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

AF447 Thread No. 3

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

AF447 Thread No. 3

Old 30th May 2011, 21:56
  #801 (permalink)  
 
Join Date: Jul 2009
Location: Not far from a big Lake
Age: 81
Posts: 1,454
Likes: 0
Received 0 Likes on 0 Posts
Gatbusdriver
When stationary the AoA vane, which is pivoted, will be at an angle to the ground. The vane requires airflow over it to give accurate readings, I would therefore humbly suggest that the actual airspeed required for an accurate reading is 60kts.
Gatbusdriver, welcome to the fray. During your training, have you flown in ALT 2 law, or are you on the little Airbus? We are drafting all able bodied bus drivers to try to answer this question.

My personal experience with the USNavy peg, cone and vane type AOA sensors is that they would come alive in a definite breeze, perhaps 10 knots. A vane type that needed 60 knots to be reliable would be a sticky one in my book.
Machinbird is offline  
Old 30th May 2011, 22:13
  #802 (permalink)  
 
Join Date: Jun 2001
Location: US
Posts: 245
Likes: 0
Received 0 Likes on 0 Posts
WRT the Spiegel article ... Some statements in the article are incorrect, however, for instance the claim that the pax were held in their seats only by their seatbelts. At a steady rate of descent, the pax would experience 1 G.
True -- once the rate of descent stabilized at some -10000fpm. But shortly before that, they'd actually been climbing, so at some point there was a heck of a vertical acceleration, and for that period the description would likely hold true.

I can only hope that that moment passed quickly, because it must have been terrifying.

Last edited by spagiola; 30th May 2011 at 22:28.
spagiola is offline  
Old 30th May 2011, 22:22
  #803 (permalink)  
 
Join Date: Jun 2009
Location: Bedford, UK
Age: 70
Posts: 1,319
Received 24 Likes on 13 Posts
Well if gaining vertical speed the seat will push beyong 1g to accelerate the Pax. When the vertical acceleration becomes negative the seat will push up at less than 1g. If the vertical acceleration exceeds 1g down, and only then, will Pax leave their seats and be pushed down by the seatbelt.
Mr Optimistic is offline  
Old 30th May 2011, 22:45
  #804 (permalink)  
 
Join Date: Nov 2001
Location: Los Angeles
Posts: 26
Likes: 0
Received 0 Likes on 0 Posts
In French assister means to witness or be present at an event.
Garrison is offline  
Old 30th May 2011, 23:04
  #805 (permalink)  
 
Join Date: Jul 2009
Location: Not far from a big Lake
Age: 81
Posts: 1,454
Likes: 0
Received 0 Likes on 0 Posts
In referring to the Speigel article.
Hüttig is not without bias in that he provides technical assistance to the victim's families and thus probably has economic interests at play.

The description of the conditions inside the aircraft on the way down are a bit overblown. Although the nose did get pretty high in the air, the maneuvers suggest that cabin environment was close to 1 g. Probably more unsettling would have been the wing drops that the aircraft experienced. Not so bad as a roller coaster ride though.

Biggest fault with the Spiegel article is that the aircraft was "doomed" when the trim ran up to 13 degrees. If the crew had run it back down to near normal, this long thread would probably not exist and there would likely not exist a victim's family group.

There are a lot of training issues sticking out of this mess, and not all of them appear to have originated with AF.
Machinbird is offline  
Old 30th May 2011, 23:19
  #806 (permalink)  
 
Join Date: Jun 2009
Location: Paris
Posts: 691
Likes: 0
Received 0 Likes on 0 Posts
Originally Posted by Garrison
In French assister means to witness or be present at an event.
The meaning of assister is related to context.
1. être présent (participer) = to be present at something
2. aider (seconder, secourir, concourir, dépanner) = to help someone.
Where it is quoted from?
takata is offline  
Old 30th May 2011, 23:32
  #807 (permalink)  
 
Join Date: Nov 2001
Location: Los Angeles
Posts: 26
Likes: 0
Received 0 Likes on 0 Posts
"Entre 1 h 59 min 32 et 2 h 01 min 46, le commandant de bord assiste au briefing entre les deux copilotes..."

from the BEA interim report
Garrison is offline  
Old 30th May 2011, 23:34
  #808 (permalink)  
 
Join Date: Jul 2009
Location: UK
Posts: 134
Likes: 0
Received 0 Likes on 0 Posts
Originally Posted by takata
The meaning of assister is related to context.
1. être présent (participer) = to be present at something
2. aider (seconder, secourir, concourir, dépanner) = to help someone.
Where it is quoted from?
The comment in the BEA statement which was translated into English as "the Captain attended the briefing between the two co-pilots" - maybe trying to read too much into the wording - would expect the Captain to lead the briefing? As JD-EE pointed out above maybe this statement just confirms there was a formal handover as required, nothing more.
sensor_validation is offline  
Old 30th May 2011, 23:39
  #809 (permalink)  
 
Join Date: Aug 2007
Location: London, New York, Paris, Moscow.
Posts: 3,632
Likes: 0
Received 0 Likes on 0 Posts
rubbish, but, I will persist none the less
Absolutely.
glad rag is offline  
Old 30th May 2011, 23:41
  #810 (permalink)  
 
Join Date: Nov 2001
Location: Los Angeles
Posts: 26
Likes: 0
Received 0 Likes on 0 Posts
Machinbird:
Biggest fault with the Spiegel article is that the aircraft was "doomed" when the trim ran up to 13 degrees. If the crew had run it back down to near normal, this long thread would probably not exist and there would likely not exist a victim's family group.
Agree entirely. If it's true about the Captain recognizing that the airplane was stalled, then everything comes down to that trim wheel -- unless, of course, the A330 turns out to have an unrecoverable deep stall mode, which I very much doubt. But if he said that as reported by Spiegel, why did the PF not react with an AND command? Oh, maybe that's where the AND command does occur -- but is aborted because of the stall warning. What a mess!
Garrison is offline  
Old 30th May 2011, 23:46
  #811 (permalink)  
 
Join Date: Mar 2002
Location: Seat 1A
Posts: 8,548
Received 73 Likes on 42 Posts
The vane requires airflow over it to give accurate readings,
Does it? How about a system where if it is not giving a reading within 16°AoA, it signals a stall? Say it is pointing "to the ground" whilst the aircraft is airborne. What do you reckon the crew needs to know? That aircraft isn't flying ie it's stalled. It doesn't matter where the vane is actually pointing.

But in this case, just when the crew needed the most "reminding" (and who would have not been confused: VSI off the clock going down, but with speed tapes on nothing, "knowing" that only a couple of minutes before they were giving duff gen), the stall warning silenced. Had it kept screaming at them, maybe their confusion would have eventually been overcome and one of them would have stuffed the nose down to recover the thing.
Capn Bloggs is offline  
Old 30th May 2011, 23:53
  #812 (permalink)  
 
Join Date: Jul 2009
Location: UK
Posts: 134
Likes: 0
Received 0 Likes on 0 Posts
Originally Posted by Machinbird
...
My personal experience with the USNavy peg, cone and vane type AOA sensors is that they would come alive in a definite breeze, perhaps 10 knots. A vane type that needed 60 knots to be reliable would be a sticky one in my book.
For lots of detail on the AoA vanes see the Perpignan crash report. The vane may indeed generate a "local angle of attack" but "As the fuselage disturbs the flow of air, these measurements
have to be corrected to obtain the aeroplane angle of attack." I wonder if its the compensations that limit the use at lower speed, but then where does the speed come from?
sensor_validation is offline  
Old 30th May 2011, 23:55
  #813 (permalink)  
 
Join Date: Jun 2009
Location: France
Age: 83
Posts: 41
Likes: 0
Received 0 Likes on 0 Posts
Garrison: Oh, maybe that's where the AND command does occur -- but is aborted because of the stall warning. What a mess!
This does not look like good logic: if they have evidence that the ac is stalled while there is no stall warning, they should ignore it when it sounds again.
milsabords is offline  
Old 31st May 2011, 00:00
  #814 (permalink)  
 
Join Date: May 2011
Location: Melbourne
Posts: 2
Likes: 0
Received 0 Likes on 0 Posts
Abnormal Law Warnings or Messages

I previously asked the following questions:
  1. If/when the plane kicked into Abnormal Law, what warning or message would have been visible or audible to the pilots?
  2. Why was there an ACARS message about the transition to Alternate Law, but no ACARS message about any other change in Law (e.g. Abnormal or Direct)?
mm43 directed me to A340 / A330 Control: flight & laws
but having read through that, I must be blind because I don't see the answers to my questions!

It seems that whether or not the plane was in Abnormal Law (and hence had no autotrim - making the THS "frozen" at 13 degrees unless manually adjusted) is important in understanding whether the pilots had a chance of pulling out of the stall once they started putting the nose down (after the captain returned to the cockpit).

So far, it sounds like we are inferring that it was in Abnormal Law, owing to the AoA and speed crossing the specified thresholds, but can this be shown explicitly through a message or recording? And if not, why not? It may be an important point, so it would be nice to have certainty. There appears to be no ACARS message about any law other than Alternate - does that mean that Abnormal Law doesn't generate an ACARS message...?

The other question, which some others have touched on, is whether the pilots knew they were in manual trim mode. From the "flight & laws" link above, if in Direct Law the pilots will see "USE MAN PITCH TRIM" on the PFD. Is that also the case in Abnormal Law (it doesn't explicitly say in that link)?
falcor is offline  
Old 31st May 2011, 00:20
  #815 (permalink)  
 
Join Date: May 2010
Location: Boston
Age: 73
Posts: 443
Likes: 0
Received 0 Likes on 0 Posts
Sensor validation:
For lots of detail on the AoA vanes see the Perpignan crash report. The vane may indeed generate a "local angle of attack" but "As the fuselage disturbs the flow of air, these measurements
have to be corrected to obtain the aeroplane angle of attack." I wonder if its the compensations that limit the use at lower speed, but then where does the speed come from?
Th 60KT limit may also be an almost arbitrary "safe" limit withe the rational that if airspeed is that low you are not flying anyway?
This would also help eliminate spurios alarms durinfg landing.
MurphyWasRight is offline  
Old 31st May 2011, 00:21
  #816 (permalink)  
 
Join Date: Jun 2009
Location: Paris
Posts: 691
Likes: 0
Received 0 Likes on 0 Posts
Originally Posted by sensor_validation
The comment in the BEA statement which was translated into English as "the Captain attended the briefing between the two co-pilots" - maybe trying to read too much into the wording - would expect the Captain to lead the briefing? As JD-EE pointed out above maybe this statement just confirms there was a formal handover as required, nothing more.
Right. In this context, "assister" only means that he was present during the briefing. He could have either contributed to it or remained totally passive, it doesn't tell it.

You guys are again focusing on press "leaks" which doesn't look more "informed" than all the previous ones. The statement that FO2 (Pierre-Cédric Bonin) was the PF is clearly doubtful.
takata is offline  
Old 31st May 2011, 00:35
  #817 (permalink)  
 
Join Date: Jan 2008
Location: Herts, UK
Posts: 748
Likes: 0
Received 0 Likes on 0 Posts
Originally Posted by Garrison
Why is there all this talk about being "locked in" a "super stall"? If the stick had been held forward and the trim wheel rolled AND and the plane had failed to recover, this would make sense; but none of that happened.
I've got to say Garrison, I feel that's likely true.... especially if less than TOGA thrust was also selected.

It is a very remote possibility I suppose, that the PF was under 'some impression', at a base response level, that recovery from a stalled condition does not require a consistent and nose-down pitch .

If so, it's highly unlikely that Captain M. Dubois would have followed that course of action, and must have realised having made his way to the cabin, pretty well what sort of situation they were in, irrespective of instrumentation

Last edited by HarryMann; 31st May 2011 at 01:14.
HarryMann is offline  
Old 31st May 2011, 01:04
  #818 (permalink)  
bearfoil
Guest
 
Posts: n/a
howdy. PF gets Stall Warnings; a warning is not the same as the real deal.
His training (prior to AB "Stall Warning Recovery" "modification") was to fly through the warning losing little if any altitude and use power to accelerate.

A warning given at the break would not be a warning, it would be an annunciation. Having never experienced a full stall, he would likely not anticipate it by definiton, as he has had no training how to recover it, so all that would happen is an unanchored 'anxiety'. In other words, one flaw in "Display" is a gotcha without recourse. Not very nice, Miss.
 
Old 31st May 2011, 01:10
  #819 (permalink)  
 
Join Date: Mar 2009
Location: Connecticut
Posts: 79
Received 0 Likes on 0 Posts
I have thought from the beginning that a deep stall was very unlikely, but it appears that the pilot flying managed to unknowingly stabilize the airplane in a very similar flight condition. I don't know why he changed from a perfectly good pitch and power setting to get so slow, but at that low a speed, the engines were probably providing a goodly amount of nose-up pitch (along with the stabilizer trim automatically coming in to "help" him keep the nose up) so the normal pitch down occurring at stall might not be evident. Other than airspeed, which he has reason not to trust; angle of attack, which isn't displayed?; and an aural stall warning, which is apparently inhibited, how else does he know that he's stalled? What he knows is he has the throttles pushed up, the airplane pitched to 15 degrees or thereabouts (16.5 degrees) which is a familiar number for powering out of a problem, and his rate of descent is at the bottom of the tape and the altimeter is a blur, both high-order attention getters. Who among us wouldn't be confused as to why the airplane was descending instead of climbing and desperately pulling back on the stick to make it climb like it always has before?
Tailspin Turtle is offline  
Old 31st May 2011, 01:26
  #820 (permalink)  
bearfoil
Guest
 
Posts: n/a
So his forward stick and decrease in AoA may have gotten him on the way to recovery, but do we know the decrease in AoA was not just the a/c dropping her nose after stalling?

If the Captain did re-enter and shout, or command, likely it would have been something along the lines that precipitated a "just about" recovery.

You know, this discussion, read with patience, will eventually get to within 90 per cent of the actuals.
 

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.