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AF 447 Thread No. 5

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AF 447 Thread No. 5

Old 11th Jul 2011, 23:14
  #121 (permalink)  
 
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Cool

Hi,

So the basic question of the investigation is to address the real security issues, not to find who seems "guilty" of what.
As for the level of civil responsability to be shared between the manufacturer, the company or the crew, honestly, this should be left to the court to decide
Academic blah blah
I have not to learn you the fact that the real security issues will point to some actors
And the court will point exactly the same actors with some nuances ... that's a lawyers game to be performed .. for the spectators we are
Rarely a court of justice will point responsibilities to actors not already involved in the security issues
It's granted that the pilots will take the most of the weight .. and so by consequence .. AF for many negligence
Placed on the very same situation, but with hindsight about the outcome, most pilots, including any member of AF447 crew would certainly not make the same errors
Yourself have already the verdict !
All this will be confirmed in some loooong years ... when all the smoke is settled
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Old 11th Jul 2011, 23:27
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Originally Posted by jcjeant
Hi,

Academic blah blah
I have not to learn you the fact that the real security issues will point to some actors
And the court will point exactly the same actors with some nuances ... that's a lawyers game to be performed
But being on an aviation forum I find it waaaay more relevant and interesting to find out what went wrong and why than assigning blame to any of the involved parties. There are other professions who are paid to to the latter and I'm more than happy to leave that part (which I find not very pleasing) to them.
Therefore count me in for the academic blah blah as well.
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Old 12th Jul 2011, 00:10
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@ takata
Now that everything is showing that stuff involving AP & THS fantasy laws are not worth the bandwith, we should go back to the basics of Unreliable Airpseed Events... if we really want to understand what kind of situation was faced by AF447 crew, and possibly discuss what could have confused the PF and crew. PJ2, Chris Scott and few others have already tried (more than once) to bring back this thread on the cockpit confusion (hence, ergonomics and interface issues) but it looks much less sexy than talking about any Airbus Systems getting confused.
So far this thread plus the previous four total 9677 posts and counting. Apparently, questioning, probing and trying to understand technical and engineering "stuff", as you put it, regarding the aircraft and its FBW controls seems to be not the thing to do in your mind. The conclusion seemingly has been reached by you, ergonomics and interface issues were the cause, end of discussion. It will be interesting to see if in the final BEA report if they are in agreement with your conclusion. Hopefully, they will have a more "in depth" examination that goes beyond your present "bandwidth."
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Old 12th Jul 2011, 00:21
  #124 (permalink)  
 
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autotrim, stall warning, stable stall, et al...

Hard to keep up, and I am a very fast reader.

- Zorin asked about the autotrim, and others have tried to figure it out. From what I see of the tech manuals and inputs from other contributors, it looks like a basic way of providing the elevator the most authority and reducing the drag of an elevator that is "x" degrees deflected to maintain the current gee or AoA command.

Bear in mind that my primitive FBW system did not have an elevator at the rear of a horizontal stabilizer ( HS). The whole HS moved for pitch commands.

As with the 'bus, HAL "auto trimmed" to our gee command trim setting. Unlike the 'bus, we could trim for a gee, and not be limited to a one gee command.

- Gerard asked a great question, and it is one of mine.

What was the "stall warning" all about after the pilot pushed over a bit?

- Chris brought up the relatively benign deep stall characteristics. It's what got me joining this august grope of "experts", wannabe's and actual 'bus drivers. And others.

All who have flown a delta wing raise your hands! Concorde counts. Mirage variants count. The one I flew as a yute was so deceptive that it was scary - F102. Very slight "buzz", but no real buffet or burble. Great directional stability and lateral stability. But the altimeter was pegged at 10,000 feet per minute going down.

The modern commercial heavies have really great aero characteristics that can make a stall insidious. And the stall is not like the Airbus manuals depict on the lift versus AoA curve. There is no sharp break in the curve at "x" AoA. It's a very gentle curve and one can fly at fairly extreme AoA's without the sharp pitch excursion we all saw when checking out in a Chipmunk or Cessna or T-28 or......

The problem occurs when the jet reaches a certain AoA and c.g. and speed combination that prevents normal pitch down commands from being effective. It's that pitch moment graph I posted years ago ( heh heh).

The test pilot maneuver resulting in a deep stall that I posted was not the classic entry to a deep stall in the Viper. The classic entry was a fairly steep pitch, low gee, rapidly slowing speed, and running outta air molecules for that HS or THS to use to get the nose back down. Does that sound relevant here?

I gotta admit, that from this old fossil's FBW experience and perspective, that there are too many autopilot functions embedded in all the 'laws". The jet seems perfectly capable of flying to the basic limits that all the heavies, if any, can match. And my problem is the "basic" limits seem to take short shrift behind roll angles, autotrim, mach warnings, etc. etc. ad nauseum. Then I read here that one reversion law commands the motors!! BEAM ME UP!! If not in some autopilot mode, let the plane fly. Sheesh.

I thank all here for allowing a "lite" pilot with some FBW experience back when the Earth was still cooling to participate. I am now SLF, and I wanna feel comfortable about the jets I ride in.
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Old 12th Jul 2011, 00:42
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Originally Posted by jcjeant
Originally Posted by takata
Placed on the very same situation, but with hindsight about the outcome, most pilots, including any member of AF447 crew would certainly not make the same errors
Yourself have already the verdict !
All this will be confirmed in some loooong years ... when all the smoke is settled
If you were not such a , you would understand that anybody, including pilots, may be induced in error, even by serious Air France or Airbus shortcomings. So first step is to understand what goes wrong.
Stop trolling, please.
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Old 12th Jul 2011, 01:03
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Honestly, my picture of the accident includes everything I read here. I don't reject anything, you may notice my input has to do with proposing some things, some perhaps a bit bizarre, but what about this accident is NOT unusual? I do intend to embrace the Truth when it arrives, my perspective may not project that, but questions cause thought, unless rejected, and I think that is too bad.

This thread exemplifies what I think is a solid plus in analysis. There is no boardroom with a coffee maker and sandwiches which instill a faux civil atmosphere. It is a rare pilot who can be scrupulously objective. There are plenty here, and I admire all the people who post here.

As of now, it looks rather bad for the pilots, all three. I cannot figure out why in the world BEA would accede to pressure to release such an unsatisfying Note. It has made the adversarial nature of the discussion ever more polarized, not that it has any relevance on their Report.
 
Old 12th Jul 2011, 01:10
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Hi Turbine,
Originally Posted by Turbine D
So far this thread plus the previous four total 9677 posts and counting. Apparently, questioning, probing and trying to understand technical and engineering "stuff", as you put it, regarding the aircraft and its FBW controls seems to be not the thing to do in your mind. The conclusion seemingly has been reached by you, ergonomics and interface issues were the cause, end of discussion.
Certainly not. Discussing systems and engineering "stuff" is very fine with my bandwith allocation. What I'm very less interested is about such fallacious and circular argumentations based on nothing but greviances, which discards investigation work in order to insert some supposed hidden informations, revealing the cover up of imaginatory supposed "facts".

I'll give you an example:
Bearfoil's point is that the aircraft attitude at AP disconnection was in some abnormal attitude (pitched down below -13) and slow, but fast - such fact, of course is hidden by the BEA - then UAS was immediately due to "turbulent airflow" while she zoomed 3000 ft due to crazy THS systems triming her to the max because of some nose down roll tendency, but Pilots fought the roll and nose up pitch, but were few seconds later back to 3NU which was now increasing to 13NU while applying full back stick during half a minute, and so on...

Here, let me tell you that it is in fact a huge waste of bandwith, in my book.
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Old 12th Jul 2011, 01:51
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Waste of time?

I have followed this thread since Day 1 and contributed occasionally and asked questions when my personal knowledge ran out. It seems a great pity that we have to persistently wade our way through piles of cr*p to get to the 'good stuff', and most recently I have to take issue with bearfoil. With the exception of little green men from the planet Zog, it seems that any kooky idea with a shred of Airbus-itus (definition: anything built by Airbus must be implicitly designed to screw with the crew in some nefarious and more convoluted manner than it did in the previous post) must be somehow to blame, and blow me down with a feather, the crew must have been overtaken by HAL as it went increasingly 'nuts' (obviously hell bent on dashing the airplane into the ocean despite the heroic efforts of the crew).

The last post I bothered to read by bear involved some absentmindedly forgotten-by-BEA nose-down pitch (of -9 degrees!) and overspeed (I think it was), that the PF fought against resulting in the zoom-climb of doom....blah, blah, blah.

Look I'm all for theories, but let's face it - this imaginary world belongs firmly over in Rumors and News. Please take this lala-land and post it where it belongs. Please.

I have learned so much over here in the relative sanity of the Tech Log - massive to mm43, gums, Chris Scott, Turbine D, takata, henra, PJ2, DW, '33' and others. The sanity you have brought here is greatly appreciated.

I'm not sure what this post itself contributes other than allowing me to vent some...
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Old 12th Jul 2011, 02:04
  #129 (permalink)  
 
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@ Zorin 75:

Quote:
What could the autoflight have done to get this aircraft to so obviously be nibbling at aerodynamic STALL?
How's an a/c "nibbling at stall" supposed to do that 3000 ft climb?
Just before!

In NORMAL law αsw = 23 (fixed value for all flight phases)
In ALT & DIRECT Law αsw = function of M and S/F config.
S/F is not applicable, in this flight phase αsw = function of M only.

αsw---- MACH
10.8-- <= 0.28
9.9--- <= 0.35
7.6--- <= 0.53
5.2--- <= 0.75

3.8--- <= 0.866

-Inhibited M >0.866
-Inhibited on GND (if not in test)
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Old 12th Jul 2011, 02:52
  #130 (permalink)  
 
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Initial STALL STALL STALL

Originally Posted by Bearfoil
But which pilot?
Dazzle me with a theory of a Near STALL widebody at handoff. Because if you cannot, I will continue and suggest that the unreliable airspeeds were caused by the Rolling moment of a fast widebody in chop, and that the discrepant reads were made so by the airstream losing its integrity at the lower nose, while she mushed on full of gusto and KE. Not to mention plenty of NU. Hopefully BEA will fill the void they created between 2:08:07 and 2:10:05. Then I'll buy you an adult beverage of your choosing. My soul is ready, how's yours?
Well, it seems I'm the one making wishful thinking while an endless Bearboiling of circular points seems to make your own days. Obviously, what makes you think that she was near STALL at handoff, when AP kicked off, is that the STALL WARNINGS sounded twice, then stopped. On the other hand, in many UAS case, without changing anything about the flight parameters, this happened exactly the same.

From here come your insistence that she could not have been in "controled flight", no matter if everything else is pointing that she was, except a starting roll to the right.

On the other hand, I have already underlined many other cases of UAS events recorded that are obviously pointing at exactly the same "suspect" stall warnings when the FLIGHT LAW is switched from NORMAL to ALTERNATE. For me, this is certainly a major issue (if confirmed) of the Warning System because I really think that it could have played a major role during the following sequence leading to the total loss of control by the crew.

In fact, there is a VERY simple BASIC rule in the system :

* NORMAL LAW -> COMPLETE SAFE FLIGHT ENVELOPE USED BY ELECTRONIC FLIGHT CONTROL SYSTEM
* ALTERNATE LAW -> REDUCED SAFE FLIGHT ENVELOPE USED BY ELECTRONIC FLIGHT CONTROL SYSTEM

Hence, any switch from NORMAL to ALTERNATE LAW should be immediately followed by a reduction of the safe flight envelope at both ends : in clear, the safe margin should be expanded concerning both the overspeed warning and the stall warning (nonetheless, the aircraft real "flight envelope" is still the same, but its defined "safe limits" are changed due to some certification concerns about its systems state and possible manual flight).

1) In our case, the high speed limit warning would be reduced from Mach 0.86 to Mach 0.82. Also, the low speed warning (alpha-prot) could be rised (I did not find the relevant data about it, then, if wrong, see point 2).

Nonetheless, neither overspeed nor stall protections could be applied because of the current declared airspeed monitoring by EFCS : ALT2 is immediately applied, no protection could kick without a valid airspeed ; After this point, the PFD function displayed (overspeed and stall warning speed limits) will disapear from both PFD.

Next, following an UAS confirmed in ALTERNATE LAW, the calculation mode of this stall warning limit will change again from one function using an AOA corrected by a Mach value supplied by those ADRs to another one using a default Mach parameter. This would change the granularity of the AOA measured and subsequently will increase the margin for the stall warnings.

My explanation (so far) is that, when UAS is declared, there is a small time window where the limitation of the safe flight envelope is applied to the stall warning limit which last during the resolution of an UAS monitoring : it takes 10 seconds for the system in order to confirm ALT2 (after that, the system could not subsequently revert to NORMAL LAW without a full ground reset).

So in fact, the aircraft, during those 10 seconds window, without changing any flight parameter, will fly at speed closer -or below- the threshold of the STALL WARNING speed. But, following the UAS confirmation, the new function will apply another AOA warning limit. Then, this would stop the WARNINGS... if the reduced threshold has been overshot during those 10 seconds. So my bet is that the STALL WARNINGS stopped at 0210:14 and would have sounded during the 0210:05-0210:14 time window.

2) If alpha-prot calculated speed do not rise when switching to ALTERNATE, another simple explanation is that a drop of the polled speed, due to unreliable airspeed situation, is not filtered by the stall warnings during the same defined 10 seconds time window. Hence, if the polled (unreliable) speed goes below alpha-prot speed, this alarm is sounding. Once UAS is confirmed, as precedently, the new UAS STALL WARNING function is declared and the alarm is stopped.

Those 2 points are based on the history of published UAS events :
Here are the tables of the 36 UAS events declared before the publication of 2nd BEA report; one may see that 12 cases of "suspect" STALL WARNINGS were reported (33%). Moreover, those stall warnings do not let any trace outside the CVR or crew reports (they are not part of the maintenance post flight reports), and this survey was mostly incomplete about many cases listed. So it may be assumed that more cases of "suspect stall warnings" were not recorded.



Last edited by takata; 12th Jul 2011 at 03:12.
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Old 12th Jul 2011, 03:17
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Dozy, multiple quotes:
Originally Posted by Machinbird
JD-EE, we were temporarily lead astray by forum members who apparently believed that autotrim would not resume control once you made a manual trim input.

That would be me, having misread the documentation I had.

Quote:
I strongly suspect there is some misinformation adrift in the Airbus community that needs correction. I wonder how BEA will address that?
Again, it was just me - the "Airbus community" were the ones who kindly corrected me via PM.

Dozy, you can't take all the responsibility, there were others as well putting out this misinformation.
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Old 12th Jul 2011, 03:26
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Originally Posted by Machinbird
Dozy, you can't take all the responsibility, there were others as well putting out this misinformation.
To be fair with Dozy, this "misinformation" comes from Airbus itself, as the manual states in one page that the use of manual trim will "freeze" autotrim, and somewhere else that the PRIMs do not fault when manual imputs are applied, but that the PRIMS will re-synchronize with the manual trim imputs, which have the priority over autotrim.
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Old 12th Jul 2011, 04:39
  #133 (permalink)  
 
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Takata,
Quote:
Originally Posted by Machinbird
The problem with the trim is that it moved to a high aircraft nose up setting without crew awareness.
Takata
Any pilot flying an aircraft with autotrim should know that his trim will follow his stick imputs, shouldn't he?
Yes, assuming he knows he made the stick inputs.
Quote:
Originally Posted by Machinbird
It appears that a FBW aircraft requires the pilot to know exactly what mode the aircraft is operating in or else the question arises, "What's it doing now?"

Takata
Isn't it one of the basic skill needed for one wanting to be rated for a specific type? What makes you think that many FBW pilots don't know exactly in what mode their aircraft is operating?
Takata, suppose we sat a pilot down and hit him with a fire hose stream. Do you think he can remember his birthday while this is going on?

Perhaps a couple of recent accidents make me think that way.


Quote:
Originally Posted by Machinbird
In the case of the AF447 crew, they had no attention to spare to consider what the trim might be doing

Well, considering that the trim was doing what a type rated PF asked, and what it is always supposed to do in such a case, what would be the point to consider that it would take more "attention" than usually?
Takata, have you ever been in a really stressful situation while flying? From your comments, it appears that you have not. That is fortunate for you, if so, but it gives you a blind spot with respect to the effects of in flight stress. You seem to be assuming that the initial pitch up to FL375 was deliberate.
Quote:
Originally Posted by Machinbird
thus the nose up demands caused the trim to run silently to a high setting

Hence, as usual when imputs ask for a lot of nose up, what is wrong with that?
Nothing down low when setting up for a landing, a whole lot is wrong when it happens at cruising altitudes. The problem is the silent motion of the trim. They needed to know it was moving so that they could monitor it.
Quote:
Originally Posted by Machinbird
without the knowledge or anticipation of the crew.

What make you believe that a type rated crew would not anticipate it or lacked the knowledge that it will do exactly that? Do you think that it wasn't what they wanted, nose up?
Yes, I think that they didn't want all that nose up initially. Later, after the stall, who knows?
Quote:
Originally Posted by Machinbird
Once at a high setting, the trim acted to stabilize the aircraft in the deep stall that they eventually achieved.

Right, the PF achieved a full stall with the help of the side stick, thrust and THS trim. Hence, what's wrong with the side stick, the thrust lever and the THS trim?
Just an opinion at this point, but the addition of TOGA thrust coinciding with the second stall warning is too reminiscent of an airline approach to stall procedure as recently taught, except pitch control was improper/clueless as it had been since PF said"I have the controls."
Once in the stall, it was imperative that stall recognition occur, but it seems, it didn't. Without AOA indicatiors, without stall warning, without comprehending that the decreasing altitude was real, there was one final item that could have explained the situation and that was the THS trim position.
Quote:
Originally Posted by Machinbird
When the Captain arrived on the flight deck, he had to puzzle out what he was seeing. From the jump seat, the indications were essentially hidden by the wheels themselves.

Beside hindsight, what makes you believe that the Captain would have immediately recovered the situation with all the trim settings displayed under his nose? He wasn't there from the begining of the crisis and still possibly far behind the other pilots. He also might have seen the Flight Control page, where the THS trim setting is displayed, right in front of him...
There is no surety that the Captain would have been able to puzzle out the situation in time if he had seen the THS trim, but if he had noted its very abnormal position, there is a logical thought process that should follow that would lead to stall recognition. For him to check the THS position, he would almost certainly have to form the thought to check it and then lean over for a peek.
Quote:
Originally Posted by Machinbird
The THS autotrim system has virtually eliminated the problem of trim-runaway, but it has replaced that problem with a new set of problems.

I still can see the problem with the THS trim. If they had acknowlegded their stalled situation in time, they would have immediately applied full and sustained nose down imputs, hence, THS trim would very likely follow that. If, for whatever reason, THS trim would not follow those imputs, not enough elvators authority should have attracted PF attention about considering that trimming nose down could help him... at least, theoretically if his training level wasn't the issue.
We seem to agree that they likely never tumbled to the fact they were in a stall. The recent Perpignan trim related accident combined with the AF447 accident seem to indicate that there are issues in trim position awareness in Airbus land.
My apologies for a rather cursory reply, unfortunately I have limited time during the week.
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Old 12th Jul 2011, 05:35
  #134 (permalink)  
 
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CG position ?

Originally Posted by Turbine D
However, in the BEA Update, dated May 27, 2011, The weight of the aircraft was again reported at around 205 t, but the balance was changed to 29%, or in other words moved forward 8% or so.
TD, I have partially addressed your question here.
As the take off CG was very much forward (23.3%), and despite the aft fuel transfer, I figure the ideal target of around 38% for fuel saving could have been approached only toward the late stage of the cruise phase, not after 3 hours of level off.

To have a CG more fwd than aft should help for the handling, and stall recovery as well ...


Originally Posted by DozyWannabe
Really? How else am I to interpret at least 5 years of posts demanding that Airbus return to interconnected yokes and introduce a big red "Direct Law" button (as in the 777), not to mention continued belief in a conspiracy surrounding AF296 @ Habsheim?
I don't demand much, just criticize what, IMO, deserves such.
You, obviously, do not tolerate such critics to be made. Fine with me.

As you're not willing to publicly discuss Habsheim, despite my invitation, why can't you quit mentioning it ... ?
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Old 12th Jul 2011, 05:42
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Hi Machinbird,
Originally Posted by Machinbird
Originally Posted by takata
Any pilot flying an aircraft with autotrim should know that his trim will follow his stick imputs, shouldn't he?
- Yes, assuming he knows he made the stick inputs.
- You seem to be assuming that the initial pitch up to FL375 was deliberate.
- They needed to know it was moving so that they could monitor it.
- Yes, I think that they didn't want all that nose up initially. Later, after the stall, who knows?
Well, I would say that what the PF really wanted during his initial imput is quite irrelevant concerning the "THS issue". You should read again the BEA note as you seem to be the one assuming that the THS was trimmed during the initial climb to FL375 (please, don't trust everything Bearfoil is posting!). You'll discover that everything started a while later: this THS was trimmed from 3NU to 13NU between 0210:51 and 0211:50, therefore, until this point, everything seems about right about its behavior:

"0210:51, the stall warning was triggered again. The thrust levers were positioned in the TO/GA detent and the PF maintained nose-up inputs. [...] Around fifteen seconds later, [...] The PF continued to make nose-up inputs."

What would make you believe then that the PF maintained (at this stage) all those nose-up imputs without knowing it?

Originally Posted by Machinbird
Once in the stall, it was imperative that stall recognition occur, but it seems, it didn't. Without AOA indicatiors, without stall warning, without comprehending that the decreasing altitude was real, there was one final item that could have explained the situation and that was the THS trim position.
In fact, stall warnings seems to have sounded correctly at this point (see above) while the PF was trimming his THS near its max by applying sustained NU orders! Hence, this THS was fully trimmed during the stall sequence, not before it!
Without puting the sequence in the correct order, this will be fairly useless to discuss its usefulness as to alert you that you are going to stall, when you are fully stalled, but still trimming it the other way!

Beside, I also believe that there is a great deal of chance that the initial PF nose-up order, and following climb, was not voluntary but rather the result of an overcontrol of the roll tendency. Nonetheless, this is absolutely not the issue discussed about this THS setting. When THS goes there, it is quite hard to believe that the PF wanted something else than those sustained nose-up orders... Consequently, what more could he have learned from his THS setting that he already didn't knew while pulling up?

Your concern about it is only understandable with hindsight. Should they have tried to recover from a stall, at some point, this certainly would not help... but then, he put it here at the first place when it was certainly not the right thing to do at all...
My point stop here on this subject.

Last edited by takata; 12th Jul 2011 at 06:53.
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Old 12th Jul 2011, 06:53
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Hi Takata,
Just a brief note, my assumption is that the trim initially traveled slowly nose up and began to really move as the aircraft approached the stall. I do not attribute the nose up attitude to the trim as some are wont to do, it was merely the result of more nose up input than nose down input from the SS, averaged over time-that and what must have been a completely fouled up scan.

Is there any sort of pitch indication adjust function on the PFD? The PF's control inputs act like he had an erroneous level flight pitch setting. I am strictly a steam gauge guy so I've never had the opportunity to see how the other side currently lives.
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Old 12th Jul 2011, 07:06
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In fact, stall warnings seems to have sounded correctly at this point (see above) while the PF was trimming his THS near its max by applying sustained NU orders! Hence, this THS was fully trimmed during the stall sequence, not before it!
Yes it did, but look at it from the standpoint of the PF. He got a stall warning and applied what to him seemed like an approach to stall recovery, and the stall warning eventually extinguished (because he was deeply stalled). The aircraft attitude changed very little. Why should he think he was stalled. He just didn't have airspeed indications, and now the aircraft is acting really strange, dropping wings and things like that, and the altimeter is doing the digital equivalent of unwinding.
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Old 12th Jul 2011, 09:08
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associated actions

Hi Machinbird,
He got a stall warning and applied what to him seemed like an approach to stall recovery....
I agree & in 2009, there was no stall warning procedure in the QRH.
The guidance was buried in FCOM, Supplementary Techniques, Flight Controls which describes the initial actions which the PF took.

"An aural "STALL, STALL, STALL" warning sounds at low speeds. Upon hearing it, the pilot must return to the normal operating speeds by taking conventional actions with the controls:
Thrust Levers...TOGA
At the same time:
Pitch Attitude...Reduce
Bank Angle...Roll Wings Level"

Unfortunately he then lost the reference power setting he had before the UAS event. I would guess that he recalled the power and pitch attitudes he learned during his conversion course for unreliable speeds and remembered the TOGA + 15 degs pitch ... (but that doesn't work at FL 375.)
The next bit reads "Thrust/Pitch .... CL/5degs Above FL 100"
but by then they were so very deep into the stall they would have needed at least 10 degs nose down to accelerate.

Last edited by rudderrudderrat; 12th Jul 2011 at 10:25. Reason: extra text
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Old 12th Jul 2011, 10:32
  #139 (permalink)  
 
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Originally Posted by takata no.128
Here are the tables of the 36 UAS events declared before the publication of 2nd BEA report; one may see that 12 cases of "suspect" STALL WARNINGS were reported (33%).
Why do you label these stall warnings 'suspect'? BEA has investigated several of these cases and writes in its Interim Report No.2:
Stall warning. Nine cases of triggering of the stall warning were observed. (...) All of these warnings are explicable by the fact that the airplane is in alternate law at cruise mach and in turbulent zones. Only one case of triggering was caused by clear inputs on the controls.
Note: At high altitude, the stall warning triggers in alternate law on approach to the stall. The stall manifests itself particularly through vibrations.
I think there are number of other statements in your post that you may wish to rethink. Alpha-prot is the AoA at which Normal Law changes from an Nz law to an alpha-law. In this connection you are several times referring to speed where the reference should really be to AoA (*). Alpha-prot is only relevant in Normal Law and I doubt it is even calculated in Alternate Law since it has no significance in that law. In Alternate(1) there is a protection called 'Low Speed Stability' that is driven by IAS instead of AoA, and changes alternate law to direct law. It is active from about 5 kt up to about 10 kt above the stall warning speed (*), depending on weight and slats/flaps configuration. Low Speed Stability is lost in Alternate (2) Law.

P.S.:: (*) For given configuration, weight, c.g., and altitude, AoA is a function of Mach and load factor. V-alphaprot and V-alphamax shown on the speed scale of the PFD are calculated for 1 g from alpha-prot and alpha-max, respectively. V-S/W is calculated for the actual "gee" and the stall warning threshold AoA.

Last edited by HazelNuts39; 12th Jul 2011 at 17:41. Reason: P.S. Correction to state that VSW is g-sensitive
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Old 12th Jul 2011, 11:21
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Originally Posted by Chris Scott
The other unclear factor is how the C* pitch-function of the EFCS would treat the invalidation of CAS (IAS) data, when determining the crossover from g-control to pitch-control. As I understand it, that crossover is normally a gradual transition as the airspeed falls below a certain figure in routine flight.
Please, what is this transition from g-control to pitch-control you are talking about and where is it described in the FCOM? Does it apply to A-330?
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