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

Disengaging autobrakes in the 737 Classic

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

Disengaging autobrakes in the 737 Classic

Old 3rd Mar 2018, 12:00
  #1 (permalink)  
Thread Starter
 
Join Date: Jun 2000
Location: Australia
Posts: 4,189
Likes: 0
Received 19 Likes on 6 Posts
Disengaging autobrakes in the 737 Classic

I read an A330 incident report where the pilot during an abort tried to disengage the autobrake system which was on MAX (RTO in the 737?) by depressing the brake pedals. He had great difficulty doing so. The report stated that in the A330, the amount of pedal deflection required to disconnect the autobrakes from the MAX setting, is 2.5 times that required for disengaging the autobrakes from LOW setting.

Does that also apply to the Boeing 737 series because there is nothing I could find about that in the various manuals?
Centaurus is online now  
Old 3rd Mar 2018, 15:15
  #2 (permalink)  
 
Join Date: Jan 2014
Location: N5109.2W10.5
Posts: 720
Likes: 0
Received 0 Likes on 0 Posts
The report stated that in the A330, the amount of pedal deflection required to disconnect the autobrakes from the MAX setting, is 2.5 times that required for disengaging the autobrakes from LOW setting.
Why not simply stow the speed brakes?
Goldenrivett is offline  
Old 3rd Mar 2018, 16:08
  #3 (permalink)  
 
Join Date: Jan 2012
Location: USA
Posts: 39
Likes: 0
Received 0 Likes on 0 Posts
Originally Posted by Centaurus
I read an A330 incident report where the pilot during an abort tried to disengage the autobrake system which was on MAX (RTO in the 737?) by depressing the brake pedals. He had great difficulty doing so. The report stated that in the A330, the amount of pedal deflection required to disconnect the autobrakes from the MAX setting, is 2.5 times that required for disengaging the autobrakes from LOW setting.

Does that also apply to the Boeing 737 series because there is nothing I could find about that in the various manuals?
Disengaging auto brakes with manual braking requires applying heavier manual braking than the auto brakes are applying. So it makes sense that the pedal deflection would be higher for higher auto brake settings.
CallmeJB is offline  
Old 5th Mar 2018, 09:01
  #4 (permalink)  
 
Join Date: Aug 2005
Location: fairly close to the colonial capitol
Age: 55
Posts: 1,693
Likes: 0
Received 0 Likes on 0 Posts
For the classics, over the range of AB 1 to 2, there is no difference in the pedal pressure required to trip the auto brakes OFF. I don't know the exact number, but the trip pressure is somewhat lower than the lowest setting (1) brake pressure (1250psi).
vapilot2004 is offline  
Old 5th Mar 2018, 15:38
  #5 (permalink)  
 
Join Date: Jan 2000
Location: FL410
Posts: 860
Likes: 0
Received 0 Likes on 0 Posts
To cancel the autobrake on the landing roll with toe brakes you must apply a brake pressure in excess of 800psi (ie less than that required for autobrake 1).

For the techies amongst us:

Autobrake Selector / Max Pressure at Brakes (PSI) / Deceleration Rate (ft/secē)
  1. 1 / 1250 / 4
  2. 2 / 1500 / 5
  3. 3 / 2000 / 7.2
  4. Max / 3000 / 12 (below 80kts)
  5. Max / 3000 / 14 (above 80kts)
  6. RTO / Full / Not Controlled

There is an "on ramp" period where autobrake pressure is applied over a period of time. Approximately 750psi is applied in 1.75 sec, then the pressures above are reached in another 1.25sec for autobrakes 1, 2, or 3 and approx. 1.0 sec for autobrake MAX.
Skyjob 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.