A320 Brake Check

[jriv]

Hi all,

Does your company have you start to roll then check the brakes by applying them to verify they work in normal (not alternate) with zero pressure on the triple indicator?

I find it a little amateurish and think the same thing can be accomplished by pressing the brake pedals before releasing the parking brake. Release the parking brake, verify pressure goes to zero on the triple indicator, release the toe brakes and taxi away. In fact, the "A320 Family Instructor Support" from 2001 suggests that technique, but my present company's FCOM 3 has us roll forward and stop using the brakes.

Does anybody recall a reason the technique may have changed? A reason to let it roll forward then stop? Do other types require the same type of brake check?

Thanks!

[Panama Jack]

Just looked at that a few days ago and your interpretation of the Airbus guidance material is the way I also understood it.

At my company on the Airbus fleet, we also roll forward before doing the brake check, but not to the point of a stop (just checking that breaking action is there and that the braking has reverted to the Green system). It could be argued that this is a general Airmanship technique and the SOPs published by other aircraft advocate this approach.

Nothing wrong, IMHO, in doing it, but coming to a full stop, as you mentioned, seems a little over the top. Research into the reasons for this at companies sometimes reveal interesting personal preferences such as "this is the way we did it in the Air Force on the Nimrods", etc. :}

[Microburst2002]

we check two things regarding the brakes, in the old models (only one in the new ones)

1- the airplane slows down when you press the pedals
2- normal brakes are "in charge", rather than alternate brakes.

So it is better to wait until you are already taxiing to press them and check both things, rather than check one before and another after initiating taxi.
Agree there is no need to stop the airplane, but some people hardly presses teh brakes and there is hardly any noticeable braking action... I like to feel it, so there is no question that we have brakes.

however, I have a question regarding the system (in old models):

if i understand the system correctly, when during normal taxi we press the brake pedals we are pressurizing both the green hydraulic and the yellow hidraoulic lines, right? so every time it is the automatic selector valve which gives priority to the green (normal) brake system. When the pedals are untouched, there is no system "in charge".

[Field In Sight]

Because the green system is pressurised, it IS in charge as the automatic selector valve allows the green system pressure to "get to" the brakes.

If the pressure drops too much, then the yellow system pressure is able to "get to" the brakes.

[3holelover]

Because the green system is pressurised, it IS in charge as the automatic selector valve allows the green system pressure to "get to" the brakes.

If the pressure drops too much, then the yellow system pressure is able to "get to" the brakes.That's correct.

When you step on the brakes, you're actually utilizing a completely closed system, similar to a hydraulic clutch in a car.... at the other end of the closed loop the equivalent of a "slave cylinder" makes all the mojo happen with the green or yellow systems.

[Microburst2002]

But this happens only when we press the pedals and the BSCU opens the normal selector valve, right?
what I understand is that at the same time, the dual valve opens as well and then the automatic selector determines which system will be pressurized.

so I think that if the pedals are unpressed, there is no normal nor alternate braking, since both valves close again. Or is it that after the "first time" the automatic selector selects the green system (first time we press the pedals with green hydraulic pressurized and NW STRG ON) it remains in that position and then we can consider green is in charge?

[Beeline]

Green system (Normal Braking) uses a brake pedal transmitter unit to send the braking signal to the BSCU, this opens the selector valve and if hydraulic pressure available, the auto selector overrides the yellow system (valve has a larger area on green side) and sends this px down to the servo valves on the leg.

The low pressure yellow system is available all the time, this system is like the car principle of master and slave system with the dual valves, sending the pressure down to the brakes. BSCU dead, Green system unavail.

This low pressure system has been scraped in the new enhanced Airbus models. No more spongy brake snags!! Complete fly by wire braking system.

Airbus procedure for High power ground running involves holding the brake pedals down in normal braking, hence no triple gauge to act as a reference if the guy next to you gets cramp, Always thought quite dangerous.