..what is the difference between these 2 cases?

Thank you!!

[AerocatS2A]

In the second case the yellow system doesn't jump in, that's why you have to turn the switch off, to restore braking. You don't notice because you see pressure on the triple indicator, you notice because the brakes don't work anymore.

[737Andi]

In the second case the yellow system doesn't jump in, that's why you have to turn the switch off, to restore braking. You don't notice because you see pressure on the triple indicator, you notice because the brakes don't work anymore.

That makes sense...thank you all!