Thanks RRR;

BTW, .04 kWh per hour amounts to 40 W.

You gentlemen are overlooking an important mode of melting the ice/snow inside the probe.
Infrared radiation.
Some initial reading on the subject tells me that we are lining the interior of the probes with the wrong substance. From a Nippon Steel technical report on infrared spectroscopy, this telling observation: http://www.nsc.co.jp/en/tech/report/pdf/n10014.pdf
I can think of geometries that would promote both modes of melting (conduction and radiation) and which would promote development of open channels through an ice mass.
Seems to me that pitot tube heating design is stuck in the 1930's.

OK,
I've had too many cups of coffee today, but another thought occurs.:}

To get more power into a pitot tube quickly, you could couple it up to a waveguide and 'nuke' it the same way we heat water bearing items up in a microwave. http://images.ibsrv.net/ibsrv/res/sr...ilies/nerd.gif Those guys designing aircraft pitot tubes really have been stuck in the dark ages. Stick with what grand daddy always used must be their motto.:rolleyes:

Why Stainless Steel anyway? Delrin, Ceramica, Teflon, etc. Why such a sharp entry? I must be a cup behind, Radar Heating occurred to me as well.

A very thin analogue to the current problem is the Shuttle tiles. A very heat averse medium Isolates heat from the inner surface. It is as if the current design fosters the retention of the snowpack.

Pitot heating
 

I'm not sure powerful IR or microwave heating of the air within the pitot tube is necessarily desirable.

I am reasonably sure that you want to minimize changes to the temperature of the air in the pitot probe as compared with the air next to the static probe.

Technically, is the 'air' being heated? There is no flow whilst the plug/ice is being expelled, so either a constant current, or a transient one, same as current design? The Steel is maintained at a high heat (Don't Touch!) so would the downside be unmitigable? Dunno. The probe currently requires a fair current, and precise Temp control in flight is not a design consideration, is it? Also, Dunno.

It isn't just me who doesn't trust
 

Subject: Test Pilot Burt Rutan, on Airbus



Passed on by an experienced guy who worked for Lockheed and then the FAA for years. He absolutely refuses to fly on any Airbus because of their French designed fly by wire system.


Bill, These machines are mfg in Touloius, France and have certification by CAA and ICAO over there before they go for our FAA certification. It depends a lot on direction from the white house and congress as to what the FAA does when it comes to dealing with foreign governments. Some times the FAA doesn't have a whole hell of a lot to say about the end result when pressured by the State Dept on some political issue. I think the FAA core knows all about the Airbus systems that are so radically different than any we have here. The computer nerd systems on the Airbus have caused numerous crashes over many years since their inception but never enough of them at one time to get people up in arms.


Airbus is ALMOST as good as Boeing in hiding the real cause of crashes. I remember about 20 years ago when the A319 was being introduced to India. The pilot thought he had control during a landing BUT the nerds system took over on approach, throttled the engines back to idle, and the bird plopped down in the pine trees and exploded about 1/4 mile from the end of the runway. OF COURSE--Airbus found that it was pilot error since neither he nor the copilot survived. Twenty years later the same nerd systems on a A320 put Capt. Sully in the Hudson. The nerds sensors on the engines determined that the bird strike was cause for shutting down the engines and it shut down both engines and the pilot had no control to restart them. Actually the strike did nothing more than smear some goose guts over an engine PTO probe and their was NO reason to shut down the engines. If this had been a Boeing, Sully could have used the engines to make a safe landing.


The Air France 447 was another nerd screw-up in using JOY sticks to fly a huge airliner--the A330 is a huge bird!!
What makes this incident so sad is that the exact thing happened to an A330 in France five or six years ago during a demo flight by their chief test pilot. The accident was the basic responsiblity of the chief test pilot as he allowed a customer pilot (with very little flight time) to make the take -off to show him how simple it was!! On take-off the customer pilot pulled back too much on the JOY stick, and before the chief could take over, stalled, crashed and burned right in front of the control tower. Just like 447 the chief couldn't see what position the copilot JOY stick was in, as it was covered by his hand, just as the Capt on 447 couldn't see what control inputs were being made when he entered the cockpit at 18,000 feet on the way down to the water. If it had been a Boeing he could have seen the copilot pulling back on the control yoke causing the the stall. And to further the confusion in the cockpit--when the right JOY stick is moved, the left JOY stick doesn't move with it. When one moves either control yoke on a Boeing the other control yoke responds with the same movement--not so with the nerds system!!


Bill,
the only thing we can do at this point is stay the hell off Airbus equipment!!

Jim,
Where’s the FAA in all this ??

Re: It isn't just me who doesn't trust
 

Read good information and valuable discussion on PPruNe, but also a lot of rubbish......this post is beyond the last category.

Somewhere in Europe obviously. I think this ruffles a lot of feathers but Dick Ruttan is a genius with what he has accomplished in aviation and I agree with his comments. Not seeing what your FO is doing on the side stick kept me out of the air bus. That big yoke in front of you tells you when it is time to take over. It rarely happens but sometimes you need to know what the other guy is doing. In the Airbus it is difficult with the side stick from what I have been told. I chose never to fly one.

Bubbers, Not up to your usual professional standards to publish something like that "article" of unknown pedigree. :hmm:

For those wondering about the effects of "heating" the air, inside the pitot tube, remember that it should not be trapped if we can keep the tube from getting plugged in the first place, and is always flowing through the tube to the drain ports at a relatively low speed. There is no way to change the pressure in the tube then from heating the gas inside the tube. (I suppose if you got really ridiculous with heating you could start looking at ramjet theory:rolleyes:). The idea is to be able to rapidly apply energy to the internal volume of the pitot tube, and if the thing begins to fill with solid water, to rapidly convert said solid water to a liquid so that it may be purged from the probe vent holes with dispatch. To do this reliably requires sensing systems and a better means of applying energy than is presently being used.

The absorption of either infrared energy or microwave energy by the atmosphere is miniscule unless you then throw in water in some form or other. There are some relatively narrow absorption bands in the infrared spectrum from molecular dynamics.

I don't understand the pitot heat and my Dick Ruttan story having anything to do with what we are talking about. He flew around the world non stop and made a world record. He put a man in space without NASA. He has this opinion about Airbus and I agree with him. That is all.

bubbers

I think you may be confusing the two brothers. Dick flew non-stop around the Globe, Burt launched a human into space w/o the 'help' of NASA.

I don't trust Dick Rutan. Burt? He is the genius. Which one has the HO for Airbus? I have neighbors on either side here in the retirehood. Both flew the Airbus, and both love it. That's all I need to know.

bubbers44;

Re, "Bill,
the only thing we can do at this point is stay the hell off Airbus equipment!!"

Well, if that's from an aviation professional I don't care what they've done, that's just plain stupid and embarassing. It's prejudice all the way down because the author clearly knows nothing about the Airbus, doesn't want to know but condemns anyway. The stories prove that anything can be twisted to support prejudice if that's all one's agenda is.

You've made it abundantly clear over the years that you don't like, don't trust, and don't know the design. That is sufficient to make your point; there is no cause to re-argue the case each time something comes up regarding the AB discussion. It's boring because it doesn't advance discussion and doesn't contribute to others' knowledge or understanding.

OK, that is how I feel about AB. Sorry.

bubbers44, no problem. My whole point is you don't need to say you're sorry...I'm offering feedback that your views are well and thoroughly understood. I'm not trying to change your mind. I don't need you to "believe in Airbus". But it would be pleasant and interesting to advance discussions on points of understanding, most of which don't involve the Airbus.

If a Rutan or an FAA guy said those things that's really disappointing...I would have expected more comprehension and thought, but there it is and we move on.

pitot tubes
 

Bit puzzled about pitot tubes: if these are a worry why not just make them physically bigger. Would take more to block them and the thermal inertia (mass increasing with l cubed, surface area with l squared ) would increase, smoothing temperature changes.

As my user name suggests, I am not a pilot, professional or otherwise, and have no axe to grind in the A v B debate except to point out that, if we are to have this debate, the views entailed need to be supported by facts. (I am a scientist by training). The mysterious "Bill" quoted in Bubbers' post uses "facts" which are not supported by the relevant accident reports. In some instances, he is just wrong in his assertions and, in others, he seems to stretch investigator's comments to suit his agenda.

The A319 crash about 20 years ago is, I presume, a reference to Indian Airlines 605 (actually an A320 but that is irrelevant). The report is sparse in detail on the cause of the excessive descent rate, but "Bill" apparently knows more. It mentions pilot error with the flight crew not recognising that the aeroplane was in open descent rather than "approach mode". Much of the criticism of the Airbus philosophy at the time came from the French pilots' union who were unhappy about the loss of the FE in the two person flight deck. This philosophy has, of course, long since been adopted by Boeing also.

The A330 test flight accident was attributed to several causes not just the excessive pulling back on the side stick by the FO. He, incidentally. was not a customer (although Alitalia personnel were on board but not as crew) but as an Air Inter pilot on attachment to the Airbus training arm.

"Bill" seems to think that the engines on the A320 involved in the Hudson ditching were basically intact and were shut down due to, in effect, a computer reacting to a damaged sensor. However a cursory reading of the FAA investigation report reveals details of much more severe physical damage to both engines resulting from impact by particularly large birds. In the interest of balance, the report did state that the successful ditching was due, in part, to the Airbus FBW system.

My own view is that unless or until accident statistics show a significant difference between A and B (one way or another) in accident rates then it becomes a matter of personal pilot preference, which is their right. At the moment, I do not believe that the statistics show any such difference. In the context of a complex investigation into a tragic incident, such views as are declared by "Bill" should be ignored as not being fact-based. They might possibly be seen as part of the continuing propaganda war (conducted by both sides) between A and B in the furtherence of sales. Nothing wrong with that but in its rightful context.

StainesFS;

Re, "...if we are to have this debate, the views entailed need to be supported by facts."

Not to beat a really dead horse, but yes, that was the point I was also trying to make, thanks.

I know these accidents; none of these accidents occurred in the way "Bill" described, so it is just more of the same boring A vs. B propaganda. I'm surprised that the Habsheim accident wasn't trotted out again.

Apropos your comments regarding statistics you will appreciate the meaning behind the following, from Boeing. Compare equivalent A vs. B types in the numbers:

Statistical Summary of Commercial Jet Airplane Accidents, Worldwide, 1959 - 2010.

What such populist myths such as those posted above perpetuate and even legitimize is an institutionalized lack of understanding of what really happened in these accidents. That is not how flight safety and investigative work is done nor is it how training and learning from others in this business is done. "Bill", who remains unidentified and mysterious, should come to PPrUne and join this thread to defend his views and perhaps learn a bit himself. There are some here who critique the airplane thoroughly but they know it and fly it. Vive le débat!

Perhaps also of some interest may be Psychologist Daniel Kahneman's book, Thinking, Fast and Slow which in part discusses how we make up our beliefs, assess/decide upon risk using intuitive and/or rational thought. Last November Vanity Fair ran an article which may be of indirect interest to some: The Quiz Daniel Kahneman Wants You to Fail

PJ2

Neither CAA nor ICAO have any involvement in the certification of Airbus products.

Indian Airlines accident analysis in Flight International.

Algy;

Thanks for the link. I think the accident is relevant to the present discussion in the sense that taking over manually and flying the airplane was then and remains today a prime, professional requirement.

If a pilot can't do that with his or her airplane, that is a serious training and standards matter. The A330 (and all the rest) are eminently, easily flyable in manual flight. It wasn't an emergency and the "safe conduct of flight" was not at risk.

The problems only occur when one out-thinks the design and that is again an understanding/training matter, not an automation matter.

The Bangalore accident was not an "automation" accident though mode confusion contributed. All that was necessary was to push the thrust levers fully forward and actually fly the airplane which is their job. All that was necessary in the AF447 accident was to maintain pitch and power settings. The airplane was fine moments before the loss of airspeed indication, and such loss means nothing to the actual airplane itself...it was still flying, still had power and was in stable flight.

The "Idle, Open Descent" issue here was fixed twenty years ago. I used to teach it and the "mode reversion" process during line-indoc training on the A320.

PJ2

Transient in Feedback Systems II and F-GZCP Stability (part A)
 

Hi,

PJ2

Means nothing? Sir, respectfully i disagree; here is (the beginning of) WHY:

With the Synergy of a highly motivated group we can touch some "sensitives points" in our effort to understand what occurred with F-GZCP that night.

The diversity of the posts show the agenda of the posters is diversified. I think the more constructive one is to allow us to be prepared to avoid problems when dealing with similar equipment.

This can be important not just to pilots.

A Feedback System is EXACTLY what his name implies:

Something that receives "feed" back (to itself).

Tacoma narrows bridge received energy (from wind turbulence), OSCILLATED to the structural limits and was destroyed.

This was a typical POSITIVE feedback (the one that presents GROWING oscillations)

Positive feedback can be dangerous. But when controlled (by lossy components) are very useful and common in our lives.

Example: HF radio equipment used during Titanic accident. (A coiled wire, a capacitor, a switch, a spark gap and an antenna and a power source)

Another positive Feedback System: An A/C subject to an UNDAMPED oscillation when PF apply larger inputs (larger than a given threshold). This may led to the destruction of the equipment. The loss of the F4 posted by Machinbird perhaps is a good example.

During some initial discussion on the (clearly obsolete) AS probes still today used by the aviation industry we had the opportunity to understand the advantage to have a better one using a closed loop. The feedback WOULD REDUCE the time required to the Pitot to "recover" from the "cold" it frequently suffer. :) In the 30+ cases of UAS they briefly (seconds) failed to work properly.

In F-GZCP last flight the System (A/C + crew) received an "input" (heard in CVR) so important that affected the stability of the System.

The ice crystals WERE NOT ADEQUATELY PROCESSED BY AN IMPORTANT SENSOR (so important is MULTIPLE) that as per A33Zab diagram has not a TEMPERATURE CONTROL. It seems (the heater) "less intelligent" than the appliance we use to press our clothes. The pressing iron has a thermostat, i.e. a feedback system to control it's temperature.

This kind of NEGATIVE FEEDBACK improves the operation of the equipment and allows a high quality work. Our clothes are preserved, the pressing iron can operate IN THE BEST range, etc.

Another example of a feedback system is the yaw damper. "With the help" of the rudder the A/C has the directional stability greatly improved.

At that night the System (A/C) put the crew (PF) in the "feedback loop". The pilot had to act immediately. Doing so he corrected the roll. A roll we may understand started by LARGE AMPLITUDE STIMULI from the environment. A harsh one they had to do a "last minute" deviation. PF started to apply LARGE AMPLITUDE stimuli to the new System (A/C + PF) and this could led to UNSTABILITY.Machinbird and others suspect of PIO (roll) after this PF action.

Up to this point the System received 'inputs" in some degree affecting the Stability of the entire System (System+PF):

1) Ice crystals.
2) Loss of important feedback loops: A/P and A/THR
3) Turbulence
4) Large PF inputs

This facts generated almost immediately 10 other facts:

1) System was automatically reconfigured (NL to ALTN)
2) System degraded (to "another" A/C with less available resources)
3) ISIS "suffered"
4) A/C broadcasted anomalies (ACARS)
5) Crew not was informed on reason of A/P and A/THR quit
6) Turbulence became POTENTIALLY more relevant
7) HF "surfaced" (by lack of training, etc.)
8) Not use of SOPs and adequate CRM
9) Lack of understanding ("uncharted waters") by PF AND PNF
10) A persistent climb with high rate

Clearly after this facts the System was less robust than before.

A safe (and stable) System MUST BE:

FAULT TOLERANT

And show:

GRACEFUL DEGRADATION.

And i will add:

A safe System must show RESILIENCE (System + crew). The transient (perhaps up to the apogee) dominated the scene. And After "inflexion point" put the plane in a "steady state" condition lasting roughly 4 minutes falling (and circling) at near terminal speed.

For me it is clear the System at this moment (PF starting to act IN THE NEW LOOP) was showing less capability to "resist" to the initial "input" and subsequent consequences: tiny ice crystals.

(to be continued in part B)


In the meantime we must think looking to the factual information we have so far.

PS

Questions to think and take into account in our analysis:

The man machine interface became essential at this critical moments?

We will know what PF saw? (RH was not recorded and ISIS also had "impairment")



Some remarks related to AS probes: Open loop (no feedback): LONGER RECOVERY TIME (to recover from the "cold")


A33Zab

Thanks for the diagram. Amazingly the probes are just heated and their temperature is not controlled*. This fact alone may explain part of the observed problems related to air speed measurement.

As Machinbird pointed there is room for improvement. With a closed loop temperature control the time to reheat the critical internal regions of the probe would be reduced.

Anyway i am deeply surprised (negatively) with the approach used. Sensors capable to "disable" important functions of the A/C more simple than the necessary.

Much of my rationale in some posts were based in a better (closed loop) approach. when in AUTO mode. In both AUTO and ON (what i called MANUAL) the power applied IS THE SAME.

(*) And we really don't know if a ballast wire is used.

Bottom line:

The thermal "recovery" of probes takes too long (in ~20 seconds after hitting ice crystals A/P and A/THR quit). The recovery time WAS NOT COMPATIBLE with System requirements of GIGO.

The recovery time MUST BE REDUCED and i'm sure can be reduced.

The different probe characteristics of FR (now obsolete) and US (with limitations) may be explained by thermal inertia plus the factors mentioned by Owain Glyndwr

Also the materials used certainly are important like mentioned by Lyman

Up to this point (in this sensitive issue and related posts) thanks for comments/questions from: HN39, PJ2, Lyman, roulishollandais, and contributions from Machinbird, A33Zab, Owain Glyndwr and others including PM channels.

I will try to comment and answer questions made before, when possible. (asap)

Pitot tubes
 

Hi,

Mr Optimistic,

When i understood the heating approach used in the TRIPLE sensors (failing near SIMULTANEOUSLY), i tend to be,

Pessimistic,

:}

I agree with PJ2 - anyone who has flown even model airplanes can tell you that a stable aircraft does not need airspeed information to continue safe flight,

All the evidence from other similar incidents is that doing nothing was a viable (and arguably the best) option. Even in alternate law the aircraft is pitch stable - the system does not use, or need, airspeed information to achieve this. This law is in fact 'graceful degradation'. Freezing the throttles also maintains the equilibrium state.

The system was never given the opportunity to show stability in roll as it was continually perturbed by pilot input. Incidentally there was no PIO - the roll oscillations are damped not divergent and the motions and stick movements are not out of phase. What we are seeing there is a pilot struggling to come to terms with a new set of unfamiliar dynamics. He got the hang of it in about 30 secs which is not a shabby performance by any standard.

As for the probes, it it clear that the amount of heat being applied was not enough to handle the rate of ice accumulation, which is a random variable. [The proposed new icing requirements show that ice concentration can be greater over short distances than long. The heating rate would have been set up to cover conditions which were less onerous than those possible. Now that a higher limit of ice particle concentration has been identified it should be simple enough to up the heating rate to cope. no need for fancy feedback systems - KISS is still a good principle]

Obsolete AS probes
 

Hi,

Machinbird

Those guys designing aircraft pitot tubes really have been stuck in the dark ages.

Henri Pitot would not like his name being associated to dark ages. :}

Now on i will change from SUBHEATED AS PROBES to

OBSOLETE sensors,

(controlling SOPHISTICATED Systems)

PS

The pressing iron i carry in my motor home has a thermostat. :}

The ones i have in my house are SUPER ADVANCED.

PS2

1930?

When i visited the Gold mine museum in Joburg i did see ADVANCED devices. And the mine operated well before that year.

Graceful degradation of the entire System (A/C + crew)
 

Hi,

Owain Glyndwr,

Sure! :ok:

As a researcher i would prefer to deliver to pilots a better System than one that you need to "wait and see" every time. Wait and see (some kind of hysteresis) is wise, for sure.

In this case the brief failure of obsolete sensors (sub heated, high thermal inertia, etc.) contributed to a chain of events.

I am not talking about this law. I am talking about the System (A/C + PF) during the transient. And i not mentioned yet the man machine interface.

A fact.

Struggling to understand by hand "testing the plane"? :{

To control the (important) probe temperature is VERY EASY, RELIABLE and K.I.S.S. TO THE EXTREME. Einstein commented about how K.i.S.S. you can go. There are limits.

This was my first feeling: SUB HEATED.

Still k.I.S.S.

And will be forever. Leonardo da Vinci stated: Simplicity is the ultimate sophistication.

But this is to be covered when commenting on the man machine interface.:E

Important sensors and crew operating "out of specs"
 

Hi,

PJ2,

Actually before encountering ice crystal the A/C was working fine, i agree.

After increase of CVR noise and fit with OBSOLETE FR probes we may say she was no longer fine.

The clogging started and eventually affected the Stability of the System.

The bureaucracy (and other factors) was allowing the operation of hundreds of flights with obsolete sensors.

And the pilots being instructed to use "State of the art" band aids. *

I would prefer "State of the art" Systems.

:mad:

PS

With insufficient crew training (lack of) for the worst case scenario.

(*) I like duct tape, swiss army knife, band aid, and all this emergency stuff.

But i love a good design. When possible, why not to have it?

RR_NDB;

Thank you for your responses.

Hi,

Owain Glyndwr

Why? What led him to do that? No reasons?

PF was operating as "part of the feedback loop". He acted doing the opposite. What he received from the System?

He acted without any influence from the System? Doing exactly the contrary?

:suspect:

Hi,

Owain Glyndwr
I agree .. and I want to add (for be intellectually honest) that this phenomena was identified years before the AF447 accident ... and it WAS simple ... blah .. blah ...

Hi All,

I am not a pilot but an engineer. I find the pitot discussion very interesting. There have been many suggestions on how to make this speed detection devise better as it appeared to be the first thing to fail in terms of proper operation in the AF447 flight. I am going to confine my thought only to the pitot itself, not the system of the aircraft to which it is connected that interprets and responds to the signals from the pitot tube or multiple tubes.

In designing a devise of any sort, the design engineer has to know as much about the parameters the devise is going to experience and operate within. Given this information, he/she can then go about designing the devise based on this information and perhaps a data base built on prior experience. Once the devise is designed and manufactured it is then tested to parameters across the envelope it will experience in operation. If these tests are successful, then it can be placed in service with some degree of confidence that it will perform the intended function it was intended to perform. So what could go wrong? What could go wrong with a pitot tube where the basic physics and general design has been known dating back to the late 1700s? And why is it that one manufacturer's design seemingly has less problems than another manufacturer's product when both met mandatory testing and certification requirements? Why is it that when the devise is used on one aircraft, it is more susceptible to non-performance than on another aircraft?

I would postulate to you all, there is nothing wrong with the basic concept of the current day pitot tubes, they will and can work successfully across the total flight envelope without any new bells and whistles. The reason they may not is because the parameters used in the design and testing did not and for that matter, do not match what is experienced across the total operating envelope, particularly at high altitudes and high speed in icing conditions. I have thought about this for some time and wondered in the instance of Airbus aircraft, could there be a difference in pitot tube performance verses that of Boeing aircraft? Could it have something to do with installation or location or shape of the fuselage forward of the mounting point or how the air passes into it or the actual testing and certification requirements? Was Boeing lucky and Airbus unlucky?

I think it has a lot to do with everything mentioned above and some other thing not thought of. Here is some interesting information that has been developed out of the studies resulting from AF447 and commented on by Airbus regarding changes to testing and certification:

Airbus' comments go on to observe:

And,

So I think with proper design parameters, proper mating with the aircraft and proper testing requirements pitot probes from any manufacturer can be designed that work throughout the flight envelope. We are not there yet in full understanding, but it is not hard to imagine the icing problems can and will be solved very soon.

Passion for aviation due the multidisciplinary aspects
 

Hi,

PJ2,

The Synergy and motivation we can exercise here with you and other aces is great.

We must use when possible the opportunities to explore new ways to look to the issues.

The concepts and ideas i present are conceived carefully and based on memorable experiences since 1968 when i first was introduced to birds of all sizes (and it's anatomy) in a "War Surplus like" shop. i was student of Electronics avid to understand "everything". I had the opportunity to learn the basics in several areas at this time. Later on i had the privilege to fly some venerable birds like the C47 and ride in C46, Connie, etc. etc. etc.

My motivation in PPRuNe is through a minimum of understanding ultimately, try to contribute to our safety. My 3rd son is a professional pilot and may be can learn something reading our effort. :)

AS probes
 

Hi,

Turbine D,

I think so.

PS

Did you hear about a patent filed by Airbus SAS using L(alpha)ser?

(i write Lima Alpha Sierra echo Romeo and the final result is Lima @ Sierra Echo Romeo)

Anyone could explain this glitch? :*:mad:

Hi RR_NDB,

I can't explain the glitch but, I did see that Airbus file for the patent. I also think there will be some changes in the A-320neo to address the pitot icing situation and maybe in the A-350 given enough time. I don't think the technology will be radically different but will be an attempt to incorporate what they have learned since AF447.

Sometimes you need a new approach when you understand the real problem.

It find it very significant that 19 seconds of exposure to the ice crystals/pellets was sufficient to shut down the 3 airspeed sensors. The fact that a loaded up pitot tube can begin to clear itself in 30+ seconds after the blockage is not really good news.

While blocked, a pitot essentially stops collecting new ice inside, so it would appear that what takes 19 seconds to collect requires up to 49 seconds or more inside a pitot tube to begin to melt and clear. This tells me that the pitot heating system is seriously outmatched by the environment.

I think, as some of the posters earlier have mentioned, that the key problem is coupling the melting energy to the collected ice. Conduction alone just cannot do the job and maintain an open pitot tube-at least, not at realistic pitot tube temperatures.. Settling for intermittent blockages is not really an acceptable course. What is needed is a better means of coupling energy to the ice when it is collected and a wider dynamic range of energy modulation.

This is very good corroboration that the pitot heaters behaved like ballast resistors.

I would like to offer the thought that using pitot tubes with different means of heating begins to create diversity in the airspeed sensing system sources. Dinking around with more of the same (higher wattage) in pitot heaters is likely to be unsuccessful and will likely retain the cyclic clearing/clogging characteristic under worst case mixed ice conditions. Sometimes KISS is an inappropriate solution if it involves undesirable adverse characteristics. Time to move on.

At least that is how I analyze this.:(

Hi,
Turbine D
Are you sure the pitot tube failed ?
When I read the BEA report N°3 it's indicated that the plane was working as per design
The pitot tube worked also as per design
The plane and all parts of it were certified to work under certain limits
The accident of the AF447 show that the plane was put (or go .. make your choice) over the limits of certifications (and he stalled) .. as was the pitot tube (and he iced)
So the plane and the pitot tube never failed .. as .. when the pitot tube returned under the certification limits he worked fine again (nobody go outside the plane for fix it .. as he never failed)
Unfortunately the plane required some extra actions for return in the certification limits ... and those actions were no performed ...
Finally .. who failed ?

Not a glitch. Just if you write the proper acronym for the coherent light device, ads appear selling the devices to any scrote who fancies trying to blind a pilot on approach.

Turbine D

Me too, and I find myself in complete agreement with what you say.

Yep!
Or that one manufacturer’s product will work, but another’s won’t, both at the same location on the same aircraft? Or that the one that didn’t work was OK for seven years?

I completely agree!
Again I agree completely
I have wondered about that also, and it is interesting that Airbus themselves, when commenting on the proposed TSO, say:

And


But the newly proposed Appendix P to CS25 gives the TWC at -30oC to be 4.5 g/m3 BEFORE any installation effects are included. So the requirements against which the A330 was designed are miles too low against the possible ice particle exposures now envisaged.

[I should have added that Airbus say they test to their own internal requirements that exceed the JAR 25 variety, so we don't really know what theA330 probe capability was]

Worth noting also that the research and analysis work that led to this conclusion was not started until 1998, four years after the A330 went into service.
I agree with you there, with one proviso, and that is there has to be a suitable facility for testing the probes.



In AIAA 2006-206 they point out that:




Let us hope so

RR_NDB,
While your focus on the pitots as the initiating cause of the AF447 disaster is understandable, it is really irrelevant in the wider picture. Improving the pitots is necessary in the general drive for safer flying, but not as a specific outcome of this accident.

Sensors can fail for a million reasons. CB's trip, autopilots drop out, likewise. The aircraft should be flyable in this case with the proper backup systems/crew procedures. Surprise surprise, it is!

Ice was the issue in this case, but may not be in another. Your brand of hindsight may have saved AF447, but will not save the next one. The issue here is not the pitot icing, but the subsequent mismanagement of the problem, whether by the crew or the remaining aircraft systems (the stall-warning cutout comes to mind).

A couple of questions...
 

1> I know that prior to AF447 the pitot-icing had already been identified and there were steps in place to change the sensors, but was any action taken to introduce this scenario into sim. flights so that we could assess what proportion of pilots would get it right?
2> Has anyone looked at (ACARS?) data to see whether
a> Icing is rare but when it happens all sensors will ice ; or
b> Icing is fairly common but the sensor offer effective redundancy and it is rare to lose two.
I think someone mentioned before that HAL can clearly ‘see this coming’, and it would not seem impossible to add some logic along the lines of;
“Hey guys, I have just had to arbitrate a whole series of mismatched speed indications, it is becoming increasingly difficult to pick the right one with any degree of certainty so any time soon I might be handing you the plane”.