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AF447

Old 29th Jul 2009, 09:48
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Safety assessment process

RE: Hyperveloce (#3971)

(How is the "acceptable relation" between 1)-2) & 3)-4) & the overall flight safety impact defined or evaluated ?).
How it's done? Read Appendix A in this document (see for example page 86):

NTSB safety report no. SR-06/02
Safety Report on the Treatment of Safety-Critical Systems in Transport Airplanes

http://www.ntsb.gov/publictn/2006/SR0602.pdf

(Link originally provided by SPA83 in his post #3841 on page 193 (23-07-09), thank you SPA83)

Two quotes from the "Executive Summary":
The Safety Board recognizes that the findings in this report are presented during one of the safest periods in commercial aviation history and acknowledges that FAA’s certification process has contributed significantly to that level of safety. However, the Board notes that there is room for improvement. The report includes three recommendations in two areas.
The second area focuses on the ongoing assessment of safety-critical systems throughout the life of the airplane. The Board concluded that a program must be in place, once the type certification process is completed, to ensure the ongoing assessment of risks to safety-critical systems. Such a program must recognize that ongoing decisions about design, operations, maintenance, and continued airworthiness must be done in light of operational data, service history, lessons learned, and new knowledge, for designs that are derivatives of previously certificated airplanes.
regards,
HN39

Last edited by HazelNuts39; 29th Jul 2009 at 10:27. Reason: editorial correction
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Old 29th Jul 2009, 11:22
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A/B said quite some time ago (probably in this thread) that the BA probes were not offered as a solution to the icing of the AA probes. It was assumed by some that this was a weasel way of fixing the problem without warranty cost, and operators like AF proceeded to replace the AA probes with BA at their own expense.

Now, we see that A/B was honest: the BA probes are not the cure. It must be an aging or corrosion problem with Thales probes.

GB
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Old 29th Jul 2009, 11:52
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Subsequently it seems that the union representing the majority of the AF pilots have now definitively demanded that all Thales pitots in the AF fleet are replaced with the Goodrich ones that, and I quote, "have never been implicated in any reported incident".


Air France: les pilotes répudient les sondes Pitot fabriquées par Thales - Libération


The lawyers preparing the compensation claims for the AF447 accident must be rubbing their hands at all this technical prejudice.....
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Old 29th Jul 2009, 12:28
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Yes GB, I also remember that the Pitot probe manufacturer warned that his new probe was not designed to withstand increased specifications about icing conditions. I also remember that the regulatory bodies said that the replacement of the Pitot probes was not mandatory precisely because they had not the guarantee that the new probes would solve the problem. I would understand this reasonning if there was only a unique Pitot manufacturer, but it appears that there is another brand of new Pitot probes which does not fail so frequently.
...and continued airworthiness must be done in light of operational data, service history, lessons learned, and new knowledge, for designs that are derivatives of previously certificated airplanes.
Ok HN39, this might be this part that was not fully implemented: the regulatory bodies state that Pitot problems do not impact the overall flight safety (hence the not mandatory replacement). The AF 447 flight may enable to reevaluate this statement about the safety impact, but given the previous two Air Caraïbe incidents, considering that a total airspeed deprievation, alternate law 2 & prot lost, false stall alarms, unsatisfactory "unreliable airspeeds" proc. poses no problem of flight safety sounds really weird.
Jeff
PS) It seems that Cathay Pacific's large Airbus fleet has not experienced any Pitot problem with their new Goodrich probes (designed to improve anti-icing performance).
PPS) some FDR/CVR specs (requirements of ED-56A)
- Impact Shock 3400g’s, 6.5 msec. duration (half-sine)
-Deep water immersion at a depth of 20000 feet for a period of 30 days (it took 2 month to locate the wreck and more than one year to recover the CVR for the flight SA 295, in the Indian ocean at 4900 m of depth )
http://www51.honeywell.com/aero/common/documents/Voice,_Data_-_Combined_Recording_Systems.pdf

Last edited by Hyperveloce; 29th Jul 2009 at 13:26.
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Old 29th Jul 2009, 12:50
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FDR and CVR

I've searched this thread before posting and have not seen the following issue with the CVR and FDR addressed.
Is there a "crush depth" for both of these recorders? It is likely, but not certain, that the CVR and FDR are both lying on the ocean floor perhaps at a very great depth. Do the recorders have specifications as to a crush depth? And even if they were both "crushed" do to ocean depth pressure would that preclude being able to read the contents thereof?
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Old 29th Jul 2009, 13:39
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rgbrock1, the recorders are supposed to survive submerged to a depth of 20,000 feet.
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Old 29th Jul 2009, 13:58
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Le Figaro is reporting a pitot failure incident on an Air France A320 (flight 1905) on July 13 this year. It was equipped with the new Thales BA pitots
Another bit of luck? Lets hope that it continues, and that if any further events that they occur in daylight.
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Old 29th Jul 2009, 14:23
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Presumably other airlines use Thales probes? I wonder if any correlation has been made between Thales vs other makes and these temporary failures?
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Old 29th Jul 2009, 17:43
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So was it the air pressure transducers all along??

--------------------------------------------------------------------------------

Air France Pilots Report Speed Sensor Problems
July 28, 2009
An Air France flight from Rome to Paris earlier this month briefly lost its speed readings due to faulty sensors, pilots said on Tuesday, in the latest safety scare involving speed sensors.

Several problems with speed sensors, or pitot tubes, made by Thales have been reported since 2008, and investigators are looking to see if they played a role in last month's fatal crash of an Air France A330.

A spokesman for France's SNPL national pilot union, Erick Derivry, said the union would ask Air France to see whether the latest incident was similar to those previously reported.

If it was, the union would ask the airline to replace its Thales sensors on its Airbus fleet with models manufactured by Goodrich.

Air France replaced an earlier Thales model on its planes with a more recent version following the June crash of one of its Airbus A330s. All 228 people aboard died when the Rio de Janeiro to Paris flight crashed into the sea.

But the latest incident on July 13 occurred with a new model, the company said.

"This incident was caused by new sensors. It lasted a few seconds, with no consequence for the passengers, and an analysis is under way in cooperation with the manufacturers and investigators," an Air France spokeswoman said.

The SNPL spokesman said a calculator that converts pressure into a speed reading (transducer) might also have to be replaced.

In June, under pressure from another pilots' union after the crash, Air France changed all pitot tubes on its A330 and A340 planes, having already changed them on its A320s.

(Reuters)
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Old 29th Jul 2009, 18:28
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Hyperveloce

I would understand this reasonning if there was only a unique Pitot manufacturer, but it appears that there is another brand of new Pitot probes which does not fail so frequently.
Numbers - I want to see real solid numbers with regards to flights in the same conditions that SEEM to nail the Thales probes. I'm prepared to believe they are a problem. I just want real, solid, numbers on which to base it.

JD-EE
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Old 29th Jul 2009, 18:33
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UNCTUOUS

The SNPL spokesman said a calculator that converts pressure into a speed reading (transducer) might also have to be replaced.
It seems reasonable that different probe designs would have different calibration curves. It seems unreasonable, to me, that the probes do not include their own calibration function as they generate their digital output. This IS the 21st century now.

On the other paw, we are talking about a late 80s aircraft.

JD-EE
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Old 29th Jul 2009, 19:10
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Scientists are still learning a lot about water ice. It now seem that very small ice particles can melt at temperatures as low as -180C. Presumably therefore they can fuse together and refreeze.

How to make ice melt at -180 °C - physics-math - 24 July 2009 - New Scientist
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Old 29th Jul 2009, 19:11
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"It lasted a few seconds, with no consequence for the passengers...."

AF spokesperson


Both Thales are now involved, several carriers, and one Manufacturer.

By all means, take your time.
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Old 29th Jul 2009, 19:14
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cwatters

Your post could just as easily have appeared on the BA038 thread. It is also possible to freeze water at 500C. Not on this Planet, not outside the laboratory.
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Old 30th Jul 2009, 07:11
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Unreliable airspeed occurrences: does it happen more often now (e.g. past year), or merely the problem it is now getting more attention? If it does happen more often, why? Is it because some component(s) (Pt probe, transducer, etc) have degraded? Or can it be due to software changes?
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Old 30th Jul 2009, 07:47
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Airbus to fund extra search for Air France black box | World | Reuters

PARIS (Reuters) - Airbus will help fund an extended search for flight recorders and debris of an Air France airliner that crashed into the Atlantic last month, a newspaper said on Thursday.

I wonder what the conspiracy theorists who have posted that Airbus doesnt want the recorders found have to say to this ? Let me guess , "Airbus knows exactly where the recorders are and will pay for someone to search somewhere else for 3 months at considerable expense so that it looks as though they want them found " ?
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Old 30th Jul 2009, 08:22
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"I won't repubilsh their article here as I don't have permission."

As someone who makes part of my living from publishing I applaud this attitude. The availability of the Internet is not an invitation to re-publish without acknowldgement or permission.

Bye, Barry
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Old 30th Jul 2009, 08:24
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Airbus Industries has every reason to find the data recorder and CVR. The causes of this crash if at all aircraft/design related must be discovered with haste. A willy-nilly approach to avoidance is but an invitation to future losses if we do not know the point(s) of failure that led to it.

Air France on the other hand faces the ambiguities of whether their crew acted imperfectly, if perhaps weather and the aircraft systems conspired together in an unwinding tapestry of fate with an undefined X-factor, typical in certain crashes of late, that will almost always be applied in the direction of the crew when it comes to blame.
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Old 30th Jul 2009, 08:27
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KiwiAndrew

TRANSLATION

"We undertake to support extension of search operatioins with substantial funding," says Airbus President Thomas Enders to La Tribune.

La Tribune says funding will be € 12 to 20 million to extend the blackbox search by three months. It will cover two or three surface vessels and one mini-submarine.

ORIGINAL

"Nous nous engageons à soutenir l'extension des recherches en apportant une contribution importante", déclare au quotidien le président du constructeur, Thomas Enders.
Cette contribution, selon La Tribune, oscille entre 12 et 20 millions d'euros pour des recherches prolongées de trois mois. Cela permettra de maintenir deux ou trois bateaux et un sous-marin de poche sur la zone du sinistre, précise le journal

This is a pickup by Reuters.

Pasted from <Airbus prêt à financer la recherche des boîtes noires de l'AF447 - Yahoo! Actualités>


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Old 30th Jul 2009, 09:07
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Unreliable airspeed occurrences: does it happen more often now (e.g. past year), or merely the problem it is now getting more attention? If it does happen more often, why? Is it because some component(s) (Pt probe, transducer, etc) have degraded? Or can it be due to software changes?
I mentioned this several weeks ago, suggesting that increased frequency of severe weather conditions may be taking the probes beyond their original time of certification design limits.


The system design should ensure that no set of redundant components can degrade to a single point of failure, yet this is exactly what appears to be happening in the case of the probes. For a function that is so critical in terms of other systems that depend on it's data, why has this problem not been fixed ?. An engineering design issue that needs only the will and resources to find a solution. ie: If there's not enough probe heat at limit, redesign with more effective heating, perhaps with better insulation on the outer surfaces to prevent heat loss. If the probes are corroding due to excessive heat on the ground, redesign the probe heat controller to prevent this. If the drain holes are blocking, redesign. If there is a need to make the drain holes bigger, correct for this in the adc lookup tables etc.



The crew may recover in most cases, but should never be placed in a situation where they need to if the problem can be engineered out. After reading this thread for several weeks now and getting a feel for the status quo, the apparent industry complacency about this issue just beggars belief, imnsho…


Chris
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