Go Back  PPRuNe Forums > Flight Deck Forums > Tech Log
Reload this Page >

A320 Brakes: Norm + Altn Fault

Tech Log The very best in practical technical discussion on the web

A320 Brakes: Norm + Altn Fault

Old 20th Feb 2015, 08:50
  #1 (permalink)  
Thread Starter
 
Join Date: Sep 2004
Location: France
Age: 47
Posts: 161
Likes: 0
Received 0 Likes on 0 Posts
A320 Brakes: Norm + Altn Fault

FCOM says : Parking brake only.
Why braking on accumulator is not available ? I would appreciate if anyone can shed light on this
(Considering an electrical failure and not HYd)

Also on Systems description , it says : alternate braking without antiskid on accumulator is fully controlled by the ABCU. Does that mean that in case of ABCU failure , accu braking is lost?

On old 320's , with antiskid nosewheel steering switch to OFF , braking on accumulator was available.

On new 320's with ABCU fault +Norm brake fault would I be able to brake on accu by putting anti skid and nosewheel steering switch to OFF?
Citation2 is offline  
Old 20th Feb 2015, 11:31
  #2 (permalink)  
 
Join Date: Jun 2007
Location: Wanderlust
Posts: 3,403
Likes: 0
Received 0 Likes on 0 Posts
Citation2
Latest 1.8 std. FCOM says what you say. I am unable to understand why. I checked another manual which gives procedures according to manufacturers serial numbers where Norm+Alt fault is not mentioned at all. I don't see any reason why accumulator braking should not be available.

Last edited by vilas; 20th Feb 2015 at 11:52.
vilas is offline  
Old 21st Feb 2015, 02:27
  #3 (permalink)  
 
Join Date: Feb 2015
Location: Europe
Posts: 4
Likes: 0
Received 0 Likes on 0 Posts
I just checked FCOM (available Braking Schematic): "Depending on the brake pedalsí demand, the ABCU controls the alternate brake selector and the alternate servovalves."

Both valves are in line and supplied from yellow system pump and accumulators through the same line.
Only parking brake control valve bypass those 2 valves and can transfer either normal yellow pressure or accu pressure to the brakes.

It looks like that if you can't control those 2 valves, and you can't without ABCU (alternate braking fault), the only solution is parking brake. All that of course only in combination with Normal brake fault.

Following that, in case of ABCU and Normal braking failure you will not get much by putting nosewheel steering switch to OFF because everything, related to brakes, that it controls is already unusable.
Drifter72 is offline  
Old 22nd Feb 2015, 07:44
  #4 (permalink)  
 
Join Date: May 2000
Location: Glorious West Sussex
Age: 76
Posts: 1,020
Likes: 0
Received 0 Likes on 0 Posts
NORM brake fault ... it won't work.
ALTN brake fault .. It won't work.
NORM + ALTN fault .. Neither works.

Only switch which will work the brakes is PARK BRK.
This in not to do with hydraulics, but electronic or mechanical faults.
TyroPicard is offline  
Old 22nd Feb 2015, 14:47
  #5 (permalink)  
 
Join Date: Mar 2009
Location: Prague
Age: 51
Posts: 60
Likes: 0
Received 0 Likes on 0 Posts
On enhanced 320 you have only electrical signal from brake pedals feeding ABCU or BSCU. There is no other way to control normal servo valves or direct drive valves than signal from these computers. Accumulator as pressure source is still available for alternate braking controlled by DDV if ABCU works or for ultimate emergency braking via park brake. You are all correct,but probably not happy with this brake system design...

Last edited by LEVEL600; 22nd Feb 2015 at 15:21.
LEVEL600 is offline  
Old 22nd Feb 2015, 15:26
  #6 (permalink)  
Thread Starter
 
Join Date: Sep 2004
Location: France
Age: 47
Posts: 161
Likes: 0
Received 0 Likes on 0 Posts
Thank you all for this clarification. I would have expected more redundancies in the system design .
Citation2 is offline  
Old 23rd Feb 2015, 06:28
  #7 (permalink)  
 
Join Date: Mar 2005
Location: Uh... Where was I?
Posts: 1,338
Likes: 0
Received 0 Likes on 0 Posts
If something fails, it fails. It doesn't work. If both normal and alternate are faulty there are reasons for both failures and they are not available. End of the story.

However, the system is designed in such a way that you can still use the "ultimate" means to brake the airplane if you still have some pressure in the ACCU, that is, with the parking brake. I think it is a good system!
Microburst2002 is offline  
Old 23rd Feb 2015, 22:52
  #8 (permalink)  
 
Join Date: Apr 2004
Location: Kappis
Posts: 66
Likes: 0
Received 0 Likes on 0 Posts
Just out of interest.

Does anybody know, why you only have accumulator braking with emergency elec config? ABCU is powered, as well as yellow hydraulics. What's the problem giving us alternate brake without antiskid but with yellow hydraulic pressure?
Any ideas?
WhiteKnight is offline  
Old 24th Feb 2015, 02:26
  #9 (permalink)  
 
Join Date: Mar 2009
Location: Prague
Age: 51
Posts: 60
Likes: 0
Received 0 Likes on 0 Posts
Alternate braking uses both accu and yellow syst. pressure,whichever is higher regardless of electrical configuration, I think. During elec emergency you loose power for BSCU which perform antiskid and this is reason for pressure limitation to 1000 psi.

Last edited by LEVEL600; 24th Feb 2015 at 02:41.
LEVEL600 is offline  
Old 24th Feb 2015, 07:51
  #10 (permalink)  
 
Join Date: May 2000
Location: Glorious West Sussex
Age: 76
Posts: 1,020
Likes: 0
Received 0 Likes on 0 Posts
WhiteKnight
You are making assumptions...
Where does it say ACCU PRESS ONLY? Where does it say NORMAL BRK INOP or ALTN BRK INOP?
All FCOM says is MAX BRK PR ... 1000PSI
and in INOP SYS......ANTISKID

Keep up at the back!
TyroPicard is offline  
Old 24th Feb 2015, 10:54
  #11 (permalink)  
 
Join Date: Jun 2007
Location: Wanderlust
Posts: 3,403
Likes: 0
Received 0 Likes on 0 Posts
WhiteKnight
It is alternate braking without antiskid. It is not accumulator braking.
vilas is offline  
Old 25th Feb 2015, 10:24
  #12 (permalink)  
Thread Starter
 
Join Date: Sep 2004
Location: France
Age: 47
Posts: 161
Likes: 0
Received 0 Likes on 0 Posts
This is absolutely correct , notice the difference in G+Y summary it states clearly : "BRK Y ACCU PR only" whereas in EMER ELEC it says : " Alternate without antiskid "

This could also happen in combined failures like G sys lo press + DC ESS bus. With G you would loose Normal brake , with DC ESS you would loose ALTN brake.
Citation2 is offline  

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service

Copyright © 2024 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.