Air France jet missing

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Ed
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Re: Air France jet missing

Postby Ed » Sat May 28, 2011 3:06 pm

I will confess my ignorance on this issue, so I would like some enlightenment. (please feel free to cut and past as your signature Bogs).

When designing satellite control systems, they put in voting circuits to avoid ambiguous indications. The voting systems are based upon combinations of different code running and/or different processors to try to avoid pathological behavior from a single system. Is the critical system here the pitot static system? If so, what is the redundant system? To be left in the dark, going into thunderstorms with no two instruments reading the same thing is a terrifying thought. Is the control system really that "fragile"?

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Re: Air France jet missing

Postby Ed » Sat May 28, 2011 3:17 pm

I am not sure how this applies.
To Gabriel everything within a nautical mile of the word stall applies. It's his pet issue, this whole stall-and-bury-the-nose business. It's a dead horse that he not only has killed, then beat for three days, then ate, but also shit it out and ate is as his own shit again.

Nothing like OCD with illusions of grandeur. You say stall and he'll go off for fifteen pages, plus he now has a new supporter in that dipshit Evan at the other site.
To try to put a positive spin on it, in some ways it is indicative of good VFR training. It is the same story that was drummed into my head in glider and power training - nose down, nose down, nose down. I think where the problem arises is when low time VFR pilots attempt to introduce the same rules into high performance jet aircraft flying IFR at night into thunderstorms over the Atlantic Ocean. OK, the dude in Buffalo certainly needed to go back to ground school to learn about stalls, but even there it was flying in icing conditions which confounded the matter and some crew rest issues...plus, he was flying a turboprop at lower altitude.

Not having flown a jet aircraft I know all I could really say is that in general, if you know you are in stall, then lowering the nose should get you out of it. This worked for every Schweizer, Cessna, Piper etc I have ever flown. The best practice for high performance jets....I would say that I could not even start to comment.

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3WE
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Re: Air France jet missing

Postby 3WE » Sat May 28, 2011 3:34 pm

Stalls- where pilots continued to pull up- have caused a lot of crashes, Flyboy, it's that simple...
The only thing that's simple is that you're a moron, 3BS. It sounds to me that this crew was dealing with a situation where no two instruments agreed, with stall warnings that came and went, on top of some serious turbulence at night.

I will not pass judgment on this crew until I know what (if any) data that they were presented with was good. If the pitostatic system was compromised, perhaps they never saw the 10,000fpm+ descent rate, plus it appears they had three disagreeing ADIs and three disagreeing ASIs as well as three disagreeing altimeters. The comment "we have no valid data" points me in that direction.

So, they weren't just pulling the nose up, they were trying to make sense of data, none of which was making sense.
Asshat- I never said that all stall crashes were dumbass pilots pulling up, nor that this crash was dumbass pilots pulling up. I just said it's relevant. But that's too complicated of a concept for you.

Not only that, but Gabriel has been pretty clear (and lengthy) on how damn confusing it might have been for them on Air France.

Ed: Concur (and thanks for the civil counterpoint). I will say; however, that in some stall-related crashes the experts in the final report said that the pilots incorrectly pulled up when the information was clear that they should not.
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Re: Air France jet missing

Postby Ed » Sat May 28, 2011 4:37 pm

Ed: Concur (and thanks for the civil counterpoint). I will say; however, that in some stall-related crashes the experts in the final report said that the pilots incorrectly pulled up when the information was clear that they should not.
Just remember that hindsight is 20-20. If they had nosed down and hit the ground through CFIT or in-flight break-up, it would have been just as bad.

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Re: Air France jet missing

Postby flyboy2548m » Sat May 28, 2011 4:56 pm


Not only that, but Gabriel has been pretty clear (and lengthy) on how damn confusing it might have been for them on Air France.
Gabriel has never been clear on anything. The man is the master of argumentum verbosum for which morons like you fall every time.
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Gabriel
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Re: Air France jet missing

Postby Gabriel » Sat May 28, 2011 6:35 pm

I am not sure how this applies. Lowering the nose when you are into stall and your instruments indicate stall and you are sure it is a stall is one thing. The indications we are seeing right now is that there were different readouts and therefore they did not even know if the stall warning was valid.
Tho only data that was bad, as far as we know by now, is airspeed.
They had good altitude, vertical speed, attitude, and engine instruments.
The A330 FCOM says that the stall warning is valid and must be honored in a UAS event.
So they had the nose 16° up, the vertical speed 10,000 fpm down, the stall warning warning, and they didn't know that they were in a stall???
In so much as you don't want to stall these aircraft, I will make an assumption that it is equally bad to overspeed. Dropping the nose at the first sign of trouble is a good first practice for Tomahawks and Cessnas in VFR, but I am not sure about high performance jet aircraft at high altitude.
And I agree. But when the stall warning activates the only action is to reduce the angle of attack. That doesn't necesarily mean pointing the nose steeply down (or down at all). But pulling further up, as this crew did, certainly won't help. Or ask some 228 dead people if it did.

In this accident, at a high cruise altitude, at the first sign of problem the pilot took manual control, pulled up with enough intensity to activate the stall warning, pitched 10 degrees up, bringing the vertical speed to +7000fpm, but adding no thrust whatsoever, and when they peaked at the top of the unsustainable climb and the stall warning activated again, they added TOGA thrust and... PULLED UP AGAIN!!!!

What should have they done at the first sign of problem? Pulling way up? Pulling way down?
No. Applying climb thrust and adjusting pitch for 5° nose-up attitude.
But once they stalled, yes, they should have kept the AoA low as necessary to keep the stall warning quiet. I bet that 5° of NOSE UP attitude would have sufficed.

You'll see: When the nose is 16° up, lowering the nose does not necessarily mean pointing below the horizon.

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Gabriel
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Re: Air France jet missing

Postby Gabriel » Sat May 28, 2011 6:44 pm

I'm surprised an A330 does not have an AoA indicator.
You know of an airliner that does?
I don't, but Boeing offers it as on option in the PFD
http://www.smartcockpit.com/pdf/flighto ... ynamics/38

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Re: Air France jet missing

Postby Gabriel » Sat May 28, 2011 6:45 pm

And yet this will still be labeled pilot error. Something is dreadfully wrong here.
If I am understanding all the information released so far;

they did apply aft stick in response to and during a stall.
Yes.
That was the second part.
The first part is that they brought the plane to the stall by not complying with the unreliable airspeed procedure.

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Re: Air France jet missing

Postby Gabriel » Sat May 28, 2011 6:48 pm

I am not sure how this applies.
To Gabriel everything within a nautical mile of the word stall applies.
You don't mean that this accident was barely related to a stall.
Or do you?

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Re: Air France jet missing

Postby Gabriel » Sat May 28, 2011 6:59 pm

Am I interpreting this section correctly in that it is saying that even though the aircraft was in a stall situation, the stall warning stopped sounding because the speeds were so low?
Yes. I don't like it either.
However, with the nose 10° up and a vertical speed of 10,000fpm down, there should have been no doubt that they were very well stalled.

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Re: Air France jet missing

Postby Gabriel » Sat May 28, 2011 7:10 pm

Not only that, but Gabriel has been pretty clear (and lengthy) on how damn confusing it might have been for them on Air France.
3WE, to be honest, I'm more inclined to blame pilot error than Airbus systems now.

Despite all the warning and messages, they correctly identified that the AP and AT had disconnected, that they had an unreliable airspeed event and that they were in alternate law, and grabbed manual control of the plane ("I have the controls")

What should have they done:
Apply climb thrust
Adjust pitch for 5° nose up.

What did they do (even before talking about the stall)?
Not touch the thrust (this could be a passive error, and the thrust lock function might have made it worse).
Pull up into a 10° ANU / +7000fpm climb. And I don't mean letting the plane do that. I mean actively pulling up.

Only THEN we have the stall and the pilot actions contrary to recovery.

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Re: Air France jet missing

Postby flyboy2548m » Sat May 28, 2011 7:54 pm

You don't mean that this accident was barely related to a stall.
Or do you?
No, Gabiel. I mean your opinilon on stalls and stall recovery is well-enough known by now that it need not be repeated after every related of unrelated accident. I also mean that using an accident in which a quarter-thousand people lost their lives as evidence that you have "won" (gloating, in English) is pretty shitty even for you.
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Re: Air France jet missing

Postby flyboy2548m » Sat May 28, 2011 7:57 pm

Tho only data that was bad, as far as we know by now, is airspeed.
They had good altitude, vertical speed, attitude, and engine instruments.
If that's true, then AF training is even more deplorable than I thought. As I said earlier, unreliable airspeed with reliable everything else is no reason to crash an airplane, stall or no stall.
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Re: Air France jet missing

Postby Gabriel » Sat May 28, 2011 8:24 pm

... using an accident in which a quarter-thousand people lost their lives as evidence that you have "won" (gloating, in English) is pretty shitty even for you.
I didn't say or mean that, and you know it, what makes you the resilient shit that stays stuck to the WC after flushing. Unfortunately, I cannot say that that is too shitty even for you. You are that shitty.

For the rest of the forum, the "Gabriel wins" thread was about the aviation industry doing the first steps towards changing its training about stalls and approaches to stalls, prioritizing the reduction of the angle of attack to stop the stall warning (i.e. exactly what this crew didn't do). Thus the significance of that thread related to this accident.

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Re: Air France jet missing

Postby flyboy2548m » Sun May 29, 2011 12:58 am

I didn't say or mean that, and you know it...
You did too mean it, and don't tell me what I know. Show some integrity, at least own your garbage.
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Re: Air France jet missing

Postby ocelot » Sun May 29, 2011 8:11 am

What should have they done:
Apply climb thrust
Adjust pitch for 5° nose up.

What did they do (even before talking about the stall)?
Not touch the thrust (this could be a passive error, and the thrust lock function might have made it worse).
Pull up into a 10° ANU / +7000fpm climb. And I don't mean letting the plane do that. I mean actively pulling up.

Only THEN we have the stall and the pilot actions contrary to recovery.
Hold on a moment there. From the information I've seen (which may not be everything that's been released) they started off by going into a zoom climb, and as things developed the PF also applied a lot of nose-up input. But I don't think it's been explicitly stated that the zoom climb was commanded by pulling up. Maybe this has been stated and I just haven't followed all the right links yet, but if not we have to consider the possibility that this zoom climb was triggered by some interaction of automation and other pilot inputs.

The other thing I'm wondering: if you remember or look upthread several pages, at the time of the accident there was some discussion (not just here) of warm air upwellings. What effect would that have on the altitude readings, both as seen in the cockpit and as recorded in the FDR? Does the A330's INS provide altitude information? Is there GPS data? If there was such an upwelling it would presumably cause any such data to diverge from the (pressure) altimeter readout. If the crew was getting two diverging sets of altitude data it would vastly increase the confusion level. Plus, the PULL UP PULL UP behavior apparently exhibited by the PF makes a lot more sense if e.g. he thought he was in an enormous downdraft and losing altitude at a catastrophic rate. Admittedly, if he thought that one would expect the FDR to report what he was seeing and for at least something about altitude data to have been in Friday's announcement... but maybe not.

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Re: Air France jet missing

Postby Procede » Sun May 29, 2011 1:12 pm

It looks like the co-pilot (in his panic) forgot that angle of attack (AoA) is equal to pitch angle minus climb angle and a negative climb angle can thus mean you are stalled with the aircraft in a horizontal attitude. My suggestion would be to add an AoA indication to the artificial horizon, as that is probably what the pilot was fixated on.

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Re: Air France jet missing

Postby Giles » Sun May 29, 2011 3:41 pm

It looks like the co-pilot (in his panic) forgot that angle of attack (AoA) is equal to pitch angle minus climb angle and a negative climb angle can thus mean you are stalled with the aircraft in a horizontal attitude. My suggestion would be to add an AoA indication to the artificial horizon, as that is probably what the pilot was fixated on.
in alternate law is AoA valid?

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Re: Air France jet missing

Postby Gabriel » Sun May 29, 2011 4:55 pm

in alternate law is AoA valid?
The control law is a sort of dictionary that translates pilot inputs (or lack of) into control commands.
The air data and inertial data are inputs for the control laws. Depending on the quality and availability of such data, the control law can revert from normal to alternate and from alternate to direct.

What I mean is, a control law doesn't make a data valid or not valid, while the opposite can happen (an invalid data can make a control law invalid which would then revert to a "lower" control law).

So yes, if the AoA is valid for itself, then it will be valid in any control law.

But, for whatever reason, the airbus systems (before any control law is applied) considers the AoA invalid when the airspeed is below 60kts. The airplane cannot fly below 60kts, of course, so maybe the intention was to prevent spurious AoA readings while on ground, but that could have been achieved by rendering the AoA invalid when simultaneously "below 60 knots AND aircraft on ground". Another reason might be that the AoA vane, due to it's own inertia and friction, is not reliable below 60kts. The problem here is that the airspeed was way above 60kts, but due to a pitot blockage the measured airspeed was some times below 60 knots, rendering the AoA data unnecessarily invalid, and thus unnecessarily (and dangerously) inhibiting the stall warning.

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Re: Air France jet missing

Postby Giles » Sun May 29, 2011 5:35 pm

What I mean is, a control law doesn't make a data valid or not valid, while the opposite can happen (an invalid data can make a control law invalid which would then revert to a "lower" control law).
ah, i understand now. thanks for clarifying that for me.

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Re: Air France jet missing

Postby 666 » Tue May 31, 2011 1:33 am

Things can break. Pitot tubes are no exception. What's the backup method to determine airspeed?

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Re: Air France jet missing

Postby Gabriel » Tue May 31, 2011 3:09 am

Things can break. Pitot tubes are no exception. What's the backup method to determine airspeed?
None, except another pitot tube.
But you shouldn't crash a plane due to lack of airspeed information. Sure, airspeed is a very important parameter to know, but the safe flight envelope can be maintained with alternative means (basically, pitch attitude and thrust setting).

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Re: Air France jet missing

Postby Gabriel » Tue May 31, 2011 3:17 am

http://www.ukfsc.co.uk/files/Safety%20B ... 202011.pdf

I didn't knew whether to post this link in this thread or in the one titled... oh never minds.

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Re: Air France jet missing

Postby Procede » Tue May 31, 2011 10:36 am

http://www.ukfsc.co.uk/files/Safety%20B ... 202011.pdf

I didn't knew whether to post this link in this thread or in the one titled... oh never minds.
Thanks for the link, great read . This about sums it up:
- When the aerodynamic flow on the wing is stalled, the only possible mean to recover a normal flow regime is to decrease the AoA at a value lower than the AoA STALL.
- Stall is an AoA problem only. It is NOT directly a speed issue.
Best part:
The traditional approach to stall training consisted in a controlled deceleration to the Stall Warning, followed by a power recovery with minimum altitude loss. Experience shows that if the pilot is determined to maintain the altitude, this procedure may lead to the stall.

A practical exercise done in flight in DIRECT LAW on an A340-600 and well reproduced in the simulator consists in performing a low altitude level flight deceleration at idle until the SW is triggered, and then to push the THR levers to TOGA while continuing to pull on the stick in order to maintain the altitude. The results of such a manoeuvre are:
- In clean configuration, even if the pilot reacts immediately to the SW by commanding TOGA, when the thrust actually reaches TOGA (20 seconds later), the aircraft stalls.
- In approach configuration, if the pilot reacts immediately to the SW, the aircraft reaches AoA stall -2°. q In approach configuration, if the pilot reacts with a delay of 2 seconds to the SW, the aircraft stalls.

This shows that increasing the thrust at the SW in order to increase the speed and hence to decrease the AOA is not the proper reaction in many cases (this will be developed in the following chapter).
In addition, it is to be noticed that, at high altitude, the effect of the thrust increase on the speed rise is very slow, so that the phenomenom described above for the clean configuration is exacerbated.
Obviously, such a procedure leads to potentially unrecoverable situations if it is applied once the aircraft has reached the aerodynamic stall (see next chapter).

Even if the traditional procedure can work in certain conditions if the pilot reacts immediately to the SW, or if he is not too adamant on keeping the altitude, the major issue comes from the fact that once the Stall Warning threshold has been crossed, it is difficult to know if the aircraft is still approaching to stall or already stalled. Difference between an approach to stall and an actual stall is not easy to determine, even for specialists.
Several accidents happened where the “approach to stall” procedure was applied when the aircraft was actually stalled. For those reasons, the pilots should react the same way for both “approach to stall” and “stall” situations.

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Re: Air France jet missing

Postby 3WE » Tue May 31, 2011 12:44 pm

:shock:
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