A320 braking system

[Citation2]

I would like to understand the differences between the old and new braking system , besides the fact that the ABCU regulates automatically the pressure to 1000 psi .

In old 320 in case of Anti-skid fault,the alternate braking mode would automatically switch to accumulator am I correct? Although yellow pressure is available?

With the new braking system FCOM states that the ABCU is capable of 2 alternate modes without anti skid:

Alternate braking without anti skid
Alternate braking without anti skid on accumulator

Does that mean that the ABCU would switch to Accumulator only in case of hydraulic failure? So in case of anti skid electrical failure the ABCU would still use the yellow hydraulic system and regulate the pressure to 1000 psi?

So ABCU is able to be on yellow without anti skid without using the acu?

Whereas on old 320s, fcom does not state such options so it would switch to accumulator although it s just an electrical failure?


Thanks for clarifying this

[Microburst2002]

In the old models you have alternate brake with or without antiskid. When you are on accumulator only (yellow hyd system not available) then it has to be without antiskid. This does not mean that if you have no antiskid the brakes are on the accumulator.

For instance, if you lose the BSCU there is no antiskid, but if the yellow system is pressurized then you have alternate braking without ASKId and you can apply brakes as many times as you like because you are not on accu only.

As for the new models, I'm not enjoying them anymore and I don't remember well if the system is designed not to limit the 1000 psi automatically when brakes are on accu only, which seems reasonable.

[Kuchan]

The main brakes use Green hyd. with Normal anti-skid system (servo valves) to apply pressure on the green pistons of the brake units to slow down the aircraft.

It would automatically reverted to yellow braking system with alternate ant-skid in case of green pressure loss, or a failure occurs on the normal braking system. This is automatically done without crew action by automatic selector which cuts off the green hyd. to allow yellow hyd. pressure to brake on the yellow pistons of the brake units.

As each brake has one normal anti-skid valve and one alternate skid valve , A320 has a total 4 normal and 4 alternate anti-skid valves.

Alternate braking (yellow syst) without anti-skid is either electrically (A/SKID & N/W STRG switch set to "OFF" or power supply failure)- or hydraulically if the brake yellow pressure accumulator only supplies the brakes ( in the case of towing without hyd. pump on.)

[Citation2]

My query is about alternate braking without anti skid :
Fcom clearly says that ABCU is capable of:
Alternate braking without antiskid
Alternate braking without anti skid on accumulator

Which is not specified the same way for old models. On old models alternate without anti skid refers to accumulator being in control.Does that mean
that the new system is able to be in alternate mode without anti skid on yellow pressure if available? Or on accumulator if yellow not available.

Have a look at the schema of the new model , ABCU is able to function without anti skid and Alternate without anti skid on Accumulator

This distinction on new models which does not appear on old ones makes me think that on old models Alternate without anti skid means on accumulator

Or let s put it that way? Can you be on alternate without anti skid on yellow pressure on old models?

[Citation2]

As microbust said old models are equipped with alternate with anti skid( means on yellow) and alternate without anti skid referring to Accumulator

It does not say that the system is able to be on alternate without anti skid still on yellow system!

Whereas on new models ABCU clearly states both options: alternate without antu skid+ alternate without anti skid on ACcumulator

Thanks for your inputs

[Kuchan]

A/SKID & N/W STRG switch set to on = green with anti-skid.
A/SKID & N/W STRG switch set to on, if green hyd. fails= yellow with anti-skid.
A/SKID & N/W STRG switch set to off = yellow without anti-skid
A/SKID & N/W STRG switch set to off with no yellow hyd. pressure= no anti-skid and on accumulator residual pressure.

no yellow hyd pump on to supply yellow hyd. pressure = no anti-skid.