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AF447 Thread No. 3

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AF447 Thread No. 3

Old 8th Jun 2011, 16:07
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Nigel:

First of all, AIRSPEED UNRELIABLE may only be, indeed probably is, "crew assessed" not aircraft (if the aircraft assesses it it will "deal" with it).
Well there was certainly an ADR DISAGREE... but I think you're right, thinking back to earlier discussion perhaps there isn't a specific ECAM for AIRSPEED UNRELIABLE - but the system knew there was a problem.

Knocking off AoA interpretation below 60K IAS seems valid enough to me - and also at that sort of airspeed you are not just "stalled" in the normal sense of the word - you are a falling leaf
Yes absolutely, the last thing you want is nuisance stall warnings, I couldn't agree more - when you have *reliable* data. But please, if there's any serious dubiety about the data, I would doubt the wisdom of shutting off the stall warning based on IAS data that's known to be dubious...
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Old 8th Jun 2011, 16:33
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Hi NoD,

OK - even when the spec/manufacturer of the vane says the IAS is way below the validity of the vane's spec? I'd rather not...

Please go back to your basic training... if you are a pilot?
If you had blocked pitots at FL 350 with IAS showing less than 60 kts - are you seriously telling me that you'd rather not have the stall warning system active?
Are you a pilot?
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Old 8th Jun 2011, 16:36
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bearfoil:

But she was trimming for climb, automatically, so much so that the a/c stalled, having lost autothrust and assumedly, "Stall" (aPROT). So this is the deadly combination. A/P drops, a/c climbs, and Stalls. Thirty seconds over Oraro.
I suppose it's a matter of opinion, but you do have a tendency to be a little inciteful...

"She was trimming for climb, automatically..." --- really? I can't find anything that states that is true.

From 2 h 10 min 05 , the autopilot then auto-thrust disengaged and the PF said "I have the controls". The airplane began to roll to the right and the PF made a left nose-up input. The stall warning sounded twice in a row.
<snip>
At 2 h 10 min 16, the PNF said "so, we’ve lost the speeds" then "alternate law […]".
<snip>
The airplane’s angle of attack increased progressively beyond 10 degrees and the plane started to climb. The PF made nose-down control inputs and alternately left and right roll inputs. The vertical speed, which had reached 7,000 ft/min, dropped to 700 ft/min and the roll varied between 12 degrees right and 10 degrees left. The speed displayed on the left side increased sharply to 215 kt (Mach 0.68). The airplane was then at an altitude of about 37,500 ft and the recorded angle of attack was around 4 degrees.
From 2 h 10 min 50, the PNF tried several times to call the Captain back.
At 2 h 10 min 51 , the stall warning was triggered again. The thrust levers were positioned in the TO/GA detent and the PF maintained nose-up inputs. The recorded angle of attack, of around 6 degrees at the triggering of the stall warning, continued to increase. 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.
Any THS trim effect (due to PF input) did not ramp in until nearly 1 minute (46 seconds) into the reported sequence of events. There is nothing that indicates anything other than demanded trim (PF nose-up inputs).

Care to explain it differently?
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Old 8th Jun 2011, 16:44
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According to this article the french goverment has already assigned responsibility for the accident:

Rio-Paris : à qui la faute ? - L'EXPRESS
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Old 8th Jun 2011, 17:04
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Another "leak" just in time for Paris Air Show (*)

Le cabinet du secrétaire d'Etat aux Transports, Thierry Mariani, l'affirme : "La responsabilité dans l'accident du Rio-Paris, en juin 2009, revient à 5 % à l'avion et à 95 % à l'équipage.
Another () serious leak.

In this "war" the truth may be the victim...

(*) June 20-26, 2011 (12 days until the show)

Question: Who´s in control?
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Old 8th Jun 2011, 17:08
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OK, I admit it - I'm confused as to the conditioning for the stall warning generation.

According to the information I have, the following is the conditioning for Stall Warning:

STALL WARNING (No ECAM message)
An aural stall warning is triggered when the AOA is greater than a predetermined angle
This angle depends on the:
- Slats/Flap position
- Speed/Mach
- F/CTL law (normal, alternate/direct)
(my bold above)

The result of the warning is triggering of the cricket stall tone warning AND the sythetic voice "Stall" warning.

Can anyone expand on what happens in the case of unreliable airspeed with respect to the stall warning?
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Old 8th Jun 2011, 17:26
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Garage Years

Yes
. The point is that the pilot's first response to loss of auto pilot (not autoflight), may have been input while he's thinking the drop was into Normal Law, as would be the case if the auto pilot was lost due to its inability to trim within its own parameters. BEA is vague (eg: "From 2:10:05"), attributing the following displays and aspects without a specific time stamp. So if the pilot pulls the stick back, or, more importantly, it is deflected into a climbing Pitch inadvertently, then the continuous increase in Pitch, is inadvertent, and the increase in Pitch IS automatic, since the pilot is not expecting a climb, but the THS is trimming for it, and since the pressure is continuous, the Plane gains Pitch attitude inadvertently.

The Stick is an immediate unknown to the Pilot who starts to fly, but hasn't had a chance to assess the a/c orientation, and existing trimout. Rolling left may have been the only input he wished to make, but the third quadrant of the stick's deflection disc could have been entered by mistake.

This is extremely important if the AutoPilot let go due to its mechanical and aerodynamic limits being reached, and not merely due to AD rejects? We do not know that the AD losses were concurrent with a/p dropout, only that BEA reports the events w/o times, except for a starting point, eg: 2:10:05.

I am saying that if ICE was not the cause of discrepant reads, but perhaps attitude, aspect, or local flow were, it would explain what happened even more simply than what is generally accepted, absent the record.

I honestly don't mean to incite. I also don't have any conclusions to offer. What I think is important, and may well remain important even after the Final, is that certainty may be impossible, and mere Likelihood may have to suffice.

apologies for (perhaps) overly assertive style.

edit for GY you say: ":...Can anyone expand on what happens in the case of unreliable airspeed with respect to the stall warning..."

If I read Nigel correctly: "The Aircraft deals with it"

"...First of all, AIRSPEED UNRELIABLE may only be, indeed probably is, "crew assessed" not aircraft (if the aircraft assesses it it will "deal" with it)...."
 
Old 8th Jun 2011, 17:33
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Originally Posted by GY
Can anyone expand on what happens in the case of unreliable airspeed with respect to the stall warning?
FCOM :

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Old 8th Jun 2011, 17:41
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CONF iture Quote:
Originally Posted by GY
Can anyone expand on what happens in the case of unreliable airspeed with respect to the stall warning?

FCOM :




IOW, with a Stall alert (2 of them) as the immediate environment after a/p drop, what was the cause of AoA being "At Stall" ALREADY? Prior to PF's altering the a/c's controls positions?

IF IN NORMAL LAW THE STALL WARNINGS MAY HAVE BEEN FALSE.

IF IN ALTLAW THEY WERE GENUINE.

THIS SUGGESTS THAT THE A/C WAS IN NORMAL LAW AFTER A/P DROP, AND HENCE A/P LOSS COULD NOT BE RELATED TO LOSS OF SPEEDS, BUT ONLY ITS OWN INABILITY TO TRIM THE A/C. OR, THE AUTOPILOT HAD TRIMMED THE A/C INTO A STALL.

A point I have been trying to make for nearly two years. perhaps badly?

If true this suggests that the A/C had trimmed almost completely into Upset, then Stall, then LOC. It also makes Pitot ICE a remote event.

Pas de quois, Thales

Last edited by bearfoil; 8th Jun 2011 at 18:20.
 
Old 8th Jun 2011, 18:36
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Can anyone expand on what happens in the case of unreliable airspeed with respect to the stall warning?

FCOM :

Yes, absolutely. But I think the question GY was asking, and I know the question I was asking, related to the interaction between IAS data and the stall warning being disabled below 60kts.

If you have unreliable data (sources disagree more than trivially) or NO data (all pitots stuffed) I would hope the system is smart enough NOT to inhibit the stall warning, irrespective of the (erroneous) IAS!

GY earlier posted that stall warning was triggered depending on, amongst other things, F/CTL law. Is it the case that stall warning is NOT inhibited below 60kts IF you're flying anything other than normal law?
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Old 8th Jun 2011, 19:13
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R1:
If you have unreliable data (sources disagree more than trivially) or NO data (all pitots stuffed) I would hope the system is smart enough NOT to inhibit the stall warning, irrespective of the (erroneous) IAS!

GY earlier posted that stall warning was triggered depending on, amongst other things, F/CTL law. Is it the case that stall warning is NOT inhibited below 60kts IF you're flying anything other than normal law?
This bring up another data point that would be of interest:

Over the full range of IAS and other factors taken into account to adjust raw AoA value what is the magnitude of the adjustment.

Is there the min raw AoA value that means you are stalled no matter what the speed and other factors?

Point I am thinking of is the "tweaks" are needed in close to normall flight conditions but are they relevant/needed in extreme attitude, does it matter if you are stalled by 15 or 25 degrees?

Also somewhat related to difference between "stall warning" (approaching stall) and "you are stalled".
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Old 8th Jun 2011, 19:19
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What you really mean might be that IAS and warnings of any kind at low speed might be involved here. Wind Shear comes to mind.

I think the twenty-one second interval to include ten seconds prior to a/p drop and eleven seconds after ("lost speeds", "alternate Law") contain the meat of the matter. If she was actually indicating 60 knots (less), what's the point in the post Stall discussion? The focus for me is on two handovers. One, the a/p to the PF flying (disregard his seat), and the degradation of Normal to Alternate (any one of them).

a/p loss: after the loss of autopilot, there were two Stall warnings. They cannot have been genuine, for the a/c commenced a climb without adding thrust, two things that would have caused a Stall post warning, if genuine,
they were not.

Stall warnings are genuine in ALaw, and these two were false, thus the a/c was not in ALaw after a/p drop. Having preceded airdata loss, the a/p deselected itself, which means the a/c remained in NLaw, with all prots as advertised.

In the short interval between "I have the controls" and rejection of two pairs of airdata, (eleven seconds), the PF knew he was in NLAW, and handled the a/c "Exactly as he was supposed to". Whatever the cause of Pitot sensing failure, it likely was not ICE, and it certainly was not precedent to a/p drop, since loss of reliable speeds and switch to ALaw was diagnosed (reported) after loss of autopilot.

Last edited by bearfoil; 8th Jun 2011 at 19:29.
 
Old 8th Jun 2011, 19:29
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A33Zab, thanks for the BUSS reminder.
In 2007, it appears that the BUSS was not limited in its operation above FL250 as it is now the case. Would you know when that change took place ?


Originally Posted by NOD
When would you like the stall warning to go off? Even at airspeeds below which the vane can work?? These vanes are substantial pieces of metal that can withstand the best part of 500K/1.0M. They are not little feathers that will read reliably at 20K IAS
...
OK - even when the spec/manufacturer of the vane says the IAS is way below the validity of the vane's spec?
What are the vane's spec ?
Would you like to ref a manufacturer documentation … ?
Because to me, by merely direct observation of those vanes, they are pieces of metal which behave like feather …


Originally Posted by R1
GY earlier posted that stall warning was triggered depending on, amongst other things, F/CTL law. Is it the case that stall warning is NOT inhibited below 60kts IF you're flying anything other than normal law?
I like the question, and it reminds me the axiom #1 : Nothing is simple in the Airbus World.
But to answer the question, I would say no : Stall warning has been inhibited below 60kt and airplane was most likely in Alternate or Abnormal Law.
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Old 8th Jun 2011, 19:29
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Cool

Hi,

Indeed the Office of the Secretary of State for Transport Mariani know

Vive Airbus ..
Que justice soit faite

Google Vertaling

Even more pure horse manure from the "l'Express"
Even in the last twenty seconds, while all the drivers before a crash left a message for their loved ones, recorded by the black box, those of the Rio-Paris does not realize
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Old 8th Jun 2011, 19:43
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Originally Posted by Ranger One
Yes, absolutely. But I think the question GY was asking, and I know the question I was asking, related to the interaction between IAS data and the stall warning being disabled below 60kts.

If you have unreliable data (sources disagree more than trivially) or NO data (all pitots stuffed) I would hope the system is smart enough NOT to inhibit the stall warning, irrespective of the (erroneous) IAS!
...
Note that the BEA report states the indicated airspeeds in the initial problem "fell to 60kt". It appears that the control system does this so that any protection that may be disabled if <60kt are not. Is it correct that this speed is so far below that required for flight this isn't mentioned in any manuals?

At least 2 out of 3 speeds recovered before the actual stall, and assuming they stayed in synchrony it is quite likely they reported a valid Indicated airspeed below 60kt at high angles of attack/ sideslip. Pitot tubes are designed to be work without significant error over at least +/- 20 degrees AoA, but they do roll off sharply above +/25 degree, and if the nonlinearity is based on the amount of air directly impinging cos (60 degrees)=0.5
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Old 8th Jun 2011, 20:11
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Thanks to all for serious and honest thoughts and research on those sad events.
What is lacking in the last BEA report ? Almost everything. We need, at least, during the fall of the aircraft, the different control laws coming up then probably going away. We need to know which computers went off and which stayed with the crew. We need to know more about the aerodynamics of the plane (if, let us say, knowing what happened, therefore ready to act, unlike the crew, you rolled full down manual trim and reduced thrust to idle, would it work ?)
Even with the FCOM and some experience and technical knowledge, I am sure we cannot really know how for example the stall warning works. Only the engineers at Airbus or the Maintenance, with detailed wiring diagrams, can dig in this particular situation. Sometimes Speed, sometimes AOA, sometimes both, this alarm manages to work (Perpignan) with blocked AOA sensors…I flew on planes when we had a three months qualification course (yes, three months !) so then we could say we really knew the plane (which was far simpler).
But then, there were flight engineers, god bless them. On the A 320 I had a three days course on the systems, and no on line instructor ever had the courage to ask me a question on them…I probably would have done no better than the crew, but my first reaction, surprised by this unlikely event, would have been…to do nothing. The less you touch the stick, at high altitude, the better the plane flies. This rather stupid remark (forgive me) does not solve the questions, but might be of great help to youngsters on those planes. Sit on your hands, watch, wait…
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Old 8th Jun 2011, 20:32
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AOA

R1:

GY earlier posted that stall warning was triggered depending on, amongst other things, F/CTL law. Is it the case that stall warning is NOT inhibited below 60kts IF you're flying anything other than normal law?
That's not mentioned in the books !!!

Vane resolver sin and cos is input for ADR, ADR generates AOA from this input if CAS =>60 Kts if not AOA=0 and NCD. This is ADR output fed into the PRIMS/SECS and FWC.





More on AOA:

ATSB TRANSPORT SAFETY REPORT
Aviation Occurrence Investigation AO-2008-070
In-flight upset
7 October 2008
VH-QPA

Angle of attack spikes
For an A330, during all phases of flight, the typical operational range of AOA is +1 degree to +10 degrees. In cruise, a typical AOA is +2 degrees.

Complete report including detailed description of polling logic.
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Old 8th Jun 2011, 20:35
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Autotrim

Hi rudderrudderat:
In Post 1407 I wrote:
And number 2 is that when airspeed information, something that the flight control system relies on heavily, becomes unreliable, that autotrim of the THS should drop out with the autopilot.
and I got beat up about it. I'm not wild about the idea of autotrim for the reasons that gums mentioned earlier and I still think that autotrim should drop out whenever the system becomes confused. If it had, things might have been simpler for the crew of AF447.
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Old 8th Jun 2011, 20:47
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From the QF 72 report ...


Firstly, immediately prior to the autopilot disconnect, one of the air data inertial reference units (ADIRUs) started providing erroneous data (spikes) on many parameters to other aircraft systems. The other two ADIRUs continued to function correctly. Secondly, some of the spikes in angle of attack data were not filtered by the flight control computers, and the computers subsequently commanded the pitch-down movements.
The captain reported that he applied back pressure on his sidestick to arrest the pitch-down movement. He said that initially this action seemed to have no effect, but then the aircraft responded to his control input and he commenced recovery to the assigned altitude.
I extracted these two points as they relate to a comment one of our posters in this thread made, (or the RuNe sub forum thread), about length of response time (perceived length of response time???) to his control inputs during a stall. QF 72's captain related to the investigating team a perception of delay between his recovery input and response.

Depending upon the flight regime you are in, and how often you hand fly in that flight regime, you may or may not get the response form the bird that you expect. If you don't get expected response, you may make another input.

What did the PF on AF 447 expect as a response when he took over after noting "Alternate Law" once AP had been diconnected.

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Old 8th Jun 2011, 21:17
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There is a situation that occurs in jet aircraft that is extremely unlikely in your Cessna. Jets can stall both at low speed and at high speed. In a high speed stall at high altitude a lot of pilots pull the nose up instinctively in order to reduce airspeed. This increases the load and exacerbates the stall. The correct procedure is to unload the wing and reduce the thrust to slow the aircraft back into normal speed regimes...
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