Alternate Brake Check on A320/321

[Aikon]

Does anyone know what is the reason that on newer A320/321, there's no requirement to do an alternate braking system check in preliminary cockpit preparation?

Thanks.

[divinehover]

The point of the check is to ensure that the Green system has taken over from the Yellow system after eng start. The newer models have a modified brake system (a diff valve type I think) making the check unnecessary.

Some Airlines which operate old and new types make the check standard to harmonize SOP's.

[IFixPlanes]

No different valve ....... a different System.

Alternate braking system on the older A320 Fam.:
http://img222.imageshack.us/img222/5729/a320famaltbraketq5.th.jpg (http://img222.imageshack.us/my.php?image=a320famaltbraketq5.jpg)

Alternate braking system on the newer (enhanced) A320 Fam.:
http://img152.imageshack.us/img152/2521/a320famaltbrakeenhanceddd1.th.jpg (http://img152.imageshack.us/my.php?image=a320famaltbrakeenhanceddd1.jpg)

[Metro man]

During preliminary cockpit preparation in my company, PNF does a brake check. ie Park brake -OFF, depress pedals, check pressure, release pedals, Park Brake - ON.

On commencing taxi brakes are applied briefly and pressure - zero checked to ensure they have switched over.

Surely the brakes would still have to be checked once moving to ensure they worked, like any other aircraft ?

[Aikon]

Yes, we still do a brake check after engine start to be sure that the green system has taken over the braking.

What I am asking here is the Alternate Brake Check during preliminary cockpit preparation where you check the efficiency of the alternate braking system (absence of "spongy pedals").

So with the new system, you will not get "spongy pedals" anymore?

[Metro man]

From memory, when the preliminary test is performed, on some of our aircraft the needles go all the way to the top of the gauge but on others only to the top of the green arc. Anyone know if this has anything to do with the newer system ?

[idg]

As I understand it:

On early aircraft the alternate brakes are operated by hydraulic lines which actuate the selector valves. IFix Planes' diagrams show this very nicely.

Sometimes air can get into these lines and then pressing the brake pedals will not create the correct movement of the selector valve and thus pressure shown on the triple indicator will be lower on one side than the other or not reach the correct pressure on both sides.

This used to called by Airbus rather confusingly the 'spongy brake check' which I always felt was not very accurate and was trying to hark back to the car braking pedal 'feel' when there was air in the lines.

Normal brakes on old a/c and both Normal and Alt on new a/c are electronically sensed (again refer to those diagrams!) and therefore will always create the demanded pressure.

[Aikon]

Thanks idg.

A very well explanation indeed!

[Dream Land]

I may have it all wrong but I still do an alternate brake check before starting to check the accumulator, if the accumulator is bad, after one brake application, the pressure pretty much drops to 0 PSI. :confused: