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AF 447 Thread no. 4

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AF 447 Thread no. 4

Old 17th Jun 2011, 05:07
  #101 (permalink)  
 
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RetiredF4 and HeavyMetallist

Not disagreeing at all with RetiredF4's detailed post, and in fact building on it, I would like to ask a question concerning the situation once the a/c had established an AoA of about 61°.



Using the graphs in HeavyMetall's reference for the lowest aspect ratio (6), isn't it the case that stick forward, elevator down, would lead to a decrease in the lift on the THS, and hence a more nose-up attitude of the a/c?



So for a pilot getting to the bottom of his barrel of options, might that inhibit further stick forward experiments, and strongly encourage a stick back tendency?



It is true that drag on the THS would also increase and that would tend to act in opposition, but by how much?

Last edited by Jetdriver; 17th Jun 2011 at 17:51.
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Old 17th Jun 2011, 05:11
  #102 (permalink)  
 
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I've searched PPRuNe to see if this has been posted already but apparently not. I believe the AW&ST article is the first actual commentary on who was flying.
PJ2, Actually I did put a link for this one, but I certainly wouldn’t blame you for not noticing …
I don’t really want to comment further about it, but I take that opportunity to admit one more time, if needed, how little respect I have for my beloved BEA :
Originally Posted by 27 May 2011 briefing
Faced with the regular disclosure of partial and often approximate information since 16 May, the BEA wished to publish this note
Their note is nothing else than that : partial and approximate

I know you don't agree, I know how people want to trust their Institutions, but all I need is the full data, nothing more, but nothing less.

Goodnight to all !
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Old 17th Jun 2011, 08:01
  #103 (permalink)  
 
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Re RetiredF4 and HeavyMetallist

@ PickyPerkins

Thank you for doing the handywork posting the graphs i referenced to. I´m too dumb on computers to do it.
You visualized my point of view.
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Old 17th Jun 2011, 09:12
  #104 (permalink)  
 
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Originally Posted by CONF iture View Post
I know you don't agree, I know how people want to trust their Institutions, but all I need is the full data, nothing more, but nothing less.
I ask again - why is it you're asking this of the BEA and no other accident investigation bureau/institution? Is one incident forever going to preclude acceptance of any finding of theirs that includes "pilot error" as a factor?

Also, you're a pilot, I'm an engineer - but I wouldn't trust myself to derive a correct conclusion from the raw data. What makes you so sure you could?
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Old 17th Jun 2011, 09:35
  #105 (permalink)  
 
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THS

PJ2:

The A332 trim rate is 0.2deg/sec on AP and I believe the rate is the same for manual flight using the sidestick. The same 3 electric motors, (only one operating at a time, IIRC) drive the THS. Manual/mechanical trim is meant to be used and employs two hydraulic motors. The mechanical stops are part of both systems. A pawl and ratchet system prevents back-movement under air loads. From what I have been able to learn, I don't believe that the THS would return to a previous setting after a prolonged manoeuvre if the stick is merely relaxed, (neutral, no orders to the FMGEC > FCPCs). I believe the THS would remain "as is" in manual flight and the airplane would "settle" into the setting just as any airplane would. In autoflight it would of course, trim.
I’ve got these figures of THS rate.

If they stated: "there's only 1 motor in control" they mean the ELECTRICAL motors (P1,P2 & P3) whichs drives the control sleeve. Control sleeve position will be overriden by mechanical input (from handwheels)


The THS itself (the ballscrew) is driven by 2 hydraulic (B & Y) motors.

Max. Operating Load and Max. Speed (2 motors)

18940 daN (42578.81 lbf) ----- 0.4°/s
16950 daN (38105.11 lbf) ----- 1.0°/s
6770 daN (15219.56 lbf) ---- 1.2°/s

Half speed for 1 motor (1 hydr. B or Y system failure) operation.

Since the hinges are on the trailing edge and therefore the aerodynamic load on the drive spindle is in the AND (stab. Nose Up) direction (see diagram by Tailspin Turtle) it would take 12 sec. to travel from 13° back to 3° ANU. Or is that a too simple conclusion?

The rate for the BEA mentioned 1 minute to go from 3 to 13 ANU was 10°/60 = 0.16°/s.

Limit load (both compression as tension) is 32500 daN (73062.9 lbf).
I assume this limit load is mentioned as being the limit for the Hydr. motors to drive the THS.

Last edited by Jetdriver; 17th Jun 2011 at 17:49.
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Old 17th Jun 2011, 10:00
  #106 (permalink)  
 
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Aerodynamic authority / sensing the flux

Hi there,
Just wondering about the opportunity to provide to the pilots additional flight parameters such as the AoA and beyond: wouldn't it be possible to measure the efforts generated by all the control surface actuators (in response to the flight control loop orders), to estimate directly/specifically their aerodynamic authorities and display them ? (roughtly, the harder to actuate the control surface, the more aerodynamic authority it has ? or an estimation performed through more sophisticated aerodynamical models for each control surface and the airframe ?).

Last edited by Hyperveloce; 17th Jun 2011 at 10:16. Reason: trying to speak a proper english
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Old 17th Jun 2011, 14:00
  #107 (permalink)  
 
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gonebutnotforgotten
That same Air Caraibes report also said that at the time of the beginning of the anomalous air data, the indicated altitude rapidly dropped 300 ft (presumably due the lack of a vaild Mach number to correct the static pressure (? ) the BEA has already told us that with no vaild M, the stall warning system uses a value near zero...)Maybe the PF was reacting to that, admittedly 300 ft isn't much, but I suspect it looks a lot on the tape, and it would have been rapid. Perhaps this is the trigger we've been looking for.
Man-machine interface. Is the unreliable M related only to airspeed/pressure sensing, or is it also related to a TAT sensing anomaly?
mm43
I doubt if there is overly much difference between the initial FDR printouts of the Jetstar VH-EBA UAS incident and those recorded by AF447. Have a close look at what happened to the TAT, SAT and CAS traces and similarly to the altitude when the Mach correction wasn't available.
Probably worthwhile bearing those traces in mind when discussing the initial upset.
How can BEA confirm or determine if the ice and pitot tube interaction was accompanied by an ice TAT probe interaction?

I will guess that a trend line from "X" minutes prior to the event could show where Temp anomalies are or aren't likely. The recorded cockpit briefing about temperature not developing as planned/forecasts may be of no moment ... or maybe a clue pointing to TAT readings sensing beginning to degrade as Airspeed sensing began to go wrong?
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Old 17th Jun 2011, 14:41
  #108 (permalink)  
 
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Full download of thread - available?

Given the intense interest from the piloting community in this baffling event, and my previous decision to refrain from posting in case this ancient showed how out of touch she was, is there any way to bulk download this series (1-4) of threads, so that one might search previous posts on a specific topic?

(This after skimming over a post which I can't now find, which seemed to suggest that the standby instruments (ICUS, I believe they/it are called) are not fundamental, steam-driven devices, but take their data input from some branch of the computed data stream.)

I can find the printable area, but 40 posts only. I'd like to be able search any discussion point. Anyone?
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Old 17th Jun 2011, 15:02
  #109 (permalink)  
 
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Originally Posted by gonebutnot forgotten #85
I find (1) unconvincing because it was one hell of an input, sufficient to cause a 7000 fpm climb and, apparently, two stall warnings, sounds sort of deliberate to me.
Was it 'one hell of an input'? 7000 fpm is achieved after 18 seconds of 0.2 g; 12 seconds of 0.3 g, or 9 seconds of 0.4 g.

the BEA has already told us that with no vaild M, the stall warning system uses a value near zero...)
BEA Interim Report #2:
In alternate or direct law, the angle-of-attack protections are no longer available but a stall warning is triggered when the greatest of the valid angle-of-attack values exceeds a certain threshold. In clean configuration, this threshold depends, in particular, on the Mach value in such a way that it decreases when the Mach increases. It is the highest of the valid Mach values that is used to determine the threshold. If none of the three Mach values is valid, a Mach value close to zero is used. For example, it is of the order of 10° at Mach 0.3 and of 4° at Mach 0.8.
This explanation is either in error, or we are misinterpreting it (The BEA Update adds a new meaning to 'invalid airspeed'). In the case of the UAS incident documented in the Air Caraibes Memo, stall warning occurred at 4.2 degrees, with ADR DISAGREE. In the case of AF447, the stall warning must have been at a similar value, because the low-speed value of 10 degrees is well beyond stall AoA.
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Old 17th Jun 2011, 15:04
  #110 (permalink)  
 
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@JenCluse:

I think you're talking about ISIS (shown here)

http://www.samtel-hal.com/cache/isis.pdf

It's a digital display, and yes air data will still come from the pitot tubes and static vents (as would be the case with "steam gauge" hardware too), but the data is taken from standby units as I understand it - it is intended to be independent of the main systems. At present there's no evidence that any data on either the main PFDs or the ISIS display was incorrect - other than airspeed data, which was anomalous for a duration of approximately 45 seconds.
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Old 17th Jun 2011, 15:13
  #111 (permalink)  
 
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Hi JenCluse,
I'm also feeling your pain as I'm trying to catch-up with this thread after a while.
Originally Posted by JenCluse
(This after skimming over a post which I can't now find, which seemed to suggest that the standby instruments (ICUS, I believe they/it are called) are not fundamental, steam-driven devices, but take their data input from some branch of the computed data stream.)
I can find the printable area, but 40 posts only. I'd like to be able search any discussion point. Anyone?
I understand that you are refering to ISIS and what you think is, in some way, both right and wrong. Stand-by instruments are supplied by analogic pnematic sources: probe pitot 3 and static probe 3. However, both probes are used for direct sensing and/or connected to numerical Air Data Module (ADM). In this case, those ADMs are feeding ADR3 which may replace either ADR1 (Captain probes) and ADR2 (FO probes) while the stand-by gauges (ISIS) are displaying the direct measures from the same probes.

You can also refer to the BEA first report which have a detailed diagram with usefull explanation about Airdata, page 22:
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Old 17th Jun 2011, 15:31
  #112 (permalink)  
 
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LW50:
The recorded cockpit briefing about temperature not developing as planned/forecasts may be of no moment ... or maybe a clue pointing to TAT readings sensing beginning to degrade as Airspeed sensing began to go wrong?
I missed the implications of the briefing on temps not developing as expected before now but this fits well with my (just a)theory that almost every item included in the BEA note will in hindsight appear to be relevant to the final determination of the event chain.

As I have said before they (BEA) have a much better picture of what happened than outsiders so the note would have been written with the likely ultimatly signinificant factors in mind.

Also possibly significant is that the final item in the note is the mention of dual control inputs (no hint if matching) and the transfer of control.

My take on this is that beyond this point there was still (at the time the note was created) discussion/uncertainty within BEA as to whether the situation was (even theoretically) recoverable and the level of understanding of the situation in the cockpit.
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Old 17th Jun 2011, 15:40
  #113 (permalink)  
 
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finding stuff in past threads

JenCluse

is there any way to bulk download this series (1-4) of threads, so that one might search previous posts on a specific topic?
Although it isn't a download, you can achieve a search of only the 4 threads by using the following search string in Google
ths af447 site:http://www.pprune.org/tech-log/
this will search for mentions of THS in the AF447 threads of tech log only. Just change the THS in the string to whatever you want to look for. Adding the site:URL end part is the magic that restricts Google to only searching in the tech log on here

Copied to post #1 for general dissemination
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Old 17th Jun 2011, 15:41
  #114 (permalink)  
 
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THS Rates & Trim terminology

A33Zab,
That explanation is invaluable, thanks. So it's only too easy to get confused between the electric (control) motors and the hydraulic (actuation) motors...

From the auto-trim point of view, the movement from 3NU to 13NU (after FL375) was very nearly continuous? I guess it only uses the one speed of 0.2deg/sec, as quoted by PJ2. Although you state a 2-motor speed of 0.4deg/sec, perhaps limiting the speed to 0.2 would avoid any slow-down if either the blue or yellow hydraulic motor failed?

On the face of it, those who have advocated use of manual trim-wheel in stall recovery seem to be vindicated, as its 1deg/sec might be needed. The argument probably only applies in Pitch-Alternate Law. We still have no idea what the effect of full down-elevator is when the THS is at 13NU. (That is: what would be the equivalent THS setting with neutral elevators?) Sadly, the answer does not seem to be pertinent to this accident.

Quote:
Since the hinges are on the trailing edge and therefore the aerodynamic load on the drive spindle is in the AND (stab. Nose Up) direction...

Please forgive me for offering readers a warning on terminology here, from my experience of various jet transports with THS under one name or another. "Nose-up" is a term normally used to indicate the trim-effect on the aircraft, not the physical position of the THS. Because the THS is hinged at its aft spar, it's easy to think of "nose-up" as meaning that the leading-edge of the THS is up. Not so.

For maximum nose-up trim, a THS is at its fullest NEGATIVE incidence, with its leading-edge fully down. The A330's mechanical limit seems to be -14 (see PJ2/mm43 discussion). We call that "14 degrees nose-up" (14NU). For a typical take-off, the THS setting calculated on the trim-sheet by load-control might be 3NU. This requires the incidence of the THS to be -3 deg. However, load control and most pilots refer to it as "+3". Confusing, perhaps, but that's the way it is.
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Old 17th Jun 2011, 15:43
  #115 (permalink)  
 
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Originally Posted by hyperveloce #105
wouldn't it be possible to measure the efforts generated by all the control surface actuators (in response to the flight control loop orders), to estimate directly/specifically their aerodynamic authorities and display them ?
In fact the A320 system does something very similar when it compares the gross weight calculated from air data and inertial data to the gross weight calculated in the FMS from loadsheet and fuel used. In case of a discrepancy, a CHECK GW message is generated. (See Perpignan Final report). I don't know if that function is available in the A330. Using that same logic in reverse the airspeed could be calculated from the FMS weight. The BUSS presumably does something similar.
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Old 17th Jun 2011, 15:50
  #116 (permalink)  
 
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Murphy, about misunderstanding in the cockpit, it might get curiouser and curiouser ...

IF
you lose airspeed, or it becomes unreliable
AND
You are an A330 Pilot who is already reasonably familiar with previous incidents in your model aircraft ... since the manufacturer and your company put out bulletins and findings of previous UAS incidents
AND
You are in a UAS incident yourself

You do X, Y, and Z in response. (Comments in the cockpit on loss or lack of indications, which I presume it means airspeed, is what I am working with here ...)

At what point can you determine that the airspeed has stopped acting up and become reliable again?

The forensic analysis points toward about 45 seconds worth of bad airspeed, and then a return to reliable state ... how does the crew know that it has returned to reliable? Did they ever have a cue (problems with stall AoA's on pitot tubes considered) that AS was telling them good information again?

What is dwell time (human observation and perception not being a step function) between "it's bad" and "it looks good again" in a

Benign cockpit environment?
High task load cockpit environment?

Do the training pamphlets or the sim sessions devoted to UAS training address what symptoms tell you that your airspeed tapes are once again reilable?

You aren't using the old style circle gages, where the needle might stop agitating and then return to a more normal looking state. You are looking at the vertical strip. What discrete cues do you have? From the air data diagram that takata so kindly posted, it seems that the ISIS display might be the first cue, depending upon which pitot tube got itself back in order first.

I apologize for asking what might be an idiotic question, but I've not flown an A330, nor been exposed to A330 UAS malfunction/emergency training.

Hazelnuts39:
Was it 'one hell of an input'? 7000 fpm is achieved after 18 seconds of 0.2 g; 12 seconds of 0.3 g, or 9 seconds of 0.4 g.
Do you mean 1.2, 1.3 and 1.4g? (I am guessing that you meant a delta from a "stable" 1 g reference.)
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Old 17th Jun 2011, 16:40
  #117 (permalink)  
 
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Aerodynamic authority / sensing the flux

Hi,

Hyperveloce @ Post #105

Sounds a very good idea. And with a good approach: To provide extra and (redundant) important info

Considering the computational capabilities in these "advanced planes" it seems it would be quite easy to do this "pattern recognition" in real time.

Question:

What kind of sensors you imagine in order to provide the data to the System? Some are yet available?

Last edited by RR_NDB; 17th Jun 2011 at 18:34. Reason: Text impvmt
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Old 17th Jun 2011, 16:40
  #118 (permalink)  
 
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Hyperveloce, 105

Hi there, Just wondering about the opportunity to provide to the pilots
additional flight parameters such as the AoA and beyond: wouldn't it be
possible to measure the efforts generated by all the control surface
actuators (in response to the flight control loop orders), to estimate
directly/specifically their aerodynamic authorities and display them ?
(roughtly, the harder to actuate the control surface, the more
aerodynamic authority it has ? or an estimation performed through more
sophisticated aerodynamical models for each control surface and the
airframe ?).
Have been thinking about something similar, but in relation to wing loading
as an extra parameter input for the calculation of lift. For the control
surface case, this could be instrumented via strain gauge type transducers,
one would think, near the control surface root.

In the wing loading case, deriving lift force is complicated by acceleration
forces, but since other areas of the system (adirs) already measure this, the
acceleration could be subtracted out to derive actual lift on the wing. How
usefull any of this might be, I don't know, but there are times when the more
cross check type data that there is available, makes it easier for dumb logic
to determine what is really happening....
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Old 17th Jun 2011, 16:45
  #119 (permalink)  
 
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Lonewolf50;

Yes, your interpretation is correct. Added to the acceleration due to gravity, the 'sensed' acceleration values are 1.2, 1.3 and 1.4 g. The values of rate of change of velocity (dV/dt) are 0.2, 0.3 and 0.4 g. Sorry for being somewhat pedantic, couldn't help it.

Last edited by HazelNuts39; 17th Jun 2011 at 22:49.
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Old 17th Jun 2011, 16:58
  #120 (permalink)  
 
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Return Of Reliable Airspeed

LW50:
At what point can you determine that the airspeed has stopped acting up and become reliable again?
When all of your speed indications are again the same and are consistent with the pitch and power that you have been flying to prevent upset.
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