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AF447 Thread No. 3

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AF447 Thread No. 3

Old 13th Jun 2011, 04:49
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bearfoil, it is documented that AirBus was frantic with the coming air show. I presume they were demanding a release to show their aircraft is not at fault. That is about all that the release shows. The aircraft did what it was told. (It obfuscates by not showing any definitive data that might indicate the aircraft supplied the pilots with inadequate information.

The release was made.

Somebody lost incentive to leak.

Was it the victim's families? Was it Air France, whose pilot was shown in a poor light absent a "why" in the data implicating training or aircraft data or aircraft data or presentation? Was it Thales? Was it who?

Follow the money says it was AirBus.

And of course, that is purely circumstantial evidence. Are there other candidates for the leaks?
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Old 13th Jun 2011, 04:56
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bearfoil, on the second issue I took issue with the implication in your words that the mass had a great deal to do with the "heavy" being able to trade velocity for altitude. In a vacuum it had sufficient velocity to loose 300 miles per hour to gain 4000', if I remember the numbers in question. A 50% decrease in mass would not change that at all in a vacuum. In air it might change it a few percent due to the imperfect energy transfer. Some would be lost to air friction.

A balloon, if you could get it to mach 0.82 would lose way more than 300 mph to climb even a fraction of 4000' due to the wind friction of its shape. But most aircraft designed to fly up there can probably make that trade pretty efficiently. So declaring the mass had anything to do with it suggested you thought a lighter plane at the same altitude and velocity (on its own power) would not be able to make that full tradeoff.

I guess I was being nitpicky with some wording that set my hairs on edge.

I spent good money for those physics classes.
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Old 13th Jun 2011, 04:57
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bearfoil, and third....

The BEA data explicitly calls out a sudden change not any gradual process. How are the two reconciled?

edit: And it cites the sudden change as being downwards from 275 knots, the
cruise speed. So there was apparently, in the data presented, no prior increase in speed.

Last edited by JD-EE; 13th Jun 2011 at 05:19.
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Old 13th Jun 2011, 05:16
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3holeover, I'll give the bear that one. It is quite natural to anthropomorphize inanimate objects. Why else are vehicles referred to as "she" so much in America?

"The a/c thought it was ok to climb, it helped," merely expressed the concept that the plane was designed to fly and performed accordingly.

(See, bear, I jump when it seems like there are outright conceptual errors or inconsistencies between assertions or conclusions and data. When you are merely being human I'll side with you. Otherwise I'd lose the right to cuss like a sailor at my computers.
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Old 13th Jun 2011, 07:06
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@ Bearfoil: Also, a rapid and consistent increase in a/s could trigger WindshearAlert. It could also trigger OverSpeed alert, etc. These artifacts are present in the ACARS

I don't think the Windshear Alert can trigger at all. It only actively (assuming the same piece of kit is used on the 'Bus in AF design spec as in many other airlines) starts looking for windshear when the RadAlt is below 2300ftRA. That is when warnings can be given.
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Old 13th Jun 2011, 08:56
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Hi JD-EE,
Kinetic energy is 1/2 mV^2. Potential energy is mgh. So the mass washes out of the equation. So a 3000' climb would give "gh" = 1/2 v^2 = 96000 ft^2/s^2 equals about a 438 '/s velocity change or about 300 MPH.
is correct - but it ignores the total starting energy.

They were Initially flying at M.8 (about 480 kts TAS (Vi)) at FL 350 (h1).
Shortly Afterwards they were at FL 375 (h2) with a new TAS Va

I/2 (M Vi^2) + Mgh1 = 1/2 (M Va^2) + Mg h2.

If you do the maths Va = 368 kts TAS.

The reduction from 480 to 368 kts (112 kts) was converted into an Altitude gain of 2,500ft.
From time 2.10.05 at FL 350 they had an IAS of 275 kts, so would have finished at FL 375 with an IAS of about 211 kts. (275*368/480) .
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Old 13th Jun 2011, 09:00
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Originally Posted by JD-EE
...
edit: And it cites the sudden change as being downwards from 275 knots, the
cruise speed. So there was apparently, in the data presented, no prior increase in speed.
Just to point out there would be no visible increase in indicated speed if common drain blockage gradual and indicated speed is under auto control. And Mach 0.8 @ FL350 @ ISA +10 is closer to 272 knots according to my calculator, probably within 'about' and lines up with the rudder travel limit.
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Old 13th Jun 2011, 09:21
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Originally Posted by Sciolistes
Henra,
In the course of releaseing such an incomplete picture, it seems that it is perfectly acceptable for the media to insinuate that the pilots were substandard despite the aircraft switching off its warnings and dynamically changing its behaviour during what would be the upset recovery phase of that flight.
Agreed that this deduction by the media is baseless and unfounded with the information at hand.
But we should not reduce our level to the one of the mass media.

Please let's discuss it on what is known or reasonable to assume and not some blunt generalisations or completely unfounded wild speculation. Let's leave this to the media....

Last edited by henra; 13th Jun 2011 at 09:37.
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Old 13th Jun 2011, 09:53
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Originally Posted by JD-EE
bearfoil, it is documented that AirBus was frantic with the coming air show. I presume they were demanding a release to show their aircraft is not at fault.
Hmm, sounds logical at first glance.
On the other hands sales of transport aircraft is not a spontaneous decision made in the morning at 10am during an Airshow visit.

These are long running processes beginning loooong before such an event. Very often only the formal publication of an order will be communicated during the event.
And the decision processes behind are almost exclusively driven by economics, prices, fleet considerations, maintenance, etc.
Emotions do not have much place there.
Therfore I seriously doubt that this preliminary publication will have any impact on aircraft sales one way or the other.

I also can not believe that BEA will dare to paint a picture of the events only to have two months later a real report which contradicts the general lines of this preliminary note. Would be too embarassing.
All in all my assumption is that the general lines of this note will match quite well to what has happened from a factual perspective but it surely lacks the more subtle things which contributed to the why. And it is often the subtle things which make people act the way they do.
The devil's in the detail.
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Old 13th Jun 2011, 10:28
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The devil's in the detail.
I wouldn't be surprised if the outcome of this investigation reveals to some degree that automation, introduced to reduce pilot error, may be the source of making pilot error.
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Old 13th Jun 2011, 10:53
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Henra,
Please let's discuss it on what is known or reasonable to assume and not some blunt generalisations or completely unfounded wild speculation. Let's leave this to the media....
Thanks for your latitude. The point I am making (badly) is that it simply is not possible to determine any cause from the report that was relased by BEA. There are too many missing facts, ambiguous sequences and vauge quantifications. Additional evidence that it is not possible, is the hundreds of pages of posts that are no nearer to agreeing an interpretation of the report, never mind the actual causal factors.

If my point is even partially correct, just what was the point of this report update?
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Old 13th Jun 2011, 11:04
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An idle thought, prompted by some of the ideas submitted on this (and other) threads:

In gliding we are taught the concept of the 'Yates effect' (named for aerodynamicist AH Yates), which goes something like this:

Why gliders speed up when contacting lift
You may have noticed that the ASI shows a speed increase when you fly into the core of a thermal. The reason was first described by Dr AH Yates. An up-draught will increase the angle of attack because the airflow comes more from below. Since the lift from the wings always acts at right angles to the relative airflow, the lift acts further forward and accelerates the glider.




One wonders if what goes for gliders is also applicable in an airliner flying at FL350 / M 0.83. I know from personal experience (stubble fire plume entry, for example) that the Yates effect can be huge: a glider may require a rapid change of pitch of >+60 degrees (!!) to avoid exceeding max manoeuvre speed, shortly followed by an equally aggressive (zero 'gee') recovery to a 'normal' pitch attitude to avoid the stall.

An unusually severe 'seat-of-the-pants' lift force experienced at the same time as an (assumed) unusual attitude and loss of airspeed references - followed by (speculation) an incorrect recovery to normal pitch attitude - *might* have initiated this upset.
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Old 13th Jun 2011, 11:26
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DozyWannabe, 1896

Wrong again. The "test pilots" would have been quite capable of taking
the aircraft to a genuine stall as part of certification testing. You're
confusing line pilot stall/incipient stall training (which certainly
looks deficient with 20/20 hindsight) with Airbus's own testing of it's
aircraft and systems.
Ok, but "quite capable" only implies that the a/c was tested beyond
incipient stall conditions as part of the certification process. I've
read elsewhere that this is not the case, as it is considered too
dangerous. This of course begs the question: If the a/c hasn't been
tested in deep stall, with known good recovery procedure, how can
one expect the pilots to recover under such conditions ?.

I think I mentioned this in another post, but got no response. Perhaps
you have a reference to a document that describes the full certification
process, including deep stall recovery ?...
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Old 13th Jun 2011, 12:06
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Sciolistes, 1912

If my point is even partially correct, just what was the point of this report update?
Interesting question and on balance, i'm with the cynics on this one,
with regard to the air show. The damaging effect that wild
speculation can have not only on sales, but also passengers who might
refuse to fly Airbus if they think that they are in any way unsafe, demands
some sort of response. Tell a lie or smear often enough and it becomes the
truth in the minds of many.

I do think the update was intentionally vague and with incomplete information.
Such a release would be considered quite unprofessional in some quarters, but
it wouldn't be the first time that objective science has come into conflict with
politics and big business. At least, they don't burn you at the stake these days.
I don't doubt for a moment that BEA are anything but diligent in their efforts and
that they will report the truth. We don't need yet another conspiracy theory to
understand the timeline here.

In a nutshell, that's life, get over it...
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Old 13th Jun 2011, 13:37
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Some thoughts:

To those that want to divert this thread with idle speculation regarding what the passengers may or may not have been aware of - knock it off. This has no place within this thread (remember: this is the Tech Log...?) and can serve no useful purpose. Lawyers will no doubt play that game to the max when the time comes, but within these pages I can see nothing but theatrical imaginings - leave it alone, please.

to rudderrudderrat for the airspeed calc a few posts back - you seem to have hit the numbers on the head.

JD-EE: Do you not think that (a) the BEA will in the fullness of time produce a full report, that would leave them looking like a bunch of incompetent idiots unless the majority of the recent note is essentially the meat and potatoes of the incident? I mean it's going to be hard to take them seriously if they suddenly switch story-lines. What we have been given is the frame upon which, no doubt, the fine print will become overlaid. I find it hard to imagine anything being added that is so astounding that collectively make a virtual 180 with our thinking here. (b) You seem to believe that Airbus is the only player that has a significant hand in this game? Do you not think that Air France might also be rather interested in what the BEA are saying? At the end of all this a large and ugly lawsuit is lurking and some large $$$ are about to discussed, so I really can't see the BEA being pressured to apportion blame (implied or otherwise) without the data to back that up.

Several mentions have been made a 'deep stall' - why? This is a specific stall condition mostly defined as "A condition such that the turbulent wake of a stalled main wing "blankets" the horizontal stabilizer, rendering the elevators ineffective and preventing the aircraft from recovering from the stall." Neither the BEA note, or any of the more 'thoughtful' contributors believe this aircraft was in any kind of "deep stall" I think it fair to say.

For 'gums' and his musing on the Viper deep stall, I would characterize that as something different, largely due to the non-stable aerodynamics of the aircraft, that the FBW system normally kept under control - you bad boys just found a way to get into a flight condition that I figure the designers didn't think you'd find!

Finally, there has been some speculation that the pitot issue bay have been drain blockage leading to an increase in airspeed indication... where is this imaginary event coming from? Does anyone here rationally think that the BEA would not mention this? If this gradual speed increase was occurring, the AT system (prior to disconnect) would normally be attempting to compensate I would surmise? I am pretty sure that the information released would have mentioned this, since it would have been precipitous to the whole accident sequence. Finally, the zoom-climb energy calc would not work, unless the aircraft speed was not as declared (275kt).
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Old 13th Jun 2011, 13:46
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Thanks for the link PJ2.
In this case, only the left PFD speed was recorded, probably something to do with the fact that VH-EBA was not the Enhanced version of the 330 ...
It appears that the Digital ACMS Recorder DAR didn't deliver the two other speeds neither.

The similitude in the ACARS messages with AF447 is relevant, but one particular message is missing, the one Svarin is talking about :
WRG:ADIRU1 BUS ADR1-2 TO FCPC2
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Old 13th Jun 2011, 13:51
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Calculation of Mach

DJ77 (#1833), thanks for your view. Whilst the Wiki references and the descriptions of mechanical instruments (and some ADCs) add credence to the view that TAT is not required to calculate Mach, I recall that temperature is in the root of the equations.
Mach is the ratio of speed at a point to the local speed of sound; the latter definition requires temperature. As has been shown, suitable manipulation of equations can reduce the measurement requirements to pressure / pressure difference for mechanical solutions, but IIRC this involves small errors or a look up table.
However, in a digital system, where programmers might be reluctant to use resource sapping square root calculations, alternative derivations of Mach may be used.
Thus, with open mind, the question is; how is Mach calculated in the A330 ADC?


CONF iture (#1825), info noted. However, with continuing open mind, it has not been established that 7000 ft / min is a real velocity or just that which was recorded (displayed). It appears that the aircraft did climb, but to what altitude and how fast might be poorly defined. Note that VH-EBA ‘descended’ suddenly 300ft, but this was only the recorded indication.
Considering a highly dynamic situation in AF447, with many parameters ‘failing’ or outputting erroneous values it might be difficult to draw any conclusion as to what the airaft actually did, perhaps excepting AOA, e.g. if the speed altitude anomalies were partially restored, how might the VS calculation account for these sudden changes (VS is an inertial / airdate mix?)
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Old 13th Jun 2011, 14:07
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bearfoil, 1901
I agree. However, if the drain plugged first, the first invalid
excursion of a/s would be an increase. If the aperture plugged up with
the drain, stagnation, and "frozen" sense of "a/s" read while both holes
remain plugged. If the drain unplugged before the Aperture, the ias
would approach zero.
Not sure I agree or understand all this. My take on the pitot
probe fault modes and their results would be:

1) Drain hole blocked: Would only cause an small increase in
airspeed at cruise. The drain hole must be small to avoid loss of
resolution and non linearity at low air speeds, as the probe has an
approximate square law response. Whatever size hole is used, there
will be some non linearity, but this would normally be corrected for
in the sensor electronics via lookup table, in much the same way that
pressure error correction is applied for airframe probe position errors.

2) Both stagnation and drain hole blocked: This would fix the airspeed
at the last measured value before blockage. The value determined to a
degree by the sequence in time in which the stagnation and drain ends
became blocked. If the drain hole subsequently became unblocked first,
the air speed would decay towards zero. If the stagnation end became
unblocked first, the airspeed would indicate the true value + drain hole
pressure loss. Output either no change or step function.

If both ends are blocked by ice, the drain hole end will be shielded
from the cold airflow and could be expected to unfreeze first. Thus,
the airspeed would tend to decay towards zero initially until the stagnation
end became unfrozen, when the airspeed would ramp up to true value.

Take this to bits if you like ...
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Old 13th Jun 2011, 14:13
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Chris,
In a nutshell, that's life, get over it...
Fantastic, thanks for the top tip
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Old 13th Jun 2011, 14:24
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I hope this hasnt already been discussed

In the aftermath of the accident the plethora of automated signals sent from the doomed aircraft were widely publicised. Has this information been compared to the details of the accident released so far and in particular the time line provided by the BEA?

In my laypersons opinion, surely a comparison would yield some additional insight into what the pilots experienced and what caused the tragedy.

As an aviation enthusiast and very part time passenger, it boggles my mind that a modern automated aircraft could get stalled at 35 000 ft + and not carry on flying at some point before crashing.
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