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AF 447 Thread no. 4

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AF 447 Thread no. 4

Old 23rd Jun 2011, 10:09
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Machinebird

Just remember, we are outside the aircraft trying to look in to what must have happened. It is very different when you are in the aircraft, with limited and confusing displays, feeling unusual forces, and the aircraft isn't responding in a way you were trained for.
We have to remember that what seems so foolish to us outside observers might make perfect sense given the inside viewpoint. Try to put yourself in the others guy's shoes given the information he was given to act on. The results might surprise you.
If the aircraft had been able to keep its airspeed measurement systems going, none of this would have happened.
This is just my point - the human factor. Whatever happened on that night was because the humans involved did not respond in an appropriate way to the situation they were in. Nothing more, nothing less. To them it might have been appropriate but it wasn't. I suggest you reread pickyperkins (No 257) last post with the most interesting extract about what to do when in a stall. Note the date of the text - this is not new at all. There are two significant questions which in fact are key and that have nothing to do with the aircraft systems - Why did the aircraft fly into a CB when others avoided it? and Why did the PF pull up on the stick for such a long time and induce a stall? I would also suggest more caution in your final statement - you cannot know that if the airspeed systems functioned flawlessly then the accident wouldn't have happened. You can only surmise.
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Old 23rd Jun 2011, 12:15
  #302 (permalink)  
 
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I would also suggest more caution in your final statement - you cannot know that if the airspeed systems functioned flawlessly then the accident wouldn't have happened. You can only surmise.
Respectfully disagree with your statement.

System failure is (based on information so far gleaned) the trigger. BEA had taken that tack long before the wreckage undersea was finally located. Pitot tube issues and recommendations pre-dated the retrieval of the FDRs. It appears that their first estimate was well formed.

The event chain needed a trigger. Absent airspeed system failure, transition out of normal law and trimmed/stable flight state not likely => thus manual flying not required => thus the curious 30 second input not induced=> and so on.

If you wish to focus on human factors, you'll get no argument from me, but the linkage to mechanical factors is critical to the event chain. (There is a valid line of inquiry regarding "how well do you know your machine, and how well can you know your machine?" that was much discussed in one of the earlier threads, over a year ago I think).

How a response to airspeed system malfunction issues should have been addressed, and how the training of crews should have been undertaken for a known failure mode, certainly points to the human factors which include systemic / corporate / cultural human factors.

Getting into a stall in this event chain is a subordinate line of inquiry to response to malfunction. Per your earlier perkins reference, this points to a systemic issue that gums raised.

If you don't expect a stall, if you aren't familiar with what it feels and looks like, and if you don't train for it (<= not sure how valid that statement is, training may vary considerably) it is quite possible to initially react in a sub optimal manner. At that point, you are playing catch up, or as we used to say, you are behind the aircraft.

Is that a human factor? Absolutely. So too is a an altimeter winding down and what it means to you as you assess your situation from the right hand, or left hand, seat. What do you "see," and what does it mean to you?

That's the fourth act of a five act play, however. What was the lead in to that point?

EDIT TO ADD for Machinebird:
Going back to a post I made a couple of days ago. It occurs to me that if the Flight Path Angle in the developed stall was around 45 degrees below the horizon, it would be necessary for the crew to push the nose down to at least 35 degrees below the horizon to break a stall.

No big deal to a fighter pilot with altitude.
FWIW, if this was happening at, say 15K versus 35K, stall AoA would be a bit higher, so not quite as much nose down ... right? But that's a late in the game event.

Good point, though, in re what one is comfortable with.

What to me is more puzzling is the "why" behind why nose down inputs of lesser magnitude (when you didn't need something like 25-35 degress nose down pitch to unstall the beast) were not apparently made earlier in the process, closer to stall onset. This is where the interface of flight control and cockpit information resources strike me as having a critical interaction that opened the door to the condition, later, where your point on how much nose down you'd need to unstall the plane arrives.

Last edited by Lonewolf_50; 23rd Jun 2011 at 12:41.
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Old 23rd Jun 2011, 13:45
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I am in awe of those posting here who clearly have fantastic technical knowledge and also fantastic knowledge of aerodynamics, but one thought keeps coming back to me as I read these fascinating pages with the story unfolding ever so slowly.

That thought is a piece of advice I have been giving out for years:

"If ever you get to 10° NU (or more) in a transport aeroplane - other than on take off (or G/A) - you are doing something badly wrong."

There will probably be those who will now post to prove me wrong, but it has always worked for me (eg forgotten the flaps etc). It might have helped these unfortunate pilots who were confronted with a mystifying set of circumstances. We shall see in the fullness of time.
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Old 23rd Jun 2011, 13:58
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@ bubbers44

You should have said "no pilot, whatever aircraft he/she is flying," etc ...
Yet, it appears that ONE pilot did just that, late at night, in an aircraft he was familiar with, during an otherwise quiet flight but with expected turbulence, on a route he had flown several times before ...
The type of aircraft is immaterial, so keep off the ritual "B good, A bad" stuff, there's a good lad - it doesn't help anybody's understanding. And, like all of us (even the conspiracy theorists) wait for the BEA's next statements.
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Old 23rd Jun 2011, 14:28
  #305 (permalink)  
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Originally Posted by Old Carthusian
Why did the aircraft fly into a CB when others avoided it?
- this is a recurring comment here - where do you see that they did? You have read the explanations of the 'weather charts' posted on here?
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Old 23rd Jun 2011, 14:36
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I would also suggest more caution in your final statement - you cannot know that if the airspeed systems functioned flawlessly then the accident wouldn't have happened. You can only surmise.
Respectfully disagree. That was the second hole in the swiss cheese. The first was flying too close to a CB cell.
I know that if the aircraft had not lost airspeed reference, we would be looking at a very different accident at worst, and probability says strongly that the aircraft would have arrived in Paris.
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Old 23rd Jun 2011, 14:53
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Complex Systems outputs, a threath to CRM?

CRM Defined

2.1 CRM encompasses a wide range of knowledge, skills and attitudes including communications, situational awareness, problem solving, decision making, and teamwork; together with all the attendant sub-disciplines which each of these areas entails. The elements which comprise CRM are not new but have been recognised in one form or another since aviation began, usually under more general headings such as ‘Airmanship’, ‘Captaincy’, ‘Crew Co-operation’, etc. In the past, however, these terms have not been defined, structured or articulated in a formal way, and CRM can be seen as an attempt to remedy this deficiency. CRM can therefore be defined as a management system which makes optimum use of all available resources - equipment, procedures and people - to promote safety and enhance the efficiency of flight operations.

2.2 CRM is concerned not so much with the technical knowledge and skills required to fly and operate an aircraft but rather with the cognitive and interpersonal skills needed to manage the flight within an organised aviation system. In this context, cognitive skills are defined as the mental processes used for gaining and maintaining situational awareness, for solving problems and for taking decisions. Interpersonal skills are regarded as communications and a range of behavioural activities associated with teamwork. In aviation, as in other walks of life, these skill areas often overlap with each other, and they also overlap with the required technical skills. Furthermore, they are not confined to multi-crew aircraft, but also relate to single pilot operations, which invariably need to interface with other aircraft and with various ground support agencies in order to complete their missions successfully.

Question:

Is Airbus SAS advanced planes philosophy a threath to CRM? How to "work together" complex Systems in dealing with "extreme situations"? It´s possible address this issue just by training? It´s possible with the current Standards to safely manage (and operate) an advanced plane when unexpected (or unexpectable) situations arise?

Note: It came to my mind the "Flight Engineer". The third guy capable to manage the old systems (with another type of complexities) and able to act providing to the pilots the right and timely results.

How to deal with the low probability(*) but possible events in a "complex plane"?

(*) Thales Pitot "failure" was not considered a so low probability occurrence. And AF was moving" to replace the sensors...Therefore not just possible but probable to fail and create "major" reconfig. of the advanced plane System.
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Old 23rd Jun 2011, 14:56
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My sense of the human factors is;

I see some similarities in the ABX cargo DC8 positioning flight where the crew was performing stall tests at night in and out of weather.

The tests went fine until their attitude decayed (deeper than expected into stall) and they failed to realize their rapidly unwinding altitude. Their response was methodolical and calm (senior pilot training another pilot) right up until the "terrain" warning voice.

To me it looked like they lost sensory awareness to what is just a temporary aberation and what is the highest priority response.


my gut feeling tells me that if they were able to see a horizon or had considered the rapidly unwinding altitude they would have reacted differently.
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Old 23rd Jun 2011, 15:02
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Chain of events

Which one was the third? We have yet enough info to answer?
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Old 23rd Jun 2011, 15:08
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Originally Posted by Old Carthusian
Why did the aircraft fly into a CB when others avoided it?

Also, see "A Detailed Meteorological Analysis" revised June 1, 2011 by Tim Vasquez in response to the new May 27, 2011 BEA data.

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Old 23rd Jun 2011, 15:53
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"Managing and handling" advanced Systems (Human machine interfacing issue)

RR_NDB:

The crew never should be "presented" (specially at critical moments) with System "outputs" that they are not capable to understand very fast


What is not clear when output is ECAM message:
F/CTL ALTN LAW (PROT LOST)
MAX SPEED……330/.82*

How would you suggest presenting this more clearly to crew?
* actual values depend on configuration.

If you are referring to the intermittent STALLSTALL, I fully agree this should have never been silenced when AOA was above the threshold value whether speed was valid or not.


The crews, "Redundant Systems, operators" always must "have chances" to "keep flying" their increasingly complex, and not perfect (never will be), machines.

Once again, the system doesn’t make up the inputs itself, it executes them from input of PF (AP) and in ALT LAW in such a manner it would not hinder PF to recover A/C from the upset.

Last edited by A33Zab; 23rd Jun 2011 at 16:03.
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Old 23rd Jun 2011, 16:30
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Stall recognition, et al

I can see that many here cannot appreciate how "benign" a deep stall is in a well-designed airplane. When the wreckage pattern was revealed, I began thinking "deep stall" versus stall-spin or structural damage or .... I came to my conclusion that the plane hit the water in a fully-developed deep stall when BEA provided impact angles and velocities.

So I posted my excerpts from the F-16 Code One magazine. It showed the pitch moment versus AoA for our little jet, and had the statement by a test pilot concerning what it felt like - a Sunday drive except for the rapidly unwinding altimeter. Due to great aerodynamics and a control feature that used the rudder to arrest yaw once A0A was beyond the normal "limit" ( out of control of the pilot, BTW, just the confusers trying to "help" you), there is little, if any, yaw. Due to our leading edge flaps we also had very little buffet to tell you, "hey, you hamburger, you just got us into a deep stall!".

I will guarantee you that if those pilots had seen the films of the Viper in a deep stall that they would have done something else than what they did. Further, except in "direct law", the confusers are still in the game, with various "protections" disabled. So the jet is still trying to "help".

In a fully-developed deep stall in a FBW jet you could let go of the control stick and the jet would be happy to continue the attitude, heading and AoA all the way to impact. After all, it is trying to reduce AoA and still trying to achieve 1 gee ( that's the Airbus, but in the Viper could be trimmed for anything from minus 2 gees +/- to plus 3.5 gees for a neutral stick). In this case, I feel the jet was still trying for the one gee, even at the AoA limit Hence, the THS kept creeping NU. Added gee command by the pilot didn't help, but the pilot could have let go and the jet would have still remained stalled due to c.g., pitch moments at the AoA, etc.

For those wondering about the THS trimming without an airspeed input to the confusers, the gee/rate sensors are completely independent of air data/AoA and are at the core of the FBW system implemented by the Airbus, same as for my jet and the Shuttle and ...... So to provide a 1 gee neutral stick, the gee sensors will move the THS accordingly to maintain the stick deflection command versus the neutral position/command (1 gee), and those puppies are VERY SENSITIVE and are sampled at a very high rate. Think inertial navigation accelerations like less than a hundredth of a gee. Those sensors also do not require an inertial "alignment", as they can be a simple as our old needle/ball doofers for rates and strapdown piezo-electric gizmos for accelerations on all three axis.

The data plot for this accident will reveal some great things about the Airbus aero, and seemingly excellent directional and lateral control capabilities even at a ridiculous AoA. It will also provide a basis for stall recognition and recovery procedures. I think we all want to see this, ya' think? Crying shame that we finally get the data at the expense of many people and an expensive jet.

Lest anyone think I am making excuses for the crew, I'll be clear - I AM!!! I'll admit that some of the control inputs are confusing. I'll also wonder what the CVR will reveal for about two and a half minutes as the crew ponders what the hell is going on. And then I'll try to imagine a revovery at night, in clouds and a confusing array of warning and caution indications. So there, I've said it.

respectfully,

Last edited by gums; 23rd Jun 2011 at 16:46. Reason: spelling, additional text
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Old 23rd Jun 2011, 16:44
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You Can't Separate Human Factors From Aircraft Design

@Old Carthusian:
So far, though, the evidence/information points in the direction of the human factor not the aircraft.
Human factors are an integral part of aircraft design.

Manufacturers build an aircraft and then publish initial procedures according to how they believe it should be operated, based on their design. These procedures are what pilots get in training. Later, based on operating experience, procedures and training can be modified. Recommendations for modification of stall recovery training have thus already been made by AB.

An aircraft which cannot be safely and efficiently operated by human pilots is deficient in human factors.
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Old 23rd Jun 2011, 16:49
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Lonewolf_50;
System failure is (based on information so far gleaned) the trigger. BEA had taken that tack long before the wreckage undersea was finally located. Pitot tube issues and recommendations pre-dated the retrieval of the FDRs. It appears that their first estimate was well formed.

The event chain needed a trigger. Absent airspeed system failure, transition out of normal law and trimmed/stable flight state not likely => thus manual flying not required => thus the curious 30 second input not induced=> and so on.

If you wish to focus on human factors, you'll get no argument from me, but the linkage to mechanical factors is critical to the event chain. (There is a valid line of inquiry regarding "how well do you know your machine, and how well can you know your machine?" that was much discussed in one of the earlier threads, over a year ago I think).

How a response to airspeed system malfunction issues should have been addressed, and how the training of crews should have been undertaken for a known failure mode, certainly points to the human factors which include systemic / corporate / cultural human factors.

Getting into a stall in this event chain is a subordinate line of inquiry to response to malfunction. Per your earlier perkins reference, this points to a systemic issue that gums raised.

If you don't expect a stall, if you aren't familiar with what it feels and looks like, and if you don't train for it (<= not sure how valid that statement is, training may vary considerably) it is quite possible to initially react in a sub optimal manner. At that point, you are playing catch up, or as we used to say, you are behind the aircraft.
Very well summarized - agree fully.

BOAC;
I still await ANYONE who can tell me how autotrim relates to 'received' IAS input OR what baro indications the crew actually were left with. Of more interest than a hairy bat?
The BEA mini-Report cites altitudes a number of times so the parameters depicting altitude were working. There are no ACARS messages which indicate that the DMCs [Display Monitor Computers] were malfunctioning and no indications that static ports were involved. My sense of it is that the altimeters were functioning normally and I think the assumption is a reasonable one.

The autotrim does not "relate to 'received' IAS". As has been discussed, (gums, Chris Scott, Machinbird et al), pitch control is 'gee-driven' (Nz Law) in Normal and Alternate 1 & 2 Laws. In Direct Law the airplane is a B737...you have to trim it manually; no big deal, if it's trained and encouraged.

For emergency backup of GW and CG computation in case of a dual failure of the two FCMCs, [Fuel Control Monitoring Computers], the FE [Flight Envelope] part of the FMGECs calculates the GW from the WFU [Weight Fuel Used] and the CG from the THS position. The CG calculated here is a function of N1, Vc, Altitude, Mach and the GW from the FE part of the FMGEC and is memorized for used in the event of the above-mentioned dual failure, (IOW the airplane has to have something to fall back on whether in Normal or Alternate Laws because autotrim still functions in both laws).

In Direct Law, pitch trim is manually controlled through the two trim wheels on the pedestal. Manual trim is available in all phases of flight in all laws.

It is a complete mystery to me why it has been said that the use of manual trim is "discouraged". The issue is one of many which requires examination in the manner described by Lonewolf_50, (quoted above), Chris Scott, Machinbird, gums and others. (The Final Report will indeed be very challenging to write.)

Simplified, in Normal and Alternate Laws, movement of the trim wheels disengages the autotrim function during wheel movement but re-engages the autotrim when movement stops. The trim will move back to a position ordered through the AFS [Auto Flight System], which, as stated, is 'gee-driven', again, very simplified.

I think the anecdote about bats is instructive and helpful as well as fascinating...after all, the Wrights learned from observing birds did they not?... ;-)

Regarding the training of the approach to the stall, (Stall recovery is not taught at all, to my knowledge), not only the manufacturer stated, but many regulators and certainly operators, bought into the notion that the airplane was protected against the stall. Those of us who checked out on the airplane early enough to dismiss such claims, (EVERY airplane can be stalled), flew it with the usual regard for the conservation of energy. Someone said that except at takeoff, a 10° pitch attitude in any transport aircraft was cause for serious concern, (or words to that effect). Damn right. But somehow along the way, the mythology became established and that requires examination because automation in and of itself does enhance flight safety, but it has to be used as intended. gums is right...the word "protections" is a misnomer and "limits" describes it better, but the former conveys a sense of security while the latter is merely descriptive. Bluntly speaking, one is a marketing term, the other is an aviation term.

I hope this is of some use, BOAC.
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Old 23rd Jun 2011, 16:54
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Once again, the system doesn’t make up the inputs itself, it executes them from input of PF (AP) and in ALT LAW in such a manner it would not hinder PF to recover A/C from the upset.
Hmmm, doesn't the A/C makes inputs of its own in ALT law, trimming the THS ? Sure, this was due to strange PF inputs but was he really aware of the move ? Don't you agree that even without pilot input the THS would trim up once the A/C is stalled ?
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Old 23rd Jun 2011, 17:04
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So I posted my excerpts from the F-16 Code One magazine. It showed the pitch moment versus AoA for our little jet, and had the statement by a test pilot concerning what it felt like - a Sunday drive except for the rapidly unwinding altimeter. Due to great aerodynamics and a control feature that used the rudder to arrest yaw once A0A was beyond the normal "limit" ( out of control of the pilot, BTW, just the confusers trying to "help" you), there is little, if any, yaw. Due to our leading edge flaps we also had very little buffet to tell you, "hey, you hamburger, you just got us into a deep stall!".
First of all, thanks a lot for sharing your thoughts and stories, makes always for a fascinating read.

I'd be ready to go with the idea that they didn't see (or didn't believe) what their altimeters and/or ADIs were telling them, such things have happened before. But if they didn't notice they were in a stall, what did they think was happening? After all they made some pretty drastic inputs, so they were reacting to something. What could be the situation they believed to be in? To which 16 deg nose up and full thrust appeared to be a reasonable answer? I'm at a loss with this one. Hopefully the CVR will tell...
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Old 23rd Jun 2011, 17:09
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how well can you know your machine?
Covers it for me.....

When all around you everything goes to hell in a handbasket, it's not the moment to try and recall every paragraph from the "mind image" (hopefully accurate) of the aircraft systems you slowly built up during your 'on-type' training.
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Old 23rd Jun 2011, 17:22
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Thanks PJ - it would appear, then, from the BEA release that neither of them noticed the altimeter winding up!

Regarding THS then - if you managed to maintain1g flight while reducing IAS by 100kts maintaining enough pitch 'authority' with the elevators, the THS would not move - or would it simply move to maintain a neutral elevator position as a 'human' would do?

New UAS QRH drill - 'Deploy the bat'
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Old 23rd Jun 2011, 17:23
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It is a complete mystery to me why it has been said that the use of manual trim is "discouraged". The issue is one of many which requires examination in the manner described by Lonewolf_50, (quoted above), Chris Scott, Machinbird, gums and others. (The Final Report will indeed be very challenging to write.)

Simplified, in Normal and Alternate Laws, movement of the trim wheels disengages the autotrim function during wheel movement but re-engages the autotrim when movement stops. The trim will move back to a position ordered through the AFS [Auto Flight System], which, as stated, is 'gee-driven', again, very simplified.
PJ2, your description of the manual pitch trim was my initial understanding of how manual pitch trim works.
That once you let go of it, the system would again move the trim to where it wanted to move it.
Others have stated that once you handle the manual pitch trim, it stays in manual for the duration of the flight and has to be reset on the ground.

May as well sort out this detail fully. If you remained in manual THS, it would have implications for proper flight control function on some of the "protections."

Are there some old wives tales running around here, or possibly differences between aircraft types?
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Old 23rd Jun 2011, 17:59
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So is the answer MORE automation?

So we all seem to agree that +10 degrees NU in a transport category aircraft at any other flight phase than take-off is likely a bad idea?

Clearly there are reasonable 'limits' for negative climb rates -10K/min is not one in my book.

Ditto for AoA....

I think we can all sketch a flight envelope within which things are likely going well, outside of which something is likely not so good.

Sounds like the protections (limits) of Normal Law?

Normal Law works when all the expected inputs are provided and believed to valid, and is supported by autoflight systems.

However in Alternate it was possible to get the pitch to +16 degrees with a sink rate of -10K/min. Unfortunately the primary computing system in the loop (the human) did not see the flaw and it would seem did not take the appropriate recovery action (or if it was attempted, it was not sustained enough to cause recovery).

It seems to me that there is a pretty strong argument for a secondary layer of automation that would step in and prevent a sustained abnormal attitude. Sort of like a more sophisticated "stick-pusher", that would override the pilot input (if incorrect) and provide the most appropriate recovery inputs. ND stick in this case...

I'm sure this is going down swimmingly well with the majority of pilots reading this, but I do not fear "poking the bear". We HAVE to do something to prevent a momentary misjudged few seconds worth of incorrect control input sending a jet full of people to the bottom of the Ocean.

OK, so may be none of 'you' are comfortable with yet another layer of 'protection' having control authority over the aircraft? Then at least consider an advanced warning system that will take all the critical input parameters (AoA, altitude, pitch, speed, etc) and provide a prioritized audible warning cue - "Abnormal AoA - control input Nose Down required"...

At least then the PF has something prompting him to THINK is this input right?

From the available information we have so far one critical aspect seems to have been missing - something questioning the control inputs of the PF? This extrapolates from the prior discussion related to control stick deflection (or more accurately NOT) for the PNF.

Looking at the sales figures from the Paris Airshow it would seem Airbus is entirely unscathed by any fallout from AF447... something like 726 aircraft sold for $72B, leaving Boeing in the dust with 142 aircraft worth $22B.
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