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AF 447 Thread No. 12

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AF 447 Thread No. 12

Old 18th Jan 2017, 22:19
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Couldn't find anything on the topic:
http://www.pprune.org/9644344-post1258.html
Would be great if 45989 could elaborate.
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Old 19th Jan 2017, 00:03
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KayPam
What does any A320/330 do when it overspeeds Autopilot engaged?
(usually due to turbulence)
Clearly you have never flown either.
With AP/ATHR on, the ATHR will gradually reduce its power to flight idle (slower than if you put it on idle notch manually)
(In a wholly different context: In final approach, the ATHR gains are lowered in order to avoid a too "lively" ATHR when closer to the ground. So one should pay all the more attention to their speed, and never rely entirely on the ATHR. It can do a better job than a pilot but not always)
However, the ATHR will (in any case) have much trouble managing wind gradients higher than 2kt/s
If the speed increases, the ATHR will reduce but not fast enough.
The pilots can notice the increase in speed and deploy spoilers.
Another possible reaction (but less academic) is to pitch up. I even see some pilots reducing to idle notch (and some others forgetting to put it back to cruise thrust when required)

In any case, if an airbus with AP ON is accelerating, the normal law will start to pull up in order to reduce speed, once just above MMO.
Full forward stick while in overspeed will make the airplane stabilize at MD - Mach Dive (which is 0.07 above MMO on all airbus aircraft if my memory is correct, .82-.89 for the 320, .86-.96 for the 380)
Neutral stick will give you MMO (in stabilized conditions)

The High speed protection starts to really worry and to really pull up more when you're about halfway between MMO and MD or more.

In fact I am not (yet!) a qualified Airbus pilot but I do work in the very building where integration tests are carried out for the A380 and the A350, with integration simulators (Airbus factory at Toulouse Airport)

I am about 80% sure that AP will disconnect if high speed protection engages (well, you don't care about that question because in the high speed prot, wings are levelled so you would lose nav capability and you would obviously lose altitude holding as well)

So I would be very interested in knowing how easy/hard it is to fly the speed with the attitude in a wind gradient. Would there be a risk of oscillations around the target altitude due to overcorrection ?
Are pilots trained to operate manually at higher altitudes ?
A A320-pilot-friend told me it was very difficult to transition from climb to cruise manually at high cruising altitudes.

FCOM will confirm most of this (maybe not the 2kt/s value), mainly in DSC 27-20-10-20, see page 111 here : http://nicmosis.as.arizona.edu:8000/...tems_part2.pdf )
Originally Posted by Concours77
When pilot saw he was not over the runway threshold, he reverted to muscle memory, an unfortunate one. "Pull the stick, firewall the throttle." But he was not flying a Corsair, he was flying a Beech twin....

The aircraft made a small hole in the roof, not a long gash. He should have pulled the stick, and firewalled the throttles......arse about.

As to 447, the reason this discussion is eight years on, and twelve threads in, is because we yak about the part of the flight path that is fundamentally irrelevant. What was the status and attitude of the aircraft at the most important moment in the flight? As the A/P quit, and the a/c was four hundred feet low, Nose Down, and the Stall Warn was active? Oh, and rolled right?

It is the interface, Machinbird, as you say. The human is being evolved out of the equation, replaced by ever more "dependable" automation. Emotion and intuition are poison, data and speed are paramount.
Are you implying this corsair pilot pulled too much and stalled his beech ?

About AF447, going from FL370 to FL366 (there is a debate among our team of engineers about whether we can say FL followed by a number not finishing by 0 or even 5) in a short time span (as short as the one between cavalry charge for AP disconnection and the moment you look at your altimeter) would be really feelable through vertical acceleration, and the crew should have realized that.
They should have realized that they were actually in straight and steady flight without the need for touching anything. (CF the post that I wrote the other day about "it does not take exceptionnal flyings skills to do nothing")

As for attitude indication, IRS do not freeze ! (They do, however, suffer from laser lock, ATPL monkey knowledge here)

As for the Airbus stall warning.... AOA is considered invalid under 60kt (CAS invalid under 30kt, the ADR do not even try to compute it), and the stall warning was based on an AOA higher than a treshold. So invalidity of the AOA would make the stall warning stop.
According to one of our teachers in engineering school, that behavior is illegal. I hope that Airbus management decided to solve this ***slight*** problem.
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Old 19th Jan 2017, 16:20
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@KayPam

Edifying, thank you.

"As for the Airbus stall warning.... AOA is considered invalid under 60kt (CAS invalid under 30kt, the ADR do not even try to compute it), and the stall warning was based on an AOA higher than a treshold. So invalidity of the AOA would make the stall warning stop.
According to one of our teachers in engineering school, that behavior is illegal. I hope that Airbus management decided to solve this ****slight**** problem"

This aircraft was never flying at (velocity) sixty knots save for a few seconds of ballistic flight at the top of the arc. Loss of computed (indicated) airspeed then merged into computed but (erroneous) and air speeds remained unreliable the whole four minutes to impact, imo.

The intermittent StallWarn may have begun at the loss of Computed Airdata when the aircraft quit A/P.....and this resulted from ".....WindShear...." (ACARS).

It is not possible for mass to demonstrate a vertical velocity of (17,000fpm) and have an accurate and reported AirSpeed of sixty knots....

So the StallWarn, to a savvy crew, would be rejected in any data driven solution to recovery, imo.....at the outset.

The reported "< sixty knot" trigger for (inhibited) StallWarn, if true, shows a shortsightedness at the programming level. It also suggests a blunder that may have been repeated in other ways with AutoTrim.

The THS, in its travel to the Max NU stop shows a "programmatic" impetus, not pilot induced, or even "noticed" by flight crew.

In any case, it is Auto, so there is no argument. My guess is the aircraft FCM was looking for (aircraft commanded) NU authority to meet load (computed) requirements of the airframe, independent of crew input.

45989 comment? Also, reference to Escape(CFIT) Normal Law, does StallWarn activate, even though the aircraft cannot Stall if the computed AoA is valid?

@KayPam: Re: Corsair/Beech sending PM
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Old 19th Jan 2017, 17:11
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KayPam, if the altitude (ADC) is referenced to the 'standard pressure setting, then the display is 'Flight Level' irrespective of the numerical value.

Re inhibition of AoA; refer to regulations on preventing the display of 'hazardously misleading information'; in every operating situation.

Re seeing values, feeling acceleration "...the crew should have realized that."
This might be a reasonable assumption without the effect of startle, but where sensory awareness is disrupted and automatic responses triggered due to surprise, then inability to realise is to be expected.
Similarly the reasonable advice 'sit on your hands, do nothing' may not be recalled from memory because of the overriding subconscious startle response.
Thereafter, as cognitive capacity is restored, the do nothing advice may not apply in the changed situation.
The brain could be behind the drag curve for some time, particularly for conflicting demands to 'assess the situation' and 'do nothing' advice; a clash of objectives (cognitive dissonance). Resolving these problem requires great mental effort - forget 'this', do 'that', pilots have to be adaptable .

One training task is to embed knowledge such as the maximum rate of change of altitude to be expected - even in upsets, and without associated accelerations or other instrument indications (VS). Also the need to view the wider picture, multiple instrument scan, integrate body senses, and compare this with previous experiences.
Training has a great responsibility in this area, the choice of sudden situations (rarely instantaneous or extreme), knowledge of aircraft systems, accuracy of simulator / CBT situations, knowledge of the atmosphere, of human behaviour.

The purpose of training is to embed specific knowledge in memory so that it can be accessed by the fast 'system1' thinking which takes over during startle.
A vital aspect would be to teach 'know-how' opposed to know-what. This is the training debate about knowledge recall - checking vs education - how to learn and gain meaningful experience.
This is an area which Airbus has considered and may have embodied into their training.

And as for all the other 'monkey knowledge', it may be irrelevant if the industry addresses the initiating contributing factor ('root cause') instead of outcome symptoms. Fix the pitot problem before you try to fix the crew, and even then consider the crew as a resource not a threat.
The regulator has significant responsibility in is area, but may be hampered by their own safety system: - retrospective hazard identification and dependency on regulation to control; a lengthy bureaucratic process.
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Old 19th Jan 2017, 18:21
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+3 the three of us agree.

That may be the most objective, dispassionate, and reasoned essay on the topic.....(alf)

However, for those of us who still "question" the 'theory', some conclusions are not absolute....

The recorder data is "interpretive", BEA are not committed to absolutes....(bravo), and these threads have a somewhat skewed bias.(imo). Not even pitot failure is a lock....where do we see the identified ice blockage? Computer actions are suggestive of it, not based on data? Evidence of flight programming errors are patent, all we know is Airdata is NCD, by definition.....Wind Shear is far more plausible than simultaneous identical failure across three triplets?

That the CVR seems incomplete is actually a benefit, some of us entertain divergent views. For instance, when do we know crew recognized the change to AL? Eleven seconds after the Warning, not immediately, only when Robert declares it so. At 02:10:19?

I am not convinced the crew was incompetent; neither do I believe there is
certainty about "startle", or surprise. They were well aware of the weather to expect prior to loss of A/P, that was in the BEA report.

thanks for you post.
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Old 20th Jan 2017, 18:38
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"Re seeing values, feeling acceleration "...the crew should have realized that."
This might be a reasonable assumption without the effect of startle, but where sensory awareness is disrupted and automatic responses triggered due to surprise, then inability to realise is to be expected."

I meant something and did not express it very clearly I think. Here is what I meant :
Say you're in steady level flight and you loose 400ft in less than 5 seconds.
The only way this can happen is if you feel gigantic vertical acceleration. Maybe something like 0G for 2.5s and 2G for 2.5s.
I'm not gonna make a calculation but you see the idea.

So, since the crew did not feel such gigantic (relatively speaking) load factors, it must be because they did not actually lose 400ft in less than 5s.
It was only an altimeter artifact.
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Old 20th Jan 2017, 18:57
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well

"It was only an altimeter artifact."

You've had six and a half years to see and conclude that, if true. Similarly UAS was an artifact of AirData. It also fooled the aircraft, but the FCM wasn't sensing the DFDR, either. Was it static sensing?

The culture and twenty years of flying have cultivated "trust the machine".

Anticipation or Skepticism? What difference? Be ready for anything, or start the recovery (too?) late?

Four hundred feet in 5 sec is 4800 feet per minute. Compared to what happened right after, that's docile. The soon to be climb hit 7000 fpm? Turbulence? W/S?
Both reported. By pilots, and ACARS.
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Old 20th Jan 2017, 19:42
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Well, maybe the most reliable way of allowing the crew not to trust this altimeter is to include in their training that methods of calculating altitude will change if available input data will change.

Hence if any probe freezes, the indication will vary, in a non physical way.
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Old 20th Jan 2017, 22:34
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Hey

The crew were well aware of Wx, they phoned CC and warned them, they had deviated, and they Expected rough. They got it. I'm at a loss how this thread conversation turned to startle. I also recall the initial report said nothing was recorded on the right side of the cockpit.... Not indications, but nothing got recorded. So we end up with stick traces? Mystery.

If no indications were recorded, how do we know about the 400 ft low? If it was real, then fine, but how could it be an artifact and spurious but end up on the DFDR? From the right side?

There was no CVR data that showed any discussion about the AP loss, only "I have it..." ? Right?

Startle? The a/c kicked out the AP. Lacking any remarks, it's like that was expected. "we tried everything....!" Except for nose Down, or handing off to the "good" side? Or maybe having a chat about what this "everything" was?

Only initial remarks about ascent, then they quickly terminate..... Followed by everything except Nose Down?

Ever the helper, did the aircraft input some NU? Very touchy about Overspeed, this program?
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Old 20th Jan 2017, 22:50
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"I also recall the initial report said nothing was recorded on the right side of the cockpit.... "
If it said that, it's just plain wrong. There is a ****load of sensors related to the right side (only some of them frozen or impacted by the freezing), and all parameters related to anything other that what had frozen was still valid..

A 400ft low could appear on the right PFD. Then, the DFDR records from the DMC.
This low could appear due to a change in available data for computing altitude.
More precisely, TAS and Mach allow you to correct for position error. Without them, position error correction is lost.

I don't think this bus would be touchy about overspeed. It has a high speed protection law in normal law that would save the aircraft in close to 100% of situations with normal law.
However, I have no idea what the THS did during the incident.
The THS position is a truly important flight parameter and I do believe airbus should display it more clearly.
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Old 21st Jan 2017, 14:50
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Hi KayPam,

"However, I have no idea what the THS did during the incident.
The THS position is a truly important flight parameter and I do believe airbus should display it more clearly."

What it did is critically instructive. From a position of 2? Degrees Nose Up it cycled, "...smoothly and consistently Full Nose Up, and remained in that position until impact."
The THS trims automatically, and cannot be manipulated effectively (it can be "held" manually, but when released it keeps moving). Only in Direct Law is it a legitimate Flight control, in fact, it is the only way to control Pitch "Manual trim only".

The BEA report relies almost exclusively on one foundational "fact". From the instant of the abnormal, the pilot flying held ".....mostly Nose Up stick...."

So, the Trim is full Nose Up, the aircraft is Stalled, and descending quickly. The pilot's have tried everything, "try climb (Captain)" "I have, many times....." Pilot flying.....

Aircraft attitude, Stalled, in rapid descent.... In the Stall, the aircraft is in "established" descent, though no pilot would call it that, look at the ROD!! But the computer, with NCD AoA, no reliable airspeed, and VS also wild, might call it "stable", no?

Is there an "airstream audio data channel" for the computer to sense!? Is the computer's best solution to lock its commanded Pitch where it is, not to be overridden by pilots? The pilots could hear the noise, and arguably knew the descent was certainly fatal, not to be locked in, but to be corrected!!?

Back to the stick. What is this control, really? It can "command" attitude, but not directly, it can only send a request to the FCM, to be analyzed, and "normed", then modified, and applied.

The stick, actually, is nothing more than a "suggestion box" with a handle.

So WHY, when Robert was pestering Bonin to "you climb, so go down...." Did Bonin not descend? It made no difference, the aircraft was already climbing, and nothing Bonin could do would arrest this climb. What is this feature? Not Overspeed Protection. Not a mistake either, the THS would continue this auto climb when the elevators lost authority, as we see in the THS trace, and the BEA statement of fact.

Why would this happen? This aircraft's flight control system is programmed to not let the Nose drop. The Airframe is designed to exhibit neutral stability in Pitch approaching the Stall......it is "longitudinally stable". It makes no difference that there is poor annunciation of the THS travel. And as I say, this NOSE UP is not negotiable. This aircraft does not drop its nose at Stall. By design. I think by the time the crew decided to get serious and boot Direct Law (".......PRIM/SEC.....fault") the Tail was stalled, the elevators were completely ineffective, and there was no time to get the Nose to drop via Direct Law; it is a laborious process.

Last edited by Concours77; 21st Jan 2017 at 22:43. Reason: Answer
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Old 25th Jan 2017, 22:55
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https://www.youtube.com/watch?v=4WuPoVjOXLY
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Old 29th Jan 2017, 18:17
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Video

At 3:54 of the video, compare the four official "cues" of Stall with the reported attitude and aspect of AF 447 at the time of AutoPilot OFF...and review the pilot's actions. Nose up, not immediately responsive, uncommanded Roll, Stall Warn active, and from the DFDR, (inertial record) buffeting.

Question. In Overspeed, with Autopilot active, is Stall possible?
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Old 29th Jan 2017, 20:23
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In Overspeed, with Autopilot active, is Stall possible?
Realistically, it doesn't matter whether or not the autopilot is engaged. For any flight condition that is a valid overspeed at an authorized altitude, for 1 g flight, you will be above the 1 g stall speed. The worst cases are near the aircraft's ceiling. (Think of the U-2 flight envelope at altitude)

When you start talking about accelerated flight (more than 1 g) then an aircraft can be stalled up to the point where you break the airframe first, but an Airbus FBW system will g protect the airframe in Normal and Alternate law, (but not in Direct or Mechanical law.) For an autopilot to be engaged, you must be in Normal or Alternate law, so you won't be breaking an Airbus FBW airframe with over g while on autopilot barring an encounter with something like a massive thunderstorm or mountain wave rotor.

Assuming that the autopilot is receiving valid inputs. the answer to the question is no, as long as the autopilot is engaged, being in overspeed condition precludes stall in 1 g flight.

Caveat! I've never flown the Airbus, and am at heart a steam gauge pilot, but I've stalled aircraft from near ground level up to over 50,000 ft. It will not hurt my feelings if you find a flaw with my logic.
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Old 29th Jan 2017, 21:22
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Normal Law

"Realistically, it doesn't matter whether or not the autopilot is engaged. For any flight condition that is a valid overspeed at an authorized altitude, for 1 g flight, you will be above the 1 g stall speed."

I am trying to establish some possibilities related to Normal Law, Alternate Law, and loss (or add) of protections. Especially as it may pertain to FCM response to two flight modes: Stalled, and Overspeed (simultaneous).

......As it applies (may apply?) to a discussion of the forty seconds surrounding the loss of AutoPilot by the crew. Because of the conditions established by the report, and the training video, I want to have an understanding of how the pilots took the situation in, and responded, (knowing what we know, and entertaining what they may have known)?

Probably need an A 330 pilot? I asked a friend, a Captain on the 320.... As a ten year Captain, I asked him how many times he had flown in Alternate Law?

His answer: Zero.
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Old 29th Jan 2017, 21:52
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"Several flights per year" end up flying in alternate law.
The most common cause for that is either manual disconnection of 2 ADRs (there's even an airbus procedure recommending this in some specific cases), or the freezing/loss of two (I think) pitot or static or aoa probes.

New question tonight : do you think the ambiant noise could have told the AF447 crew that they were at a slow speed rather than a high speed ?
The copilot thought they were fast. Maybe that was due to unusual noise, because of the wierd airflow around the airplane ?
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Old 29th Jan 2017, 23:48
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There are questions that arose from beating the ACARS to death for two years! As to ambient noise, which is likely given "turbulences forte", ACARS "WINDSHEAR", and "do you think we have some crazy speed...?" Etc.

If due to an unusual sound of airstream, it is recorded on the Cockpit Area Microphone...
To my knowledge, few people have heard that recording, with its nuances, intonation, alerts, etc. but an easy take once heard, I should think.

Also, by 'crazy' Bonin could mean slow, fast, or sideways (slip)..... To include the turbulent airmass of cruise in the ITCZ.....

One would need experience of flight at or near Stall in high speed, actual Overspeed, and the "personality" of the airframe in jet upset.....

If Wind Shear occurred, it might help an understanding of corrupt AirData, and altitude reporting. The ingredients were present for fluctuations in performance leading to A/P quit?
Trigger a protection?
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Old 30th Jan 2017, 01:09
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In French, crazy would likely refer to fast, with no certainty of course.
I don't think there was any windshear involved. AP quit due to loss of anemo data only.
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Old 30th Jan 2017, 02:27
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Speedbrakes

It was really unfortunate that Robert came down so hard on Bonin when he put out the speed brakes thus causing them to be immediately stowed.

You would think that someone would have tumbled to the fact that they were not hanging on their shoulder straps following deployment.

That should have lead to a productive line of thought about being slow, but given the level of fear in that cockpit, who knows?
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Old 30th Jan 2017, 20:44
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"That should have lead to a productive line of thought about being slow, but given the level of fear in that cockpit, who knows....?"

Indeed, who knows? I venture to say anyone who listens to the record, the CVR!!

Now this speed brake issue happened after the initial Stall, and mushed descent?

It underscores why the aural record is so critical. The transcription is so abridged, it even casts doubt on the report....?

Why did Robert so easily abandon his position re: climb? With the g, the altitude, and the reduction of airstream noise, one would think Robert would have gotten apoplectic? Instead, he joins in to tell the Captain they have "... Tried everything...." Evidently, something satisfied Robert that A) the climb was not subject to pilot arrest, or B) Nose Down had been "tried".......and failed, repeatedly......

That two pilots would disagree so vehemently about spoilers meant they had at least two divergent views on recovery? Where is the follow up? This lasted four minutes, I would expect some chatter, not the apparent "restraint" of voiced "concerns"?

KayPam,

"AP quit due to loss of anemo data only."

That's interesting.... What about The Stall Warning, and uncommanded Roll, plus unresponsive control?

This aircraft will not Stall in Normal Law. It wants to be In Alternate Law to Stall...that had nothing to do with loss of Auto Pilot? I repeat my question: if at Vs, (past alpha Max (and Vmax) , and already in Alternate, wouldn't the AP drop via the FCM? And, if this is so, and Pitch was commanded Nose Down, via Protection, isn't it quite possible the result may have been Overspeed?

Last edited by Concours77; 30th Jan 2017 at 20:56.
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