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AF 447 Search to resume (part2)

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AF 447 Search to resume (part2)

Old 26th May 2011, 22:47
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"ne comprends pas" means one thing, "ne...riens" another. This snippet, if accurate, says so much. It is a closure, a juncture of CRM. The flight is being re-set in the view of at least one pilot. I think the comment is within the boundaries of "Aviate," alone, not comms or Nav. No one would get to this point re: the mundane. Not even atrocious and frightening weather weather. The airplane is an unknown to him here, and shows a frustrated pilot partially into a situation with which he is greatly uncomfortable, and has no experience of. This moment is the initial onset of upset, or the immediate prelude. Again, if accurate, a year's worth of speculation coalesces into epiphane for all of us connected in any way with this tragedy. They are speaking to us.
Without context its difficult to say. If we were to only look at the four words presented, not knowing what preceded or followed, I'd "transform" this as "I don't get it!!". This sounds more like a verbalization of puzzlement (as in being confronted with contradictory information) than anything else. This is from my experience of living in France back in the day. Native French speakers may confirm or disagree with me. Its hard for me to read anything more into it (assuming the content of the leak is true).
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Old 26th May 2011, 22:55
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> We still have the problem of what to do when the reading is invalid on multiple sensors.

Mechanically would it be possible to have 2 on a turntable, one always inside (warmer) and if the hot wire on the outer one indicated a block, the turntable rotates the outer one in. I realize this is a mechanical mess and adds all the unfavorables (cost/weight/complexity) but if it could be done, it would certainly get you a fresh ice free pitot for a little bit.
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Old 26th May 2011, 22:58
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Factual

Here is french "Rapport d'expertise Rio-Paris"
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Old 26th May 2011, 23:03
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We still have the problem of what to do when the reading is invalid on multiple sensors.
You've hit the nail on the head. IMO, the goal should not be to "eliminate" pitot ice. This may be all but unattainable. The goal has got to be a graceful degradation of the system if pitot ice happens. In my naive view, the former goal will lead to a more complex system, where as the latter to a simpler system. IOW, if we can't prevent pitot ice, force it to ice asymmetrically and force it to do it at the earliest opportune moment.

In the words of Sir Isaac Newton, If the apple doesn't fall, go shake the tree!

Last edited by CogSim; 26th May 2011 at 23:23.
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Old 26th May 2011, 23:13
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JD-EE,

CogSim, the last line of your recognizing icing posting prompted an "Oh goodie!" from me - in a very sarcastic tone.

"Under some icing conditions, even a 3-minute exposure can substantially affect the handling of the aircraft."
That was kind of the point. We think that there is more than a good chance that the pitots iced. In our discussions we are isolating the problem. We are implicitly assuming an otherwise clean a/c. Who know's what else iced. As the NASA tutorial snippet shows, a lot of structures may have accreted ice. We just don't have enough information to know what that means for the chain of events, if anything.
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Old 26th May 2011, 23:16
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Originally Posted by Lonewolf50
With the above airspeed limits in mind, how benign do you think an unexpected ten degree nose down pitch is while on IMC, and possibly in turbulent air, with those limits considered?

NOTE: this is not a declaration nor an assertion that such is what happened with AF 447, but an inquiry regarding, as a pilot, your tolerance for a sudden ten degree nose down event.
Where did I express 'tolerance' for an uncommanded 10° pitchdown?

The speeds you mention are not 'limits', but recommendations designed to minimize the risk of exceeding structural and controllability limits.

Although I fully agree that unusual flight control system behaviour such as occurred in QF72 and in the A340 Airprox incident should be kept in mind, there are at present no indications that these occurrences have any relevance to AF447.
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Old 26th May 2011, 23:22
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Machinbird, "We still have the problem of what to do when the reading is invalid on multiple sensors."

At least the scope of the problem is reduced if until that report the plane was flying nominally. It's not going to accelerate or decelerate very suddenly if the attitude is kept constant, throttles kept constant, and the bad spot is simply waited out. "Don't just do something, sit there!" wins again?
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Old 26th May 2011, 23:25
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Thinking of that last statement of mine, it may make even more sense when you dig into it. The pilots are given control of a plane the computers cannot handle. (Ran out of program memory or design knowledge base?) That would imply to me that the computer has already tried to apply "conventional wisdom and procedure" to at least some small degree. So the trick is to sit there and think of what the computer may not have seen.

Of course, that requires almost line by line understanding of the software. <sigh>
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Old 26th May 2011, 23:28
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CogSim, in other words he experienced what is known in the vernacular as a WTF event only in politer and more professional words. (And that may well indicate either upbringing or more likely the fact that he was not panicked yet. He was still working logically.)
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Old 26th May 2011, 23:38
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From BEA's Interim #2:
-40 °C is the commonly accepted value below which no more supercooled water exists and thus the risk of ice accretion on the aircraft airframe.
A number of recent posts fail to appreciate the difference between the icing conditions that produce ice accretions on (unprotected) parts of the airframe and the conditions that are suspected to cause blockage of heated pitots.
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Old 26th May 2011, 23:57
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From BEA's Interim #2:
Quote:
-40 °C is the commonly accepted value below which no more supercooled water exists and thus the risk of ice accretion on the aircraft airframe.

A number of recent posts fail to appreciate the difference between the icing conditions that produce ice accretions on (unprotected) parts of the airframe and the conditions that are suspected to cause blockage of heated pitots.
Yes, I failed to understand this assertion by BEA. Is it possible to have conditions that on the one hand overcome pitot heat to clog them up, but OTOH, don't accrete ice anywhere else? I'm not questioning BEA's assertion. This is an honest question.
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Old 26th May 2011, 23:59
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Of course, if we now take it as a given that a mostly uncontrolled and rapid descent form FL350 to sea level occurred, there is almost certainly going to be one of the flight crew offering an expletive or two, indeed, 'I don't get it' (none of this adds up) would be expected earlier rather than later.

Let us brace ourselves if much at all of the CVR is published... this is going to be heartbreaking of course

It is that subsequent (apparent) instability and lack of response, not the sudden pitch up itself, that is worrying me.

And let us remember that adjacent to highly unstable air masses, substantial increments of airspeed can be added or subtracted over very short timespans.
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Old 27th May 2011, 00:07
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I'm trying to think of KISS aircraft attitude instruments that would not be affected by electrical (hardware or software) failures, physical properties of aircraft ambient air, initial calibration concerns and attention distraction by synthesized sounds. Spirit suspended turn-and-bank indicators and magnetic compasses come to mind. Pitch and roll only dependent on gravity and yaw only dependent on the earth's magnetic field. Unfortunately you can't patent any of that so there's no money to be made pursuing development and lawyers still can't find a loophole in the law of gravity to bill for.
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Old 27th May 2011, 00:10
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Originally Posted by CoqSim
Is it possible to have conditions that on the one hand overcome pitot heat to clog them up, but OTOH, don't accrete ice anywhere else?
From what I've read in the papers linked in this thread, mostly dealing with engine anomalies in these conditions, I believe the answer to that question must be yes.

I sometimes cannot help thinking, doesn't anybody posting ideas on on this thread about the 'stupidity' of airplane and equipment manufacturers, and regulators, think about the difficulty of finding out what happens. How on earth do you establish in these incidents what ice is accreted elsewhere, what happens inside the pitot tube, why it happens, while so many airplanes fly through the same clouds of ice particles every day without incident, why one type of pitot probe is more resistant (but still not immune) than others?

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Old 27th May 2011, 00:16
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Originally Posted by Svarin
Then why the aircraft that can be flown by "concierges" ? If not to recruit, train, pay, and respect pilots like "concierges" ? Remember the late eighties. Refusing to see an intent there is naive.
Unhelpful. One man (a man who by all accounts is now very elderly and frail), in a state of exuberance, said these controversial things 24 years ago. He was employed by Airbus Industrie as a product evangelist, but I can categorically state he was not speaking for the engineers who designed and built the system. We now know this, and as such this should be disregarded with the benefit of 20/20 hindsight. Airbus have acknowledged this - why can't some people just let it go?

Originally Posted by rudderrudderrat
I wish AI had fitted a big red switch to turn off the Flight Control computers and place it into Direct Law. I am led to believe that B777 has one fitted?
What good would that do? Captain Sullenberger is universally regarded as a pilot's pilot and yet he chose to start the APU - in part to keep the protections online as a backstop if things got hairy - which is precisely what they were designed to do. If the Airbus systems were as unreliable as some on here are trying to claim, why didn't he just sod the APU and wait for the RAT to drop (which would have given him standby instruments and Direct Law)?

I've already said three times on this thread that the Airbus FBW design had input from pilots central to the requirements-gathering stage (and have provided supporting evidence from my late professor that this was indeed the case). Some pilots may resent the technological intrusion, and this is something that has been true going all the way back to the first hydro-mechanical stick-pusher devices (hat-tip D.P. Davies). This is not something that has its roots in the move to FBW.

Originally Posted by Svarin
What is specific to FBW aircraft is the changing of Flight Controls Computers, through successive software versions. This is done very discreetly. Some mistakes get corrected before they have a chance to do damage. Some are corrected after a fact (or not). But more than that, the very multiplicity of successive versions of such a critically critical piece of software and equipment will introduce a whole new set of potential problems. Specialists call these Byzantine faults, in reference to an ancient war involving traitorous generals.
And everything possible is done to ensure that the chance of that kind of fault happening is mathematically extremely remote, which in this day and age is the closest thing you'll ever get to a guarantee it won't happen from an honest engineer.

Originally Posted by Svarin
IBut I will not accept to play scapegoat for a system that claims to be safer than I am when it is easy, and that evades responsibility when things go wrong.
You mean you don't believe in Silicon Heaven? (but where would all the little calculators go?)

In all seriousness - as a software engineer, albeit of a grade significantly lower than those who specified and built the systems we're talking about, I've patiently tried to explain exactly why all the old rubbish about concierges, pilotless airliners, and preventing pilots from doing what is necessary to rescue the aircraft is - indeed - rubbish, and I've tried to explain that the engineering disciplines behind the systems that are there, which are designed to assist the pilots - and nothing more - are every bit as stringent, if not more so, than the mechanical and hydraulic engineering disciplines that made the previous generation of jet aircraft possible.

But it feels like I'm talking to a brick wall in this case, because none of the posters who keep pushing the software failure theory appear to be taking a blind bit of notice of what I'm saying. If I was to take the same attitude against the pilots on here, it would be considered the height of rudeness, and I'd probably be banned toute-suite. However as this is a pilot's forum I have to accept this as my lot, and I'm fine with that.

As a software engineer - one who takes my discipline seriously - I'm fully aware of what can go wrong with software, and yet I'm perfectly sanguine about getting on a FBW airliner, much as I am any other. If I had to pick a bone with Airbus, I'd worry more about the continued use of Kapton wiring insulation that I ever would be about the possibility of a Byzantine software failure causing an accident. In the late '90s, I had to be sanguine about getting on 737s, despite the knowledge that the rudder hardover problem had not been satisfactorily solved. I've had to be sanguine about getting on an old 747 jumbo in the summer, despite no movement on inerting systems being fitted to the central fuel tank. I've had to get on a Fokker F-28 in foul weather, knowing that if deicing wasn't done properly we'd be in significant trouble. Hell, I've sat in an RAF Chipmunk knowing that the cables are right underneath my feet and the engine design dates from a time before my grandmother was born!

I boarded these aircraft in the certain knowledge than almost none of my fellow passengers were as aware of the specific potential dangers as I was, and yet at no point did I feel the need to jump up and declare "Hey, this aircraft is known to have a major safety issue! If I were you I'd get off this 'plane and maybe sue the airline and manufacturer for ever suggesting you would be safe getting on it!". I'd have documented evidence proving that the statement was categorically true, but I wouldn't be helping anyone because the chances of such a thing happening on that particular flight were infinitessimally small.

So why is it that it's considered OK to bash FBW Airbus designs on here with absolutely no evidence that software had anything to do with the accident? Why is it OK to keep rehashing ill-advised remarks made by a single Airbus employee twenty-three years ago to claim that Airbus are somehow complicit in the "dumbing-down" of pilot training, when it's clear that if and when it does happen it is clearly the fault of the airlines who abuse the presence of automation in this way? Why is it that some are quick to blame the Airbus computers for handing control back to the pilots, when this is something that has affected many airframes from many manufacturers over the years? And why is it treated as a certainty that pilots would have been able to recover from this particular pitot-static failure incident (if indeed that does turn out to be a major factor), when prior evidence suggests that pilots are no more capable of diagnosing pitot-static failures at night over water and providing the correct remedial action than the computers are (re: Birgenair, Aeroperu)?

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Old 27th May 2011, 00:18
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.. and hot-wire anemometry has been around a long time, (was playing with such in 1973), initially for turbulence (good bandwidth) and useful for boundary layer work.
I'd imagine that if hot wire (more likely hot film) techniques were up to the environment and didn't degrade, they'd be used in 'some' capacity or other (robustness/longeveity problems in i.c.engine AFMs are not unknown)

KISS may well be relevant to the persistance of the pitot-static solution because it is so easy to read dynamic head (Q) directly, giving IAS without further ado
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Old 27th May 2011, 00:52
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Early warning for (entire) System Graceful Degradation

Hi,

The goal has got to be a graceful degradation of the system if pitot ice happens
We donīt know "the algorithms" used. We could imagine. There is a lot of powerful things you can do with the "signal" from the sensors before sending their data to "upper levels".

Very probably we could introduce a "band-aid" to alert when the "error" between the sensors "start to increase". And this may help in providing an early warning in dealing with the "product limitation" of current available sensors.

I am assuming the Pitotīs are not "transformed in "altimeters", etc." immediately. The events are gradual, i guess. And we need testing to understand how the sensors "freeze" (temperature. and valid signal) This is an "analog world" with the "richness of mother nature".

From an Engineering point of view i consider an absurd what we are facing.

We need (the aviation industry) to do ASAP R&D on the issue. And we need "analog field" Engineers with Henri Pitot like expertise. The "bitīs engineers" need "better data" for their Redundant Systems.


The system being the a/c (Systems + Crew)

I think we may say the aviation industry is facing a "product limitation" (specs, cert, design, etc.) and not a "technology barrier"
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Old 27th May 2011, 01:21
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Cool

Hi,

So why is it that it's considered OK to bash FBW Airbus designs on here with absolutely no evidence that software had anything to do with the accident?
You certainly must be right about the software ...
If you take the time to read this primary report from the group of judiciary experts (prčs du tribunal de grande instance de Paris) .. they point responsabilities to Air France and Airbus (and some others) for many reasons but not for softwares problems.
It's seem they also exonerate pilot errors so far ..
This is not tabloîd blah blah ...... (this the third official document I read about AF447 .. the 2 formers were the primary reports of BEA)
rapport d'expertise Rio-Paris
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Old 27th May 2011, 01:25
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What good would that do? Captain Sullenberger is universally regarded as a pilot's pilot and yet he chose to start the APU - in part to keep the protections online as a backstop if things got hairy - which is precisely what they were designed to do. If the Airbus systems were as unreliable as some on here are trying to claim, why didn't he just sod the APU and wait for the RAT to drop (which would have given him standby instruments and Direct Law)?
Starting the APU to keep the protections ...
DozyWannabe, your are in Love, but the APU should deserve a bit more consideration.

Beside that, Sullenberger would have been better served by direct law in his attempt to flare as he wanted to ...
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Old 27th May 2011, 01:35
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CONF, with the utmost respect - you're sounding like a broken record. I have yet to see any assertion supporting your statement claiming the pilots were unhappy with how the aircraft responded. In fact I haven't ever seen anyone other than yourself bring it up.
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