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Old 31st Jul 2009, 19:16
  #4061 (permalink)  
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A similar idea in English ?
It's "CYA". Cover Your A$$.
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Old 31st Jul 2009, 19:28
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umbrella vs cya

The latter *does* lack a little of the elegance of the French expression....
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Old 31st Jul 2009, 19:39
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Mandatory Replacement of Pitot Tubes

EACA issuing AD requiring at least two Pitot tubes on A330 and A340 be replaced.

The European Aviation Safety Agency plans to propose an airworthiness directive mandating that all A330 and A340 currently fitted with Thales pitot probes must be fitted with at least two Goodrich probes, allowing a maximum of one Thales to remain fitted to the aircraft," said a statement released by the agency based in Cologne, Germany.
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Old 31st Jul 2009, 19:41
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The latter *does* lack a little of the elegance of the French expression....
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Old 31st Jul 2009, 19:45
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With all due respect, the topic has become divergent design, a very important idea, one that was used by Boeing in its software developments, as well as AirBus.

It is especially pertinent to ETOPS, since Redundancy was relinquished for Safety critical system design.

Essentially, independently engineered solutions for the same spec. sheet.
It's not exactly spitting in the wind, though it seems like it is reliant on separate approaches to be immune from parallel and identical chain fault.

For example, if the pitots here were different makes, it is quite possible that what failed all three would possibly have failed only one, perhaps due to slight differences in thermal engineering, alloyed surfaces or finish techniques. It is cross applicable to 038 because the 777 has virtually identical plumbing architecture between powerplants, with exact hardware compliance, and of course identical Fuel. It isn't simple to explain, and subject to alot of Flaming, for that reason. What isn't understood irritates easily.

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Old 31st Jul 2009, 20:03
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Airbus utilizes design diversity in computers to lessen the chance that redundant systems would fail at the same time in the same way. Funny this principle was never applied to probes.
Very interesting comment and quite relevant. There are unfortunately other instances in which that 'principle' has never been applied to AB designs and from my perspective they are not at all funny (although I understand your different context use of the term).

Read the following report and it may give you some insight into how AI responds to repeated anomalies experienced in some of their products.

If that is how they respond to problems then I have no regrets at never having had the "pleasure" of piloting one of their aircraft.

How would you all like to be flying an A320 that loses all 6 displays and has a standby gyro with a life of 5 minutes? Their SB's and fixes don't work. They change their "new" models but do not retrofit. Sorry, but I'm not impressed.

The same pattern appears to exist with these alleged multiple pitot probe failures and the difficulties they appear to cause. They know there is a problem but, they don't seem to know what it really is and their efforts to eliminate it so far could only be classified as lame.

Tempting fate isn't a game that should be played in commercial aviation, IMHO.
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Old 31st Jul 2009, 23:54
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What isn't understood irritates easily.
For put it simple
The two pilots don't eat the same food

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Old 1st Aug 2009, 01:44
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Ice crystals

Last night I tuned into the last part of a TV documentary filmed in Australia dealing with thunder storms and the size of ice crystals in ice clouds near and around these systems, but particularly in the cap of a cell. While no definitive conclusion was reached, it was newly discovered that crystals can vary in size by considerable amounts, with corresponding different effects on pitots tubes. Two of their test airplanes while attempting to collect samples, experienced loss of airspeed indications, and had to make emergency landings in the middle of these storms. I am not sure when these tests were done, as I say, I tuned in at the end of the film. Perhaps someone else can provide additional info
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Old 1st Aug 2009, 02:56
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wes wall, a frequently encountered hazard is the failure to read the thread, and to use the search function:-
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Old 1st Aug 2009, 16:15
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If Pitots are the smoking gun...

It would be a great shame if the main conclusion from the loss of AF447 is to change the supplier of the pitots, and consider 'problem solved'. The criticality of IAS seems to be in need of an urgent rethink from a safety/system engineering perspective, too many serious incidents have already occurred involving unavailable/misleading IAS to consider that a simple fix is going to be sufficient.
Three sensors, using the same technology, in the same area on the outside of the aircraft are obviously vulnerable to 'Common Mode Failure' due to rain/ice/debris/birds etc., regardless of the supplier. To then use this vulnerable source to derive a parameter (IAS), which is used by other systems in a way that is critical to aircraft safety should be unacceptable. Is this a case of 'we have always used pitot tubes, they meet the regulations so they are safe, precedent is set'? A method that uses different technologies should be mandated; there are a wide range of technologies already being used for anemometers such as rotating cup or propeller speed, torque on a fixed vane; there are even laser Doppler and ultrasonic anemometers. There seem to be enough alternatives that 3 completely different sensors could be used, and then take the average of the closest 2.
Critical avionic systems should be designed to cope with 'bad data'; garbage in, garbage out is not an appropriate paradigm for safety critical avionic systems; the fundamental problem is an aircraft level safety integration problem, which (IMNSHO) is an issue that needs a lot more attention.
Industry are not to blame (nor are they blameless), they have to work to the the regulations; nothing less, but also nothing more. If a supplier 'over-engineers' their product, they are likely to become uncompetitive. The initiative must rest with the regulatory authorities (FAA, EASA, et al.), it is they that need to raise the crossbar in order to continually improve aviation safety.
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Old 1st Aug 2009, 23:01
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Flight AF 422 (FGLZT) Paris/Roissy -Bogota

Quick translation of an ASR summary of the AF census of Pitot problems (08/2008)

Cruising at FL 380, weather radar ON (CAL mode ?), PAX ON, entering a cirrus veil. Suddendly, severe turbulence, A/P manually disengaged, deployment of the airbrakes to avoid MMO, Mach 0.78 selected, airbrakes retracted and A/P reengaged. Then again, new brutal acceleration, A/P automatically OFF, many red echoes on the weather radar, ice is beginning to accrete on the windshield. Altitude is maintained +/- 200 ft.
Many thunderbolts around, key phrase to the PNC in the cabin.
In a blink of an eye, the airspeed rolls back in the red area, recovers its value, then again the two airspeed indications are lost on the PFD and stall alarms are sounded. I was about to implement the stall procedure, before I even had the opportunity to send a MAYDAY, when the airspeeds recovers and are back on displays, then VFR conditions. All flight systems are back, verbal exchange with the cabin crew, they had the time to fasten their seat belt. Message ATC, Dispatch, ATL writing.
fortunate to get the airspeeds back soon enough.
different pitot freezing event durations (between 2 and 4-5 mn, less than 1 mn for the last BA type probe recently), but no time indication here (sounds sudden and of short duration), and the stall alarms occur immediately
I don't get why people focus on airspeeds problems in the media, ok it is a problem but a problem with a clear solution (pich & thrust), but the very difficult troubleshooting (fault isolation) and the false stall alarms in this context seem to be the real evil, a problem pilots are seemingly not very well trained to.
PS) These Pitot problems seem to have increased very rapidly in 2008 on the Thales AA, despite new maintenance rules adopted in 2003, why ? (this may be an explanation for the apparent lack of reactivity of the authorities, they may have been taken by surprise). Problems with the drain manufacturing qualifity were observed on certain AA probes, but if the pollution removal was correctly operated, does this suggest that the problem could be a gradual corrosion (aging accentuated by the initial manufacturing process) ?
PPS) I don't know whether AF had correctly evaluated the problems posed to air safety as seen through the cases it was gathering or through the Air Caraïbe cases, but I would like to know whether these ASR related to Pitot problems had been communicated to the DGAC, BEA, Airbus and to the EASA.
PPPS) CS-25 -General Certification Considerations -
(ii) Airspeed.
Display of airspeed in the cockpit is a critical function.
Loss of all airspeed display, including standby, must be assessed in accordance with CS 25.1333(b). *
Loss of primary airspeed display for both pilots must be improbable
Displaying hazardously misleading airspeed simultaneously on both pilots’ displays, coupled with the loss of stall warning or overspeed warning functions, must be Extremely Improbable.
could this kind of requirement be the reason why the stall warning or overspeed functions are still available in alternate law 2, even if the airspeeds are corrupted (ADR Disagree), even if this stall/overspeed warnings are largely plagued by false alarms ?
In the same vein, I really wonder why the (false) speed trends are still displayed on the PFD when the airspeeds are corrupted ? The AF 908's PF reacted to stall alarms because he was reading -50 kts of speed trend while the stall warning sounded at FL350 (these -50kts are most likely a measure of the roll back due to the obstruction, but indeed this must be a worrying signal at high altitude where the aerodynamic margin is reduced). This makes two misleading signals (plus the misleading procedure about stall warnings) and an immediate decision to take. Plus a possible airspeed chase by the A/THR to set the stage (and degrade the aerodynamic margin). Plus night hand flight & possible turbulences. Plus workload and attention split.

Last edited by Hyperveloce; 2nd Aug 2009 at 02:59.
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Old 2nd Aug 2009, 08:37
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"CYA" indeed, or, in air force jargon "Watch my six" and variants, as where "six o'clock" means "right behind you."
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Old 2nd Aug 2009, 11:03
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Quote Hyperveloce : Displaying hazardously misleading airspeed simultaneously on both pilots’ displays, coupled with the loss of stall warning or overspeed warning functions, must be Extremely Improbable.
This casts doubts on the way the certification process is thought and approved…There are fine engineers and test pilots at Airbus, but it seems that the problem lies « upstream » in the process. The FHA (functional Hasard Assessment) studies the failures analysis and their threat to the safety. This is studied in part 1309 of FAR 25, with an advisory circular (AC 1309) explaining how to understand and enforce the rules…If I understand it correctly, you must look closely at the different causes especially if the failure comes from false raw data, or bad transcription, or erroneous comparisons etc…That is the Failure Mode and Effects Analysis. It seems to me, but I shall be happy to be corrected, that this has not been done thoroughly as far as the « Pitots » and their information are concerned. It was understood (wrongly) that a single event (in this case the icing of the three probes) could not interfere, or pollute, all the channels downstream. Thus angle of attack measurements with perfecly health vanes is polluted by erroneous airspeed indications…The Perpignan crash of a 320, even if due to reckless decisions in a hasty test-flight, should have started a strong reaction from the BEA as far as the « Vote-validated inputs control » is concerned.
Many cases are not covered by the certification in those new generation airplanes, and apart from changing the probes (which should have been a prudent recommandation by the BEA…but no, it is Airbus and EASA who make the move ) it will be necessary to strenghten and question the certification process.
Will it be done without pressure from the pilots ? Rather unlikely, I fear.
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Old 2nd Aug 2009, 11:47
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So I guess a lower voltage is applied on the ground (ie: V/2 = P/4) to mitigate overheating, but it's still not optimal. One of the advantages of having temperature sensing and closed loop control is more capable bite in terms of ice detection, heating element or temp sensor failure. Agreed, the simplest solution may do the job 90% of the time and should be the most reliable since there are fewer parts, but in my experience, the electronics part of any modern system design is usually the most reliable, assuming conservative design rules. The problems are nearly always with the mechanical bits and of course connectors.

As for resistance elements, most of the commonly available resistance wires have only a small positive tempco. For example, nichrome is around 300 ppm per degree C, so they must be using some pretty fancy alloys for the function to get the (?) square law characteristics required.

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Old 2nd Aug 2009, 12:01
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In 33 years of various jet aircraft operations equipped with dual Pitot/Static probes, never had any airspeed indication problems due to probe icing. Perhaps they should go back a few years in technology and recyle some of the pitot tubes from the Arizona aircraft cemeteries.
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Old 2nd Aug 2009, 13:43
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is there any correlation between the pitot icing cases geographical/flight level location and other newly developed patterns in weather (possibly to global warnimg ?)

As this is recently happening much more frequently there must be some reason to this:
- technical design - unlikely as there is still substantian number of planes with the same technology being used for last 10 years and more
- flight patterns - i have no knowledge to check this - needed input from more experienced, but the only thing that comes to my mind is smaller plane separation due to higher traffic (mignt not be the case when flying to/fro SA)
- weather patterns - most probable as we are still learning about the weather phenomenon internal structure. Warmer seas (an clearly established fact) mean more energy available to build higher cb and transport huge masses of air and water into high elevations

The production/certification tests are based on some standard repeatable conditions which may be currently not standing up to real life requirements
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Old 2nd Aug 2009, 16:18
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a stalled Boeing 757, corrupted airspeeds & stall recovery (Icelandair flight 662)

On October 19, 2002, about 2000 eastern daylight time (EDT) [or 0000 coordinated universal time (UTC)], a Boeing 757-200, TF-FII, operating as Icelandair flight 662, experienced a stall while climbing from flight level (FL) 330 (i.e., 33,000 feet) to FL 370. The flight lost about 7,000 feet during the recovery and then diverted to Baltimore-Washington International Airport (BWI), Baltimore, Maryland. There were no injuries to the 191 passengers or 7 crewmembers and no damage to the airplane.


During the takeoff roll as the captain was about to call "eighty" knots, the first officer called "hundred." The captain noted that the standby airspeed indicator agreed with the first officer's and decided to continue the takeoff and address the anomaly of his airspeed indicator after takeoff. The pilots indicated that EICAS messages appeared and disappeared several times after takeoff and during the climb, including the messages MACH/SPD TRIM and RUDDER RATIO. Checklists for MACH/SPD TRIM and RUDDER RATIO messages did not mention an unreliable airspeed as a possible condition. The modifications associated with Boeing Alert Service Bulletin 757- 34A0222 (and mandated by FAA Airworthiness Directive 2004-10-15 after the incident), which had not been incorporated on the incident airplane, would have provided a more direct indication of the airspeed anomaly. According to information in the Icelandair Operations Manual, these EICAS messages (in conjunction with disagreements between the captain and first officer airspeed indicators) may indicate an unreliable airspeed. Overspeed indications and simultaneous overspeed and stall warnings (both of which occurred during the airplane's climb from FL330 to FL370) are also cited as further indications of a possible unreliable airspeed. The crew did take actions in an attempt to isolate the anomalies (such as switching from the center autopilot to the right autopilot at one point during the flight). However, this did not affect the flight management computer's use of data from the left (captain's) air data system, and the erroneous high airspeeds subsequently contributed to airplane-nose-up autopilot commands during and after the airplane's climb to FL370. During the climb the captain's indicated airspeed began to increase, and the overspeed warning occurred. The first officer indicated that at this time his airspeed indication and the standby airspeed indication both decreased to about 220 knots and his pitch attitude felt high. Despite agreement between the first officer and standby airspeed indications and the pilots' belief that the captain's airspeed indicator was inaccurate, control was transferred from the first officer to the captain. Pitch attitude continued to climb and airspeed continued to decay after the captain assumed control. The airplane's pitch attitude became excessively high until the airplane's stick shaker activated and the airplane stalled. Although stall recovery was eventually effected and the airplane was leveled at FL300, the lack of appropriate thrust and control column inputs following the stall delayed the recovery. Evidence from the investigation indicates that anomalies of the captain's airspeed indicator were caused by a partial and intermittent blockage of the captain's pitot tube. The reason for the blockage was not determined.
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Old 2nd Aug 2009, 18:09
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Around 1990 or so I had this very scenario occur on a 767 during climbout over the Rockies one dark, overcast winter night. The captain's airspeed was the problem as the F/O's airspeed compared correctly with the Standby Airspeed. We flew the F/O's airspeed to destination and the Captain's airspeed slowly corrected as we descended into warmer air (relatively speaking - it was minus 15 or so), on final.

The same EICAS messages occurred to us as did on the Icelandic 757. We did not have to use pitch-power responses as my airspeed was unaffected. We wrote it up of course.

As industry experience shows, the problem, although extremely rare, isn't new, isn't isolated to the Airbus A330 and almost never leads to an accident if the causes and the procedures for dealing with the failure are understood. Going back to "old designs" is not the solution.
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Old 2nd Aug 2009, 18:40
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Agreed, PJ, nothing new under the sun, and it has been happening since the first pilot took off with his pitot head cover or static port plug in place, but as I said before (4031 and earlier) what appears to be new is either a multiple failure of probes or some software effect. All the 'examples' we are getting here involve ONE of the sensors. I think, however, the ?AeroPeru' crash had all the statics blocked?
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Old 2nd Aug 2009, 18:48
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So the question becomes what is different about the bus' reaction to discrepant a/s? Are we certain that three pitots failed on 447? No.
What is AB's plan for unreliable air speed driven a/p? I'm reading about pitot/a/p problems in Boeing, in climb, and single failure as well.

If the AD calls for r/r of two pitots only, and AB believes all three failed on 447, you see the problem? Something doesn't fit.
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