|
the changes coming from this crash will be evolutionary (as in "bugfixes") instead of revolutionary.
Of course this will be the case. It has been so ever since the early days of regulated aviation. No one is suggesting that we will ever go back to steam driven aeroplanes as representing the state of the art - in spite of the deluded and fond views held by many of us dinosaurs ... :E:} From that sort of viewpoint, this mishap is no different to any other - an aspect of the investigation will be to look at what changes might be appropriate within the design and operating paradigms. The interesting aspect here probably will/might be that the evolution may be more significant than what we might have seen in most previous mishaps ? |
That is a good point though... (MM43)
Why is there not at least one reversionary A/P mode, when it's either turbulence or UAS that kick it out. As a short /temporary pre-handover mode, a sensible Pitch / Power should not be beyond its grasp, accepting that it's basically a heavily fedback airspeed-centric loop (which is far too inflexible, surely ?) "Here you are, things are getting difficult for me, but we seem to be flying a stable AoA at a sensible thrust setting - Handing over now " |
bearfoil
There was an intermittent post from bearfoil that seems to have disappeared. There were some important points about how Anomalous Design works. I just wanted to add that in the scenario I envisioned apropos discrepant pitot heat, the probes would still be triple redundant in non-icing environment. In an icing environment, however, they would "switch" to the so called anomalous design mode. I call it switch, but this would of course be completely passive on account of the fact that the heat is applied uniformly through out the entire flight.
This is way outside my areas of expertise, and I may be completely misunderstanding the concept of redundancy, so this post is purely for my own edification. |
Bearfoil removed his post (although it is still there in the aether, so to speak). You might like to ask him to reinstate it. I thought it a good post
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bearfoil: request to reinstate
Dear bearfoil,
I'm writing to officially request you to reinstate your post re Anomalous Design. Sincerely yours, Cog :) |
FLY THE AIRCRAFT. Still, whenever I hear this, it makes me squirm. As the pilots among us know, sometimes its easier said than done. It's important to keep that in mind come Friday. Peace. |
cogsim
As the design consideration is approached in real time, redundant systems simply fail together. If one system has sensors that have different designs, the chance of double or triple fail becomes remote. Identical fuel systems in BA038 failed their TRENT 700's only seven seconds apart. The failure tracked identically as each engine spooled up, then starved, and settled, with very close EPR's. And that is a complex system. A third engine, or two more, would the failure have been the same? Very likely. A redesigned Heat Exchanger, and the problem is solved. Pitots are extremely simple, yet they have remarkably vulnerable features. A narrow aperture surrounded with a sharp leading edge that ices faster than a blunt one. If ICE is the consideration, three separate design approaches would likely produce three anomalous solutions to the goal. Redundancy works well if in a "fallback" position, so I like your anomalous heat solution. Exposing three identical devices to the exact same conditions will produce three failed devices. If three concurrent readings are desired, better each device has different characteristics. This is why I never understood the need to "sample" and then ask for a vote. Likely the results of the election will be the same. If not, they soon will be. So this is why anomalous design works well when Redundancy is simply a siren song. This is from memory, so apologies if it isn't what you saw. I think I inserted a snarky comment about "Backup systems". So tell Air France to cancel their Goodrich deliverables, purchase the BUSS from Airbus, and happy skies...... My apologies - I presumed that Bearfoil could see and reinstate the original post which he had deleted. FYI, mods can see a deleted post and reinstate it. All deletion does is hide it from general view. There is one caveat - delete post #1 and the thread disappears into the never never.In future, if you want a deleted post undeleted - simply ask and your wish will be granted. JT |
Exposing three identical devices to the exact same conditions will produce three failed devices. If three concurrent readings are desired, better each device has different characteristics. |
BEARFOIL
As the design consideration is approached in real time, redundant systems simply fail together. If one system has sensors that have different designs, the chance of double or triple fail becomes remote. Yes, additional sensors will increase the logistic tail required to support an aircraft. I would not advocate wholesale replacement of pitot tubes with a 'new concept' system, that would destroy diversity, not improve it. Some are pointing to the fact we have documented ~18 instances of Airbus pitot tube freeze up with no adverse result. If AF447 is the one with the adverse result, then how do those statistics look? Pretty P poor. Even if we had 500 instances with one bad result, the rate is still unacceptable. The key to good outcomes is avoiding unnecessary risk. Suppose there is a functional laser airspeed system available already. Suppose the barrier to its use is "we already have a good system with the pitot tube." Don't you think it is possible that by being technological Luddites, we may be holding back a promising new development that only needs a foot in the door to advance? (And to the best of my knowledge, none of my $$ is invested in such a company offering such an airspeed monitoring system.) In the near term, I like MM43's idea about tiding the aircraft over until things can be stabilized. Give those easily confused computers some realistic data to chew on.:ok: |
Thanks for the post bear.
If ICE is the consideration, three separate design approaches would likely produce three anomalous solutions to the goal. Redundancy works well if in a "fallback" position, so I like your anomalous heat solution. |
Hate to state the obvious, but how many Boeing/Douglas/Lockheed airliners have suffered multiple pitot clogging from ice?
When the pitot get iced, I have seen no mention of windshield getting iced, which means windshield heaters are more robust than pitot heaters. |
the egg or the chicken
(Beg your mercy beforehand...)
If the rumour is right and there was an uncommanded "pitch-up": Which really might have happened: 1 - iced pitots leading tho this pitch-up ? 2 - this pitch-up leading to a reduction higher than 30knots in measured airspeed and (not really sure) consequently to the famous acars message about the probes (and maybe the probes weren't "iced" at all) ? |
GB
how many Boeing/Douglas/Lockheed airliners have suffered multiple pitot clogging from ice? I suspect that the question is better asked from the FBW/ Non-FBW perspective. There are differing dependencies as mentioned earlier. Does anyone know of a FBW airliner that does not use airspeed in the control gain calculations? Isn't comparing windshield and pitot heating like comparing apples and oranges? Very different systems, performing different functions with different operating principles. |
guys,
why don't you wait a few days to get the result, instead to come with xxxx thousand of hypothetical answers.? get a life! |
Machinbird:
Isn't comparing windshield and pitot heating like comparing apples and oranges? Very different systems, performing different functions with different operating principles. I don't think FBW by itself is such a big deal, except it would seem easier to incorporate a reversionary pitch/power mode. |
Very different devices, sure, but they're heated just enough to keep ice from accumulating. They're in the exact same icing, which is reportedly outside of certification requirements, yet no report of windshield icing over? http://img13.imageshack.us/img13/5715/ice1n.gif http://img218.imageshack.us/img218/4587/ice2u.gif http://img225.imageshack.us/img225/1273/ice3.gif |
@GB
When the pitot get iced, I have seen no mention of windshield getting iced, which means windshield heaters are more robust than pitot heaters. or possibly just that the windshield is less prone to icing than the pitots ? My (non-expert) understanding was that small items protruding ( such as pitots) ice up more easily than large surfaces (such as windshields) . |
John Thanks, I'll remember that.
******** If a particular type is prone to eccentric behaviour it can be banal or it can be lethal. Boeing Rudder Actuator, TRENT FOHE, MD screwjack Mx demands, etc. I take particular note of NASA's warning re: Probe Icing. Rather than wait for UAS as a predictor of Probe Icing, how about a lit probe just out the F/O's side glass? Kidding aside, Pitots are simply not the problem, not the proximal problem, anyway. There is a "procuring cause" but that remains to be seen. OK465 "If the devices in question are state of the art, then would not the characteristics required of the other two be a step back? " See below? Anomalous design? The bold after "most definitely". Machinbird "I would not advocate wholesale replacement of pitot tubes with a 'new concept' system, that would destroy diversity, not improve it." Most definitely. "The original code for this system was written in isolation by three separate teams." Different is good, but not in sensors? The AD's spend all their time assuring the three probes are not discrepant, then go all wonky when they are? Good mission, no follow through? This just smells like over reliance on development, and over confidence in outcome. Otherwise UAS would be a yawner. kiwiandrew You and cogsim crossed. If the leading edge of the Probe aperture needs to be razor sharp for less drag, why not polish the radome instead and make the business end of Thales a doughnut? It isn't the pitots; with a boring flip (FMS) to the PF, who needs state of the art pitots? The bottom line for me is that the system looks superb, but someone went to lunch instead of the meeting where the Pilots and the FMS were introduced. Someone gas up the forklift. I think Friday, Truth be told, will be about humans, not pitots? Machinbird: Pitch rate/g-rate transparency, Perpignan? |
I don't think FBW by itself is such a big deal, except it would seem easier to incorporate a reversionary pitch/power mode. Here is some "homework" for those who wish to get their minds ready to understand a bit more about what makes FBW different. Fly-By-Wire A Primer for Aviation Accident Investigators The quiz question is: How does the pitch feedback in the A320 at 180 knots differ from that at 230 knots?:8:eek::} |
Anyone here that can comment on ultrasonic airspeed measurement ?
I did a little googling of this potential alternative (??) to pitot sensing and found out that there are commercial "high grade" products available for wind sensors as well as for helicopters. But the limits of its accuracy seems to be around 150 knots top speed. Any hope of developing this for airliners? (Wikipedia does note that "Another disadvantage is lower accuracy due to precipitation, where rain drops may vary the speed of sound.") Another potentially usable technology would be the hot wire mass flow sensor, where the air flowing past cools down an electrically heated wire and the airspeed can be calculated from the wire's electrical resistance which changes according to temperature. But this is not seen on airliners either. Anyone knowing if this is due to inherent drawbacks compared to pitot tubes, or just an aversion to try new technology? Obviously these technologies must have some drawbacks compared to pitot tubes, otherwise they would already be in widespread use. It would be interesting to know where the problem areas are. ****** Bearfoil how about a lit probe just out the F/O's side glass? |
Hi Machinbird,
Thanks for the very interesting article. That's the first time I've read and understood that the flight control Law on A320 is pitch rate below 210 Kts and delta g above. 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? |
snowfalcon2
"Another potentially usable technology would be the hot wire mass flow sensor, where the air flowing past cools down an electrically heated wire and the airspeed can be calculated from the wire's electrical resistance which changes according to temperature." Kinda like the Pitot/HEAT combo, but without the Pitot? Shows promise. That will save expensing for three pitots. cheers:ok: |
FBW article
Machinbird posted a link to an article by F/O Stowe from Delta.
I cannot resist quoting this : If loss of control or aircraft handling qualities are suspected in an FBW accident, first assume that the FCS--and not the pilot--induced it until proven otherwise (it might be "designer error"). |
Originally Posted by snowfalcon2
(Post 6473848)
Another potentially usable technology would be the hot wire mass flow sensor, where the air flowing past cools down an electrically heated wire and the airspeed can be calculated from the wire's electrical resistance which changes according to temperature. But this is not seen on airliners either. Anyone knowing if this is due to inherent drawbacks compared to pitot tubes, or just an aversion to try new technology?
I suggest it is impossible to stop pitot tubes from ever blocking when snowballs thrown at them, but it must be possible by design to ensure the drain hole stays clear of ice. The ability to generate a false reading, which is 'live' with altitude changes when blocked, has been the killer in the past. Perhaps could use microwave heating of the pitot cavities so not rely on conduction from metal surface to sharp ice crystals? Currently most heat will be lost by the 'wind-chill factor' on the outside of the tube. But even just upping the applied heating voltage by say 20% (power by 40%) without any mechanical/electrical pitot design change would take years to introduce even if feasible... |
Why not give the pilots angle of attack information?
|
Hot wire mass flow sensors
The first wet motor race using hot wire mass flow sensors to determine fuel flow rate was an interesting disaster. Don't know if they overcame the problem, or changed the sensor type!
|
Originally Posted by Machinbird
(Post 6473804)
Maybe we will learn something Friday regarding how different FBW is.
Here is some "homework" for those who wish to get their minds ready to understand a bit more about what makes FBW different. Fly-By-Wire A Primer for Aviation Accident Investigators The quiz question is: How does the pitch feedback in the A320 at 180 knots differ from that at 230 knots?:8:eek::} There is also the question of what the FBW uses to calculate gain in the event of unrelaible airspeed - last-known-good value (which might be wrong...) or fixed mid-value or some other calculated value ? I doubt it uses known-bad data, so if you do have 180-indicated at 230-real, that doesn't mean you'll get the gain set to the normal value used at 180. Am I on the right track ? A page or so back in the thread, someone posted on an airline investigation showing pitot issues -> unreliable airspeed on one in 80k flights (!) - by my reckoning that's a lot of issues over the years worldwide (even if only Thales equipped buses) , far more than just the other events listed in the reports, yet without planes falling out of the sky. So on that track, the answer to "How does the pitch feedback differ" would be: not by enough to cause a serious problem if the speed indication is wrong. Until 447. Something different to all the other cases happened on this flight, what, we don't know yet (maybe the VS really did fall off :E). Tomorrow we may know. |
Originally Posted by DType
(Post 6474059)
The first wet motor race using hot wire mass flow sensors to determine fuel flow rate was an interesting disaster. Don't know if they overcame the problem, or changed the sensor type!
|
Pitot tube failure protection
I believe that Airbus software is probably missing simple protection in airspeed data readouts. At least manuals in previous posts do not describe any such measures.
If ALL Pitot tubes freezes and IAS deviates by 1-50% then computer before admitting that airspeed data is correct should check the acceleration/decelaration rate from inertial sensors. This simple cross check would protect from any type of tubes failure (freezing, blockage etc) |
SLF here. Forgive me for butting in, but what I find very puzzling about all the discussion on pitots, icing, FBW, human-machine interface, etc, is that none if it seems to consider why all this is coming up now. The A330, whatever its faults, was not introduced yesterday. It has been in commercial service since 1994. More than 700 of them are plying the world's airways. It flew in commercial service for 15 years without a fatal accident. Countless gazillions of miles have been flown by A330s, surely in all conceivable combinations of weather, crew experience, captain-in-cockpit-or-not, etc etc.
So what has changed? Why are icing pitots now a concern? Why is FBW now a concern? Why is lack of an AoA indicator now a concern? If there was something awry with the design philosophy of the A330, wouldn't it have shown up years ago? The A330 is, I presume, pretty much the same today as it was in 1994. So is the weather, and the way that pitots ice or don't ice. What does that leave? Is it the pilots that have changed over the past decade? |
What has changed ?
Gibon2,
you are absolutely right. Did the aircraft change over the years ? Yes and No. No it did not go through any kind of major re-design, and its various versions are quite stable. Yes, some things change in this aircraft, like in any other. 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. You can add to the can of worms the parallel evolution of other components software versions, like Air Data Computers for example. All these computers and their brand new updated versions do communicate together all the time. Extremely well, usually. Unfortunately, the public will not be educated on this subject by the upcoming inquiry, I would wager. Of course, such faults as I hint to in the previous paragraph happen very rarely, and that is a blessing. But they do happen, and those who know what they are talking about in IT knew about the potential for it for years, too. Statistically speaking, it would be very difficult to say that such aircraft is inherently safer or more dangerous than this one in the field of modern commercial aviation. However, it is a certainty that Airbus is on the side of "the computers are always right and will have the last word". Boeing would say "the computers are very good, use them, and if you feel like you are better, you are free to give it a try, but dont come back to us crying". A difference in philosophy, not in numerical safety. Did the pilots change over the years ? Certainly. Nowadays, at some airlines, an instructor or examiner will slap your hand if you choose to fly manually during some parts of a sim check. It is forbidden to touch the manual pitch trim of any Airbus if it is not flying in Direct Law, which never happens in the sim, except for one minute and a half upon initial training so the appropriate box can be ticked. Yes, airline pilots had to go through major rethinking of their role, function, skillset, attitude, etc... It is called "progress". Those who resist this are called "Luddites" or "dinosaurs", regardless of age, by the way. So, dear Mr Passenger, here was a short answer to your very relevant questions. Best regards Svarin May 26th 2011 at 1205UTC - This post has been edited by parties unknown to me. Profanity was removed. I can accept that. However, Airbus "philosophy sentence" has been modified. I rest my case that a vast majority of professionals -including myself- perceive this particular manufacturer as always trying to deflect blame for an incident or accident from its own design towards so-called "pilot error". This would not be a responsible attitude. |
So what has changed?
It's not quite as simple as that - (a) certification processes are very comprehensive and address a generalised set of requirements held to provide a very high probability of successful in-service operation. (b) the aircraft as it comes through the certification process will have shown compliance with the set of certification requirements pertinent to the design (c) however, the certification standards don't provide an absolute guarantee that the aircraft will be able to weather every conceivable set of circumstances with which it might be tested in service (d) sometimes (and this may take quite some time to materialise) a set of circumstances will arise which conspire to defeat the capabilities of the aircraft and the presumptions which went into the design and certification processes. It may turn out that this sort of situation confronted the crew of the mishap aircraft which is the subject of this thread. (e) sometimes a comparatively simple problem within the state of the art knowledge combined with significant design advances will present a problem. The early Comet fatigue problems are a useful instance of this. (f) sometimes the man-machine relationship may not quite work as well as was presumed and intended. This sort of consideration may turn out to be material in the present case under discussion. It is common to see progressive minor changes to an aircraft Type as in-service knowledge is accumulated. Sometimes such development is subtle in that it is not evident to the wider Industry. Instances include routine engineering design and maintenance practices changes. All Types experience this sort of development throughout the life of Type. Sometimes changes may need to be effected quickly and these usually end up as Airworthiness Directives. I can't bring to mind any aircraft which has not been the subject of ADs. Very occasionally, a Type may have problems arising sufficient to warrant a revisit of the Type Certification process. Not many Types are subject to this re-examination. At the end of the day, do I worry about flying on either a Boeing or Airbus (or any other reputable) aircraft ? Of course not. Having been involved in the design and certification processes for just about all of my working life, I am content to accept the low risks inherent in flying in certificated aircraft and equally content to accept that they are not perfect and come with flaws. If the flaws are minor, such are worked around by engineering, maintenance and operational standard practices - if major, by modifications, as appropriate, to aircraft or procedures. All part of normal aeronautical processes. |
@Gibon2
Good question, I've seen raised elsewhere too (more below) @Svarin Good points, especially the piloting changes - I don't think any of the a/c designers, A or B or other, intended the result of improving the plane/automatics side of pilot+plane to be that the airlines then dumb down the pilot side to compensate :( I would venture to add: Unique circumstances is possible - even after all those years. BA038 fell out of the sky after almost the same length of exemplary 777 service. The design failing blamed has been there from the start - it just took that long to show up. The investigation went through probably millions of hours (175k flights) of past 777 flight data and found that the BA038 flight was unique. No other flight in all that time went through the same environmental conditions. Selective reporting is also possible - maybe the pitot events have always been happening but not reported. Usually the events last only seconds and cause few or no problems. After one or two incidents raise the profile (before 447), maybe you start to get more events acutally reported. After BA038 I think there were some other brief transient rollbacks reported (at altitude where didn't cause a problem) that may well be the same cause, but were just never reported before. |
infrequentflyer789 wrote :
I don't think any of the a/c designers, A or B or other, intended the result of improving the plane/automatics side of pilot+plane to be that the airlines then dumb down the pilot side to compensate |
Windshield Heat
OK, I apologize for the wrong way detour, comparing pitot icing to windshield icing. At some point I knew better.
Should I remove the errant posts, or just leave them? |
Hi,
maybe the pitot events have always been happening but not reported In December 1995, Airbus was the finding of a lack of certification of pitot probes: Ice crystals clog the probe which causes severe degradation of calculating flight parameters. This is not a failure, it is a defect of the Pitot probes. According to the regulations in force on the day of the accident, Airbus had an obligation to correct this defect. Instead of eliminating this defect, Airbus decided to ask the drivers to ensure accountability through the application of the procedure: Following the amendment of the Aircraft Flight Manual for the A330 Airbus, the DGAC imposed in February 2001 a new procedure for pilots titled "Unreliable airspeed conditions" in case of loss or inconsistent speeds measured [AD 2001-069 (B)]. The FAA took over the DGAC AD in June 2001, but noting that this initiative was in response to an "unsafe condition" that could lead to the A330 outside its flight envelope [AD 2001-13-13]. The regulations in force at the time of the accident did not allow a manufacturer to remedy a default by the application of a procedure. In addition, this procedure will be difficult to apply when two precursor events of the accident of Flight 447. Airbus will admit eight months before the crash on 1 June 2009, but nothing will change: At the end of August and early September 2008, two A330s for Air Caraïbes Atlantique (ACA) encounter severe icing conditions that cause the cruise blocked pitot probes Thales SA and inconsistent measured velocities. During the following October, the Directorate of ACA initiates a meeting at the premises of Airbus in Toulouse. According to the report of the Flight Safety Officer, Airbus engineers have understood at that meeting "the difficulty encountered by the crew for a rapid implementation and effective procedure SPEED INDICATION unreliable and" thinking therefore a modification of checklists. This procedure made available to drivers to compensate for the lack of pitot probes and "unsafe condition" that resulted was not only inappropriate but also ineffective. But after the crash of Flight 447, Airbus that did not stop to remind drivers that this procedure should be applied in case of inconsistency of measured velocities (Accident Information Telex No. 2 dated 4 June 2009) 1995/Novembre December 1996: TFU 34.13.00.005 (see document). Airbus made the finding of a lack of certification on pitot probes and Launches Development of the probe Goodrich P / N 0851HL. "STRONG cumulonimbus (Cb) A HIGH DENSITY OF Containing ICE CRYSTALS CAN BEEN COUNTERED, PARTICULARLY IN THE Intertropical Convergence Zone (ITCZ). IN AN ICY SUCHA AND TURBULENT ATMOSPHERE, THE A / C AIR DATA PARAMETERS (PRESSURE DEPENDENT) MAY BE DEGRADED Severely, Even Though THE PROBE HEATERS WORK Properly. IT HAS THE CHARACTERISTICS OF THAT Appeared SUCHA AN ENVIRONMENT COULD EXCEED THE WEATHER SPECIFICATIONS FOR THE PITOT PROBES Which ARE CURRENTLY CERTIFIED. THE WEATHER SPECIFICATIONS (ICING / LIQUID WATER CONTENT / GUTLET SIZE) TO THE PITOT PROBES Which RESIST SHALL HAVE BEEN UPDATED WITH MORE Therefor Stringent REQUIREMENTS ON THE BASIS OF THE FIELD EXPERIENCE AND RECENT EXTENSIVE FLIGHT TESTING. AIRBUS HAS LAUNCHED THE DEVELOPMENT OF THE modificiation followin: 1. DEVELOPMENT OF A NEW PITOT PROBE ABLE TO MATCH THE NEW REQUIREMENTS. ALL FLIGHT AND WIND TUNNEL TESTS TESTS ARE COMPLETED AND NOW SUCCESSFULL: THE CERTIFICATION OF A NEW PITOT PROBE HAS BEEN IN EARLY NOVEMBER Obtained 1996 (NEW PITOT PROBE: P / N 44836 851HL MOD). "(See document) November 1996: The probe Rosemount P / N 0851GR is replaced by the probe Goodrich P / N 0851HL, (Service Bulletin A330-34-3038 for Model A330-301, -321, -322, -341, and -342 Series Airplanes) (ref. FAA states that this replacement is made necessary because the inconsistency of measured velocities can cause the A330 outside its flight envelope). This new probe is duly certified by Airbus. December 1998: Emergence of the probe Sextant P / N C16195AA who replaces her as the probe Rosemount P / N 0851GR but for a limited number of A330 (Service Bulletin A330-34-3071 for Model A330-301 Series Airplanes) (ref.FAA). How the new probe has it been certified by the DGCA considering the experience Rosemount? For more demonstrates its inefficiency! August 2001: The DGAC mandated these two replacements by AD 2001-354 (B) (see document): "The following measures are rendered mandatory from the date of entry into force of this AD: Before December 31, 2003, unless already done, remove the pitot probe type ROSEMOUNT P / N 0851GR and replace them either by probes BF GOODRICH AEROSPACE type P / N 0851HL, according to the instructions of SB A330-34-3038, or by type probes SEXTANT P / N C16195AA accordance with instructions of SB A330-34-3071. " July 2002: In the ILO 999.0068/02/VHR SE (see document), Airbus made the observation of defects of the probe Thales (formerly Sextant) P / N C16195AA THE AIM OF THIS IS TO INFORM THE ILO OPERATORS THAT SEVERAL OPERATORS HAVE REPORTED SINGLE AISLE AIRSPEED ON AIRCRAFT FITTED WITH Discrepancy THALES PITOT PROBES PN C16195AA. . Following is a series of conflicting decisions that demonstrate the inability of Airbus to get rid of one type of probe that meet standards dating from 1947, unsuited to the reality of the environment in which the aircraft ( see previous notes). The observation made for the probe Rosemount in 1996 has obviously not been used for the probe C16195AA! September 2007: In a Service Bulletin (see document), Airbus recommends replacing the probe Thales P / N C16195AA by sondeThalès P / N C16195BA following further serious incidents. September / October 2008: defects of the probe C16195BA Thales, "which was not designed to address the problems of icing, are recognized by Airbus and Air France (see the document Info TFN No. 5). June 9, 2009: One week after the accident of Flight 447, the A330-F GZCP probe was equipped with Thales C16195-AA, Airbus launched an investigation into the case of inconsistency between the measured speeds reported by operators on Airbus A330/340 and took in early August decision to focus the probe Pitot Goodrich P / N 0851HL. EASA followed of course ... One issue on which the DGCA must be answered is "How the Sextant pitot probe (later Thales) C16195-AA she was certified in 1998 given the experience Rosemount? " |
Originally Posted by mitrosft
(Post 6474148)
I believe that Airbus software is probably missing simple protection in airspeed data readouts. At least manuals in previous posts do not describe any such measures.
If ALL Pitot tubes freezes and IAS deviates by 1-50% then computer before admitting that airspeed data is correct should check the acceleration/decelaration rate from inertial sensors. This simple cross check would protect from any type of tubes failure (freezing, blockage etc) United States Patent Application 20110071710 Kind Code A1 Puig; Stephane ; et al. March 24, 2011 METHOD AND DEVICE FOR DETECTING AN ERRONEOUS SPEED GENERATED BY AN AIR DATA INERTIAL REFERENCE SYSTEM |
Philosophy
It must be stressed here, mostly to attention of the potential reading public, that safety, especially safety as a statistic, is not at stake when discussing the various merits or failings of this or that design. Another simpler way of putting it is, as a passenger, it doesnt matter which type of aircraft one flies in. In the modern day, all recent aircraft types have a very excellent safety record.
As a pilot, it becomes very different. At one end of manual, old-school, dinosaur-like thinking, the pilot has all authority and all responsibility. At the other end of fully automated drone-like transportation system, the system itself, its computers, have all authority and all responsibilty. The real philosophical question faced today by passengers is whether they would entrust their lives to a (very well-trained) human pilot (who will share their fate), or to a (very well-designed) computer. In our subject matter, the problem is the aircraft and its designers claim full authority in the name of "envelope protections", which could allow a "concierge" to fly the airplane, but then when things go wrong, some fault is always found with the pilots which somehow shadows that of the design. Ultimate authority cannot be separated from ultimate responsibilty. The only difference is not in numbers but in philosophy. As a passenger, I can entrust my life to someone who puts his own life on the line with mine. I can accept responsibilty and pay the ultimate price if I fail to deliver that promise as a pilot. But 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. |
Dependability of a system is that property of a system which allows reliance to be justifiably placed on the service it delivers.
Models and meta-models can never account for all the situations and unplanned events in the real world. Dependance on services provided by systems (be they mechanical, electrical, meteorological, organisational, biological, hardware or software) is what every pilot must contend with to operate within safe limits. It would make sense to use multiple air data sensors (N-version redundancy), of multiple designs (diversity of design), using various watchdogs (error detection) to monitor the health of each sensor and provide the pilots with pure go-no-go data. Technology exists such that a pilot should never be in a position where he or she has to question the quality of primary air data. Air data systems on passenger A/C without the aforementioned should be rated VFR only IMHO. |
sensor-validation, Interesting find on the Airbus Patent Application. You won't mind if I post a direct link?
METHOD AND DEVICE FOR DETECTING AN ERRONEOUS SPEED GENERATED BY AN AIR DATA INERTIAL REFERENCE SYSTEM - AIRBUS OPERATIONS |
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