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AF 447 Search to resume (part2)

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AF 447 Search to resume (part2)

Old 25th May 2011, 19:22
  #2381 (permalink)  
 
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Airspeed indicators & diversity

Pitot tubes have been around for a long time, but they are not the end-all solution for airspeed measurement. Other technology even predates that. Take this example from WWI:




Diversification has posted links to two companies doing work with [email protected] measurement of windspeed. Previously we noted another set of patents related to use of [email protected] for airspeed measurement.

FBW aircraft have unique requirements for airspeed information that is not obvious to the casual observer. They need to know the airspeed in order to properly set system gains. This is critical for proper performance of the control servo loops.

The increasing prevalence of FBW technology is exacerbating the pre-existing problems with pitot icing.

Used to be, you iced up the pitot enroute, no big deal. Leave the trim and power set and pretty soon it will come back. And if it doesn't, it still flies like an aircraft and you can keep in a safe speed range by proper use of power, speed brakes, attitude, AOA, or whatever else works on that aircraft for that purpose.

On a FBW aircraft that trims itself, the situation is different. The aircraft suddenly has no idea if the power is set correctly, no idea if the control system gain is set correctly, and once it tries to change trim, has no idea if that is set correctly. The designers wisely pass control to a higher level computer that can figure this out.
Unfortunately, the higher level computer may have been processing other tasks, and has not been involved with actual control of the aircraft since 2 landings ago.

Add to this an array of messages sent by the computer relinquishing control trying to describe its problems and advising corrective actions, but initially delivered out of priority sequence. Further add to this what must be a cacophony of bells, clicks, alert tones, and short musical sequences in the audio spectrum.

If the FBW aircraft flew like an aircraft at this point, and I had flown it before in that configuration, probably no big deal, but the computer is still trying to help me out and I am lulled by its help. Four of five critical tasks are still being handled by the computer.

All I have to do is remember to handle the last critical task, wait for the display to settle, and push buttons, turn knobs in a carefully considered sequence.

When you consider the implications of loss of airspeed information on a FBW aircraft in full detail, it is an unacceptable risk.
It is time to provide more diversity in airspeed sources.
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Old 25th May 2011, 19:38
  #2382 (permalink)  
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BOAC's thread about cockpits

Thanks for the link, BOAC. I had seen the thing two years ago when looking here for rumors and facts and opinions from "professional" pilots concerning the AF crash. I didn't post here then, but prolly should have joined the fray.

Despite one poster's complaint here, I have been compelled to add my 2 cents worth as I had experience with both FBW and "modern" cockpits/avionics. Granted, my background was military, but I assure you that several here prolly fly with the Guard or Reserve. point being, the AF crash will certainly raise questions as to FBW and the human interface with the plane. Anyone disagree?

Call me a dinosaur, but I adapted, maybe even prospered. From cables/pulleys/pushrods to hydraulic valves operated by the stick ( zero feel from the control surfaces) to a complete "electric jet" whose performance was only made possible by a FBW system.

On the cockpit side, I went from a fairly sophisticated interceptor with an awesome autopilot and avionics suite for its time to a completely manual, pushrod system and no autopilot or radar for four years, and then to a cosmic jet - the A-7D. Then to the F-16.

The human interface in the cockpit of the 'bus is sure to become an issue after this Friday, ya think? Trust me, I prolly flew with an inertial system and other things before many here. The jet, A-7D, had a HUD that displayed speed, altitude ( radar or baro), AoA and the magic flight path vector with associated pitch lines. It had a projected map display coupled to the nav system and a super ground radar we could use for bombing, navigating and avoiding storms. See the article about the map by Capt McAdoo ( gums in his earlier years with all his teeth, heh heh) here:

http://sluf.org/misc_pages/fwr_winter_1973.pdf

The Vought human factor folks did an awesome job, and we WERE NOT overwhelmed with a deluge of data or confusing failure messages/warnings/cautions when things turned to worms. The biggest thing was reduced pilot workload. Navigation capability was a quantum leap ahead of all other military jets at the time, as was bomb delivery capability. We still carried our circular slide rule and paper maps, but they were for emergencies.

Apparently, some folks are concerned about the human interface in modern airliners, and I go with the folks that desire/demand a better interface. I fully understand the change from "flying" to "managing systems". But I don't understand a cockpit that can overwhelm the crew with a plethora of warnings and cautions and beeps/chirps/etc. And I also don't understand a cockpit that does not supply a straightforward means of reverting to basic flight control laws upon demand by the humans in the cockpit.

Somebody show 'bird how to change the size of his graphics! Doggone page is now a thousand characters in width, gasp.
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Old 25th May 2011, 19:45
  #2383 (permalink)  
 
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Talking about pitots

Main problem this equipment (amongst others) is not its technology (simple and sturdy) but its certification specification dating back roughly to the early jet age in the last millenium.
Today's long-haul operations are led a a far more stringent environment than in those (golden, some of the posters will surely say ) days.
We can be certain that the people who had established and validated the pitot's specification had never thought about flights at FL 350+, at -50° (and even below) and during several hours.
Time is up to revisit this type of "old" specs to ensure that they are still applicable in today operations.
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Old 25th May 2011, 19:52
  #2384 (permalink)  
 
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Apologies if posted before but details of release on Friday now up on BEA site
  • 25 May 2011 briefingThe BEA has decided to publish a note with information on the first facts established, based on analysis of the data from the flight recorders. This note will be put on line on Friday 27 May at the beginning of the afternoon and will be available in English, French, German and Portuguese. There will be no press briefing.
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Old 25th May 2011, 19:56
  #2385 (permalink)  
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Well. A Boeing with 8 turbojets and swept wings flew to 50k and higher.
The design is Sixty years old.

The technology is the problem, by process of elimination. Either the computer in the Airbus cannot fly without IAS, or it is incapable of retreating from the stage without insisting it be paid attention to first. Without BUSS, a pilot who has come to lean on a seemingly steady platform (with the encouragement and training and paychex of the operator) is sol. Wouldn't be the first time a lady seduced a gent to his doom.
 
Old 25th May 2011, 20:01
  #2386 (permalink)  
 
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bear

I dunno about that.
We can even talk about the Blackbird regarding altitude performance !

But, if we come back to airline ops, I guess my point remains valid.
We have a piece of equipment that is designed against specs that are not in line with today's requirements.
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Old 25th May 2011, 20:16
  #2387 (permalink)  
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llagonne66

You may be right. Some one soon is going to ask if the flight was survivable.

By that I mean, some blend of autoflight (NOT AUTOPILOT), and Captain/FO could have punched through to Paris (Or Afrique, or...). In two years I have been unable to come up with a good story Air France (and Airbus) could use to deflect liability. If there is one, I'm stumped.

Because it looks like she made it to the water with both engines alight. If it is a couple ounces of frozen water, then that makes a poor wall behind which to hide.

You said.... "....But, if we come back to airline ops, I guess my point remains valid. We have a piece of equipment that is designed against specs that are not in line with today's requirements...."

By equipment did you mean PRIM? or PITOT.........
 
Old 25th May 2011, 20:25
  #2388 (permalink)  
 
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bear

I have strictly no trouble with the liability of anybody in this sad story (Airbus, AF, Thales, ..).

Equipment = pitot of course !!!
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Old 25th May 2011, 20:32
  #2389 (permalink)  
 
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Originally Posted by bearfoil View Post
The technology is the problem, by process of elimination. Either the computer in the Airbus cannot fly without IAS, or it is incapable of retreating from the stage without insisting it be paid attention to first.
Good work, Professor - guess we can all pack up and go home now.

Yeesh...
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Old 25th May 2011, 20:38
  #2390 (permalink)  
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High altitude jets

Everything you wanted to know about the Blackbirds is here:

SR-71 Online - The Blackbird Archive

And it wasn't FBW.

The other plane was/is the Boeing B-52.
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Old 25th May 2011, 20:55
  #2391 (permalink)  
 
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Originally Posted by gums View Post
The Vought human factor folks did an awesome job, and we WERE NOT overwhelmed with a deluge of data or confusing failure messages/warnings/cautions when things turned to worms.

...

But I don't understand a cockpit that can overwhelm the crew with a plethora of warnings and cautions and beeps/chirps/etc.
This is nothing new, and certainly not manufacturer-specific:

This is on a Hawker-Siddeley Trident 1C (useful part is from 0:00-2:20, especially the last 30 seconds)


This is on a Boeing 757 (as is the next) - useful part is 6:30-end


(useful part is 7:30-end)


Also, SR-71 wasn't perfect - the FSMs required to set the shock cone occasionally "went rogue"...

http://www.pprune.org/military-aircr...ml#post4005221

Last edited by DozyWannabe; 25th May 2011 at 21:18.
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Old 25th May 2011, 21:15
  #2392 (permalink)  
 
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gums:

I recall from an A-7 jock the following comment (or something like this): the A-7 has one pilot and 1.3 pilots worth of workload.

He tried walking me through which finger on his left had he used to pickle what, and when, during a bombing mission, and I nearly followed him, but got lost ... some years gone. The A-7 guys at the time made a big deal about being single pilot, and leaving the bats to those that needed them. (bat ~ NFO/BN/RIO).

EDIT: from your SR-71 site.
On 24 May 1963, CIA pilot Ken Collins was flying an inertial navigation system test mission. After entering clouds, frozen water fouled the pitot-static boom and prevented correct information from reaching the standby flight instruments and the Triple Display Indicator. The aircraft subsequently entered a stall and control was lost completely followed by the onset of an inverted flat spin. The pilot ejected safely. The wreckage was recovered in two days and persons at the scene were identified and requested to sign secrecy agreements. A cover story for the press described the accident as occurring to an F-105.
Some interesting thoughts on how to improve a pitot tube. If the research into this high altitude ice phenomenon can provide sufficient data to create an improved spec, I don't doubt that the engineers at Thales, Goodrich, and others will be able to provide a more resistant probe.

That would address one of the holes in the cheese, but perhaps not all of the holes in the cheese for the AF447 crash.

Last edited by Lonewolf_50; 25th May 2011 at 21:27.
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Old 25th May 2011, 21:19
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System needs, the Pitot issue and Redundancy (I)

Hi,

Anticipating what we expect to hear about Pitot tubes from BEA there are many of us "looking" to the sensor. The invention of Henri Pitot is in the spot light.

Actually is a very simple and reliable invention. So good that is used in every a/c. And until now, a "killer product" (A trully K.I.S.S. invention)

The current a/c Systems (used by Airbus SAS, Boeing, etc.) need a reliable information of air speed. Certainly much more (than the logged 38, since 2003) cases occurred and created problems.

It seems to me there is an error when dealing with Redundancy in this issue:
(in the "extreme cases")

Why you put Redundancy in a design? When the fail rate of a single critical element is not compatible to your spec of (System) Availability. The need is obvious for "complex items" like computers (that can "fail" by Hardware, Software, etc.). EADS put 3X Redundancy ("acting as 5X")

In the case of a (vital) sensor extremely simple i don´t understand (and not agree) to use "on line" more than one! It seems an unjustifiable use of Redundancy. Perhaps "amplifying" existing limitations of current Pitot sensors (that could create a complex "soup" mixing SW, HW, Laws, etc.) with potential to result in stressful (even lethal) scenarios for pilots.

One may ask: And if the device breaks? (Bird impact, etc.). And if the device becomes the nest of the wasp? And if the heater fail? And if the Transducer fails? And if the wiring breaks? etc.

Any of those possibilities IMO not justify to have 3 on line (allowing a voting scheme) (being monitored/scanned) and "capable to degrade" the a/c when there is a AS "disagree". There are other possibilities or reasons to justify the redundancy? Please list! You can do "averaging, etc, by "software", for identical sensors, submitted to quite identical conditions? Why?

If you prefer to have redundant Pitot, no problem: You may put 2, 3..n with just one "on line". You could (should) "interrogate" the others to check if they are alive. Energy to them? Can be supplied. We can optimize this. Ideal number? May be 3.

If the "US made" is better (IF really is) let´s analyze and make ASAP a joint effort (US-EU) to improve the existing models. This is good for the entire Aviation industry.

We need (to deal with the rare "extreme cases") ASAP R&D for better Pitot´s. Redundancy (for identically unreliable sensors) is almost useless. Just tell you (immediately? not sure!) the important sensor(s) are failing.

The reading of n sensors could be used to "anticipate" the Main sensor is going to fail. Alerting the crew before the a/c starts to "degrade". (I´m using the term "degrade" just to simplify). As an alarm of "closeness of extreme conditions".

(to be continued)

Question:

If we make a bigger (size) one (scale 2X, 3X, nX) the "ice issue" could be improved? A bigger one, power modulated (up to 1KW) could solve the issue? No tiny holes easy to clog? (Up to 1KW? Or a non electrical, heater? Or dual heater?)

Why not to test (in real world) the "anti icing" characteristic of new designs (new size, geometry, max power, similarity to "US" model, etc) comparing (in actual flights) to the existing ones. (Checking in real time against the current US and Fr. existing models).


It seems there is a "deadlock" among the players (Cert., Mfrs.,Operators). Time now (and opportunity) to competent technicians to work and SOLVE* the issue. Keeping "bean counters" just waiting the results of the necessary R&D.

*I mean, a Pitot with better characteristics when facing the "extreme conditions"

Last edited by RR_NDB; 25th May 2011 at 23:38. Reason: Comm. impvmt.
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Old 25th May 2011, 21:37
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pitot heat

Here's a simple idea. Apply different heat settings to the three pitot probes. In the event of all 3 probes icing up, at least this could ensure an asymmetrical failure. This seems to be a more graceful failure mode than automatics being fooled by wrong readings for some time before the UAS condition finally arises.

Just sayin'...
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Old 25th May 2011, 23:01
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Here's a simple idea. Apply different heat settings to the three pitot probes. In the event of all 3 probes icing up, at least this could ensure an asymmetrical failure.
Sorry for the drift, if my post is impropriate pls disregard.
I was and still am very interested in this awfull accident.
I posted in june 2009 a reply at which I got "hit at" so i did not reply thereafter.
Apparently my suspision was right, the capt was not on the deck, and no, i do not and i don´t want to be right!!

I have read and learned a lot of all the aspects of this accidents, esp. the technical ones here on PPRuNe.

But, why was this A/C lost while others finished there flight, e.g. IB only 10 or so minutes behind them (but they diverted, 70 miles around or so?)

I am afraid it will turn out to be pilot-error; as mentioned earlier: pitch and power is performance, as far as i know that works in every airplane, A, B, C, E, F etc.

Maybe another simple idea: let pilots fresh from flightschool first do some (tough) turbo-prop flying, in stead of going straight for the big jets, with all the computers, software, defences, back-ups etc etc.

My most importand CRM/MCC is: FLY THE AIRCRAFT.

Hope i am wrong.......
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Old 25th May 2011, 23:03
  #2396 (permalink)  
 
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leave the pitots alone... arright? ;)

With all due respect to the brilliant minds on this forum who have been discussing alternate solutions for the pitot issue and without sounding insensitive to the families and friends of those lost to this tragic event:

The issue of pitot ice, IMVHO, is not something that warrants a complete rethink/redesign of a major sub-system like the pitot-static system. Even if this was possible, it would take years if not decades to get this done. Inferring from Airbus and other airlines' response to this problem, its reasonable to assume that they think this issue can be fixed with minor tweaks/fine-tuning of the existing well-proven system. If this is in fact their assessment, I have to say, I agree with it, notwithstanding the scale of this tragedy. Are there any reported cases of pitot ice triggered UAS events on a/c with Airbus recommended fix (of replacing the pitots) applied?

Having that said, we may learn on Friday that pitots played a more important role in the chain of events than we imagined. Even so, it is hard to conceive of a chain of events that would warrant an extreme reaction like redesigning the entire pitot-static system. Does anybody else think this is the wrong approach? We may end up creating more problems than we solve.

Then again what do I know, I'm only a pilot...
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Old 25th May 2011, 23:43
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redundant airspeed indication

Just a wayward thought from an engineer. We know GPS is not accurate enough to be used as a backup airspeed indicator because it tracks ground speed rather that airspeed. the two are often vastly different. Might it be possible to derive a backup airspeed indication by looking at the doppler shift of weather radar returns? After all, the cloud droplets are suspended in the same air mass that the aircraft is flying through. This would only work when there were echo returns present, but then again those are the times when pitot tubes are likely to be fouled by ice.
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Old 25th May 2011, 23:57
  #2398 (permalink)  
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Perhaps the pitot redesign brigade's thrust is analogous to the engineer with a solution looking for a problem (and most of us have been guilty of that at times ..)

As at least one poster suggested a few posts back, if the underlying problem is found to be pitot icing, then the appropriate first tack is to

(a) look at icing requirements in the design standards,

(b) identify and redress the Standards deficiencies and

(c) move via AD (as appropriate) to fix the presumed heating deficiency.

Such, at least, chains up the initiating problem.

That is not to suggest that the Standards ought not to be revisited in respect of automation paradigms and the philosophy of degraded modes and flight deck presentation.

If, and that's still a big if, the fallout is along the lines of the crew's being overwhelmed by mode degradation and associated alerts, then one foresees a period of Regulatory navel gazing (both certification and operational standards) in the coming months.
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Old 26th May 2011, 00:02
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I read the whole thread, and in my personal and unqualified opinion as a mere SLF, it's quite clear that on friday, all the doubters of modern aircraft design philosophy and the conspiracy theorists will have a field day - regardless of what will be revealed, it will be either the fault of Airbus, the BEA or a big coverup... So many people here already know what happened and don't need any facts to change their opinion...

I think it's interesting to see how many people either propose new gadgets designed to fix the "AF447-problem" or just see the modern reliance on computers and automation as the cause of the crash, but fail to prove that those "fixes" are more reliable than current "modern" technology. Because that's the design case, to reduce the number of "avoidable" crashes. Not just to fix the cause of this crash, but to improve the whole safety record. None of the doubters of "computerised planes" proved that older planes are safer, and it could very well be that these technological advances (?) improve safety for 99,999% of the flights, and that "fixing" these methods might decrease the safety of 99,999% of all flights, just to fix the freak occurance on 0,001% of all flights. (All figures are made up )

I'm not judging because I just don't know enough, but in my opinion it's up to those people to prove that on the whole balance, the safety of all flights would be improved by their proposed changes - not just the safety of those flights that encounter the same conditions as those on AF flight 447. So in my opinion it's quite obvious that the changes coming from this crash will be evolutionary (as in "bugfixes") instead of revolutionary.

But we will all know more on friday, for sure...
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Old 26th May 2011, 00:07
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Eliminate the Suprise factor

Originally posted by CogSim ...

...it is hard to conceive of a chain of events that would warrant an extreme reaction like redesigning the entire pitot-static system.
Maybe not, provided that in the CRZ pitch and power along with static pressure and altitude is automatically monitored independently and if UAS starts to become an issue for the A/P it switches to flying the "pitch and power" equivalent to the last valid pitot data. Signal the UAS condition and at the same time show the FPV value. The crew are now aware of the condition, and the "suprise" factor has been mitigated.

As an after-thought, GPS Altitude and GS could be incorporated into the monitored triangle as a backup, should one of the other two components become suspect.

I know its not the total answer, but who/what judges the Judges?

Last edited by mm43; 26th May 2011 at 05:08.
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