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

B744 Ditching Checklist Autobrakes OFF?

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

B744 Ditching Checklist Autobrakes OFF?

Old 27th Feb 2018, 14:27
  #1 (permalink)  
Thread Starter
 
Join Date: Jun 2009
Location: Worldwide
Posts: 33
Likes: 0
Received 0 Likes on 0 Posts
B744 Ditching Checklist Autobrakes OFF?

Can anyone enlighten me why Boeing wants the Autobrakes OFF for a ditching on the B747-400?

The Ditching checklist in the QRH specifically requires the Autobrakes NOT to be armed (checklist item 4), and in the Deferred Items the Autobrakes need to be set to OFF. The ditching itself should be done with the gear up.

Anyone?
NGjockey is offline  
Old 27th Feb 2018, 15:55
  #2 (permalink)  

Avoid imitations
 
Join Date: Nov 2000
Location: Wandering the FIR and cyberspace often at highly unsociable times
Posts: 14,572
Received 412 Likes on 217 Posts
Perhaps they don't want water in the system.....
ShyTorque is online now  
Old 27th Feb 2018, 17:54
  #3 (permalink)  
 
Join Date: Oct 2004
Location: Near sheep!
Posts: 915
Likes: 0
Received 0 Likes on 0 Posts
My guess. This is something to do with a system logic that is triggered by activation of auto braking this logic then being prohibitive towards a successful ditching.

That's me done.
WindSheer is offline  
Old 27th Feb 2018, 20:16
  #4 (permalink)  
 
Join Date: Mar 2006
Location: USA
Posts: 2,513
Likes: 0
Received 0 Likes on 0 Posts
Originally Posted by ShyTorque
Perhaps they don't want water in the system.....
I'd imagine it's more to do with certification. The autobrakes were only tested to a certain depth of water. I doubt wherever you opt to ditch was within the test parameters.
Check Airman is offline  
Old 27th Feb 2018, 20:53
  #5 (permalink)  
 
Join Date: Aug 2007
Location: Utterly insignificant little blue-green planet, unregarded yellow sun, unfashionable end, western spiral arm, Milky Way
Age: 38
Posts: 276
Received 0 Likes on 0 Posts
To prevent aquaplaning.

I’ll get my coat.
semmern is offline  
Old 27th Feb 2018, 21:48
  #6 (permalink)  
 
Join Date: Dec 2001
Location: GA, USA
Posts: 3,196
Likes: 0
Received 23 Likes on 10 Posts
Let me reverse your question.
Why would you want the auto brakes ON? You wouldn’t.
Leaves the mystery as to why it’s even mentioned.
Not my best effort I admit but I’m guessing it has to do with air-ground logic.
The autobrake system allows a specific deceleration rate with info coming from the IRS....
Now I need to open a book
B2N2 is offline  
Old 27th Feb 2018, 21:49
  #7 (permalink)  
 
Join Date: Aug 2007
Location: Seattle KBFI
Posts: 117
Likes: 0
Received 0 Likes on 0 Posts
Like some of the other checklists, the ditching checklist has deferred items on the "Descent Checklist" part. Since it takes the place of the normal descent checklist, they have to show something for an autobrake setting to fill in that spot to keep things the same. So "OFF" just take the place of whatever setting you might otherwise consider or reply to in normal operations.

In terms of system operations, I don't think that it makes a difference at all, if you were to select a brake setting.
bigduke6 is offline  
Old 27th Feb 2018, 23:04
  #8 (permalink)  
Thread Starter
 
Join Date: Jun 2009
Location: Worldwide
Posts: 33
Likes: 0
Received 0 Likes on 0 Posts
I would agree, if it weren't for checklist item 4, which is NOT in the Deferred Items part. Number 4 specifically states "Do NOT arm the autobrake."

Why would Boeing stress that fact if it didn't make a difference systemwise?
NGjockey is offline  
Old 28th Feb 2018, 05:31
  #9 (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
I know the descent "PRALA" items are standard across most of the Boeing fleet, and since such different aircraft most likely utilize differing system logic, the setting of AUTOBRAKE OFF could be to keep the descent checklist consistent as Bigduke suggests.
vapilot2004 is offline  
Old 14th Mar 2018, 01:19
  #10 (permalink)  
 
Join Date: Sep 2016
Location: Australia
Posts: 38
Likes: 0
Received 0 Likes on 0 Posts
bigduke6 is absolutely correct. There's no system consequence by selecting something other than OFF, it's simply there for checklist consistency.
andmiz 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.