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

Interesting note about AA Airbus crash in NYC

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

Interesting note about AA Airbus crash in NYC

Old 5th Jun 2008, 08:27
  #381 (permalink)  
Join Date: Apr 2001
Location: various places .....
Posts: 6,497
Most things are possible, but the concern looks to be a rolling pullup with the increased inertia loading due to tank fuel load .. asymmetric and severe ... I wouldn't really be losing too much sleep about turbulence encounters of the normal kind ...
john_tullamarine is offline  
Old 5th Jun 2008, 15:41
  #382 (permalink)  
Posts: n/a

Stands out for me, in reading the AR is how touchy the Pedals/Rudder interface is. The PIO potential, and guesswork needed by the Pilots. I also want to say I don't understand how the VS could separate before the Rudder. The Rudder is a trimming device, the VS is life itself. If at 1.96x Load Limit the whole deal sheds, then I would think the Rudder would (should) separate at some value less than 1.96. Now it could be that is the case, and separation was Composite fracture related, but that isn't what NTSB concluded relative to fracture stabilisation in less than failure condition.

Old 5th Jun 2008, 20:02
  #383 (permalink)  
Join Date: Apr 2001
Location: various places .....
Posts: 6,497
I would think the Rudder would (should) separate at some value less than 1.96.

.. but that would presume that RF values are constrained either to be constant or follow some hierarchy across a design .. while one could do that it is not a normal design driver.
john_tullamarine is offline  
Old 5th Jun 2008, 20:40
  #384 (permalink)  
Posts: n/a

I don't disagree, however, in reality structures have limit load. To say that the Rudder should be less robust than the VS is intuitive, whether for practical or aerodynamic reasons. I could have worded it differently. The Rudder can create unsustainable loading without itself failing simply because of it's mechanical advantage. So my approach to the result may be a bit cart before Horse. There is a conclusion that can be reached in this accident that does not reflect well on the A/C's control systems. Would you agree that the VS would likely not have separated if the Pilot had resisted his urge to manouver? Was over control the result of a lack of "feel"? The deflection of the Rudder on the annunciator was dramatic, no recovery would need that much Rudder. My sense of this failure is that there was some zone, some "No Man's Land", where the Pilot was "out of the loop" and the A/C didn't guard itself from unnecessary loads, limits. Again, the structure was found to be compromised, but not to and beyond structural failure.

Old 5th Jun 2008, 20:56
  #385 (permalink)  
Join Date: Apr 2001
Location: various places .....
Posts: 6,497
(a) aircraft are not perfect machines.

(b) pilots need to stay within the boundaries of the design (and underlying design standards) - this consideration was at play with this accident

(c) given that pilots (generally) have little knowledge of the design standards, there is a need for both operator and pilot to be cautious, careful, and considerate .. lest misplaced enthusiasm smite them. In a nutshell, unless one knows why the OEM says "do this" or "don't do this" then it is a wise man who follows the guidance ...
john_tullamarine is offline  
Old 5th Jun 2008, 21:04
  #386 (permalink)  
Posts: n/a

Very well then.
Old 5th Jun 2008, 22:57
  #387 (permalink)  
Join Date: May 2002
Location: Brisbane
Age: 72
Posts: 1,406

Let's just hope the truth comes out one day.
airsupport is offline  
Old 20th Apr 2009, 02:38
  #388 (permalink)  
Thread Starter
Join Date: Nov 2004
Location: Here, there, and everywhere
Posts: 697
Interesting how one comes across small similar things years later.


In this accident report about a China Airlines A-300-600 in 1994 for unrelated causes, there was concern about wake turbulence on final. This was the conversation about that concern.

"F/O: It seems quite often to pick up other's wake turbulence here, doesn't it?

CAP: You are right.

F/O: It's strange, is it because of the terrain? Today it seems we are in the wake turbulence from the beginning til the end.

CAP: Step firmly on the rudders. Will be good. It will not sway so hard."

Many crews back then were unaware of the dangers of large rudder inputs even at speeds below Va back then.
punkalouver 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.