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AF 447 Thread No. 5

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AF 447 Thread No. 5

Old 11th Jul 2011, 18:47
  #101 (permalink)  
 
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Alpha-floor protection

Dozy;

While I agree with the entire post, just a minor semantic correction in your last paragraph to avoid confusion:

The protection that commands TO/GA (the EEC controls the spooling up) is named alpha-floor. IIRC it is activated in normal law when the AoA exceeds the corresponding threshold (between alpha-prot and alpha-max), sudden or not.

Last edited by HazelNuts39; 11th Jul 2011 at 19:10. Reason: semantics
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Old 11th Jul 2011, 18:51
  #102 (permalink)  
 
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Hi Dozywannabe,

But "tactile feedback" has been artificially driven in every major airliner designed since the late '60s,....
Correct. When manually flying I could "feel" the aircraft getting slow because the elevator would feel heavy in order to maintain altitude (until I manually trimmed the elevator). No so with AB FBW.

Also, the FBW computers coped just fine with the loss of airspeed information. The A/P and A/THR kicked out,....
I wouldn't call that "coped" - I'd call that given up!
Even my old Boeing 707 A/P would have remained engaged, all that would have been required would have been manual thrust adjustment.
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Old 11th Jul 2011, 19:00
  #103 (permalink)  
 
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Even my old Boeing 707 A/P would have remained engaged, all that would have been required would have been manual thrust adjustment.
If I recall, those old 707/727 autopilots would also remain engaged with a complete hydraulic failure (A&B) even though they couldn't "fly" the aircraft from that point.

I think they put in a special red light for that.
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Old 11th Jul 2011, 19:01
  #104 (permalink)  
 
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Originally Posted by Bearfoil
To me, if Pitch transits got out of phase with Power, their could be trouble? Insofar as rate, I think Power up when Nose down would be problematic, as would the reverse. If the THS is in there, what is the calculated rate for stopping speed and Pitch excursions that are (or have become) unnecessary?
First, you should try to put those events into the right sequence, then your questions should be answered by themselves.

Autotrim large change took place past 0210:51 : "The trimmable horizontal stabilizer (THS) passed from 3 to 13 degrees nose-up in about 1 minute and remained in the latter position until the end of the flight." [BEA]

Why would you put absolutely this aircraft out of pitch trim before this point, beside trying to fit something squared into your rounded mind?
If THS trim, for whatever reason, was something else than 3 deg NU before 0210:51, it reverted to this setting, then reached 13 deg NU between 0210:51 and 0211:50.

How does it fit now with your question?
Ask yourself.
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Old 11th Jul 2011, 19:04
  #105 (permalink)  
 
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Cool

Hi,

At the risk of parsing too closely, In the audio where the pilots are noticing "No indications", is it surprise one senses? Or Betrayal?
There is a subtle difference between the French and English about this conversation
In the French text is "indication" (singular form) and in the English version is "indications" .. ( plural form)
This is very different
I wonder how it's possible to make a difference of plural or singular form .. when a french tell "indication" as it's no difference for mark (voiced) the plural !!
So why make a difference between the versions
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Old 11th Jul 2011, 19:14
  #106 (permalink)  
 
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Originally posted by HazelNuts39
I wonder on what consideration you base that assumption. On the basis of how a pitot tube 'works', it is not plausible at all.
From Airbus Abnormal Procedures 2.05.80:
Drain Holes Free:
The IAS may fluctuate or drop quickly towards the sticker shaker speed. The IAS behavior depends on the condition of the pitot tube drain holes.
The sensed Pt drops quickly towards static pressure (Ps).
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Old 11th Jul 2011, 19:15
  #107 (permalink)  
 
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Originally Posted by rudderrudderrat View Post
Correct. When manually flying I could "feel" the aircraft getting slow because the elevator would feel heavy in order to maintain altitude (until I manually trimmed the elevator). No so with AB FBW.
Thus far we have not had a serious UAS incident on the 777 to see what the latest generation of "artificial feel" will do when a significant data source is compromised.

I wouldn't call that "coped" - I'd call that given up!
Even my old Boeing 707 A/P would have remained engaged, all that would have been required would have been manual thrust adjustment.
I think you're misunderstanding the point I was making - the FBW system is distinct and separate from the Autopilot/FMC system. They pass data back and forth where necessary, but they are entirely different in terms of purpose, hardware and software. Now, as to what you're saying about old-school autopilots, IIRC in the 707 we're not talking much more than a wing leveller and altitude hold with a turn function. It didn't have an autothrottle or try to manage your speeds, ergo pitot information had no bearing on the design of the thing. Modern aircraft are very different in that respect and autopilot/FMS functionality much more all-encompassing.

Personally I think Airbus made the correct decision to disengage A/P upon confirmed ADR DISAGREE, and yet again we're back to Birgenair, where the A/P did continue to try flying the aircraft with blocked pitot and an erroneous overspeed warning. The result was that the aircraft had a very high pitch angle and it was only the massive amounts of thrust and a hard limit on FMC authority that kept the thing in the air. For all the stick Airbus come in for due to supposedly "encroaching on pilots' authority", their systems are designed to put the pilot in charge very early on in the failure sequence.
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Old 11th Jul 2011, 19:27
  #108 (permalink)  
 
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jcjeant,

I suppose you didn't notice the other difference, the Special Foreword To English Note?

To me, the noticeable element in this exchange is that the PNF acknowledges the PF's announcement, but at the same time corrects it, by adding the word 'valid'. IOW, there were indications but they were not considered valid.

Last edited by HazelNuts39; 11th Jul 2011 at 19:49. Reason: 2nd para
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Old 11th Jul 2011, 19:38
  #109 (permalink)  
 
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Hi jcjeant
Originally Posted by jcjeant
There is a subtle difference between the French and English about this conversation
In the French text is "indication" (singular form) and in the English version is "indications" .. ( plural form)
This is very different
Agree... and it is not the only one.
The reference text is the French version, in any case, the English one being a hurried translation (as to your "why?").
Another point very badly translated, where Bearfoil's is driven to interpret it as a non-sense, is this one:
English: "The airplane’s pitch attitude increased progressively beyond 10 degrees and the plane started to climb" -- here was also the error with angle-of-attack.
Bearfoilly's : "At PITCH +10, the a/c began to climb."
French : "L’assiette de l’avion augmente progressivement au-delà de 10 degrés et il prend une trajectoire ascendante."

In fact, the poor French syntaxe (in context) was badly translated in English, and Bearfoil's reading was, at the end, completely wrong ("only when pitch reached +10°, the aircraft started to climb").

What it means basically was :
"pitch attitude increased progressively (above +10°) while the aircraft trajectory was starting to climb".
As, of course, the climb did not start only when the pitch was above +10 (plane attitude changed smoothly), despite all those inertial forces involved.
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Old 11th Jul 2011, 20:12
  #110 (permalink)  
 
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Hi Dozy,
Thus far we have not had a serious UAS incident on the 777 to see what the latest generation of "artificial feel" will do when a significant data source is compromised.
I'm not qualified on 777 - but I am led to believe Boeing have fitted the "big red button" - so that it would fly just like a very large 737. (with all the tactile feed back one could want aka Direct Law).
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Old 11th Jul 2011, 20:22
  #111 (permalink)  
 
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A question for the BEA

According to the Update, between 2:10:16 and 2:10:50 'the speed displayed on the left side increased sharply to 215 kt (Mach 0.68)'. At 2:11:06 the speed on the ISIS increased sharply towards 185 kt, and was then consistent with the other recorded speed.

If one of the PFD's had been switched to ADR3, would that be recorded on the DFDR?

Last edited by HazelNuts39; 11th Jul 2011 at 21:09. Reason: typo - thx takata!
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Old 11th Jul 2011, 20:44
  #112 (permalink)  
 
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Originally Posted by rudderrudderrat View Post
I'm not qualified on 777 - but I am led to believe Boeing have fitted the "big red button" - so that it would fly just like a very large 737. (with all the tactile feed back one could want aka Direct Law).
I'm no expert on the 777, but as I understand it there are no "laws" to the system design akin to those of the Airbus system. Now - you've got your "tactile feedback", but it's computer controlled, based on the inputs the flight computers are receiving from the various sensor systems. Take those inputs away and I'm not sure what the back-driven system will do in response.
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Old 11th Jul 2011, 20:59
  #113 (permalink)  
 
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Originally Posted by jcjeant
my feeling is:
The pilots were rated on type ... but nevertheless were not qualified for the situation of AF447 was
They had not knowledge of basic flying skills
They don't know how the Airbus systems work

So we can conclude that:
The formation and training of those pilots is very low
So Air France bear all the responsibility for this accident by not providing adequate training to their pilots or not detecting by exams (simulator) that those pilots were not qualified for fly a Airbus A330
At least and even if this above is not entirely true .. Air France stay bear the responsibility of this accident as the contract between Air France and their passengers was to transport them from A to B and they failed....
Are my feelings good ?
Certainly not.
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 : basically, they would understand quickly that they will stall, or that they are already stalling, then certainly they will act properly to recover. Nonetheless, everything is pointing that this did not happen during this night.
Maybe, this very same scenario, played in the simulator (up to the point it could play it), with the same crew could have ended differently... who knows? Maybe the PF records during his sim checks was also near perfect? 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. In the future, we'll be certainly allowed to comment its conclusion to the death. As a matter of fact, for me so far, any actor involved is possibly responsible of something wrong in the process leading to this catastrophe. But then, I need first to understand what it was exactly and why he was acting like that.


Hi HazelNuts,
Originally Posted by HazelNuts39
I wonder on what consideration you base that assumption. On the basis of how a pitot tube 'works', it is not plausible at all. The BEA Update speaks of 'a sharp fall from about 275 kt to 60 knots in the speed displayed on the left PFD, then a few moments later on the ISIS'. The Air Caraibes Memo speaks of 'une diminution tres rapide de la CAS'. On the basis of the ACARS Fault message PROBE PITOT, BEA's Interim no.1 attributes the initiating event to 'a decrease of more than 30 kt in one second of the polled speed value'.
Spot on!
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.

Originally Posted by HazelNuts39
According to the Update, between 2:10:16 and 2:10:50 'the speed displayed on the left side increased sharply to 215 kt (Mach 0.86)'. At 2:11:06 the speed on the ISIS increased sharply towards 185 kt, and was then consistent with the other recorded speed.
If one of the PFD's had been switched to ADR3, would that be recorded on the DFDR?
I guess that what is recorded is ADR1 & 3 airspeed channel, independently from where it is displayed (hence the choice of ADR3 instead of 2 as it could be displayed to Captain's PFD). Note, your typo about 215 kt (Mach 0.86)?!

Last edited by takata; 11th Jul 2011 at 21:10.
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Old 11th Jul 2011, 21:16
  #114 (permalink)  
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I await the news of BEA next report as everyone does.

Perhaps it will clear up this confusion. When autopilot dropped out, the PF made immediate inputs, and heard the STALL Warning, two times.

What could the autoflight have done to get this aircraft to so obviously be nibbling at aerodynamic STALL? If dropping a/s reads, would the ap have increased power to such an extent that both engines were blazing away, and altitude still was dropping?

By definition, this is UPSET. At some point later, the onset of zoom climb qualifies technically as Loss of Control (LOC).

We hear the PF "I have the controls". So after the uncontrolled zoom climb starts, we will certainly hear PNF on the radio reporting "Out of...."

Will there be a MayDay in there as well? I believe we will hear at least one.

takata, you are wishful thinking. I know the feeling, and you have it.
 
Old 11th Jul 2011, 21:19
  #115 (permalink)  
 
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Originally Posted by jcjeant View Post
....In the French text is "indication" (singular form) and in the English version is "indications" .. ( plural form)
This is very different
Obviously you do not know any spoken French, or you wouldn't have posted this.
Spoken French tends to elide the last letter of most words.
In 99% of cases that's not a problem, since the meaning is obvious from context.
In this case it isn't... but please stop playing Sherlock Holmes, when you have no significant clues, and English is clearly not your mother tongue either.
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Old 11th Jul 2011, 21:23
  #116 (permalink)  
 
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Originally Posted by bearfoil View Post
takata, you are wishful thinking. I know the feeling, and you have it.
Pot, meet kettle.

Seriously - takata's going on the evidence we have so far and you're still working on the supposition that the aircraft must have done something on it's own despite everything that we've been told - because, as you said before, you don't want to believe that the PF made a basic error and then compounded it.

We don't have anywhere enough information to make a call yet, but if you expect us to take your input seriously then you must also equally consider the possibility that - aside from the pitot issue - there was nothing wrong with the aircraft and that the upset was pilot-induced.
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Old 11th Jul 2011, 21:35
  #117 (permalink)  
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Doze. 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?

Lily White Auto?
 
Old 11th Jul 2011, 21:49
  #118 (permalink)  
 
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Hi Christiaan,
Originally Posted by ChristiaanJ
Obviously you do not know any spoken French, or you wouldn't have posted this.
Spoken French tends to elide the last letter of most words.
In 99% of cases that's not a problem, since the meaning is obvious from context.
In this case it isn't... but please stop playing Sherlock Holmes, when you have no significant clues, and English is clearly not your mother tongue either.
You are of course totally right concerning the CVR transcript but let me complete the explanation for people who don't know that, in French, the pronounciation of such sentences would be phonetically exactly the same :
« je n’ai plus aucune indication » <=> « je n’ai plus aucune indication(s) »
« on n’a aucune indication qui soit valable » <=> « on n’a aucune indication(s) qui soi(en)t valable(s) »
Nonetheless, in both case, the plural form is incorrect ; the correct written form would be a singular "aucune indication" (not a single indication)... which, in turn, could also mean that they have lost "all indications"... go figure!!
This would be a problem with most transcript when spoken and written forms could have different meanings as this is really ambiguous to be sure what exactly "indication(s)" is aimed at.
It could be : "je n'ai plus aucune indication [de vitesse] => lost all speed indications, or anything else lacking on his instruments pannel as it is "undefined". This could be addressed with context as it could be about whatever "indications" they were talking about before, or after. Beside, I also believe that jcjeant is also fluently speaking his mother tongue.
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Old 11th Jul 2011, 21:57
  #119 (permalink)  
 
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Originally Posted by bearfoil View Post

Dazzle me with a theory of a Near STALL widebody at handoff.
bearfoil,

please bear in mind that the gap betwen Alpha = 2,5° (Cruise AoA) and Alpha = 4° (Stall Warning) is not really much if you are forcing the aircraft from level flight to a RoC of 7000fpm within seconds.

A Pull- Up sufficient to achieve this RoC in a short time would be easily sufficient to briefly exceed the STALL WARNING threshold (which is btw not the real stall AoA), especially when some turbulence contributes to it.
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Old 11th Jul 2011, 22:00
  #120 (permalink)  
 
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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?
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