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Old 1st Jun 2011, 02:21   #61 (permalink)
 
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FlexibleResponse:

But WHAT caused the horizontal stabilizer to be at 13 degrees?
I understand the freezing part but WHAT is just as vital.
rgbrock1,

Sorry, I used the term "freezing" in the English English sense as opposed to American English. I meant to say the stabilizer stopped working automatically and maintained its last position at 13 deg because of the change of flight control law to ABNORMAL ATTITUDE LAW.

The reason the STABILIZER was at 13 degrees was the zoom climb performed by the PF to pull back and climb to 38,000 feet from cruise altitude, which traded the kinetic speed energy at cruise to potential energy of height gain (and consequential speed loss).

The stabilizer happily auto-trimmed more and more nose up during this manoeuvre as speed was rapidly lost until the aircraft sensed at least one of the extreme parameters that activated ABNORMAL FLIGHT LAW. That event stopped the stabilizer where it was at that instant.

From that moment, the fate of AF447 was sealed unless one of the pilots re-trimmed the stabilizer to the NORMAL RANGE range.

What is the NORMAL RANGE?

NORMAL RANGE for STABILIZER

1. Preflight - 4 deg NU
2. Takeoff Range - Approx 4 deg NU
3. Cruise range - 0 to 2 deg NU

MAX RANGE for STABILIZER

1. Maximum NU - 15 deg NU
2. Maximum ND - 4 deg ND

The detail is all from memory and anyone who is current on type should feel free to correct me.
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Old 1st Jun 2011, 13:23   #62 (permalink)
 
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Thanks for the explanation FlexibleResponse. 'Preciate it.
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Old 1st Jun 2011, 14:25   #63 (permalink)
 
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Flight Controls did NOT switch to Abnormal Law - Flight Global

If this report is correct, then there goes another theory on why the THS remained at 13 deg NU until impact...

Stalled AF447 did not switch to abnormal attitude law
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Old 1st Jun 2011, 16:19   #64 (permalink)
 
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Disclaimer: I've never been in an AirBus cockpit or simulator. I'm just a retired airline pilot.

FlexibleResponse - Don't give up so easily.

I have no idea why AF447 "did not switch to Abnormal Attitude Law", especially since the BEA release appears to indicate that the parameters that should cause this were in fact exceeded. So, if it didn't - why not? Was this just one more failure of the infallible computers to act as expected?

If on the other hand it did go into Abnormal Attitude Law, was there a failure of the sytem to record that fact? How do we know if it failed to go or merely failed to record that it did?

If the computers behaved as programmed, then why did the THS reach 13 deg NU and stay there for the remainder of the event?

The assumed answer is: The pilots continued to apply and hold full or near-full NU control stick. Why? Because they "didn't know it was stalled"?

As a simpleton, I don't buy it. It doesn't matter whether they knew it was stalled or they didn't. They certainly knew they were descending at a rapid rate, whether or not they had accurate IAS or no IAS at all.

If they (or PF) were continuously applying NU control input - and it obviously was not changing the situation - would they just sit there and not try something (anything) different - such as opposite (ND) control input? My concept of "logic" just doesn't seem to be working in this tale of tragedy.

Did they also lose all attitude references, altimeters and VS indicators as well? It appears they did not. They couldn't observe an apparent 16 deg nose up attitude? They somehow believed that would keep them in level flight and not cause a significant loss of airspeed (even if they couldn't read the airspeed tapes)?

I mean, according to what we are told, they were in level flight - cruising. They lost airspeed indication - for whatever reason(s). Their AP/AT disconnected. Would that change the a/c attitude all by itself. Why?

Is there something in the systems that would cause the THS to move towards NU, or for that matter ND (before the AP disconnected) as a consequence of the loss of reliable airspeed data? [I am not suggesting it did - just asking if it could].

Based on what I've read so far, there's a huge fly in the ointment somewhere that none of us seems to fully understand. It doesn't compute! <pun intended>

At some point I hope we get enough information to reasonably understand what might have ocurred on that fateful night.; why two fully qualified pilots were apparently unable to maintain level flight in a fully functional aircraft that has lost no more than the input from its pitot tubes (if that is in fact proven beyond doubt). Why it would seemingly "zoom up" some 3000 ft without them noticing or doing anything to prevent/correct/stop it? It just doesn't make sense to me and I'm not ready to crucify them until we know much more.

Meanwhile, me thinks this aircraft was somehow automated out of existence.
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Old 1st Jun 2011, 16:30   #65 (permalink)
 
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Quote:
I have no idea why AF447 "did not switch to Abnormal Attitude Law", especially since the BEA release appears to indicate that the parameters that should cause this were in fact exceeded. So, if it didn't - why not?
The only parameter to trigger Abnormal Attitude Law which was experienced by AF447 was the Angle of Attack - however before the AoA reached the limiting value, the air data was disregarded as unreliable by the system. The other parameters required to trigger Ab. Att. Law (50/120 degrees pitch/roll) were never met.
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Old 1st Jun 2011, 17:08   #66 (permalink)
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MODS!

Please - we don't need 3 threads on the 447 crash!
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Old 1st Jun 2011, 23:02   #67 (permalink)
 
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When the aircraft first reached 60 kts it could go directly to Abnormal Attitude Law.

Then the AoA which is independent of the AirDataComputer (speed) should have triggered the Abnormal Attitude Law.

Why when we have Unreliable Speed we do not disregard the AoA warnings?

Am I missing something here?
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Old 1st Jun 2011, 23:19   #68 (permalink)
 
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Quote:
If they (or PF) were continuously applying NU control input - and it obviously was not changing the situation - would they just sit there and not try something (anything) different - such as opposite (ND) control input? My concept of "logic" just doesn't seem to be working in this tale of tragedy.
The reason why they failed to recover? I don't know, even with full nose up trim full forward stick would have significantly reduced the AoA. One thing I am sure of though, when I ask Captains what the unusual attitude recovery recall is, I seldom get the right answer. It seems to me that everybody knows how to reject a take-off, deal with an engine fire etc. But I have never had unusual attitude recovery on a sim syllabus and because it isn't practiced most guys seem to forget it is there in the back of the Boeing QRH. Perhaps a similar issue with Airbus trainng?

Maybe the thrust being retarded to idle is a clue that somebody started to try and resolve the situation, but if so it seems hard to explain why full nose down stick wasn't maintained.
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Old 1st Jun 2011, 23:36   #69 (permalink)
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I have to agree with BOAC. This thread has morphed from stall considerations to being a subset of the main one.

Probably best to close it and keep the discussion in the one pot.
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