A320family braking logic question

[Uber05]

Hi there, my first post in this excellent forum. It’s a tech question. I was wondering... how does the FWC on the A320 family inform the crew about a shifting from normal green braking to alternate yellow braking - let's say due to a failure detected by the BSCU ( not necessarily a failure INSIDE the BSCU which would be presented as BRAKES: SYS 1 (2) FAULT )? Does the system inform the crew only with the memo ALTN BRK on Ecam WHEEL page ? No single chimes ? No audio warnings at all ? I mean I could go landing expecting to be on green electronic braking and instead I could find me braking on yellow electronic braking ONLY by checking the two alternate brake pressure indicators rising or the memo ALTN BRK on WHEEL PAGE during my landing roll ? Thanx for any help.

Manuel

[Cityliner]

Usually you get an Information on the ECAM about any abnormal.
The Statuspage will be automaticily displayed after selecting Flaps one.
I'm not 100% sure but i think when on alternate braking sys the Autobreak is inop.


Edit:
After reading your Post again I thought my answer is rather less helpfull.
I think any failure in the BSCU or detected by the BSCU must be presented on the ECAM. The status page must advice that alternate Brakes are active.
I can' t think about any failure which may hide that you are losing green Brakes.

[westinghouse]

hi,

the instance what you referring to is Alternate Braking without Anti-skid.

normally occurs when auto brake and anti-skid is inop or aniti-skid is deactivated ( anti-skid switch is off or hydraulic G+B low pressure). this appilies to the 330.

the only way you know when to look at the needles is when you have one of these failures and on the ecam inop coloumn it will state normal braking+ alternate braking not available.

if it was a brakes- anti skid fault you get an ecam warning mentioning to modulate the brake pressure to 1000psi.
if its a hydraulic fault its mentioned in the summary as well as the inop coloumn.

hope this was helpfull.

[mcdhu]

Uber05 - welcome to the forum.
A good example might be (A319):
Brakes: Normal Brake Fault (FCOM 3.2.32)
The Ecam will tell you the following: ''Crew Awareness'' ie there is nothing you can do about it, Apply the landing distance procedure, Altn Y Brake with Anti skid, and Cat 2 only.
Under 'Inop Systems' will be: Cat3, Normal Brake and Autobrake.
So, because the braking system is well monitored by the 'system', you will get full information on where you are and what to do.
Don't forget that the ''Loss of Braking'' procedure (on the runway) is a memory item.
Cheers,
mcdhu

[IFixPlanes]

Maybe this helps:
http://img256.imageshack.us/img256/9153/normalbrakingfault01ud3.th.jpg (http://img256.imageshack.us/my.php?image=normalbrakingfault01ud3.jpg)...http://img205.imageshack.us/img205/3739/normalbrakingfault02ti4.th.jpg (http://img205.imageshack.us/my.php?image=normalbrakingfault02ti4.jpg)


Ingo

[sergejv]

If green pressure drops:
- Yellow pressure takes over automatically,
anti-skid is available and nose wheel steering
is lost.
- Auto brake cannot be armed.

"ALTN BRK" indication appears if the braking system
is in alternate mode.

[Jetset320]

Best be careful with generic statements.

Newer aircraft now have ABCU (.....1000psi limit taken care of.....) as well as Nosewheel Steering now normally on the yellow hydaulic system. Can get confusing unless talking about a specific model!

[Uber05]

Thanx alot guys for the answers and the help! So I guess that most of the time the system informs the pilot about the switching from green to yellow by an ecam warning and the wheel page ALTN BRK message. But not in the case that I am trying to understand. I'll share it with you: autobrake not selected ( manual braking ), after touch down and an ecam BRAKES : AUTO BRK FAULT, PF starts braking and there is no braking. PNF notices in the triple indicator the yellow pressure rising on both sides while the PF is pressing the pedals. But there is still no braking. So we have here two weird things : 1) The system shifted from green to yellow without notification to the crew. 2) Pressure from yellow system did not reach the brakes, it surely reached the alternate servovalve ( antiskid ) as indicated by the triple indicator.

This is what I'm trying to figure out.
Thanx for any help.

[sergejv]

1.BSCU with ADIRU data control breaking systems.
Alternate braking is automatically obtained :
- in case of green pressure loss,
- if a failure occurs on the normal braking system during operation or BSCU test.
Also you can switch manual to Alternate by set A/SKID & N/W STRG Switch to Off.

When on Alternate and Yellow Eng pump is inop the accumulator only supplies the brakes.
With the accumulator pressure only, a maximum of 7 full brake pedal applications can be performed.

[Thunder08]

Hi Jetset320!!!
What model are you talk about????:confused:

[Jetset320]

Perhaps 'version' would have been a better word!

Newer versions (~2004+) have some revised systems including alternate braking, which is now controlled through the ABCU (Alternate Braking Control Unit). Essentially the main difference is that when using the accumulator, the ABCU restricts pedal pressure to 1000psi max (it does this by itself....no more "decrease left" or "decrease right"!).

Another difference effecting this topic is that these versions get nosewheel hydaulic from the yellow system rather than the green in older versions.

[tarik123]

Is it possible to lose normal and alternate braking without any warning?
also is it possible for the brakes to work normally when brake pedals
are depressed and then at lower speeds be lost without warning although
brake pedal pressure was maintained?

[Thunder08]

Thanks buddy!
I really didn't know about that.:bored:
Our newest Acft is from the year 2003:(
All our fleet uses BSCU:{ (unfortunately)
All the best...
T8