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

Changing auto brake setting during roll out

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

Changing auto brake setting during roll out

Old 4th Nov 2018, 12:55
  #41 (permalink)  
Gender Faculty Specialist
 
Join Date: Mar 2002
Location: Stop being so stupid, it's my turn
Posts: 1,702
I did it yesterday. 3 would have required a large backtrack due to WIP at one of the exits and max would have meant stopping too soon. So I went from max to 3. It worked, we kept the advantage of auto brakes and if you hadn't guessed by now I am still alive.
Chesty Morgan is online now  
Old 4th Nov 2018, 13:41
  #42 (permalink)  
Gender Faculty Specialist
 
Join Date: Mar 2002
Location: Stop being so stupid, it's my turn
Posts: 1,702
Of course.
Chesty Morgan is online now  
Old 4th Nov 2018, 14:48
  #43 (permalink)  
 
Join Date: Dec 2014
Location: Crewbunk
Posts: 38
Originally Posted by Nightstop View Post
I was a passenger in a FR 738 some time back when the crew inadvertently selected what I believe to be RTO during the landing roll out. The sudden decelaration was enough to propel me into the seatback in front, I sustained a minor injury to my right hand while trying to save myself. Very unpleasant and no explanation from the flightdeck. Senior Cabin Crew was in the flightdeck during disembarkation asking WTF was going on..
No . Your wrong. Its not possible to arm RTO while in the air.
Cloudtopper is offline  
Old 5th Nov 2018, 09:09
  #44 (permalink)  
 
Join Date: Jan 2006
Location: US
Posts: 2,069
Originally Posted by Chesty Morgan View Post
I did it yesterday. 3 would have required a large backtrack due to WIP at one of the exits and max would have meant stopping too soon. So I went from max to 3. It worked, we kept the advantage of auto brakes and if you hadn't guessed by now I am still alive.
So you think using MAX right after landing, and later reducing to 3, was better for the aircraft than using 3 and then increasing brake pressure after your speed had decreased??
misd-agin is offline  
Old 5th Nov 2018, 10:20
  #45 (permalink)  
Gender Faculty Specialist
 
Join Date: Mar 2002
Location: Stop being so stupid, it's my turn
Posts: 1,702
I used the aircraft the way it was designed to be used.

Are you implying that using MAX is bad for an aeroplane?
Chesty Morgan is online now  
Old 5th Nov 2018, 10:23
  #46 (permalink)  
 
Join Date: Nov 1998
Location: United Kingdom
Posts: 1,492
Originally Posted by Cloudtopper View Post
No . Your wrong. Its not possible to arm RTO while in the air.
I didn’t say “in the air”, the event was during the roll out after landing.
Nightstop is offline  
Old 5th Nov 2018, 12:32
  #47 (permalink)  
 
Join Date: Sep 2012
Location: Europe
Posts: 167
Originally Posted by Chesty Morgan View Post
I used the aircraft the way it was designed to be used.

Are you implying that using MAX is bad for an aeroplane?
By your logic in the second line, aren't you now implying manual braking is not how the plane is designed to be used and bad for the airplane? I'm sure you managed fine and are still alive. Personally I'd still prefer to keep my attention outside and hand and feet in standard positions instead of going for knobs/buttons during rollout. To each their own.
Intrance is offline  
Old 5th Nov 2018, 12:51
  #48 (permalink)  
Gender Faculty Specialist
 
Join Date: Mar 2002
Location: Stop being so stupid, it's my turn
Posts: 1,702
Originally Posted by Intrance View Post
By your logic in the second line, aren't you now implying manual braking is not how the plane is designed to be used and bad for the airplane?
The use of autobrake reduces brake wear and minimises brake temperatures whilst still achieving what you want to achieve. Brakes are obviously designed to be used without autobrake or brake pedals wouldn’t be fitted and whilst manual braking is not necessarily bad for the aeroplane it is, categorically, not as efficient as using autobrakes.
Chesty Morgan is online now  
Old 5th Nov 2018, 21:17
  #49 (permalink)  
 
Join Date: May 2000
Location: Seattle
Posts: 3,123
Originally Posted by Chesty Morgan View Post
The use of autobrake reduces brake wear and minimises brake temperatures whilst still achieving what you want to achieve. Brakes are obviously designed to be used without autobrake or brake pedals wouldn’t be fitted and whilst manual braking is not necessarily bad for the aeroplane it is, categorically, not as efficient as using autobrakes.
Apparently you are not familiar with the concepts behind your first statement, but are only trying to justify a practice that is not supported anywhere that I have seen.

First, using MAX autobrakes when they are not needed will NOT minimize brake temperature or brake wear. To minimize temperature, you use as little braking as possible while the airplane is at high speed. As others have pointed out, in your case you should have started with Autobrakes 3, then increased pressure after the airplane had slowed down.

Second, the practice of changing the Autobrake setting during the landing roll is not supported in any Boeing document that I have seen, and was actively discouraged - effectively prohibited - at my airline. Trying to move a switch, that is unnecessary and which may not remain in the newly selected position, during the landing roll is a major distraction at best and a dangerous risk if the switch solenoid happens to release or fail during the attempt. Use of the brake pedals to manually modulate brake pressure is the proper way to override the Autobrakes setting.

From the Boeing 747-400 Flight Crew Training Manual:
Use an appropriate autobrake setting or manually apply wheel brakes smoothly with steadily increasing pedal pressure as required for runway condition and runway length available. Maintain deceleration rate with constant or increasing brake pressure as required until stopped or desired taxi speed is reached.
. . .

For normal landing conditions, autobrakes 2 or 3 optimizes brake wear, passenger comfort, and stopping performance.
. . .

To minimize brake temperature build-up, use the following landing techniques:
. . .
use an autobrake setting, consistent with reported runway conditions, that will result in the use of all available runway length. A stopping distance safety margin should be used in accordance with airline policy. Although the autobrakes initially increase brake temperature, the brake contribution is minimized after reverser deployment
Intruder is offline  
Old 5th Nov 2018, 21:37
  #50 (permalink)  
Gender Faculty Specialist
 
Join Date: Mar 2002
Location: Stop being so stupid, it's my turn
Posts: 1,702
Well my dear MAX was the minimum needed to ensure we made the exit. But thanks for your input on a flight you have no knowledge of.

And, FYI, autobrake will minimise brake wear when compared to manual braking. A concept I assume you are aware of.
Chesty Morgan is online now  
Old 5th Nov 2018, 21:44
  #51 (permalink)  
 
Join Date: Aug 2000
Location: Almost horizontal
Posts: 111
B737 bulletin CEX-5 certainly hints at not changing the autobtake setting during the landing roll as the RTO mode CAN be inadvertently activated (a service bulletin provides a fix to the RTO logic that allows this).
Too Few Stripes is online now  
Old 6th Nov 2018, 00:05
  #52 (permalink)  
 
Join Date: Sep 2012
Location: Europe
Posts: 167
Still not quite sure why you would prefer fiddling with knobs when your focus could be outside, all limbs on the necessary controls and ready to react to anything non-standard. Again, to each their own.

Pretty sure in the near future, we'll have pilots who have no idea what it feels like to slow a plane down with manual braking.
Intrance is offline  
Old 6th Nov 2018, 11:02
  #53 (permalink)  
 
Join Date: Nov 2000
Location: Netherlands
Posts: 247
This discussion is such BS. The airplane has the ability to change AB setting during roll out. No, it is not described in the FCOM. Neither is the use of the lights!! Airmanship comes into play!! When transitioning from AB to manual braking often times you have to increase pressure on the pedals beyond the braking pressure being applied by the AB system giving an uncomfortable jolt in braking when transitioning!! I find it much more comfortable to apply brake pressure just before the point where the AB system kicks off and then asking the PM to select AB off, this gives a much smoother transition to manual braking!! I have on occasion asked the PM to increase the brake setting to a higher setting to make an exit. Again this is usually a smoother transition than applying manual brake.!!

the notion that you could inadvertently select RTO is absolute nonsense!! The RTO mode won’t arm unless speed is less than 60kts and then will only engage with speed above 90kts! How is this going to happen during landing!!

Yes, I have spent the first half of my career flying airplanes without AB and I do now how to brake without AB. However, the system is there, use it! And NO, I don’t change it myself!! I simply ask the PM to change it “set autobrake off” while looking outside!! DUH!!

And yes, I have used AB max as well! granted, probably 3 or for times, but flying a heavy 900 sometimes that’s what needed! Shortest runways I fly to are ABZ and AMS rwy22 under stormy conditions. AB 3 won’t be enough with the 15% increase( it is there for a reason!). Simple PA to the PAX, ” due to WX conditions/ short runway we will be landing on today we will use a higher braking setting, please make sure that your seatbelts are securely fastened, please don’t be alarmed, it is normal under the circumstances to guarantee maximum safety”, done!!!!

some of the comments I read here, really, are you that insecure about your flying skills that you have to constantly propagate about manual skills versus using the automatics the manufacturer build into the airplane?

Last edited by flyburg; 6th Nov 2018 at 11:50.
flyburg 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 © 2018 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.