AF 447 Thread no. 4 [Archive] - Page 4

DozyWannabe

4th Jul 2011, 19:26

Not sure exactly what you mean by "calculate", but if not fully capable how could it offer Pitch-Alternate Law?

Hi Chris - what I'm saying is that your initial suggestion was that the "G"-loading system would possibly trim the aircraft nose-up at stick neutral as the speed appeared to decay. What I mean by "calculation" is that if the aircraft systems know that there is an double or triple erroneous airspeed indication, it drops to a mode whereby any protection or flight logic relying on airspeed is disabled. Surely this should be the case with the scenario you're describing - while "G" measurement itself is independent of the air data (thanks A33z), the logic you describe requires that data to work. So without airspeed data, how would the FCUs know to trim the aircraft nose up to maintain "G"?

To DozyWannabe #657. OK, AS is derived from 3 pitot tubes that could lead to problems if two of them are wrong but close enough to be taken as valid. Then why not compare AS history with GPS derived speed (history) together with thrust/attitude. I mean : compare the trends. If the plane is level flight, if thrust is not changed (even in turbulent weather) and a dire discrepency is noted (IAS significantly increasing/falling while GPS speed no change) wouldn't that be the case that AS should be highly suspected to be wrong ?

I don't mean the A/C should do something with that ! But the pilots might be warned.

Hi, and welcome.

The problem with what you're describing - as with any extra logic - is that you get into the engineering reliability maxim, which is that the more complex one makes a system, the probability of introducing errors also increases. The pilots are warned with the current system - an ECAM message "ADR DISAGREE". It's easy for such messages to get lost in the heat of the moment when things start to go pear-shaped however.

Why didn't they notice it? It wasn't in their scan because they apparently were trained not to touch the pitch trim wheel(s) since pitch trim is always automatic and since it's automatic, why would you care?

Surely an attitude indicator displaying mostly blue would be a hell of a hint, however - and if you're trying to tell me that the ADI was not part of their scan, then that would highlight a terrifying oversight in their training (I suspect that isn't your position, however).

Also, at present we do not know AF's policy regarding training on the trim wheels. Svarin said that his current airline discourages their use, but he does not - as far as I know - fly for AF.

I think the inexperienced Colgan pilots resorted to a previous aircraft the captain had flown that had a tailplane stall recovery procedure that was opposite of wing stall recovery. This wasn't a problem in their aircraft and all pilots are taught to lower the nose in a stall, they raised it causing the crash.

That explains the Captain's reaction, but not that of the F/O, who I believe came straight to the Q400 and did not spend any time on the Saab. They both pulled back hard almost simultaneously. It's a well-known tendency for new pilots to instinctively pull back on the stick when receiving a stall warning (or indeed any unexpected shock) and is something that has to be trained out early on. As I recall the inference from the NTSB report on human factors suggested that fatigue and exhaustion may have caused this instinctive reaction to take over.

Something motivated them to pull back and all I can think of is an overspeed warning that was false.

I think if it was as simple as that then that information would have been released in the press note and the report would be coming along a lot sooner - along with a service bulletin or AD relating to the warning systems in the A330/340.

The fact they are holding all the pertinent information back that they have makes me think we will have some big surprises when they finally have to reveal it to the public.

I suspect that the BEA are in the process of a long drawn out human factors investigation to answer that question - these things take time. I don't think they're holding information back any more than any other investigative agency would at this stage, certainly not for any nefarious reasons - I think they honestly don't know (or didn't know at the time of the "note"'s release) why the PF reacted in the way he did. So in answer to your later question (paraphrased) of "why haven't they released the final report?" the answer is simply because it is not ready yet. I've already said several times that I doubt the NTSB or AAIB would be under so much pressure to release information early from some quarters on this board in the way the BEA currently is. Why is that, do you think?

And the growing complexity concerns me.

Yet you're still advocating more technical solutions to implement in the design - surely if you were *that* concerned about complexity this would not be the case? The logic implemented in these aircraft (and those FBW airliners from other manufacturers) is actually pretty basic in modern computing terms. Asi I've said many times before it also uses obsolete technology (and always has) because the characteristics of obsolete hardware were already well-understood.

Folks - why waste time on speculation? It is not rocket science to find out who was in the RHS. I guess that IF we need to know BEA will tell us. In any case, does it really matter?

With all due respect (and I do respect you - I remember you may well have "flogged [me] round in a Chippy" in my youth. For this and other reasons I will always think very carefully on the knowledge you share about aviation-related matters) - that's a bit rich.

We've had four threads and hundreds of pages, largely of speculation from people - some of them pilots - who nevertheless either do not/have not flown the Airbus FBW aircraft and/or do not understand the systems - including what they can/can't/will/won't do. These speculations have involved - among other things - wild theories about the computers going haywire due to a lightning strike, long-hidden software bugs coming out of hiding to neuter the unsuspecting pilots' authority and software designers and engineers wilfully ignoring pilots' input and building a confusing system out of hubris and a sense of superiority just for starters. Then we move on to the more subtle, but still noticeable digs at the technology - e.g. "confusers", "HAL", that old chestnut "Airbus one man/one dog flight deck" and an intent on the part of engineers to "reduce pilots to systems operators and monitors".

I realise that it is a privilege to talk with you all as a non-aviator myself, but if you can find me an aeronautical engineering forum where an undercurrent of disrespect towards pilots of that magnitude exists, then I believe you would consider it the height of rudeness and complain vociferously. Taking this attitude on the chin is IMO a small price to pay for what I get out of the time I spend on here, but I do ask that you think about what you're saying sometimes.

For the record, at present there is *no* evidence that the pilots were ever "confused" by what they were presented with. Alarmed, certainly - and with good reason - but not confused. There is also no evidence of any overspeed indication, no evidence of software-commanded flight controls outside of what was coming from the PF's sidestick and no evidence of any departure from their intended flight path which caused surprise. When the report arrives, we'll know better. It's also worth remembering that while we pore over the ACARS messages and the apparent crew actions, that the crew were not trying to diagnose the situation based on ECAM messages alone, but with a full set of available and functioning instruments with the brief exception of airspeed. I'm pretty sure that the "WRG" message, as I said before, was simply the FCUs playing catch-up with the already-triggered pitot data failure message, which would have led to the "ADR DISAGREE" message appearing on the flight deck. We're talking seconds and fractions of seconds here - in human terms, the computation delay was minimal.

Mr Optimistic

4th Jul 2011, 19:37

HN39, OK but eventually the AoA went well over and the aircraft stalled. It is inconceivable that somehow the fwd speed got to 60knots unstalled, so at some stage it should have been continuous until the fwd speed did indeed reach 60kts. One can only surmise that knowledge of previous false stall warnings in UAS conditions were somewhere present in their minds but if the plane was flown upto and into a stall wouldn't the warning have been somewhat insistent ? Is there some other condition of validity which would silence it ?

daved123

4th Jul 2011, 19:37

PJ2
You may find Google more effective in searching PPruNe.
A search on "pprune pj2 rr-ndb" will show all your posts in which rr_ndb is mentioned and conversely all posts from rr_ndb in which pj2 is mentioned.

HazelNuts39

4th Jul 2011, 20:19

OK but eventually the AoA went well over and the aircraft stalled. It is inconceivable that somehow the fwd speed got to 60knots unstalled, so at some stage it should have been continuous until the fwd speed did indeed reach 60kts. One can only surmise that knowledge of previous false stall warnings in UAS conditions were somewhere present in their minds but if the plane was flown upto and into a stall wouldn't the warning have been somewhat insistent ?About 40 seconds later at 2:10:51 the stall warning was triggered again. The airplane probably stalled between 5 - 10 seconds after that, just before reaching its apogee of FL380 at 2:11:06. The airspeed probably remained above 120 kCAS during the descent. The low indicated speeds of 60, then 30 kt were caused by pressure disturbances at extreme AoA - the pitot pressure being lower than the free-stream total pressure and the pressure at the static source being higher than the ambient pressure.

BOAC

4th Jul 2011, 20:19

what topics YOU THINK are relevant - well, in respect of this thread, this one of yours is not.,

rudderrudderrat

4th Jul 2011, 20:27

Hi DozzyWannabe,
Then we move on to the more subtle, but still noticeable digs at the technology - e.g. "confusers", "HAL", that old chestnut "Airbus one man/one dog flight deck" and an intent on the part of engineers to "reduce pilots to systems operators and monitors"….. but if you can find me an aeronautical engineering forum where an undercurrent of disrespect towards pilots of that magnitude exists
Will this do?

"Flying for the airlines is not supposed to be an adventure. From takeoff to landing, the autopilots handle the controls. This is routine. In a Boeing as much as an Airbus. And they make better work of it than any pilot can. You're not supposed to be the blue-eyed hero here. Your job is to make decisions, to stay awake, and to know which buttons to push and when. Your job is to manage the systems."
— Bernard Ziegler, former Airbus Senior Vice President for Engineering.
Great Aviation Quotes: Piloting (http://www.skygod.com/quotes/piloting.html)

DozyWannabe

4th Jul 2011, 20:44

Bernard Ziegler

*sigh*

We've already dealt with Ziegler on this very thread and others, at great length. An intelligent and gifted pilot with a flair for communication certainly, but some of the things he said weren't very diplomatic or clever*. Airbus has long since adopted a very different line, and dragging that old quote up is not unlike us software folks having a giggle at Bill Gates' alleged "640k should be enough for anyone" statement in 1981 - by which I mean it's an entertaining and valuable lesson in hubris from a point in history, but in no way relevant to the current state of affairs.

He was there to make headlines to support sales, not determine engineering practices, and as such I'm also pretty damn sure that there were Airbus engineers just as mortified by some of those statements as some pilots were.

* - As has also been stated, he is now a very elderly and frail man, so I have no wish to haul him over the coals again.

RR_NDB

4th Jul 2011, 20:47

Hi,
DW,Yet you're still advocating more technical solutions to implement in the design - surely if you were *that* concerned about complexity this would not be the case? The logic implemented in these aircraft (and those FBW airliners from other manufacturers) is actually pretty basic in modern computing terms. Asi I've said many times before it also uses obsolete technology (and always has) because the characteristics of obsolete hardware were already well-understood.
The use of the "obsolete" building blocks is not a reason to allow a simpler analysis, as you know. My concern is if we really have a "sufficient recording" to understand EVERYTHING that (possibly) happened during certain moments. Suppose during a glitch (a time dependent failure, not stable). Like the one Svarin discussed or other possible reasons that could affect the "output" of the "engineering black box". The always concerning, Testability issue.

I am thinking on that and preparing to answer PJ2 and to CJ post (http://www.pprune.org/tech-log/454653-af-447-thread-no-4-a-38.html#post6552247).

I hope i am wrong with this suspicion. If wrong will be better. My objective is to raise only important and relevant issues.

I am busy during this week but "in parallel" watching the thread, posting when possible after considering useful.

gums

4th Jul 2011, 20:49

Salute!

First, I'd like to address the concern/question by Doze.

You do not need "q" or total pressure to trim the jet for a gee ( Nz). And it is disturbing to find from A33Z that the FLCS uses the same attitude reference system that is displayed to the crew. Hence, I continue to question some basic design implementations for the 'bus. It is too easy for the FLCS to have internal accelerometers and rate sensors and even air data sensors besides those the displayed to the crew. A layer of redundancy and a "core" system we humans can rely upon. If those embedded sensors go to "east jesus", then we're flat-a$$ outta luck. Sierra happens.

There are too many autopilot and "convenience" features that degrade one by one until in the "direct law". TOGA for engines and FLCS, "flare", Alt 1, Alt 2, sheeesh!

Once there's a problem, the basic flight control laws should be very clear from an aero aspect and a crew aspect. We don't need bank angle "protection"/overspeed "protection" and such in various modes. What we need is a well-designed plane that has basic control laws that 99.9% of the pilots can fly using basic airmanship. And not be concerned with losing one thing or the other along the way.

The 'bus looks to be a very well designed jet, or you couldn't have a "deep" stall, or a deep stall, for over 3 minutes without going into a spin or worse.

So I will continue to advocate a very straightforward system that has a myriad of autopilot functions as "inputs", not "protections". Once the A/P disconnects, the jet reacts to pilot inputs in a very straightforward manner. I fully understand control surface deflection rates, aero gains, etc. I fully understand why the THS trims to retain elevator effeciveness ( will be a contributing factor in final report, IMHO). I would not want to fly a jet that moves the elevator or commands spoilers and ailerons at the maximum possible rates regardless of the "q" or mach. But when those values are unreliable, the jet must still be flyable and not have all the "protectons" commanding stuff that we pilots don't want or need at that moment. Just let us fly the basic plane!!!

sorry for the rant. ....

RR_NDB

4th Jul 2011, 20:50

Hi,

DWBill Gates' alleged "640k should be enough for anyone"...

:}

BOAC

4th Jul 2011, 21:02

Now it has quietened down again, can I ask if anyone knows exactly which other bits of RHS 'important' data (apart from IAS) are not recorded?

Thank you, Gums.

RR_NDB

4th Jul 2011, 21:13

gums

What we need is a well-designed plane that has basic control laws that 99.9% of the pilots can fly using basic airmanship. And not be concerned with losing one thing or the other along the way....So I will continue to advocate a very straightforward system that has a myriad of autopilot functions as "inputs", not "protections". Once the A/P disconnects, the jet reacts to pilot inputs in a very straightforward manner. I fully understand control surface deflection rates, aero gains, etc. I fully understand why the THS trims to retain elevator effeciveness ( will be a contributing factor in final report, IMHO). I would not want to fly a jet that moves the elevator or commands spoilers and ailerons at the maximum possible rates regardless of the "q" or mach. But when those values are unreliable, the jet must still be flyable and not have all the "protectons" commanding stuff that we pilots don't want or need at that moment. Just let us fly the basic plane!!!

Perfect! :ok:

Or a plane (a/c+crew) that never do K.I.C.S. things sometimes.

C.=Complex

DozyWannabe

4th Jul 2011, 21:14

But when those values are unreliable, the jet must still be flyable and not have all the "protectons" commanding stuff that we pilots don't want or need at that moment. Just let us fly the basic plane!!!

Again, gums, where is the evidence that the flight computers did anything they were not commanded to by the handling pilot? The whole point of the graceful degradation in laws is that the guy in the seat notices as little difference in how he was handling the aircraft before compared to how the aircraft handles if something has gone south as possible!

You've basically just described the A330 (A320, A340, A380) and B777!

Machinbird

4th Jul 2011, 21:21

Along the lines of what Gums is talking about, It should be possible to measure roll rates achieved for small control deflections and then properly set roll gain after a loss of airspeeds thereby avoiding having to go to a roll direct law (Alt 2). Subsequent control inputs would update the gains. If in dead still air, the system could periodically recalibrate with small doublet inputs.
If wing flexibility causes delays in sensing, you could put accelerometers in the wings to get more timely information.

BOAC

4th Jul 2011, 21:22

Again, gums, where is the evidence that the flight computers did anything they were not commanded to by the handling pilot? The whole point of the graceful degradation in laws is that the guy in the seat notices as little difference in how he was handling the aircraft before compared to how the aircraft handles if something has gone south as possible! - may I (as an aeronautically trained engineer, of course...) ask you

Where is the evidence it did not? and

is not the second part of your para the whole nub of the accident? They would 'appear' not to have noticed.

Machinbird - yes, let's put even more electronics and gizmos in the loop to go wrong.:ugh: Look! We can have a whole extra page of ECAMS, bells, whoops and God knows what. What gums and I and a few others want to see is a stick that just moves the ailerons, and pilots who can use it..

DozyWannabe

4th Jul 2011, 21:41

Folks - why waste time on speculation?

BOAC, sir, I'm getting mixed signals from you.

I took this post of yours as a well-intentioned move to stick to the evidence at hand, and when I ask a reasonable question of gums - namely whether he has any proof that the aircraft did not do exactly as the PF commanded (suspecting that he has no more evidence than I), I get a dose of whataboutery from your good self!

I want to make it crystal clear that at no point have I directly speculated on the actions of the crew. I can assure you that any refernce I have made to other accidents such as Birgenair and Colgan Air have been purely for the purposes of providing background information. Am I now to understand that speculation on possible mishandling by the crew despite a largely functioning airliner is beyond the pale, yet myriad speculatory accusations of poor design and engineering practices putting the helpless crew in an aircraft that was, for want of a better phrase, trying to kill them is somehow tolerated?

Talk about your double standards...

RetiredF4

4th Jul 2011, 21:46

Quotes all HazelNuts39
The AoA in level flight at FL350/M.81/275kCAS is 2.55 degrees.

The speed was .8M for turbulence, as the crew stated. Or do you say, they where still in decelerating mode? The AOA value was reached by the sudden pitchup to 10° pitch, which needs an acceleration and changes the stall AOA significantly. I cant tell you the numbers for the bus, but an AOA gauge in front of my nose taught me that over a considerable flying time.

4 degrees is the stall warning threshold at M.81 and would produce about 1.42 g normal acceleration. I don’t think “gee” exceeded approx. 1.4 because it then becomes rather difficult to match several constraints imposed by the FDR data released in the BEA Update.

Which one, please elaborate.

At 10 degrees AoA, M.81 the airplane would be fully stalled, but that didn’t occur here but much later. According to the BEA, “pitch attitude increased progressively beyond 10 degrees” between 2:10:05 and 2:10:50. Therefore I think that the ‘mean’ AoA got close to but did not exceed the S/W threshold at this stage, i.e. the triggering of S/W “twice in a row” was probably due to ‘light chop’ causing some AoA fluctuations between 2:10:15 and 2:10:25.

On what fact do you ground your statement?
The speed sure as hell was already decreasing after the initial exaggerated pullup, so it was not .80 Mach any more after the start of the pitchup. At 02:10:20 FL 375 was reached graph from A33Zab (http://www.pprune.org/tech-log/454653-af-447-thread-no-4-a-35.html#post6549447), at 02:10:55 TOGA was selected and at 02:11:00 FL380 (apogee) was reached. That is a 500´feet altitude gain in 40 seconds. Its prudent to assume, that the initial climb rate was higher, decreasing to zil, and increasing again after TOGA selection (02:10:55 TOGA, 02:11:07 the speed was 185 valid and pitch and AOA 16°. So most of the beyond 10° pitch in that timeframe produced only AOA and not much climb at all.(Aircraft level flight at 10° pitch resembles 10° AOA. And yes, it was stalled, therefore the stallwarning was present and then TOGA selected.

It does not make sense to compute the angle of attack under steady and unchanged lab conditions. The ship was handflown with changing speed and pitch and later on power in unfavourable WX conditions with limited or no protections in an altitude they couldn´t reach just one minute before. Any change of pitch first adds to the AOA. and only leads to change of climb rate (and therefore flight path vector, which influences AOA) with a delay, if the lifties say "Yes" to the pitch change.

bubbers44

4th Jul 2011, 21:52

Our airliners and all other 70+ types of AC I flew had at most an aural warning when the automation failed if we had automation. The worst that could happen is you would have to put your coffee cup down and handfly the rest of the flight or until you could get the automation working again.

We never knew if they were going to work or not so when they worked we felt blessed. I felt the same in the Lear Jets and the Boeings. They are handy but not at all required for flight. My airline dispatched us in a new, to us, 737 from LAS to MSP and back with no autopilot and we took it because the MEL said it was legal when I was a new captain with a 1st time FO. Hand flying for 3 hrs each way isn't much fun but remember "Fate is the Hunter?"

A stick or a wheel should suffice for any airliner with a competent crew to get you to your destination no matter what fails.

Depending on automation to get you there is a recipe for disaster.

Mr Optimistic

4th Jul 2011, 22:00

HN39, thanks. So in a known UAS condition the system took what it knew to be unreliable airspeed data to inhibit the warning ?

Machinbird

4th Jul 2011, 22:47

Machinbird - yes, let's put even more electronics and gizmos in the loop to go wrong.:ugh: Look! We can have a whole extra page of ECAMS, bells, whoops and God knows what. What gums and I and a few others want to see is a stick that just moves the ailerons, and pilots who can use it.. BOAC, What was suggested would allow the 'Bus to soldier on without getting worse than Alt1 law, without the need to seize the stick firmly, without any great excitement except quieting all the bells and whistles.
It is not a complex thing to generate once the basic calibrations are done in the design phase.

There is much to be said for allowing sleeping dogs to lie quietly. If the aircraft was out of balance laterally, the computer would handle it just the way it had moments before the AP disconnect. If turbulent, the wings would be stabilized. The only difference is that the PF would have to tell the machine where to go and to set the power since the Flight management system wouldn't be doing that for a while.
The next reversion down from Alt 1 would then be Direct law.

Mr Optimistic

4th Jul 2011, 22:59

Didn't they have everything they needed; reliable attitude, altimeter and engine settings - why would any more help ? The problem may have been the knowledge that it is a complex system and therefore may fail in complex ways. All the imagined failure paths, fault trees and so on may just have prevented timely focus on what really mattered. So the automation failed them but itself wasn't at fault. Make sense ?

HazelNuts39

4th Jul 2011, 23:06

The speed was .8M for turbulence, as the crew stated. BEA's 275 kCAS at FL350 equates to M=0.808. Yes, pitching up results in an increase of AoA and vertical acceleration, and FPA, for example AoA=4.5, FPA=5.5, Pitch =10 degrees at about 1.33 g.

Which one, please elaborate. All of them: max 7000 fpm, min 700 fpm, 215 kt at FL375 at 2:10:50, maximum altitude FL350 at 2:11:06, just to name a few.
At 02:10:20 FL 375 was reached (according the graph from A33Zb, ...)I don't know how that has been derived, I would put it closer to 2:10:53. I don't think the difference between CLB and TOGA at FL375 is that significant.
So most of the beyond 10° pitch in that timeframe produced only AOA and not much climb at all.Between 2:10:15 and 2:10:35 pitch was reduced to about 5 degrees in order to reduce RoC from 7000 to 700 fpm.

I hope that explains the flight mechanics.

HazelNuts39

4th Jul 2011, 23:16

So in a known UAS condition the system took what it knew to be unreliable airspeed data to inhibit the warning ? At that point the original UAS condition was no longer present, the pitots had returned to normal. But there was anew ADR DISAGREE condition due to high AoA, that also caused the low IAS value.

OK465

4th Jul 2011, 23:47

So without airspeed data, how would the FCUs know to trim the aircraft nose up to maintain "G"?

Dozy:

I’ll steer clear of the ongoing “Why can’t I have Chocolate?” discussion, but…

I’ll offer an analogy to the inertial sensors, which may or may not address this adequately.

In non-FBW fighter-type aircraft, for a given stick position (i.e. constant pitch control surface position) my body was an adequate sensor to determine commanded G was changing as a result of airspeed changing…without ever looking at the airspeed or knowing specifically what it was.

If G was dropping off I pulled harder (importantly only to a point). If G was building I relaxed the pull. Absolutely no direct reference to airspeed required, but directly a function of airspeed changing. I was a veritable human auto-trim system.

Don’t let them re-design me…

Relax; I agree, pilots are notoriously difficult to deal with.:)

A33Zab

5th Jul 2011, 00:08

Look! We can have a whole extra page of ECAMS, bells, whoops and God knows what. What gums and I and a few others want to see is a stick that just moves the ailerons, and pilots who can use it..

Stick left or right will do it for A. or like any other brand let AP handle this. Already in the 70's you were flying 'Fooled' by Wire and once they remove your 'beloved' yoke and the cable loop which drives it and suddenly it is not worth to call it an airplane?

The brand with the yoke uses the same philosophy on FBW, they fitted some other stuff to keep you guys satisfied and used different naming but have also mode degradation, ADIRU's and Flight Control Computers and a lot of warnings and bells.

Where is the evidence it did not?

Because only AP or P(N)F can do that, if a remote! Failure in a FCPC would do that it would be rewarded with an outvoting and an ECAM message.

BEA:
"The thrust levers were positioned in the TO/GA detent and the PF maintained nose-up inputs."

On the T/L and SS only multiple resolvers (which can't drive the T/L or SS), the only input is by hand (or other object)

If automation can bring one to outer space and back, automation can bring you also from A. to B. and (for the skeptic) from B. to A.

Svarin

5th Jul 2011, 00:12

DozyW wrote :

wild theories about the computers going haywire due to a lightning strike, long-hidden software bugs coming out of hiding to neuter the unsuspecting pilots' authority
You need to realize that each successive software version, for the FCPCs, for example, would have a lifespan of around a year. Version 19 was out last time I checked. What is the age of this type ? So, a software "bug" (a very small oversight as I see it in detail) could have been introduced, less than a year before. This could perhaps help you realize it is much more likely than one would like to see. Especially as this gets mixed with a similar potential problem regarding ADRs from a different manufacturer ! But these things communicate together. All in all, quite a feat. There are bound to be some minor stuff from time to time, dont you think ?

By the way, if someone could please enlighten yours truly regarding the certification process applied to flight controls computers software versions released after the initial certification process, I would be extremely grateful.

I'm pretty sure that the "WRG" message, as I said before, was simply the FCUs playing catch-up with the already-triggered pitot data failure message, which would have led to the "ADR DISAGREE" message appearing on the flight deck. We're talking seconds and fractions of seconds here - in human terms, the computation delay was minimal.The WRG message CMC time-stamp is 02:10.
The ADR DISAGREE message CMC time-stamp is 02:12.
Two minutes.
If you can provide a consistent theory to explain this gap, I for one will be happy to read it.

I do have a theory myself, of course. I explained it in multiple ways already. It is solidly based upon facts : ACARS messages content and timing, AMM, FCOM, BEA reports, schematics, design principles, multiple accident reports. When your theory relies on similarly solid background, we will have the opportunity for a fascinating discussion ;)

glad rag

5th Jul 2011, 00:19

Where is the evidence it did not? BOAC,oh come on; it's a bunch of peeps, with no access to the official, pertinent data, making it up as they go along.

Some have a clue, some more than others, some not.

Some have an axe [large/fictional] to grind, some not.

Evidence? the only evidence you'll get on here is advertising revenue.

Roll on the final report!

wallybird7

5th Jul 2011, 00:21

If automation can bring one to outer space and back, automation can bring you also from A. to B. and (for the skeptic) from B. to A.

Note: NASA does not take off or land when there clouds in the sky.

Automation is great -- IF it is working. When it is all iced up it does not.

Something iced it up. Why was Weather Avoidance Radar ignored?

DozyWannabe

5th Jul 2011, 00:23

@Svarin

Mate, your theory is no more grounded in fact than anything I can come up with. All we can do at this point is wait for the report. I do however expect that if such a transitory software bug was introduced it would have manifested itself many more times than once by now. In any case the "bug" you're talking about could only have affected the displays. By the time they were in Alternate Law, the AP was off and the FCUs could not command a significant change in flight path. On top of that it is down in black-and-white that the elevator and trim movements can largely be explained by the PF's inputs based on what we have so far.

Having said that, like the "wear down fluid channels with contaminated hydraulic fluid -> freeze it -> pump with hot hydraulic fluid" process that finally unmasked the 737 PCU failure mode, this aircraft accident reverse engineering lark is a tricky business.

Svarin

5th Jul 2011, 00:25

A33Zab wrote :

If automation can bring one to outer space and back, automation can bring you also from A. to B. and (for the skeptic) from B. to A.I agree that it can be done. But is it desirable, from a human perspective ? After flying, what else would you latch automation upon ? How many human endeavours will end up robotized ? What do we do while the machines do all the work and the rest ? Watch TV ?

if a remote! Failure in a FCPC would do that it would be rewarded with an outvoting and an ECAM message.Possibly, although you know I disagree. At the very least, I am greatly interested in the time it takes for the system to sift through the Byzantine generals lies, or power struggle, as I see it in the "PRIM2 reverted to Normal Law" theory.

DozyWannabe

5th Jul 2011, 00:43

I agree that it can be done. But is it desirable, from a human perspective ? After flying, what else would you latch automation upon ? How many human endeavours will end up robotized ? What do we do while the machines do all the work and the rest ? Watch TV ?

Write books? Make music? Paint pictures? Solve complex mathematical/physics theorems? Design and build spacecraft to explore beyond our little world?

I jest, but the whole point of human endeavour is that it is supposed to progress. Being knee-jerk against something just because it might in several generations make one's job obsolete is a pretty dismal place to be. Do you think the night-soilmen of centuries past wanted their great-great-grandkids to be doing the same thing?

Possibly, although you know I disagree. At the very least, I am greatly interested in the time it takes for the system to sift through the Byzantine generals lies, or power struggle, as I see it in the "PRIM2 reverted to Normal Law" theory.

I think you underestimate how strict the development and deployment process of real-time safety-critical systems is. I'm not saying it's perfect by any stretch of the imagination*, but I think you do the people on the engineering side of the fence a great disservice by saying that it would be easy to introduce such a failure.

* - Just in case I haven't made it clear enough in the past...:rolleyes:

bubbers44

5th Jul 2011, 01:14

gums

5th Jul 2011, 03:27

Salute!

After private posts with members of this august group.......

Make no mistake, I do not advocate an instant reversion to direct commands of the control surfaces using an RC model logic. The FBW implementation allows many "tweaks" that we did not have in the fully-hydraulic systems that we lites flew 50 years ago. Even into the 90's, the heavies had actual mechanical connections to some things - imagine that?

My philosophy is a bottom-up control law that the humans can depend upon regardless of all the bells and whistles and so-called "protections" provided in the higher-tier modes.

It appears to this old fossil that the 'bus has really fine aero characteristic. Otherwise, I would have expected a spin or some weird maneuver. So I question all the bank angle "protections", the seeming multiple AoA "protection" modes, and the beat goes on.

With autopilot engaged, all of the neat features seem logical for reducing workload and making things nice for the SLF's. But when things turn to worms, there has to be a basic, core control law that utilizes all the benefits of FBW and yet exploits the aero design/characteristics of the jet.

As with OK, don't take my seat-of-the-pants sensors away from me. I shall overcome the "leans" in prolonged IMC with no autopilot engaged and maintaining 10 or 15 feet from my flight lead. Some glances at the ADI and other gauges shall save me from my belief that I had been flying inverted for the last 3 minutes, heh heh.

In my second career ( afer hanging up the g-suit), I worked mostly on the crew-vehicle interfaces for the more advanced jets. Working with the end-users, we always had a straightforward means of going to a well-understood, basic display or mode. One of my "laws" was "if you don't like what you see, hit another button". our sfwe engineers implemented extremely rigid state machines that simply would not do weird things based upon weird inputs. If an input was not defined, the machine just sat there waiting for another switch or aero condition or seeker acquisition or ..... If you wanted to start over, then we had the 'start over"button, heh heh.

later,

HazelNuts39

5th Jul 2011, 07:08

HZ39, when their high pitch reduced to 5 degrees after their 7,000 fpm climb bringing it down to 5 degrees doesn't that seem like what would happen after their zoom energy had been used up? At that point they were in a deep stall and about to fall like a rock.At that point they had about 215 kCAS and were not stalled. If they had maintained that nose-down push a few seconds longer they would have avoided the stall altogether. Instead they pulled nose-up, increasing pitch, AoA and rate of climb, using the remaining zoom energy to reach FL380, and stalled.

P.S. Fourth update on TE-plots Fig1v4 (https://docs.google.com/leaf?id=0B0CqniOzW0rjNTIwZDI2ZWYtY2ExZi00ZjE0LTkyNDItNDA2MDY zZDI3YWE2&hl=en_GB), Fig2v4 (https://docs.google.com/leaf?id=0B0CqniOzW0rjYzZmNGU0NDItM2Q0NS00YjNlLWJkMTItMmE2YWZ hMDBjYzIz&hl=en_GB), and Fig3v4 (https://docs.google.com/leaf?id=0B0CqniOzW0rjMGExYTc5MjQtNDRiNy00MTk0LWFiMDYtYTUxMzN mYmFkYjc0&hl=en_GB).

PA 18 151

5th Jul 2011, 09:08

For the record, at present there is *no* evidence that the pilots were ever "confused" by what they were presented withI'm not sure you can say that (and this one of the very few things you have said that I disagree with).

From the evidence:

The PNF at least very quickly realised what was going on, a matter of seconds after autopilot disengaged

At 2 h 10 min 16, the PNF said "so, we’ve lost the speeds" then "alternate law […]".

No confusion there whatsoever, in fact the BEA are telling us that the FD acknowledged that they pretty much realised what the critical information was within seconds of the aircraft handing over control..

But later:

At 2 h 12 min 02, the PF said "I don’t have any more indications", and the PNF said "we have no valid indications".

That, to me at least, indicates confusion. Either

1) There were no valid indications
or
2) They misunderstood, or were confused by, what they were being shown

My money is on 2)

Confusion of that nature can possibly be caused by
1) Aircraft limitations
2) Pilot limitations
3) Combination of the above

We don't know which of those it was, and the answer (if it can be found) is probably key to the reason why the pilot input was mainly nose up (fact) and the aircraft subsequently stalled into the ocean (fact)

auraflyer

5th Jul 2011, 09:26

Gums, you've neatly summarised one thought of mine that I have not had time to elaborate fully (and don't at the moment either, but will raise in summary form).

From a human interface standpoint, the idea of multiple "laws" does not seem to me to be the optimum way of structuring things, trying to remember what is or is not in each law. My own intuition is that it would be more intuitive to have a clear indication of what "protections" have been lost that you formerly relied on.*

It would therefore seem that the better way would be:
(a) to know through training what "protections" you have when things are "normal";
(b) when things go wrong, errors are expressed in terms of each "protection" that is lost -- one indication for each protection lost (or, where there are multiple levels of degradation, what degree has been lost and what is left).

So that where one or more protections may be lost depending on the fault, your attention is specifically directed to what you no longer have - (eg simplistically: no rudder travel limiter, no abnormal attitude protection, or something like "no autotrim available - check trim and trim manually" etc). You wouldn't have to think in terms of "law", but rather in terms of dealing with the indication of what has been lost and what you might have to do in response.

This might assist where there is some obscure or not easily remembered (or easily overlooked) protection that is or is not lost when in some sub-law -- to try to avoid the situation where you don't realise you have or haven't lost something.

I realise that since I am not directly qualified to comment, and I am working off what I have gleaned here about laws and sub-laws, with permutations of outcomes. I have not had time to sit down to check this objectively, though, which I would normally do before posting, and won't for quite a long time due to work. so I apologise for that. If I am wrong, and this is effectively what happens now, then what I suggest may at best be a distinction without a difference.

* In CS terms, the point is sort of that laws are effectively "modes", which is what computers are good at but humans aren't as much. In my experience, people are better equipped to deal in terms of the contents/specifics/characteristics associated with a mode, not the fact itself of being in a mode.

A33Zab

5th Jul 2011, 09:45

Finally found it, it is in BEA report #1 page 122
It is in french so I skipped it in previous reading:

"Procedures anormales"
Urgence / secours

CONFIGURATION LISSE

Au dessus de 190T; FL 250 a FL 370
Vitesse 260Kts: Assiete (Pitch) 3.5 / POUSSEE (Thrust?) N1 90%

In comparision to my Hi power ground run tables
90% N1 ~ 80% thrust (temp effects taken in account)

Another 20% is a considerable amount of thrust (and pitch-up) they put in when moving T/L to TOGA. (=100% thrust).

IMO was the first action of capt. to retard to idle, and demanding a ND command. He did realized what was going on.
Unfortunately he couldn't see the position of THS (if F/CTL SD page not selected) and if not already too late to recover.

A33Zab

5th Jul 2011, 10:02

(b) when things go wrong, errors are expressed in terms of each "protection" that is lost -- one indication for each protection lost (or, where there are multiple levels of degradation, what degree has been lost and what is left).

O no, even as engineer I don't think a crew do like (and has the time) to read a novel on his ECAM.

The rules are simple:

NORMAL = I can do with the stick what I want.
ALTERNATE = I have to be gentle with the stick because I lost the protections.
DIRECT = I have to be very carefull with the stick because movement equals control movement.

There's more to Law degradation than only the pitch channel, other functions are inhibited or arranged in another way and/or during flight phase change.

auraflyer

5th Jul 2011, 10:08

Thanks A33Zab - point taken, and you have confirmed my initial reluctance to post my thoughts.

CONF iture

5th Jul 2011, 10:42

Au dessus de 190T; FL 250 a FL 370
Vitesse 260Kts: Assiete (Pitch) 3.5 / POUSSEE (Thrust?) N1 90%
That's the answer to an UAS after opening the QRH.

Another 20% is a considerable amount of thrust (and pitch-up) they put in when moving T/L to TOGA. (=100% thrust).
But this one is very different as it was the answer to a stall warning.

DozyWannabe

5th Jul 2011, 10:53

2) They misunderstood, or were confused by, what they were being shown

My money is on 2)

Not that I want to get into a semantics parsing issue, but misunderstanding is *not* the same as confusion, except maybe as a literary device - for example I've always considered "mode confusion" to be a misnomer, as accidents involving mode "confusion" rarely showed the pilots unsure of the setting they'd selected - they were convinced that they were in the right mode, all the way down to the ground in many cases. I think it means what it says - that they weren't getting any valid readings on an instrument (or possibly instruments), my money being on the ASI.

rudderrudderrat

5th Jul 2011, 11:08

Hi 33Zab

I agree but would add:
NORMAL = I can do with the stick what I want.
ALTERNATE = I have to be gentle with the stick because I lost the protections.
& it will maintain pitch attitude all the way to the stall threshold.

DIRECT = I have to be very carefull with the stick because movement equals control movement
but it is now longitudinally speed stable.

A33Zab

5th Jul 2011, 12:01

I know and maybe I was not clear in the question, with excuses.

I tried to figure out what would be the initial movement from the Thrust locked condition. as this was the first ECAM drill "THR LEVERS....MOVE" @ 2:10:05.
Don't think they waited untill 02:10:51 to perform the drill, so the T/L was initially moved to a position between CLB and TOGA.

if the UAS value is known, which is safe pitch/thrust relation, it would be more or less the position of the A/T N1 value with T/L in the CLB detent before the event (transient IAS speed loss) took place.
So the initial THR LEVERS.....MOVE action was movement of T/L fwd to intercept ~ 90%N1.

Thanks for info.

Chris Scott

5th Jul 2011, 12:17

Quote from PA_18_151:
At 2 h 12 min 02, the PF said "I don’t have any more indications", and the PNF said "we have no valid indications".
That, to me at least, indicates confusion. Either
1) There were no valid indications
or
2) They misunderstood, or were confused by, what they were being shown
My money is on 2)

Agree. It's a puzzling exchange, and the reason I'm still not entirely convinced that ASI2 was giving similar, intermittent, under-readings as ASI1 and the ISIS ASI. On the face of it, Pitot1 and Pitot2 might be expected to suffer similar icing characteristics, as they are symmetrically situated. But their heating performance might not have been identical on the night. This brings me back to a possibility others were discussing yesterday, which has been nagging me since May27.

It is possible to infer from the PF's remark that he had recently been relying on an indication that had just been removed. The words seem to have been spoken some time after they had passed FL350 in the descent. If the Pitot2 had been blocked both at intake and drain-hole, this would not explain the INITIAL pitch-up that we assume the PF made from FL350. But once the climb had been started, the ASI2 readings would have gradually increased to the FL380 apogee, then gradually decreased in the (stalled) descent. Simplistically, if Pitot2 remained completely frozen, the ASI2 reading would have dropped to the original cruise value when the static source (thought) the aircraft was passing FL350 in the descent. After that, the ASI2 reading would progressively drop to zero.

Although I think the above scenario is unlikely, because the trap is understood by most pilots, it would be frustrating if it cannot be disproved by QAR data or otherwise.

HarryMann

5th Jul 2011, 12:58

The 'bus looks to be a very well designed jet, or you couldn't have a "deep" stall, or a deep stall, for over 3 minutes without going into a spin or worse. That crossed my mind too, a long [stable]descent without lateral divergence or serious oscillatons :D

Even Airbus might not have credited that degree of spin-resistance... just needed a giant hand to tilt it down again and a PIC to let that stick alone....

It doesn't condemn sidesticks out of hand, but it certainly does their reputation no favours, especially since their detractors have been saying this sort of thing for years; about immediate, indisputable visual & mechanical position feedback. Feel would also be a good deal more intuitive (to the hands rather than the odd finger, whether recently blood blistered at home doing DIY or not).

Fact is, however small or large part of this sequence the physical pitch control device is... it did happen (stick held back) and is relevant.

Now the Captain of DH 121 Trident BEA 548, may well have fought the stick (shaker) all the way down, indeed it was soon switched off, but that was not a long descent, thankfully just a few tens of seconds... so we'll hopefully not make comparison here..

RR_NDB

5th Jul 2011, 13:46

PJ2 and CJ in recent posts, commented on FDR capabilities:

I'm genuinely interested in any push to improve flight data recording

I 'did' FDRs late in my engineering career, so at least I'm familiar with the concepts
I need to present 3 (conceptual) questions (important to the analysis and understanding of the intriguing climb):

1) All information (except WX radar) being presented to PF and PNF are normally recorded in the SSFDR used in AF447? RHS not recorded could affect the investigation team analysis capability? Could affect the analysis in order to to understand PF (if confirmed at RHS) behavior?

2) Internal System information like redundant inputs to the System (e.g. individual ADM outputs) are recorded?

3) Internal information (of the System) is recorded to allow a clear analysis of how System operated when something (anything) affects the "redundancy degree" of the System? (causing it to operate less redundantly)

BOAC

5th Jul 2011, 14:56

RR - re your 1) - that is why I suggested the FDR be 'biased' to PF rather than LHS as appears at present.

Lonewolf_50

5th Jul 2011, 14:58

Catching up has been most informative. A couple of issues that caught my eye.
1. The question jcjeant should really be asking is why was the PF trying to use aileron to counter wing drop.
If you refer to a post stall roll problem, PF probably didn't know he was stalled. Others have answered in more depth with notations on the BEA report timelines. Had he known he was stalled, I suspect he'd have dropped the nose.
At the point in question, AF447 was already in a super-stall, although we have to assume that the PF had not diagnosed it.
Not early in the event. That "super-stall" was after the climb's apogee. The roll inputs appear to have been a running battle from early in the alt law event.
2. If we knew the reason for the nose up pitch inputs, we would be well on the way to understanding the accident. IMHO, inadvertent pitch input while controlling the roll axis seems to be the most likely cause. Alt 2 is a funny law. You have to stay off the pitch axis, but fly the roll axis. That does not seem trivial to me.
How often does one practice this flight control problem? If you don't train for the difficult flying tasks, you'll tend to perform them poorly.

When I was a flight student, I didn't much care for simulators, and made such complaint one day to my instructor. He gave me a "come to Jesus" lecture (brief, but powerful) about how important rehersal is for performance. He used the football game prep as an analogy:

"You practice the way you intend to play. Any play you don't practice will tend not to work on the field at game time. Any chance you get to rehearse, or to practice, you take, and you make the most of it." (Add a few more words meant to get my attitude properly adjusted. :E)

Years later, I heard a similar cliche from a different source: "train the way you intend to fight, and you'll fight better." It was in reference to the Fort Irwin National Training Center. (Armored warfare training with serious intensity/complexity).

3. This post is a nice one by PJ about how one trains one's crews.
http://www.pprune.org/tech-log/454653-af-447-thread-no-4-a-37.html#post6551107

It's an AF matter, but a matter that influences how well their pax are taken care of.

gums

5th Jul 2011, 15:09

TNX for nice words, Aura. And A33Z seems to homing in on the concept I advocate - to some extent.

There is absolutely no reason to diminish the capabilities of a FBW system in the "basic" law.

- Nz and alpha for pitch commands, roll rate command and HAL stops when control pressure released, with some body rates and control surface aero characteristics and servo-actuator limits and.... all thrown into the mix. This is the same as all the direct hydraulic systems we have had since the F-86 and some British lites way back in the 50's. In those days, the hydraulic pressures were physically modified between the control stick/wheel/yoke and the final control surface movement ( rate and deflection).

- In the most basic "law", I have a jet that flies like all jets, but more precise bank control and a known pitch command if I release the stick/yoke in any axis. For a heavy, I like the 'bus implementation, as it's biased about a one gee command. My Viper could be trimmed for a gee at neutral stick ( minus 2 or so and plus 3.5 gee), but this doesn't seem practical for a heavy.

- All the bank angle and pitch angle stuff seems more like an autopilot function, and is all well and good until things break. What I want and need (as do all the SLF's paying to have a safe, comfortable ride), is something to hang my hat on.

With all the discussion about the air data being unreliable or completely FUBAR, I can't understand the lack of a simple "standby gains" feature that HAL uses for "q" and total pressure. Ours was about 140 knots gear down and 300 knots gear up. So yeah, if flying at the speed of stink the jet was twitchy ( technical term we lite jocks use), and if slow the jet was sluggish. But we still had alpha limits, rate limits, gee limits, and the beat goes on. NOBODY COMPLAINED. We never lost a jet if the air data went south except for the pelican strike that took away AoA, pitot-static and had damage to the actual FLCS computers just in front of our feet. Big deal.

In other words, a basic loss of the air data is no big deal, and we can throw out all the 'protections" and simply have a basic, well-designed jet to fly until we get all the right inputs back in the green. I am confident that even a newbie flight officer could fly the jet at almost any flight condition if this were the case. I would not pay my fare if I didn't believe this.

My concern of the accelerometer and rate inputs to HAL is valid, IMHO. They should be embedded in the basic FLCS, and should be the "core" of the system.

DozyWannabe

5th Jul 2011, 16:10

It doesn't condemn sidesticks out of hand, but it certainly does their reputation no favours, especially since their detractors have been saying this sort of thing for years; about immediate, indisputable visual & mechanical position feedback.

Not necessarily, remember we don't have a complete picture of the PNF's actions and reactions as yet!

PJ2

5th Jul 2011, 16:51

RR_NDB;

My responses in blue font:

"I need to present 3 (conceptual) questions (important to the analysis and understanding of the intriguing climb):

Let me preface my comments by stating again that I support and advocate for any and all ways to improve flight data recording.

To take FDR from its present state to the state you envision requires an understanding of all aspects of flight data recording and analysis. Any such understanding also requires a keen understanding of how flight data analysis actually works in practise. Such an understanding addresses the view that "if only we had ALL the information we could determine what happened." A detailed recording of "all" parameters is not necessarily a solution to understanding what happened. "All parameters" may not be needed, not because it can't or shouldn't be done but because such fine granularity may not be necessary. I can tell you that such granularity is unbelievably expensive to do, especially any retro-fitting, which brings me to the point I made in my first response - what is available in terms of parameters is driven purely by money, not flight safety or our need to know absolutely everything that goes on in each of the EEPROMs, computers and systems. The industry is just not going to pay for such a system even though, from an understanding POV, a case can be made.

"1) All information (except WX radar) being presented to PF and PNF are normally recorded in the SSFDR used in AF447? RHS not recorded could affect the investigation team analysis capability? Could affect the analysis in order to to understand PF (if confirmed at RHS) behavior?

No, not necessarily. I took some trouble to discuss FDRs in Post #715 (http://www.pprune.org/tech-log/454653-af-447-thread-no-4-a-36.html#post6550828), were you able to read it? There are no formal (legal) requirements for recording all such information and I describe why in the post. The fact that the #2 AS was not recorded is nothing more than it likely wasn't considered necessary, the airspeed already being "covered" by recording the #1 and the Standby, (and that is already well beyond minimum requirements).

It must be kept in mind that what is recorded is a matter of LFL, (logical frame layout) construction. Beyond the 88 legally-mandated parameters, this is not a process which is specified beyond the manufacturer. Boeing may have several hundred data frames for the B737 type for example, and they will be very different because the aircraft are very different. For older aircraft especially, DFDR and QAR data frames are specific to the individual aircraft simply because these aircraft get modified by successive owners who may desire certain parameters over and above the legal minimums. Many aircraft flying today only record the legal minimum and (from experience) it is not the case that all parameters are even working or recording correctly.

The SSFDR on AF 447 recorded, we are told, about 1300 parameters. Many of these parameters will have been the engine and engine system parameters, primarily used by maintenance for troubleshooting. Comparatively speaking, the requirement to "troubleshoot" EFCS components is rare - the boxes are pulled from the 800VU rack, sent to the manufacturer for troubleshooting/repair and a new (multi-million dollar) box is placed in the rack. The SSFDR will not have recorded very many EFCS parameters because it is not the airplane manufacturer's job to supply such parameters - it is done as a matter of discussion between the various parties...manufacturers, airlines, sometimes even flight safety people or pilots.

One great frustration in doing flight data analysis work is, as you point out, not knowing what the crew saw in terms of text messages on the FMA, the Lower ECAM, the status page and so on. To do so is very expensive because the data frame must be programmed to receive these parameters in binary format and change them into engineering units or text messages, but it is assumed that the computers (FWC in the A330's case) are correctly sending these messages to be displayed for the crew and the process therefore isn't necessary.

"2) Internal System information like redundant inputs to the System (e.g. individual ADM outputs) are recorded?

For the reasons given above, it can't be said whether they are or not. It can be done, but likely is not.

"3) Internal information (of the System) is recorded to allow a clear analysis of how System operated when something (anything) affects the "redundancy degree" of the System? (causing it to operate less redundantly)"

Again, not necessarily, for the reasons given.

=====Discussion:

The other important approach to flight data analysis work is not making the mistake of believing that "if only one had enough data, we could say exactly what happened". There are two reasons why this mistake is made:

1) Complex accidents such as AF 447 require that the work is very often interpretive and not just a summary of all the parameters in order of "causality". This is not a function of the available information, it is a function of ensuring that, a) human factors, and b) the nature of the data-recording process, are both taken into account when trying to understand (interpret) what the data is saying. How one "builds the story from mere data" is an entirely interpretive act requiring knowledge, skill and experience to do accurately.

2) The second reason is the nature of the recording process itself. In the same way we could never just look at the time-stamps on the ACARS messages and say that's the order in which things occurred, the problem of timings, sequence and therefore causality, is Vast if one is recording every EEPROM state, decision and output. The CAP 731 AAIB document to which I referred discusses data frames, recording frequency and binary-to-engineering conversions. It may be readily understood that recording frequencies can vary from say, every four seconds, (for fuel quantities) to four times a second (for pitch or roll, and pitch/roll rates), to sixteen times every second (for gee). But if you wish deep granularity we could argue that many parameters should be recorded at 26 frames per second, or data at video rates. The processes are entirely open to design capabilities and the imagination and at the same time are limited by the practicalities of cost and need.

One may find answers in the millions of parameters which would be required to capture such a level of data but the questions of practicality, of capability, of need and of expense all have contributions to make in such a discussion regarding whether to create such a system or not.

In most investigative work, (I am not an accident investigator), the number of parameters required to reach good conclusions is surprisingly small where the described knowledge, skill and experience are available. A clear example of this principle at work is the investigation into the QF72 PRIM incident. Indeed, the aircraft is not the only source or place to derive data; the manufacturer will have source code, testing facilities and their own experts who know how the computer(s) should behave and, if they didn't (as in the QF72 case), why they didn't.

While we await the next report from the BEA, I genuinely hope that this is helpful RR_NDB.

syseng68k

5th Jul 2011, 16:55

gums, #791

Have been thinking about the application of technology. At opposite ends of the spectrum, we have two motives:

1) To simplify complex processes.

2) As an exercise in intellectual self abuse, to demonstrate how clever it all is.

After being shocked at times by the revelations in this thread during the past couple of years, i'm not really sure where the application of technology is taking us w/regard to aviation. If the primary focus for this is towards improved safety, then they have failed imho. While the technology has resulted in various control laws to improve safety and efficiency, it's application looks like a camel and has done nothing to improve the chances of safe recovery in an emergency, just at the time when it's most needed. Not smart enough by half, in that an appropriate function would, for example, recognise things like pf commanding a zoom climb or other sequence of events outside the expected operating conditions at a given stage of flight and at least provoke the suggestion that it is perhaps not a good idea. "I'm sorry, but I can't do that Dave", springs to mind. Perhaps amusing, but the sort of thing that could contibute to safe operation. I'm not arguing for more or less automation, but more intelligence in terms of trend analysis, resolution of ambiguous situations and timely warnings where operation is tending towards potentially dangerous situations.

Found the 4 part a330 fcom on the web a couple of weeks ago. I couldn't help thinking how much it reminded me of consumer electronics user guide, rather than a proper technical manual. A full TM would describe (eg) how all the various information sources logically combine, their values and conditions, to initiate the transitions between the various control laws, in tabular or flowchart form. While you do get some of this in the user guide, it's spread bits and pieces style all over the place, making it more difficult to visualise the big picture. Quite a disappointment really and if I were a pilot flying one of these boxes, it's something I would need to understand, for all kinds of reasons.

To paraphrase your sentiment, if the crew ever find themselves in a situation where the state of the a/c is not resolvable within a few seconds, in a completely unambiguous way, then the design is at fault and technology has not been applied correctly. There's really no excuse for this at all, however it's spun.

Away doing some real work for a couple of weeks and looking afresh, find myself in quite critical mood. Correct me if i'm wrong here...

Khashoggi

5th Jul 2011, 17:09

^^ your not wrong. Your spot on.

PA 18 151

5th Jul 2011, 17:19

Not smart enough by half, in that an appropriate function would, for example, recognise things like pf commanding a zoom climb or other sequence of events outside the expected operating conditions at a given stage of flight and at least provoke the suggestion that it is perhaps not a good idea.Like a stall warning perhaps?I'm not arguing for more or less automation, but more intelligence in terms of trend analysis, resolution of ambiguous situations and timely warnings where operation is tending towards potentially dangerous situations.From the Evidence (fact)

At 2 h 10 min 51, the stall warning was triggered again........

The aircraft appeared to do exactly the sort of thing you are saying it should.

There isn't a lot of evidence, but what there is is quite powerful stuff.

syseng68k

5th Jul 2011, 17:22

Svarin, #784

By the way, if someone could please enlighten yours truly regarding the
certification process applied to flight controls computers software
versions released after the initial certification process, I would be
extremely grateful.
If you want to get an idea of what's involved in the development process,
you could google "DO178 standard" for a start. You probably won't find
the whole document unless you pay for it (expensive), but you will get a good
overview. It's not just about software development standards, but also
about the ways that the various parts of development chain link together, in
an effort to eliminate pathways that could result in errors. In the case of
software updates, full regression testing would be required and more to ensure
that changes in one area haven't broken anything else.

I think that if there were bugs (unlikely), they would be found at the level
of subsystem interaction, where timing issues and concurrency make it much
more difficult to model at the design stage. That in terms of the myriad
possible failure scenarios and their timing at the limits of
system capabilities. This would be a systems engineering, managing complexity
issue and not one of software as such. Seems very unlikely that there would
be any significant bugs in the individual subsystems, as their behaviour is
tightly defined and thus easier to model in design and subsequently testing...

RR_NDB

5th Jul 2011, 18:12

PJ2I genuinely hope that this is helpful

...I support and advocate for any and all ways to improve flight data recording

My concern is about important internal (volatile) info that would be lost (if you don´t record it). Without this approach you may face situations (during the investigation) that do not allow us to reach a (reliable) conclusion. One may argument you may just look to inputs and outputs of the “engineering black box” . But i suspect that in certain situations (when you are inside, participating of the feedback loop) and the System is under failure mechanisms you need internal data to understand pilot actions. I strongly suspect the way the approach the recording is (still) made is more effective to put responsibilities on crew errors.

Thanks for the extra motivation. In my answer i will try to contribute with some ideas concentrated (like CJ mentioned) on conceptual aspects.

RR_NDB

5th Jul 2011, 18:13

syseng68k I'm not arguing for more or less automation, but more intelligence in terms of trend analysis, resolution of ambiguous situations and timely warnings where operation is tending towards potentially dangerous situations.

R&D is necessary! Not a simple Development.

...has done nothing to improve the chances of safe recovery in an emergency, just at the time when it's most needed.

With the trend towards System complexity this may get worse. Again, R&D is necessary! Not a simple Development.

gums

5th Jul 2011, 19:02

To Doze, et al.....

I see a sub-mode of all the plethora of laws that implies the jet tries to achieve an alpha, even with stick neutral. This could explain the continued pitch up and THS trim, especially if HAL was reacting to the overspeed warning and the reversion to control law "x".

As with Chris, PJ and other 'bus drivers state, this plane is sound, and robust. There is no reason for ambiguous cockpit indications of the current state or control law, and what I have to rely upon when I move the stick. The plane is well-designed. I realize that with an elevator-stab configuration ( versus an all moving stab) that the THS must be trimmed manually or by HAL. So I am confident that this feature of the FLCS will shall recieve some attention in the final report. Trim nose up due to constant back stick by the PF, trim nose up all by itself to maintain the alpha prot value, trim nose up due to decreasing "q" and requirement to have full elevator authority, and the beat goes on.

So bottomline from this old fossil and system engineer and pilot is we have to deal with too many "sub" modes and their associated "protections". Syseng has pointed out a few human factor aspects that the sfwe engineers must recognize.

I do not absolve the crew, hard is that to do being a pilot. But I agree with syseng that many of the 'bus documents I have been provided courtesy of this forum seem more like marketing brochures than tech orders.

I also do not believe all the pilots need to be engineers or Yeager types. 'nuff said.

DozyWannabe

5th Jul 2011, 19:04

@gums:

There was no overspeed warning*. As I understand it, Chris Scott's theory is predicated on a possible attempt by the computers to compensate for the initial slight back pressure on the stick - as a theory it makes sense, but like so many theories there's not enough evidence to go on right now to say one way or another. My suspicion is that the "how" in this case will be simpler than the "why" - so I'm waiting for the report with interest.

* - based on the information released so far. I'm pretty sure that if there was one they'd have mentioned it - it would have saved a lot of argy-bargy on here, that's for certain!

PJ2

5th Jul 2011, 19:14

RR_NDB;

Sorry, I guess I don't really understand what you have in mind. I think we're talking past one another. I'm not sure what you feel is missing which absence has the potential for misleading investigators. It isn't that complicated and the flight data analysis process works quite well in finding out what happened in an accident, whether technical, weather, or human error-related (and likely an inter-relation of all three, plus lots more factors, etc).

The thesis that the causes of aircraft accidents may primarily lie empirically and theoretically and possibly nefariously below the awareness and therefore the control of flight crews and where involved, the investigators, may or may not be viable but that has not been what I've read and seen. I have offered my views on flight data analysis and the investigative process, both of which, if I may offer the thought, you need to understand before you can reasonably substantiate your views on the FDR.

As ChristiaanJ has commented, data from the "black boxes" was being recorded on Concorde, and from what I know about the A320 and B777 boxes sufficient information, but not every "decision", is available for a good analysis. Again as ChristiaanJ has I think correctly observed, even PPRuNe is not really the place for a detailed discussion on FDRs, especially on the AF 447 thread.

PJ2

5th Jul 2011, 19:39

Hi Chris;

(Images of the PFD deleted here and updated in a later post).

Someone mentioned the THS Wheel and trim scale. Here's what it looks like from the Left Seat in a dark cockpit. Viewing from behind the pedestal standing up (as the captain likely would have been) would, I think, have been much less clear. Note that the THS indication is 4NU:

http://www.smugmug.com/photos/i-Gdp89HC/0/L/i-Gdp89HC-L.jpg

Mr Optimistic

5th Jul 2011, 19:42

'if HAL was reacting to the overspeed warning and the reversion to control law "x"'

From the report.......(edited down)

At 2 h 10 min 51 , the stall warning was triggered again. The thrust levers were positioned in the TO/GA detent and the PF maintained nose-up inputs. The recorded angle of attack, of around 6 degrees at the triggering of the stall warning, continued to increase. The trimmable horizontal stabilizer (THS) passed from 3 to 13 degrees nose-up in about 1 minute and remained in the latter position until the end of the flight. The PF continued to make nose-up inputs.

Is there any need to postulate a malign machine ?

Also, once in the descent with ROD constant, it would have felt like 1g through the seat of your pants. If the ROD increased with ND input, the sudden resurrection of the stall warner plus the feeling of lightness can't have helped convince that was the right thing to do.

Lonewolf_50

5th Jul 2011, 19:59

Mister O
At 2 h 10 min 51 , the stall warning was triggered again. The thrust levers were positioned in the TO/GA detent and the PF maintained nose-up inputs. The recorded angle of attack, of around 6 degrees at the triggering of the stall warning, continued to increase. The trimmable horizontal stabilizer (THS) passed from 3 to 13 degrees nose-up in about 1 minute and remained in the latter position until the end of the flight. The PF continued to make nose-up inputs.

Is there any need to postulate a malign machine ?

Also, once in the descent with ROD constant, it would have felt like 1g through the seat of your pants. If the ROD increased with ND input, the sudden resurrection of the stall warner plus the feeling of lightness can't have helped convince that was the right thing to do.

FWIW, from the perspective of one who has now and again been behind an aircraft (luckily without fatal result ...)

If you are stalled, and in that stalled state the stall warning is not sounding, HAL would seem to be a part of the problem, not part of the solution. (The core problem remains ... "What, you stalled this airplane in cruise flight?" :eek::eek::eek: but bear with me.)

If you've lost confidence in X (in this case airspeed), what confidence have you in
a stall warning
or
what you might perceive as a spurious stall warning while you attempt to catch back up to the aircraft?

At what point did any member of the cockpit crew first determine "We are stalled, we must unstall this airplane?"

I'll offer a guess. It was the Captain, when he came back in and at the moment before he ordered the throttle reduction. Hopefully that guess will be confirmed or buried when a more detailed report is issued.

I confess a bias: having learned how to use an AoA guage in my dim and distant past, my opinion is that being able to see AoA, and use it as a cross check, might well have alerted the flying crew to what was going on a while before the great descent began, and acted as a trigger to a more prompt recovery.

RR_NDB

5th Jul 2011, 20:40

PJ2

guess I don't really understand what you have in mind.

With the growing complexity of Systems, intended to a safe, reliable and efficient operation of the airplane and with this inexorable trend to spread even to smaller planes, my feeling is: Despite we can "reconstruct the facts" with not all data (i agree), considering the System is acting progressively like an extra crew, considering it can fail (or induce crew errors) i think more and more insight to it´s working is very probably necessary to fully understand some cases. The reason why i raised the (probable) need for more data is because this could be related to AF447. And relates to redundancy, because amoing other reasons, degraded Systems could present extra issues. (this point relates to the redundancy method used in F-GZCP) QAR, non volatile memories, etc. could be destroyed so is better to preserve something more important info in the SSFDR. Specially if what the pilots "sees" is not all recorded. But as you and ChristiaanJ think the same (or very similar) may be i am exaggerating and concerned too much.

Again as ChristiaanJ has I think correctly observed, even PPRuNe is not really the place for a detailed discussion on FDRs, especially on the AF 447 thread.

I agree. I was preparing something conceptual, not detailed. I will just think about it. Thanks for CAP 731 link.

There is any bias against automation, protections, etc. But i don´t feel comfortable when we learn on "strange behavior" of the Systems that can be related to hidden faults. You know how difficult was for NTSB to understand the Colo. Spgs. 737 crash(a completely different "part" and non redundant). Why not, much more complex Systems could fail (or make difficult to be understood timely by the crew) at critical moments. And like you posted (Possible x Probable) despite being low probability (near zero, i agree) failures they are possible and the only one capable in certain situations, to save the day is a well prepared pilot who normally performs very well at the edge. Even when Systems "try" :} to fool him. :)

So, going back to, Why the mysterious climb?

RR_NDB

5th Jul 2011, 21:07

PJ2

5th Jul 2011, 21:39

Is there any indication if the PF (and PNF) understood the cause of the Law change was the simultaneous failure of AS sensors? (considered as of negligible probability in the a/c System design) I.e. they realized that (if) the start of the events were caused by "just" the "icing limitation" of the (inadequate) AS sensors? Or also they never understood the reason of AP/AT disengagement and subsequent "steps"?
When the autopilot and autothrust disconnect in cruise, one takes over and manually flies the aircraft. With no speed information, the last thing one should do is change anything...pitch or power. The airplane was stable just before the loss of airspeed data.

While there are indications on the PFD that the aircraft is in Alternate Law, they don't need to know what law the aircraft is in to take over and fly manually, and they don't need to know the reasons for the speed failure. They must fly the airplane, period, with tiny, steady inputs, and wait...and get the QRH out for pitch and power settings while selecting the GPS page on the MCDUs, to watch altitude and groundspeed. That's a short-term solution, while they settle down and maintain control. No computers are going to prevent that.

The notion may have been proposed but it has not been demonstrated that either "automation" or "the computers" were preventing them from doing just that.

For emphasis, the absolute first thing to do is stabilize the aircraft and keep it there. Stabilizing the airplane may even mean doing nothing except ensuring that the pitch and power stay the same. Then one watches the trend very carefully to see if slight adjustments are required.

I cannot emphasize enough that this is not an emergency but an abnormality which has a specific and straightforward response, (which was executed in all other UAS events).

Examining computer behaviour through detailed parameters in this case, is, I think, going to be all after the fact, that they had nothing to do with the pitch-up. Further, if the initial causes of this accident actually lie in the electrons and decision gates, we're all doomed because compiling software or building chips without mistakes is something no one doing that work can or will claim as possible.

That does not mean that confusion about the aircraft's situation is improbable. I think it is quite possible and very probable, and the sources of are long before and well beyond the cockpit.

What we should expect is that the computers do not prevent the pilot from doing his or her job. I know of no case in transport flying where the computers prevented the pilot from flying the airplane and doing what he or she needed to do to maintain control and prevent an accident.

OK465

5th Jul 2011, 21:46

Just for info...

With a simple, constrained dual ADR failure, the FPV is still available, but the FD is removed.

DozyWannabe

5th Jul 2011, 21:51

(considered as of negligible probability in the a/c System design)

When it was designed yes, but at the time of the AF447 accident there were known issues with the Thales pitot probes - in fact there was a service bulletin in effect and operators communications from Airbus giving guidance on what to do should the fault arise.

As has been stated, it's not like the aircraft is a joy to fly in Normal Law and becomes squirrelly and unpredictable in any other regime - the whole point of the law degradation design is to keep control of the aircraft as transparent to the pilot as possible. The only major thing to bear in mind outside Normal Law operations is that the hard-limiting protections are no longer there, other than that it's largely business as usual.

With a simple, constrained dual ADR failure, the FPV is still available, but the FD is removed.

So are you saying that had they known about it, AoA information was available?

OK465

5th Jul 2011, 22:04

My apologies, I was only commenting on one of the PFD images presented, and its relation to a particular failure(s), nothing further.

I have no idea if what they were dealing with was a "simple" dual ADR failure.

PJ2

5th Jul 2011, 22:12

OK465, I corrected that right after I posted it as I knew it was in error. But there was an FPV flag and the FPV was not available on AF 447. Someone has posited that perhaps the captain pressed the Hdg-V/S - Trk/FPA button on the FCU to verify the descent path.

infrequentflyer789

5th Jul 2011, 22:19

I know of no case in transport flying where the computers prevented the pilot from flying the airplane and doing what he or she needed to do to maintain control and prevent an accident.

PJ2

Whilst appreciating and agreeing with practically all of your well written posts, I might just have to call you on that one.

The A320 crash at Bilbao I think does meet that criteria (Accident of an Iberian Airbus A320 in Bilbao (http://www.iasa.com.au/folders/Safety_Issues/others/Bilbao.html)) - alpha protection activating in windshear and dumping the plane onto the runway as the pilots attempted GA. Maybe the GA was too late, ill advised, and would have crashed anway, I'm not sure - but alpha prot activation logic was changed by Airbus as a result.

Also there's the "locked" controls (A/P incorrectly on - computer changes control feel) at VR issue on a certain type. Now, the mfr's argument was that you could, and should, pull through the resistance and rotate normally, so maybe the computer didn't "prevent" the pilots flying... but fact is that several crews felt the controls were "locked" to the extent that they aborted at VR. Luckily on long runways...

The software was changed to fix that one too. [by Boeing, not Airbus, of course in this case - but for some folks that necessarily makes the incidents fiction since B-FBW is perfect :E].

CONF iture

5th Jul 2011, 22:23

I tried to figure out what would be the initial movement from the Thrust locked condition. as this was the first ECAM drill "THR LEVERS....MOVE" @ 2:10:05.
Don't think they waited untill 02:10:51 to perform the drill, so the T/L was initially moved to a position between CLB and TOGA.
More probably, the T/L had to be moved to a position aft of the CLB detent in order to match a usual requested N1 for FL350 at M.80
Then, in this saturated environment, it is also very possible that the T/L were simply forgotten and remained in the CLB detent for 45 seconds until they were moved directly to TOGA.

But BEA knows ...

Not necessarily, remember we don't have a complete picture of the PNF's actions and reactions as yet!
Enough to say that the PNF did not touch his sidestick before 10000 feet ... BEA told us.

PJ2

5th Jul 2011, 22:33

infrequentflyer789, thanks very much. I'll take a look at it to understand more, but it appears to be the case and the software was changed. Without wriggling loose from the exception, the notion of mode confusion may be a distant cousin of this type of accident in a kind of psychological way, where one isn't "prevented" by the airplane from acting but by oneself, (human factors), though the material effects may be similar. Thanks again...

RR_NDB

5th Jul 2011, 23:06

PJ2,

The reason of my question was because i always considered useful, we could say, important and in extreme cases, crucial to know what triggered a change in normal conditions. In at least two opportunities this was very important to me. In one, i suspected, made a quick test and proceeded immediately (and perfectly) after clearly understanding the "threat" in the very beginning. In another opportunity i had a no consequences, incident. After trying to understand the reasons (equipment failure) unsuccessfully, i tested the equipment to figure out why it led me to the incident. After the test i finally found the problem, a serious one. And saved my life because if i didn´t test i would not understand what was going on and would be more vulnerable or even involved in a very serious accident. So the idea is: ASAP the pilot understand precisely what´s happening, better. Why? Because his mind would proceed much better (and faster) to correctly "manage" the situation, that departed from normal.

For emphasis, the absolute first thing to do is stabilize the aircraft and keep it there. Stabilizing the airplane may even mean doing nothing except ensuring that the pitch and power stay the same. Then one watches the trend very carefully to see if slight adjustments are required.
Absolutely very similar to what i learned in smaller (piston) planes, 35 years ago. :) Keep flying. Don´t add other issues to the first problem.

But before continuing to your other 3 paragraphs, Did they realize (first) were starting to face an UAS event? I mean, in the very beginning? It seems to me this is a philosophical point. Option #1 The System acts, the PF "start to fly" the a/c and proceed doing the required. Option#2 The crew receives the UAS warning, the System acts and the PF "start... IMHO for an important parameter (AS) after the simultaneous loss of "redundant" sensors it would be safer and better have this information (technically absolutely feasible) immediately. Or i´m exaggerating? :)

Just important or critical? If in the design they put 3 may be was considered a critical element.:confused:

RR_NDB

5th Jul 2011, 23:30

When it was designed yes, but at the time of the AF447 accident there were known issues with the Thales pitot probes - in fact there was a service bulletin in effect and operators communications from Airbus giving guidance on what to do should the fault arise.

If the crew realized, in the very beginning there was a serious AS measurement failure this would help the PF to act "better"? As per BEA he executed "persistent NU..."

As has been stated, it's not like the aircraft is a joy to fly in Normal Law and becomes squirrelly and unpredictable in any other regime - the whole point of the law degradation design is to keep control of the aircraft as transparent to the pilot as possible. The only major thing to bear in mind outside Normal Law operations is that the hard-limiting protections are no longer there, other than that it's largely business as usual.
The important "transparency" is IMHO much better preserved (attained) if you understand why there was a degradation. In this case (by inadequate sensors) easily manageable as PJ2 commented. My point is: An important parameter (AS is so important, the design put 3 elements to measure it) should be reported immediately to the crew. Or i am exaggerating? And the System can take care without "disturbing" :rolleyes: the crew?

bearfoil

5th Jul 2011, 23:58

RR-NDB

Transparency to the pilot is not evident in this particular accident. The first reported condition was a/p loss. Why did it drop? Ordinarily, if for reasons of control limits, the a/c remains in NORMAL LAW after a/p loss. It was eleven seconds later that the pilots together noted, "So, lost Speeds".... and "Alternate Law".

And if for reasons of a/p unable, why would a PF NOT input immediate stability corrections?

"The aircraft was stable just before loss of AS data"....PJ2

How do we know that?

We don't. And since the PF was present, and he input left, NU, I'll defer to the record, and the PF's attempt to correct a roll right, and either a descent or ND, even Overspeed.

Elsewhere, a "New" timetable has appeared which pegs the UAS (sic), at 2:10:06, ONE SECOND after loss of Autopilot. Where did that come from?

If 15 seconds of Data before and after a/p loss were available, in its entirety, I believe that "done" could be put to the deal.

RR_NDB

6th Jul 2011, 00:47

Examining computer behaviour through detailed parameters in this case, is, I think, going to be all after the fact, that they had nothing to do with the pitch-up. Further, if the initial causes of this accident actually lie in the electrons and decision gates, we're all doomed because compiling software or building chips without mistakes is something no one doing that work can or will claim as possible.

When working in maintenance (since i was 15) i learned we can´t be biased because can led you to fail. In one case i considered impossible a fault to be caused by a certain part. After several days fighting to understand the reason of a "glitch" in an engine and after "intense parts swapping" i realized the culprit was a brand new item, with a manufacturing defect. The only one i considered "certainly good". On "the initial causes" i would like to know what was PF "seeing" during his "persistent NU". "we're all doomed " makes me remember a training on EMI/EMC i had when the instructor told us about EMP. (the electromagnetic pulse from a nuclear blast). This is really serious. The "decision gates" could be transformed instantaneously in "diodes" :} and the data buses in "DC bars" :} For a plane, not so near to the blast. :E (the real "butterfly" sensation, butterflies in stomach)

That does not mean that confusion about the aircraft's situation is improbable. I think it is quite possible and very probable, and the sources of are long before and well beyond the cockpit.

I prefer to wait some few weeks. We must be prepared. The first (LF) leak was very clear, assertive and very fast. Let´s wait.

What we should expect is that the computers do not prevent the pilot from doing his or her job. I know of no case in transport flying where the computers prevented the pilot from flying the airplane and doing what he or she needed to do to maintain control and prevent an accident.

I have a different perception on that. And will comment some cases IMHO directly related to the System (the highly reliable redundant "computer"). But first we must define what is the computer? A non optimal interface can be considered "part of the computer"? IMO, Yes. For us, designers it´s very easy to implement a very reliable computer. Specially for simple tasks. The art, IMHO in the Aviation industry is on "how it work together" as a reliable partner (i fired the "crew member" :ok:) specially during unexpected, critical, urgent and complex situations. In the a/c, the computer is just an element. As you said, one that is prone to fail. So much that you need 3 or for certain functions, 5. Therefore a non reliable element. What the crew need is a reliable partner. It came to my mind Albert Schweitzer´s phrase: "Confidence is the greatest asset of any successful enterprise. Nothing useful can survive without it"

TLB

6th Jul 2011, 00:53

As with OK, don't take my seat-of-the-pants sensors away from me. I shall overcome the "leans" in prolonged IMC with no autopilot engaged and maintaining 10 or 15 feet from my flight lead. Some glances at the ADI and other gauges shall save me from my belief that I had been flying inverted for the last 3 minutes, heh heh.

OFF TOPIC.
Reminds me of one flight I had during my CF-101 Voodoo experience (2,000 hrs). I was wing man and while in IMC, lead called me into line-astern position for maneuvers. After a few minutes I remarked to my backseater that - gosh, did I ever have the leans - and I could swear that we are inverted right now. He responded: "Yep we are - this is the last half of three rolls" !
Back ON TOPIC

PJ2

6th Jul 2011, 01:01

Hello Bearfoil;

Understand what you mean but there is no indication in the BEA Update that the aircraft was not in stable flight, likely level, not climbing or descending. The QRH drill and checklist are clear. The meaning of "stability" in this context has to do with steady-state power settings and a level pitch attitude as required by the QRH checklist. Certainly there are going to be pitch variations around a "nodal point" in turbulence but the power isn't going to change once the AT is disconnected.

An autopilot disconnecting in cruise is not a big deal but one certainly, immediately, looks for the cause. I recall from discussion with people who knew the airplane well (when learning the airplane in 1999) that the EFCS is "way ahead" of all systems - and responds much faster than the pilot can to changes or system problems. That it took ten seconds or so between the AP disconnect and the annunciation of the pitot problem may be due to the extensive BITE test processes which ensure the accuracy of the fault, (correlation) and both communication (SDAC > FIDS > FWC1 > FWC2 > CMC, CMS & DMCs). Lack of correlation will cause a WRG fault to be included in the fault message. During that time we do not know what either crew member saw on his PFD in terms of failing AS. We cannot know what the #2 PFD displayed but I have argued elsewhere that it was about the same as the other two; no pilot would try to control high speed with such a pitch-up. The power would be brought back first, then possibly speedbrakes used. We will know soon enough.

Regardless, a loss of airspeed information is no time for swift action, especially in weather. It is time for deliberate, measured action that is slowed down and closely coordinated with the PNF, (announcement by the PF of the drill or checklist, PNF's participation in the checklist or memory item and/or concurrence if a change in flight path/direction is indicated, completion of the challenge-response checklist, securing the aircraft after the abnormal is over, communicating with ATC, Company, F/As).

It is no time for individual action which leaves the other crew member unaware of the course of action and therefore unable to assist. We do not know what occurred during this period except that which the BEA Update includes. Again, we will know soon enough.

The failure to log onto DAKAR still bothers me. In itself it is no big deal providing communications are established on HF (which they were) but they needed a clearance to deviate off-course and didn't get it. CPDLC makes such clearances easily and quickly obtainable. It didn't seem to be an emergency diversion around a build-up they didn't see. Anyway...another item for the BEA to think about.

RR_NDB

6th Jul 2011, 01:07

bearfoil Transparency to the pilot is not evident in this particular accident. The first reported condition was a/p loss. Why did it drop? Ordinarily, if for reasons of control limits, the a/c remains in NORMAL LAW after a/p loss. It was eleven seconds later that the pilots together noted, "So, lost Speeds".... and "Alternate Law".

Question: During their ordeal the System presented a transparent (an clear) picture to the poor guys? :confused: They were informed why the plane "degraded". They were reliably informed they were stalling? The stall warning worked as expected by a crew badly needing reliable information? IMHO this is "little bit" closer to "partner opacity". :}

The "persistent NU..." (from BEA) is coherent with "transparency" from the partner to the PF? :confused:

HarryMann

6th Jul 2011, 01:30

It has occurred to me, that when comparing the flyability, ergonomics, shock resistance & recovery ability of the Airbus FBW cockpit and control systems, as a flight control centre, it should be borne in mind that effectively what Airbus did in a decade or so was:

re-invent the cockpit form a pilot's perpective. Throttle levers that don't feedback, sidestick control, glass display including 'digital' and 'text' (albeit some strip) instruments replacing mostly analogue, etc.

A pretty monumental paradigm shift - but did everyone truly admit that this is what it represented, rather than perhaps Airbus & others leading the industry to describe (even excuse) it somewhat as 'not really different in principal'.

It is in fact very different, all-round, and in principal to what three-quarters of a century of flight up to that point had evolved as a modern cockpit...

It has been 'bedding down' ever since, into the aviation world's sub-conscious. Additional settling in is still taking place... the investigation of this accident, as so many before with more conventional cockpits had done, will be another step to fully accepting some of the imperfections that this man-machine interface represents and correcting them.

Only by being very open about the crew's cockpit experience, and their response - what was expected and what came naturally, can we further improve the modern 'cockpit flight centre' by integrating the best of both worlds.

Like the last UK Govts attempt at a 'truly joined-up government policy', the dots might all be there, but most are still quite some way from being even crudely connected, let alone integrated as a comprehensible, efficient and finely optimised cockpit for flight control.

It seems inevitable that mistakes were made in many areas of design as well as pilotage; even at this early stage it worries me that justifying them (individually) is quite possible, but never as a joined up whole for safely governing an aeroplane's flight under extreme and singular conditions.

jcjeant

6th Jul 2011, 01:34

Hi,

When the autopilot and autothrust disconnect in cruise, one takes over and manually flies the aircraft. With no speed information, the last thing one should do is change anything...pitch or power.The airplane was stable just before the loss of airspeed data.
Why always repost this speculation ?
By myself I read (and it's not a speculation .. but a fact!) the aircraft was stable because he was in a cruise flight stabilized by the autopilot and auto throttle
When autopilot and auto throttle go out of the loop .. we don't know if the airplane stay "stable"
So maybe .. instead of touch nothing (hands off) the pilot had to act immediately for stabilize the plane
Remind .. the plane immediately banked to right (unfortunately no clue about the bank angle from BEA note ....)
So will the pilot wait the aircraft go in a 30° or more bank angle before react ?

bearfoil

6th Jul 2011, 01:38

Hi PJ2

Thanks for such a quick reply. I am happy to see you acknowledge that BITE may have forestalled a cockpit annunciation of the problem. Would this not mean that the PF directly after a/p loss would be flying with the assumption of NORMAL LAW? Otherwise you are condemning this man to a blunder: to wit, not being patient with the a/c post auto? At the least it establishes that there may have been confusion re: LAW.

As I have said, if the PF was performing as you state he should, then some control inputs would be most normal in NORMAL? His acknowledgment of "So, lost speeds", is an admission in fact that ALTERNATE LAW is a new development for the crew, occurring as it did eleven seconds after a/p loss. This is a very long time to be unaware in a task laden cockpit, with MASTER CAUTION, and a STALL STALL in the interim twixt a/p drop and observation of "Lost Speeds", No?

The Note states that the a/c passed through ten degrees NU and increasing "Before it started to climb", why so long if the a/c attitude was stable at 'Level'? Was this a/c starting from a ND? BEA doesn't give a clue.

However, if in any way established nose down, (descent), this would explain the extra time it took for her to reverse her nose transit to "UP".
It also would explain a lagging and exaggerated AoA at the initiation of the zoom. 7000fpm for 35 seconds is 3500 feet (+). Yet we are told that she had PF ND inputs which reduced the Vs to 700 fpm, and continued to 380.

Had she started to climb from 350, she would have flown to 385 and then coasted up to 390. This is not the case, and makes a good argument for her beginning this post a/p climb lower than we think.

I also appreciate your acknowledgement that mechanical issues may have been in play. A Speedbrake deployment is ripe for explaining the onset and chronic display of Right roll. A left Roll correction would drop the Outer (right) aileron, and complete a split surface drag that would be remarkable. If the spoiler was not retracted for any reason, the Starboard wing would continually want to horse the a/c down and right.

Kind regards, and deep respect.

HarryMann

6th Jul 2011, 01:41

jcjeant

But the a/p does 'give up' before the a/c is out of control or in an excessive or unusual attitude, surely. That is what it is programmed to do, and not wait until pitch or lateral control is as good as lost. It's a fair or reasonable assumption, though one could postulate a single upset that 'might' at one and the same time disconnect the a/p and fully upset the a/c...

Seems from the last BEA report that's not what they are thinking though...

bearfoil

6th Jul 2011, 01:52

Harry Mann

Hi. The a/p is required for flight into turbulence, and its limits are virtually identical to what is defined as "Upset". So, the a/p could easily have been bumping up against its mechanical limits for continued select. Technically, then, the PF was (may have been) in upset when he "I have the controls"....? LOC came with the STALL, and the initial STALLSTALL may have been quite valid, exceeding the AoA threshold for warning as the ship climbed (rotated) smartly at .81M. Comes the MASTER CAUTION, and the CAVALRY CHARGE, and the workload (and sensory load) get rather.....extreme?

cheers

PJ2

6th Jul 2011, 03:34

HarryMan;
Only by being very open about the crew's cockpit experience, and their response - what was expected and what came naturally, can we further improve the modern 'cockpit flight centre' by integrating the best of both worlds.

Like the last UK Govts attempt at a 'truly joined-up government policy', the dots might all be there, but most are still quite some way from being even crudely connected, let alone integrated as a comprehensible, efficient and finely optimised cockpit for flight control.

It seems inevitable that mistakes were made in many areas of design as well as pilotage; even at this early stage it worries me that justifying them (individually) is quite possible, but never as a joined up whole for safely governing an aeroplane's flight under extreme and singular conditions.
Yes, I think so. Each paragraph in your post has something important to say about the change, or rather "the shift", but your last paragraph is exceptionally important, the justification being economic.

The traditional controls (even the stick) are a concession to history, but in truth, because it is all digital, the thrust levers, (for example) could have been four push-buttons (for each detent) or sliding dimmer switches. The "cultural" collision has been between the necessary ultra-conservative, (as in extremely slow to change/alter familiar controls which we operate on an entirely sub-conscious level) and the entirely new developments in control (with a bow towards ergonomics) made possible by reliable, light-weight chips and wires. (I do not mean to downplay here the complexity and vision of the concepts which underlie the design).

The failure hasn't been in the concept and resulting design but in the lack of anticipation of the philosophical change in "world view" from the cockpit with regard to very specific technical tasks, right down to the practical "how do it know?" puzzlements of crews brand new to the airplane. Your comment regarding "being open" means (and meant) to me that if one didn't like what it was doing, one disconnected it and flew it like a DC9 or a B737. My 15-year experience reified that view completely.

One just simply didn't accept that this airplane, any airplane, couldn't be stalled and so flew it with the same respect and knowledge one had for the boundaries of controlled flight and certification limits as one always had with one's aircraft. It doesn't take much observation to see that that understanding has changed over the years.

In early years of "the shift" however, it wasn't "more of the same" in the sense that the shift from piston-to-jets, straight-wing to swept wing, mid-altitude to high altitude flight took beginning in the late 50's was still with a conventional cockpit with conventional controls. The accidents were due to slower acceleration (engine and therefore airplane rates - no big 'wash' over the wing from the props, - higher weights, higher altitudes where yaw dampers and Mach number meant something, an extremely clean profile, and the effects of buffet boundaries never encountered in piston flight.

Indeed, if one is entirely open it can be successfully done and to a very large extent, has, as the accident data has borne out. The other side of "the shift" is reading into the design and the aircraft, more complexity than is there which leads to second-guessing and out-guessing the solutions to the problems of flight, which, as gums consistently discusses so well apropos his fighter experience, still are new to transport aircraft. Despite the complexity underlying the relative simplicity of the cockpit, the airplane remains an airplane when one "looks through" the levels of automation. Despite minor disagreements, BOAC's and NoD's comments, as I have read them, reinforce this important notion. In this accident, I think that there is very rich learning for those well beyond and upstream of the cockpit.

jcjeant

6th Jul 2011, 03:51

Hi,

Well at today technology available a plane like a Airbus can be piloted with some tactil (touch) screens .. a keyboard and a mouse as bonus ...
All is available for that ....
It's already at work in some industries ......
And all this can be remote controlled if necessary ..
The ingenuity of humans and progress never stop ... :)
We go on the Moon ... after all .... :D

john_tullamarine

6th Jul 2011, 04:49

Ah, yes.

However, I think PJ2 is more concerned about the problem of "when it's working it's real fine but when it falls in a heap and dumps the lot in the pilot's lap ... what have we done to ensure that the average line pilot - and, in this case, the average pair of line F/Os - is up to the task on the day (or the dark and stormy night, as the case may be) " ?

We should all acknowledge the overall fine record of the Airbus approach to life and the general statistics of the safety record but, when I look at the postulated attitude presentation (http://www.pprune.org/6554443-post819.html) a couple of pages ago and consider that that looks not unlike an early jet A/H (think, say, a 733 with the FD selected OFF) - which, together with a handful of throttles, we could all use to pilot the aeroplane quite nicely .. I am left wondering just a little whether the Industry has been seduced by the siren of Gee-Whizzery and, perhaps, lost the basic pilotage competence plot .. at least just a bit ?

gums

6th Jul 2011, 04:54

TNX for nice words, PJ.

I only jumped in here because I am now a SLF and it's really hard to "ride" when I see things happening and wonder what in the hell the troop up front is doing, or is capable of doing. I just want to feel safe!

If we all wish to have the remote operator back in an air-conditioned room, with all kindsa displays and such, who "steers" the jet, then I will quit riding.

When I look at all the "protections" such as bank angle, AoA limits, auto-throttles that depend upon various flight phases, etc. etc. ad nauseum. I get scared. Don't get me wrong, as I used my autopilot a lot in the lites I flew. I used them to reduce workload, and not to accomplish the mission. But this 'bus implementation seems too much of a pinball machine or video game for 90% of the mission. And the philosophy is reflected in all the "laws" and "alt laws" and sub laws.

The plane we're discussing seems to be a very fine jet, with great aero performance and stability and...... It does not appear to have any terrible or unusual flight characteristics that a basic pilot could not handle. The big "BUT" for me is the plethora of "protections" and laws and sub-laws and on and on that do not seem necessary. I fully understand autopilot functions that ease the workload. So my big "BUT" is the extent to which those AP functions are integrated into the jet's flight control laws. And IMHO, they need not be so closely coupled.

Sorry to rant...

Svarin

6th Jul 2011, 06:02

syseng68k,

thank you for your response regarding "certification after initial" for computers and other parts. Will look it up.

I think that if there were bugs (unlikely), they would be found at the level
of subsystem interactionDo you mean subsystems inside one given computer/unit, inside one PRIM or inside one ADR for example ?

Or could we have interaction between systems (one PRIM talking with one ADR), such interaction being along a multiplexing line shared by many other units ? How is this last one dealt with in "recurrent-next-version-testing" ?

This would be a systems engineering, managing complexity
issue and not one of software as such.I understand you might wish to distinguish between these two issues, although from the perspective of the "user", this still appears as a "bug" (and not as a feature :}). I mean "bug" in the sense that a computerized system acted in ways unexpected both by its user and its designer. It remains explainable and tracing the lines of code one would understand why it did that. But the main issue is that behaviour of the system is not expected by anyone.

As a native speaker told me : "I know it's not what you meant, but it's what you said." This about sums up a workable definition of a "bug" for me, both from the programmer's point of view, and the user's.

Graybeard

6th Jul 2011, 06:15

Back to the PFD illustration. Is there any evidence the altitude display had been removed as shown?

CONF iture

6th Jul 2011, 06:20

gums,

I do agree, the 320 and followers would have been much better aircrafts without such complexity.

FBW was needed to save weight and attract the clients, fine, were the protections their request too ... I don't think so.

Starting with the autotrim under manual flying ... who needs anything like it ?
To have to trim under manual flying has always been part of the pleasure and understanding of what it's all about piloting.
Raise your hand if you thought that an autotrim under manual flying was a necessity (Remember your time on the other types ...)

AF447 has been autotrimmed to the max up position under STALL WRN ... something is awfully wrong here !
At least, leave to the pilots that responsabillity if such was really their wish ...

BOAC

6th Jul 2011, 08:27

I am left wondering just a little whether the Industry has been seduced by the siren of Gee-Whizzery and, perhaps, lost the basic pilotage competence plot .. at least just a bit ? - John - why not come over to the Safety forum and join my thread - the water is lovely and warm:)

piperp2

6th Jul 2011, 08:34

Unfortunately I am not a pilot and this is my first post on this tragedy, but from my limited understanding of the trim function, it is to take the load of the control column or stick to reduce or maintain a balanced feel with no loads felt.

Obviously in the Airbus with the stick having no feedback on control surface loads, I therefore assume the trim is there to reduce hydro-mechanical /electro mechanical loads on the actuation systems during ascent, descent and level flight modes. If this is the case how would the pilot manual trim in alternate law?

What would be his indications to make the corrections? Why with the stick back would auto trim go to fully max with such a low horizontal speed (i.e. elevator control surface loading would have been at a minimum if the aircraft was at or below stall speed , does vertical speed have an influence here?)

BOAC

6th Jul 2011, 10:52

May I rewind to thread #1? As we approach 900 posts on this thread (4), we are really no further forward, 'experts' having 'dissected' the computer logic, argued with each other over what 'latches', 'defaults', 'degrades' or 'votes' etc etc - and we are all ignoring the basic puzzle.

Why did they climb so steeply? I still remain suspicious of the limited CVR release from BEA. I cannot accept that ANY pilot, out of line training, would sit idly by while the other pitches up to a large angle and the altimeter (and IVSI?) scream skywards. Why is this part missing? Let me make it clear, I do not wish to hear 'the voices', but where is the crew inter-action?

So, either PNF saw this climb or he didn't. If he saw it, what was said? You just do not zoom up that level at that weight in the ITCZ, if anywhere.

Now to the second option, he didn't. Way back on thread #1 I asked whether the ADIRU in this failure situation would degrade to IRU or lose all, and I was assured that attitude and inertial info would 'remain'. Suppose it did not.

What do we have?

We are expected to accept a silence in the cockpit while this manoeuvre takes place (and indeed much of the to and fro on these threads ignores this) following

PNF "so, we’ve lost the speeds" then "alternate law […]" followed by

PF "I don’t have any more indications", and the PNF said "we have
no valid indications".

None of this fits with Mr Occam.

If we are looking at the former option, huge and worrying questions on the philosophy of operation of this aircraft in general and AF training arise.

If the second...........

Instead of all the pilots here proving how clever they are at deciphering the IF....THEN and WHILE....WENDs why do they not address the basic PILOTING illogicality of all this? After the first 2 stall warnings, none further during the climb. PF makes 'nose-down' inputs, the climb continues but levels out. NO sign up to now of any more stall or overspeed, indeed no sign of the extant stall recovery actions of stick back and TOGA - until a new stall warning. So why climb? I just do not understand. Is it to be believed that two adult, trained pilots would react this way?

cwatters

6th Jul 2011, 11:18

It might be called "auto trim" but "trimming" seems to be only part of it's function. From descriptions here and in the reports it sounds more like a form of "power assisted steering". It sounds like when you call for a lot of up/down elevator it's the auto-trim that (eventually) delivers a large part of it?

With that in mind I'm unclear why the auto trim function is lost in direct law? Let me re-phrase that.. I can see why automatic control might have to disconnect but not why the pilot should be left with reduced maximium control throws and have to use manual trim to supliment them?

The available throw from the trim system seems to be very large? Under what conditions do you need so much up/down trim? Landing only?

or am I missing something?

DozyWannabe

6th Jul 2011, 12:02

Enough to say that the PNF did not touch his sidestick before 10000 feet ... BEA told us.

But you can't infer from that information that the PNF was unaware of what was going on because he wasn't getting any feel through his sidestick. Perhaps he felt that the other pilot was doing what was necessary, perhaps he didn't feel confident enough to intervene (see Birgenair again), perhaps he got absorbed in the "PNF" role to the extent that he was more focused on the ECAM messages than his PFD or - and I know this will be controversial - perhaps he'd fallen asleep and was woken by the alarms. All of which are possible, but we don't know - we'll find out with the arrival of the report.

Otherwise you are condemning this man to a blunder: to wit, not being patient with the a/c post auto? At the least it establishes that there may have been confusion re: LAW.

I disagree - saying that the system behaved as designed and that design is logical is categorically *not the same* as blaming the pilot. You're taking a technical aspect of the discussion and trying to make it emotional.

Also, confusion re: Law is (IMO) not the issue. At its most basic (and this is something I've been trying to get through to gums on as well), all you have to know about Law in a pressure situation like the one these guys were in is that you can't rely on hard protections once you're out of Normal Law - the very existence of the Alternate laws is to make sure that the aircraft handles much as it does in Normal Law, and we've had several posts from current FBW Airbus pilots stating that this is indeed the case.

I still remain suspicious of the limited CVR release from BEA. I cannot accept that ANY pilot, out of line training, would sit idly by while the other pitches up to a large angle and the altimeter (and IVSI?) scream skywards. Why is this part missing? Let me make it clear, I do not wish to hear 'the voices', but where is the crew inter-action?

As I said, I expect this aspect of the case will be causing a very thorough human factors investigation on the part of the BEA - if they didn't release it last month, I suspect it's because they're unsure of the significance of what (if anything) was said.

Instead of all the pilots here proving how clever they are at deciphering the IF....THEN and WHILE....WENDs why do they not address the basic PILOTING illogicality of all this?

I think you'll find that it's been us techies trying to decipher the logic flow rather than the pilots "trying to look clever". And the fact is that occasionally pilots do illogical things. All this back-and-forth isn't really getting us anywhere and is simply giving those with an axe to grind an opportunity to hammer the square peg of this case into the round hole of their preconceptions.

(Also, you're definitely showing your age with the WHILE/WEND comment, as am I by acknowledging that I know what it means... :8 (I haven't written any Pascal since I finished my A-Levels, and it was pretty old hat even then!))

In early years of "the shift" however, it wasn't "more of the same" in the sense that the shift from piston-to-jets, straight-wing to swept wing, mid-altitude to high altitude flight took beginning in the late 50's was still with a conventional cockpit with conventional controls.

Well - kind of but not really, especially from the late 1960s onwards. The cockpits may have *appeared* conventional but were in fact masking a complex fully-hydraulic system with no direct connection to the flight surfaces in the traditional sense, as some early DC-10 pilots and the crew of JAL123 sadly learned the hard way.

I know you know this by the way, just putting it down in the record. :)

The accidents were due to slower acceleration (engine and therefore airplane rates - no big 'wash' over the wing from the props, - higher weights, higher altitudes where yaw dampers and Mach number meant something, an extremely clean profile, and the effects of buffet boundaries never encountered in piston flight.

And the aforementioned "loss of hydraulics" accidents in the third generation jets.

Lonewolf_50

6th Jul 2011, 12:39

BOAC:

To answer your pilotage question, Mr Occam suggests to me a scan breakdown (and PNF heads down in a display/ECAMS series of tasks) in the style of

artificial horizon/attitude indicator
+
altimeter/altitude strip

dropped out of the PF's scan in favor of something else (something to do with airspeed or secondary effects of that system having a hiccup).

Attention thus diverted, a small input in the stick over time became substantial THS deflection ... hence the 30 seconds of inexplicable nose up input, and beginnings of roll series.

This guess derived from a few years of testing two seat crews with a variety of malfunctions and seeing some focus (as a team) on the malfunciton, and others dividing tasks, one flying, one troubleshooting.

The CVR info might be helpful in understanding how close a guess this is to actual events.

@bearfoil: it does not appear that a/p is required to penetrate turbulence, though I think every AB pilot would prefer it. From what the AB pilots have shared in the various threads, one could (gasp) hand fly by using conventional scan pattern and gently setting and keeping an attitude (nose) and wings as level as possible as one rides out the bumps.

DJ77

6th Jul 2011, 12:51

Starting with the autotrim under manual flying ... who needs anything like it ?
To have to trim under manual flying has always been part of the pleasure and understanding of what it's all about piloting.
Raise your hand if you thought that an autotrim under manual flying was a necessity (Remember your time on the other types ...)

Auto-trim is necessary in order to implement a load factor demand pitch law. The aim is to get a constant path free stick behavior, i.e. a path independent of speed, thrust or configuration. I didn’t try it myself but it could well be that with a sidestick controller such a behavior is better and preferred compared to a more conventional “trim to speed” system. However, you need to add protections at both ends of the longitudinal flight envelope if you want the system certified for commercial operations, hence the high speed and high angle of attack protections.

Problems appear at less than Normal Law due to protections removed but then basic certification requirements don’t apply. You are left with stall warning only in ALT 2 law.

AF447 has been autotrimmed to the max up position under STALL WRN ... something is awfully wrong here !
At least, leave to the pilots that responsabillity if such was really their wish ...

100% agreed.

There is something paradoxical with this new “space aged” flight control system. Certainly the airplane is easy to hand-fly in normal mode, perhaps a bit more “touchy” in alternate mode where default gains are used and again more sensitive in direct mode. Easiness has been used as a commercial argument to customers, suggesting savings in training. We, old pilots, having used “dinosaur” flight control systems regularly disconnected automation, even at altitude, when we felt we could do better manually, which was often the case. At the time, we were never really in need to “update” our skills in this respect and today the background experience is still there.
Now think about the current situation of young pilots. They are just given a taste of direct law in the sim, not necessarily at altitude, a few minutes once every 4 or 5 training session and the rest of their hand-flying life is Easy Law, follow-the-FD-it-is!!! Yet, they are supposed to have a decent level of flying skills when they are abruptly passed a less than optimal system. The paradox is that making the task easier erodes the necessary skills i.e. does not systematically result in enhanced safety.

Mr Optimistic

6th Jul 2011, 12:53

Roll control was maintained which indicates attitude data OK.

Lonewolf_50

6th Jul 2011, 13:02

Mr O.

Ideally, roll control being maintained would mean to me the PF remained wings level when that was the called for flight regime: maintain course and speed to get to next navigation point.

You are probably right, but the BEA reports roll excursions. One need not fault the attitude indicating system for that ... other explanations have been offered that do not point to a failure, for which various data to date have lacked one labeled "inertial reference/AI" failure.

bearfoil

6th Jul 2011, 14:02

A/P is "required" by SOP via Airbus, not in some mechanical requirement. Leaving the controls alone is not unwise in turbulence, where "maintaining" trumps "maneuvering" yes?

There is one other interface in the mix that gets little attention, that being auto v. mechanical?

The Sidestick would seem to be an attempt at "feel" retention. As such, perhaps jcjeant's touchscreen would be a more honest approach? The THS is powered by a jackscrew via hydraulic pressure, not the speediest method of response. Trim implies "relief", not control.

TRIM accomplishes a stability in pressure, independent of deflection. This is a valuable resource when "maneuvering", for it communicates the a/c demands and wishes to the flyer. Does the FCS have need of this "feel"?

Such a valuable resource to eliminate from the endeavor! As to certification, why would a THS be required to plant at max deflection and stay there whilst a recovery is attempted? And if not required for certification, the a/c must be recoverable with elevators only, I would think. So why is the HS even allowed such an excursion?

This thread is generally peopled by those who would grant the system a pass on criticism in the LOC/event arena. Yet the pilots are referred to as "Why in the World...?"

Either the PF knew not the position of the THS, or he disregarded it.

Again, the answer, for me anyway is to be found in the seconds leading to a/p disconnect, and those few that elapsed at the initial climb.

The PF completely ignored the TRIM WHEEL? He commanded a ridiculous climb at low energy? He held backstick seven miles down into the SEA?

Absolutely not. From the outset, BEA has been manipulating public opinion re: this accident in the worst of ways, impugning the pilots, to include those who were open to continued UAS events. Does anyone doubt the motive behind the "Note"? Airbus got, and then sent, the message, n'est-ce pas?

bear, It is impossible to slander without abusing the TRUTH.

Lonewolf_50

6th Jul 2011, 14:41

bear, in re words and terms, and a little too much "all or nothing" in your reply:

A/P is "required" by SOP via Airbus, not in some mechanical requirement.
Leaving the controls alone is not unwise in turbulence, where "maintaining" trumps "maneuvering" yes?
No. You make an assumption there, that not having A/P available means that controls are left alone. I respectfully disagree, having flown in turbulence more than once, with and without an autopilot function (though not on an Airbus, of course).

There is one other interface in the mix that gets little attention, that being auto v. mechanical? The Sidestick would seem to be an attempt at "feel" retention.
Not as described in a myriad of posts by pilots who fly Airbus airliners, no. You and I may have gleaned different messages from same posts. Perhaps I am the one misreading.
As such, perhaps jcjeant's touchscreen would be a more honest approach?

No idea. Haven't tried to fly a plane by touch screen.
The THS is powered by a jackscrew via hydraulic pressure, not the speediest method of response.

It seems to work pretty well, doesn't it? I don't know if speed of response is the critical metric, given that rate damping and control damping are features common to various FBW aircraft, as well as some AFCS and EFCS suites in non-FBW aircraft.

I also recall that the elevator is generally involved in THS lift adjustment under all laws but direct. The way I read the block diagram, when you use trim wheels, the elevators don't do much, so you are moving the THS, but I may be misreading that block diagram. That would explain why those who have used it have to be very careful with trim wheel control of pitch, as the fine pitch trimming, or fine pitch control, via elevator adjustment isn't to hand in that case.

If I have misread the block diagram, my apologies.

Beyond that, any semantic argument about what trim should mean isn't as important as what you learn in type training, and follow on training, about how your flight control system and auto pilot functions work, in full up modes and in degraded modes.

The first fleet helicopter I flew had a different trim system, and different AFCS, than the second fleet helicopter I flew some years later. Just because the trim systems didn't work identically doesn't mean that I could not trim the aircraft, didn't understand how to, or was somehow at a loss.

You learn to fly your aircraft.
It's what good pilots do.
It's what professional pilots do.
If for one reason or another there is a systemic obstacle to such systems familiarity, that must be addressed.

EDIT: I may be dating myself. AFCS "automatic flight control system" and EFCS "electronic flight control system" (now DFCS??) which abbreviations may no longer be in general usage.

bearfoil

6th Jul 2011, 15:19

Lonewolf 50

This thread is impossibly iterative, and requires, imo, a lot of leeway in particular opinions. For example, SmilinEd said ages ago that a/p in turbulence may need a look see. It may not keep up with its own mission, relative to trend, and rapidity of surface deflections required, which may not be appropriate. Airbus strongly recommends using the a/p at all times, and each operator generally demands the same of each flight crew.

Is there an "EASY!" switch on otto? A mode that will tolerate serious bumps and puckering ride in patience, while anticipating some relief soon?

AF447 was in the bump city, by BEA portrayal, via Captain duBois. Yet the crew remained in a/p, as expected, and when it quit, there was the mundane handover, "I have the controls". No big.

The THS' jackscrew works fine, it is appropriate for a large airliner that needs gentle and deliberate deflections. That it took sixty seconds to travel from three degrees to thirteen seems appropriate for its size, that of a large dancefloor used to manipulate 150 tons of mass.

Without assigning any rating to each post, relative to experience and knowledge, my goal is to be critical of the failures here in man and machine, and learning as much as possible in the process. Please continue to correct where necessary, :ok:

CONF iture

6th Jul 2011, 15:24

Auto-trim is necessary in order to implement a load factor demand pitch law.
But, IMO, direct law would have done just fine whenever AP is OFF.
Anyone here complaining about flying the 320 in direct law ?

But you can't infer from that information that the PNF was unaware of what was going on because he wasn't getting any feel through his sidestick. Perhaps he felt that the other pilot was doing what was necessary, perhaps he didn't feel confident enough to intervene (see Birgenair again), perhaps he got absorbed in the "PNF" role to the extent that he was more focused on the ECAM messages than his PFD or - and I know this will be controversial - perhaps he'd fallen asleep and was woken by the alarms. All of which are possible, but we don't know - we'll find out with the arrival of the report.
From my personal experience, I just don't know what my partner is doing with his sidestick. At best, and it's not necessarily better, I'm guessing ...

When the captain came back, he probably took the middle jumpseat, from where, you hardly see any of the sidesticks ... How can he evaluate the flight control inputs ?

And forget about falling asleep at that time. Did the captain fall asleep as well after entering the cockpit ? Is it why the BEA could not publish any comment from him ...

Chris Scott

6th Jul 2011, 15:41

bearfoil, BOAC, and others,
At risk of unnecessary repetition, the BEA Interim Report #2 (Page 48) shows that, with a sudden drop in the perceived dynamic pressure (blocked pitots) the ADR will infer a drop of altitude of the order of 300ft. So, while maintaining FL350, the altimeters might have dropped suddenly to indicate 34700ft erroneously. It's conceivable that this might have been the reason for the PF's initial pitch-up command.

In their most recent Update, the BEA says that ASI1 dropped from 275kt to 60kt, but I have to admit that at the moment I don't know which altimeter reading that would have affected. Perhaps one of our ADR students will shed light?

Chris Scott

6th Jul 2011, 15:44

PJ2,
Thanks for the PFD and centre-pedestal pictures (http://www.pprune.org/tech-log/454653-af-447-thread-no-4-a-41.html#post6554443) yesterday. At what stage would you say the ASI strips on each PFD might have ceased to indicate the current IAS/CAS calculated by the ADRs, and what would cause that? Must admit to being confused about this.

Are you hinting that its disappearance on PFD2 may have provoked the PF's remark at 02:12:02:
"I don't have any more indications" ?

Linktrained

6th Jul 2011, 15:51

We have seen a number of threads speculating on "how to stall" an AB 330.
Does anyone have access to a suitable simulator to see if or how the Captain might have recovered the aircraft, when he arrived on the flight deck ?
(AB are said not to have any data about a full stall - or it is not available.) A few attempts with our own or somebodies "Made-up" data might show - something instructive, even if it needed several attempts.
If there is some success whilst Pitot and Static are used, then try again, this time without. What is there to lose - for us ?
A couple of 747s have glided successfully ( if not intentionally).
Wasn't Cully's an AB...

bearfoil

6th Jul 2011, 15:52

Chris Scott, would AS1 be LHS? Pitot #1 is directly out the Captain's glass, and above Pitot #3? Straightforward, but I could not say for sure.

Chris Scott

6th Jul 2011, 16:01

bearfoil,
Yes, that's my understanding. But I'm not sure that ADR1 displays both CAS and altitude on PFD1 (the L/H PFD). Now, where was that schematic that someone kindly posted an eon back? :{

takata

6th Jul 2011, 16:02

Hi bear,
why would a THS be required to plant at max deflection and stay there whilst a recovery is attempted?
The more important questions we are left with are:
- Was a stall recovery really attempted? If, yes, when did it take place?
So far, I really can't say anything about it as we'll need the full cockpit conversations and many other data in order to settle this matter.

Same remark about the PNF "late" acknowledgement of "speed lost, Alternate law". Was it ever acknowledged by the PF?
What the PNF was trying to say to the PF then? Maybe his message was: "hey! no speed, alternate, no protections... what are you doing? we are climbing!"

Here, the question of each F/O aircraft experience seems critical to me. If the PF, like I think was the most senior with five times A330 more hours than the junior one, the PNF could have no choice left but to call for the Captain in support rather than taking-over. This may explain his early emergency calls.

All we can suspect, so far, is that the PF was attempting to do something as we have those stick imputs recorded. But what exactly was he really attempting to do? For me, it looks like he was trying to fly alpha-max as, at each STALL alarm, he reacted the same way by applying back stick imputs. It is called tunnel vision, sticking with the wrong choice by thinking that it is the good one.
We'll see.

Lonewolf_50

6th Jul 2011, 16:12

All we can suspect, so far, is that the PF was attempting to do something as we have those stick imputs recorded. But what exactly was he really attempting to do? For me, it looks like he was trying to fly alpha-max as, at each STALL alarm, he reacted the same way by applying back stick imputs. It is called tunnel vision, sticking with the wrong choice by thinking that it is the good one.
I wonder why you call it tunnel vision instead of a conditioned response to procedural training, pattern mapping, or learned behavior.

PJ2 has time and again pointed out that a malfunction need not be treated as an emergency, nor turned into one, and I agree with that with the following caveat: once stall warning horn goes off, perhaps the crew went into emergency mode rather than malfunction mode. What was the last training session (that this crew participated in) involving stall warning horns dedicated to?

Recency and proficiency are training factors that must be considered.

(Once again, the pitch and power chorus will ask
'where was that conditioned response when warranted?'
in a lyrical, multipart harmony.)

takata:

When's the last time you taught someone how to do something?

How did you do it?

ChristiaanJ

6th Jul 2011, 16:14

We have seen a number of threads speculating on "how to stall" an AB 330.
Does anyone have access to a suitable simulator to see if or how the Captain might have recovered the aircraft, when he arrived on the flight deck ?With over 800 posts even here you're excused....
The answers, already discussed earlier, are
a) no, there is no "suitable" simulator, since there are not enough aerodynamic data in the "full stall" domain to program a simulator accurately. Simulators are programmed for this domain by extrapolation, and "best guesses". And yes, it IS being looked at by work groups, etc. ;
b) we have nowhere near enough info about what happened in the AF447 cockpit to be able to write a "scenario" to try out what could have been done, even if we had that "suitable" simulator.

takata

6th Jul 2011, 16:22

Hi Lonewolf,
I wonder why you call it tunnel vision instead of a conditioned response to procedural training, pattern mapping, or learned behavior.
I respectfully disagree with such statement.
So far, there is no such "conditioned response" measured behavior, including several other AF crews, as those many previous cases won't show any pattern of similar behaviors.
The more I can say, as there is not such a pattern during similar events, is that a specific training was lacking in most recorded case.

PJ2

6th Jul 2011, 16:37

Chris;
But I'm not sure that ADR1 displays both CAS and altitude on PFD1 (the L/H PFD). Now, where was that schematic that someone kindly posted an eon back?

This the one?

http://www.smugmug.com/photos/i-Sp8P439/0/L/i-Sp8P439-L.jpg

The photographs of the PFD without speed and altitude information have caused confusion for some - please accept my apologies.

In the post I did indicate that the altitude information would have remained, that the THR LK wouldn't have been displayed and that the FPV would not have been available, that there would have been a red "FD" flag and it was just the speed information that was missing, (removed if there is there is no data to display). I wanted to convey a sense of the display rather than portray it exactly as it was which of course isn't possible until we have more information.

The image below of the PFD is perhaps a more realistic representation of what the PFD may have looked like at the start of the climb. I caution everyone that this image is a composite, manipulated, Photoshopped picture and is just a guess and NOT related to anything other than my imagination. It is intended only to represent what the PFD may have looked like given what we know from the BEA Update.

http://www.smugmug.com/photos/i-QxQTz3m/0/L/i-QxQTz3m-L.jpg

Lonewolf_50 - yes, agree...My view has always been that the UAS event was not an emergency but it slowly turned into one the moment the pitch-up began and of course a stall is a full-blown emergency requiring an immediate response.

Notwithstanding notions that the aircraft was pitched down and the "correction" was to pull back on the stick, (doubtful I think), pitching-up and leaving "stable" flight meant that the last known-and-established variables, "pitch-and-power", were themselves intentionally varied, leaving no way back to stable, level flight, not, at least, without immediately setting pitch and power to the QRH settings and waiting (a very long time) for the aircraft to re-stabilize.

Others have said, and I agree, that even at the apogee, a full nose-down-stick-held-to-the-stops-power-off response, perhaps even without rolling the THS forward to something around zero degrees, would likely have led to recovery if not outright avoidance of the stall, (someone else said the aircraft was still at about 215kts and not stalled at the apogee).

ChristiaanJ

6th Jul 2011, 16:42

Total red herring question probably, from a Concorde AFCS ancient.

When the air data part of an ADIRU goes 'belly-up' (in this case because of UAS) does that mean that the possibly still valid data such as altitude and vertical speed (static pressure data only) are also thrown out with the bathwater, or are there separate 'flags' (F/Ws) for separate data such as IAS, Mach, TAT, Alt and VS ?

IIRC, on Concorde all we (i.e., the AFCS) got from the ADCs was an ADC (1 or 2) failure warning. Period.
The AP and/or AT would drop out from internal command/monitor discrepancies between the ADC data, and in most cases also on an ADC F/W.
Since the INS was a totally separate system, it didn't really enter into the air data "discussion".

For clarity I should maybe add, that, for various (mostly irrelevant) reasons, between Concorde (the first FBW airliner....) and A320, the separate ADS (air data system) and inertial reference system (IRS) ended up inside the same system/box, now better known as the ADIRU.

bearfoil

6th Jul 2011, 17:00

takata

howdy sir. I think the CVR reports thus: (2:10:16?)

PF: "So, the speeds are lost."

PNF: "Alternate Law"

So, No mystery twixt the two at this point? If "simultaneous" mutual acknowledgment of the problem, a strong case exists for this being the first 'arrival' of Alternate Law (subject to a 1-2 second P(N)F recognition?)

If this voice is one only pilot, still, the recognition is established as well after autopilot drop.

takata

6th Jul 2011, 17:11

takata
howdy sir. I think the CVR reports thus: (2:10:16?)
PF: "So, the speeds are lost."
PNF: "Alternate Law"
Usual Tunnel reading?
At 2 h 10 min 16, the PNF said "so, we’ve lost the speeds" then "alternate law […]".
Not a single word from the PF, hence this is an imaginatory mutual aknowledgement of the problem!
Those informations are displayed on the pilot flying PFD though. And this would be shown at 0210:05 from the DFDR tracks (alternate law prot lost, loss of speed function for caracteristic speed computation, etc.).
Please, don't make up the few data we have in order to fit your theories.

DJ77

6th Jul 2011, 17:14

Question raised 3 days ago by bubbers44:

They were cruising at M .80 at FL350 so how much static pressure change with a climb would it take to go above mach limit with a blocked pitot tube?

Assuming a blocked pitot (business end + drain) and total pressure trapped inside the tube at FL350 / 275 KCAS / M 0.808 yelds:

FL375 / 302 KCAS / M 0.922
FL380 / 306 KCAS / M 0.944

NB: corrected from an erroneous previous post which I deleted.

MurphyWasRight

6th Jul 2011, 17:49

Try to think about they "why" of the mostly NU inputs during the deep stall ride down I realized I do not have a real "feel" for what the PF was sensing as opposed to seeing on his displays.

So the question to those who know how to calculate such things are:

A: What was the force vector through the PF's seat during the descent given the pitch and other forces?

Aka what would the water in a glass do, we all know where the cat would go (firmly atached to nearest scalp by all available claws).

B:How does this compare to the "real" forces experienced during simulator sessions where due to movement limits some forces (such as acceleration) are simulated by brief movements followed by pitch?

Looking for why the extreme pitch up being indicated may have been disregarded by the PF.
(PF's remark at 02:12:02: "I don't have any more indications" ?)

Could he have been (against training of course) be fooled into thinking the plane was in level flight.

Aplogies in advance if I have missed this I have read most of the posts as they arrive but could have missed some, please provide a link if this has been analyzed before.

DozyWannabe

6th Jul 2011, 18:00

From my personal experience, I just don't know what my partner is doing with his sidestick. At best, and it's not necessarily better, I'm guessing ...

And we know you don't like it - lord knows we've heard it enough times... Doesn't mean it's necessarily worse either.

When the captain came back, he probably took the middle jumpseat, from where, you hardly see any of the sidesticks ... How can he evaluate the flight control inputs ?

He could definitely see the fact that they were nose-high, which was clearly visible on the ADI indicators - that should have given him a hint. To my eyes it also looks pretty difficult to judge a traditional airliner yoke fore/aft position from the angle of that seat, so I'm dubious as to how much difference it would have made. Please don't try to make the situation fit your particular gripes with the aircraft.

And forget about falling asleep at that time. Did the captain fall asleep as well after entering the cockpit ? Is it why the BEA could not publish any comment from him ...

Note I said "perhaps" - by which I meant I'm speculating way out in left field. I'm not saying that's what happened, I'm not even saying it was likely. But given that we've exhausted what we can glean from the data at hand and we're into equally left-field suggestions of byzantine software failures and the like, I thought it should be mentioned as a possibility.

It's amazing that the design and systems (and by implication those that designed and built them) can come in for all kinds of bashing from those who do not know or understand them and it is accepted as normal, yet advance the possibility that a pilot may have lost focus, or the miniscule possibility that he might have fallen asleep and some people are up in arms.

Lonewolf_50

6th Jul 2011, 18:06

With respect, takata, I don't think you understood what I was talking about.

It would be useful to consider what the reaction to stall warning training is and how it is done. (Or was). Some pages back, a very useful description of the 2005 vintage of that procedure was linked to.

The condition/response set isn't the same issue to address as "reaction to UAS training," which is a malfunction of a lesser order.

EDIT for clarity: what the crew was confronted with is the classic training challenge of dealing with cascading and / or compound malfunctions/emergencies. (Note: some will argue that the more dire may have been a crew induced, but that doesn't change what problems they were faced with solving).
Here's your situation, handle it like a good crew should, oh, and here's another on top of that, off you go ... In situations like that, how you train has substantial influence on how you act (and don't act) in the air.

Perhaps best to leave the tunnel analysis in the Alps, near the Brenner Pass. ;)

PJ2

6th Jul 2011, 18:07

Hello CJ;
When the air data part of an ADIRU goes 'belly-up' (in this case because of UAS) does that mean that the possibly still valid data such as altitude and vertical speed (static pressure data only) are also thrown out with the bathwater, or are there separate 'flags' (F/Ws) for separate data such as IAS, Mach, TAT, Alt and VS ?

Vertical speed is a baro-inertial computation. The display is normally inertially-based but the VS based upon barometric computations can be displayed in "degraded mode". Altitude is also a baro-inertial computation, the complexities of which, from what I have read, would take the rest of the thread to convey - but I suspect that both VS and Altitude information would be displayed as depicted in the picture of the PFD just posted. The problem I had in thinking it out was, although the static ports are unaffected and so the source data for baro readings would be available, I just don't know whether an ADR would still transmit valid information while not transmitting invalid information, or whether the entire ADR shuts down. I strongly suspect the former.

The diagram below shows all cautions and warning flags which may be displayed on the PFD.

http://www.smugmug.com/photos/i-FgLRHVn/0/L/i-FgLRHVn-L.jpg

hetfield

6th Jul 2011, 18:09

I'm confident BEA will put the main fault upon the pilot(s), beside some training and A/C design recommendations, to make AB look good.

In turn, this may raise the question, which planes (AB or B) were subject of a hull loss due to "overstress" (AA 587) or simply "not to understand" (A320 XL Airways) the aircraft.

A33Zab

6th Jul 2011, 18:09

In addition to questions raised and answers given.

The lowest speed value on the speed scale = 60 knots.
CAS set itself on 0 and invalid (NCD) if CAS < 30 Knots (SPD FLAG).
MACH will be 0 and invalid (NCD) if M < .1 = (MACH FLAG).

ADIRU 3 data (normally ISIS) can be used by LH or RH PFD by means of rotary switch.

A33Zab

6th Jul 2011, 19:11

In respect of Capt, IMO he realized exact what was going on!
After entering cockpit ordered or pulled T/L into IDLE and ordered ND inputs! see LINK (http://www.pprune.org/tech-log/454653-af-447-thread-no-4-a-35.html#post6549447)

But - if F/CTL SD page was not selected -he was unable to see THS position from this 3rd seat.

henra

6th Jul 2011, 19:12

So the question to those who know how to calculate such things are:

A: What was the force vector through the PF's seat during the descent given the pitch and other forces?

Here we have to make a simplification, because we have no real data about the decelleration of the AC during the descent.
If we assume a linear decelleration from 400kts to 110 kts during ~200s
we have a horizontal decelleration of 0,075g.

Then we have to add the effect of the attitude:
If we take the attitude as being 15° we would see:
~0,96g vertically
~0,25g horizontally
with regard to his seat.
From the horizontal 0,25g we have to subtract the 0,075 *0,96 so we end up with +0,18g felt horizontal acceleration with regard to the seat axis and close to 1g vertically.

All in all the pilots should have felt a relatively stable acceleration feeling with normal vertical g during the descent phase after reaching the -10kfpm
Taking into consideration that the decelleration might have been degressively, the acceleration feeling could have been progressive to some extent.

CONF iture

6th Jul 2011, 19:22

DozyWannabe,

That I like it or not does not really matter, that the sidesticks as implemented by Airbus deprive a multicrew from 'very nice to know' information is a fact that you're apparently not in the best position to fully appreciate.

To my eyes it also looks pretty difficult to judge a traditional airliner yoke fore/aft position from the angle of that seat
Let me tell you your eyes are pretty wrong here.

It's amazing that the design and systems (and by implication those that designed and built them) can come in for all kinds of bashing from those who do not know or understand them and it is accepted as normal, yet advance the possibility that a pilot may have lost focus, or the miniscule possibility that he might have fallen asleep and some people are up in arms.
That 3 pilots got very confused seems obvious - At least we'd like to see the full data, not tomorrow, but yesterday.
There is no free bashing, only constructed critics, but you don't seem to be ready to even consider.

A bit scary to think, and I'm not shy to acknowledge, that after 12 years I still don't know or understand my equipment ... or is the equipment a bit complex after all ?
Never mind, I'll take the next 12 hours at 350 to open my books ... and try to get rid of that ignorance.

bubbers44

6th Jul 2011, 19:25

Question raised 3 days ago by bubbers44:

Quote:
They were cruising at M .80 at FL350 so how much static pressure change with a climb would it take to go above mach limit with a blocked pitot tube?

Assuming a blocked pitot (business end + drain) and total pressure trapped inside the tube at FL350 / 275 KCAS / M 0.808 yelds:

FL375 / 302 KCAS / M 0.922
FL380 / 306 KCAS / M 0.944

NB: corrected from an erroneous previous post which I deleted.

Thanks DJ77. The only reason I brought this up is to explain why he pulled the nose up. Your data confirms that they had an overspeed warning due to the climb with frozen pitot tubes causing the overspeed warning when static pressure reduced to the lower pressure.

Doesn't this explain how this accident happened the way it did? The PF started a climb when the AP disconnected, got an overspeed and pulled up into a deep stall.

Mr Optimistic

6th Jul 2011, 19:33

Re forces, yep once at terminal velocity for the attitude there is no vertical acceleration, in other words the forces up and down match so drag/lift component vertically = 1g. Gravity is pulling your backside down with 1g and the reaction from the a/c via the seat is 1g. Same as in cruise. 40 degree roll excursion may spill some water though.

If a ND input acted to increase vertical speed, sensation of weight would have decreased as you accelerated downwards reaction from seat < 1g as the difference gives the net acceleration. So if the stall warner sounded then you might conclude you were on the verge of stalling. If you think that then clearly you can't be stalled now can you. :8

RetiredF4

6th Jul 2011, 19:36

bubbers44
Thanks DJ77. The only reason I brought this up is to explain why he pulled the nose up. Your data confirms that they had an overspeed warning due to the climb with frozen pitot tubes causing the overspeed warning when static pressure reduced to the lower pressure.

Doesn't this explain how this accident happened the way it did? The PF started a climb when the AP disconnected, got an overspeed and pulled up into a deep stall.

And how do you explain TOGA in an overspeed?
Just curious.

DozyWannabe

6th Jul 2011, 19:39

@A33Zab - you're quoting CONF, not me...

A bit scary to think, and I'm not shy to acknowledge, that after 12 years I still don't know or understand my equipment ... or is the equipment a bit complex after all?

I suspect you'd understand it better if you didn't have such a problem with it since 1988. If you hate the Airbus FBW flightdeck so much, why haven't you transferred to Boeing?

Your data confirms that they had an overspeed warning due to the climb with frozen pitot tubes causing the overspeed warning when static pressure reduced to the lower pressure.

No it does not. The numbers are threre to trigger the overspeed warning *if the numbers are valid*. The numbers at that time were not valid, and so if the design flows the way I think it does, the overspeed warning is inhibited.

HazelNuts39

6th Jul 2011, 20:08

someone else said the aircraft was still at about 215kts and not stalled at the apogeeJust in case my post #792 (p.40) was unclear:
At that point they had about 215 kCAS and were not stalled.I was referring to the point where v/s had been reduced to 700 fpm, before climb was resumed. I believe stall occurred around 02:11:00 just before apogee, speed at apogee would have been about M.6/185 kCAS (BEA data 2:11:06).

PJ2

6th Jul 2011, 20:14

Thank you HN39...I do recall now.

Mr Optimistic

6th Jul 2011, 20:33

A33Zab, pls be a little patient with this SLF but where is the evidence for a sustained ND input ? The whole discussion about the relative authority of the elevators v THS seemed to be along the lines that failure to manually trim frustrated the efforts to get the nose down. I didn't understand any of that from what I have read as I didn't see a sustained attempt at ND, and in any case there was a post claiming that the elevator design does provide enough authority (although in that dirty air who can be sure).

Sorry if I have misrepresented your argument.

GarageYears

6th Jul 2011, 20:48

A33Zab:

In respect of Capt, IMO he realized exact what was going on!
After entering cockpit ordered or pulled T/L into IDLE and ordered ND inputs! see LINK (http://www.pprune.org/tech-log/454653-af-447-thread-no-4-a-35.html#post6549447)

I don't see it quite as definitively, but I suspect you may be right on the TL's to idle. If the ND inputs were ordered I'm surprised (but only a bit) that the BEA didn't include the CVR for that exchange - in my opinion that would be quite significant.

BEA:

At around 2 h 11 min 40, the Captain re-entered the cockpit. During the following seconds, all of the recorded speeds became invalid and the stall warning stopped.

The altitude was then about 35,000 ft, the angle of attack exceeded 40 degrees and the vertical speed was about -10,000 ft/min. The airplane’s pitch attitude did not exceed 15 degrees and the engines’ N1’s were close to 100%. The airplane was subject to roll oscillations that sometimes reached 40 degrees. The PF made an input on the sidestick to the left and nose-up stops, which lasted about 30 seconds.

At 2 h 12 min 02, the PF said "I don’t have any more indications", and the PNF said "we have no valid indications". At that moment, the thrust levers were in the IDLE detent and the engines’ N1’s were at 55%. Around fifteen seconds later, the PF made pitch-down inputs. In the following moments, the angle of attack decreased, the speeds became valid again and the stall warning sounded again.

At 2 h 13 min 32, the PF said "we’re going to arrive at level one hundred". About fifteen seconds later, simultaneous inputs by both pilots on the sidesticks were recorded and the PF said "go ahead you have the controls".

Immediately following the Pilot's arrival, we have 30 seconds of sustained NU though. :ugh:

A33Zab

6th Jul 2011, 21:07

stall occurred around 02:11:00

Just for the record.
Totally agree with this.

I like to add that 2nd Speed drop took place around @ 2:11:50
and triggered the NAV ADR DISAGREE message after 10 sec and
FPV Flags on both PFDs.
This event was not caused by Pitot Icing but due to the insensivity of a
pitot probe at hi AOA and pitch (40 + 15) and air flow disturbance due to
fuselage at such a flight path.

"At around 2 h 11 min 40 ,the Captain re-entered the cockpit.
During the following seconds, all of the recorded
speeds became invalid and the stall warning stopped.

Note: When the measured speeds are below 60 kt, the measured
angle of attack values are considered invalid and are not taken into
account by the systems.
When they are below 30 kt, the speed values themselves are considered
invalid.

The altitude was then about 35,000 ft, the angle of attack
exceeded 40 degrees.... The airplane’s pitch attitude did
not exceed 15 degrees......

At 2 h 12 min 02, the PF said
"I don’t have any more indications", and the PNF said "we
have no valid indications".

Around fifteen seconds later, the PF made pitch-down inputs.
In the following moments, the angle of attack
decreased, the speeds became valid again and the
stall warning sounded again.
........
The angle of attack, when it was valid, always remained
above 35 degrees. "

bubbers44

6th Jul 2011, 21:07

PJ2, I reviewed our posts 715-720 and your response was if he drifted one or two thousand feet high the CAS increase with trapped pitot and drain pressure could not significantly be increased. I agree but how about mach limit? That will be the first limit you hit and DJ77 said with less than a 2500 ft climb that limit would have been exceeded by a significant margin. I don't know how to verify that information but when the CVR report comes out we will know. If someone knows how please post it. DJ77, where did you find it?

Mr Optimistic

6th Jul 2011, 21:11

The only things I feel I believe for sure out of all this are that not latching the stall warning is a clear design oversight and that trimming to near the maximum authority deserves a big red light all for itself (irrespect of 'use manual trim') -that was also a factor at Amsterdam wasn't it ?

However, even if they had recognised the condition and then acted appropriately, recovery from 20000ft would have needed at least a continual sustained 2.3g positive acceleration, and from 10000ft 3.6g. A non-optimal response would have needed more by a factor. With the instruments they had with degraded protections, was subsequent recovery even likely ?

Edit: thanks HN39, merely a factor of 60 out so pls ignore the g's.

Chris Scott

6th Jul 2011, 21:22

CONF_iture,
Are you sure the sidesticks are not visible from the P3 seat, even if you lean forwards? They are on the A320.

A33Zab, quote:
"In respect of Capt, IMO he realized exact what was going on!
After entering cockpit ordered or pulled T/L into IDLE and ordered ND inputs!
But - if F/CTL SD page was not selected -he was unable to see THS position from this 3rd seat."
The THS scale should be clearly visible from the P3 seat, I think: rather more easily than from the P1 and P2 seats, from which you would have to turn your head. In the P3 seat, it would be under your nose.

bearfoil,
My copy of the BEA Update has the PNF making BOTH statements at 02:10:16, quote:
"so, we've lost the speeds" then "alternate law [...]"

PJ2,
Thanks for re-posting that schematic, but what I was trying to confirm is that PFD1 normally gets all its data from ADR1, and PFD2 from ADR2. That seems to be the case.

Re your latest graphic of a possible PFD configuration at start of climb, are you suggesting that the PFD CAS scales had both gone blank? When the PNF announces, at 02:10:16 (before the climb),
"so, we've lost the speeds",
what does he mean? My understanding has been that he is referring to the "characteristic" manoeuvring-speed indices such as VLS, green-dot, and Vmax, not the actual (current) CAS. The "SPD LIM" flag would have appeared next to the strip. At this stage, the ADR1 and ADR2 had not been invalidated – surely that came later?

PJ2

6th Jul 2011, 21:34

My thanks, Bubbers44 - not trying to be "right"... heaven knows there are enough theories floating about to fill a tanker, but wishing to have the argument at least countered so it can be dismissed, pondered, etc.

My point was, if the aircraft was essentially level, there would be no increase in indicated airspeed as a result of any blockage. By all indications we have access to, the pitch-up occurred from level flight. It is true that the airspeed may have increased as altitude increased by the former was not the instigating "cause" because the airspeed required the increase in altitude to increase in indication.
It was asked on a previous page, why TOGA if it was an overspeed?

But as just about everyone here now has pondered/asked/puzzled...why pitch-up just for an unreliable airspeed?
I suspect the Stall warning was a result of aggressive pitch up, not a cause for the PF to pull up but as it got worse, the PF (essentially) pulled more, and longer. It isn't the first time a stall warning has been associated with a hard pull on the control column.

Perhaps too, the upcoming BEA 3rd Interim will cover this and many other questions now on the board.

BTW, I have seen significantly different (lower) Mach numbers in the calculation done by DJ77, (more along the lines of the first ones he did) so perhaps confirmation of how the result was derived might be in order. I'm not qualified to do the math but the question needs to be asked. As expressed in an earlier post, I've had an increasing airspeed in climb (B767) and while it reached the overspeed limit it took much more altitude than 3000ft (FL250 > FL280 approx) to do it. Now it's thicker air and the drain may have only been partially blocked reducing the rate of increase.... ;-7

HazelNuts39

6th Jul 2011, 21:43

Mr Optimistic;

Pls check your calcs.

Mr Optimistic

6th Jul 2011, 22:13

HN39, be warned I am an ex-physicist so admire the precision but be wary of the decimal point and I also admit they were wine and excel affected.

Edit^2: see your point, who uses feet per minute ? You are quite right, thanks and apologies to all.

A33Zab

6th Jul 2011, 22:17

Agreed for the 30s, but from his position it will be difficult to see the SS pitch inputs (maybe the L/R inputs to fight the roll oscillations).
Required some time to be informed what took place in the previous minutes?

@CS:

Disagree, the THS indication will be covered by the trim wheels from P3 seat. see picture PJ2: LINK (http://www.pprune.org/tech-log/454653-af-447-thread-no-4-a-41.html#post6554443)
I've seen pictures from A320 series and here is an obvious difference with A330.

A33Zab

6th Jul 2011, 22:30

These statements will clarify some questions asked.

The system compensates almost 100% for trim changes, due to speed and configuration changes. Trim
changes, due to thrust changes, can be too large for the system to compensate, and the aircraft may
respond to them in pitch, in the conventional sense, and then hold the new attitude at which it stabilized
after the trim change.
The pitch trim wheel moves as the control law compensates for these changes.
---------

IF TRIM LOCKED > 8 UP :
MAX SPEED....................................................... ............................................................ ...... 180 KT
If trim is locked above 8 degrees UP, pitch down authority may be insufficient for speed above 180 knots.

bubbers44

6th Jul 2011, 22:36

PJ2, I'm not trying to be right either, just trying to figure the puzzle out. Since I am also a B757/767 guy I don't know much about the A330 and how all that stuff works, just how airplanes in general fly and wonder why a pilot would zoom climb at high altitude into a deep stall.

I looked up the speed limitations of the A330 just now and see VMO is 330K and mach .86 is mach limit. They were cruising at about 280K and M.81 so the puzzle was with trapped pitot pressure and climbing 2500 ft what would the indicated mach speed be. I have no clue. I agree if they didn't change altitude nothing would change but they apparently did. When the CVR comes out I have a feeling the overspeed warning will be well heard in the background.

Mr Optimistic

6th Jul 2011, 22:48

A33Zab, thanks.

Linktrained

6th Jul 2011, 23:44

ChristiaanJ, #871

I was not proposing that any of "my" sets of data should be used on an aircraft ( even if I knew how to prepare such stuff... I don't !)

Of the cast for the "scenario", two are seated, Left and Right...

As I am sure others must have hoped, to achieve some initial, almost a gliding performance, to give TIME.

I had read a lot of the last 400 posts but got distracted reading about Birgenair's black and yellow Mud Dauber Wasp. I had had one or more in my Pitot tubes in 1969, spotted at about 80 kts at KIN. Engineer sent from Base, old catering bad, dumpped,No pax catering available,( Bank Holiday), request Diplomatic Over-flight from Cuba, fly to Toronto for food,fly back to UK using my discretion with a double crew, only a couple of days late. My Chief Pilot thought I had taken all 130+ for a sightseeing tour. It as easier to leave it at that...

DJ77

6th Jul 2011, 23:47

bubbers44 and PJ2, re CAS / Mach with trapped total pressure.

I computed them with functions from an old (but long tested) homemade personal software (hey, I can do sfwr). It is not rocket science but I don't know how to post a picture of the formulas used and I fear it would not be clear enough if I tried to edit it here so I think it is better to look at the formulas for CAS (subsonic speeds) at Calibrated airspeed - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Calibrated_airspeed) and for Mach number at Mach number - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Mach_number)
To use these formulas you need:
ps = static pressure, pt = total pressure, qc = pt -ps.
p0 = 1013.25 hPa
a0 = 661.479 kts
________FL350 __ FL375 __ FL380
ps (hPa) 238.42 __ 211.48 __206.46

If anyone wants to check this and find different results, please let me know.

I find the overspeed hypothesis not very convincing because it does not add up with TOGA thrust selection, don't explain the zoom climb and I believe it was not observed in previous incidents. However perhaps it should not be completely discarded.

Chris Scott

6th Jul 2011, 23:54

A33Zab,
The link you posted is to a photo taken from the P1 seat, probably in its aft position. AFAIK, we do not yet know where the captain sat or stood during his all-too-brief return to the cockpit. He may have managed to sit in the P3 seat, as I think you suggested.

Regret I don't have a plan of A330 seating, but the P3 seat is likely to be the one used by third crew members, including training and check pilots. It has to offer the best viewing position behind and between the two operating pilots, usually at the back of the centre console. It was my job to spend many hours in such a seat on the A320, so I'm only too familiar with the concept. You MUST be able to see everything to do that job properly, so there has to be such a seat.

Perhaps PJ2 or CONF_iture can comment.

Turbine D

7th Jul 2011, 00:07

Chris Scott,

According to the flight deck layout from Airbus, you are correct in that the third seat is directly back from the center console. There is also a folding fourth seat that is at an angle behind the FO right seat.

A33Zab

7th Jul 2011, 00:13

View from Seat P3. (I linked PJ2s picture because you can see the trim wheel being above the indication)

http://i474.photobucket.com/albums/rr101/Zab999/TWA333rdSeat.jpg

wallybird7

7th Jul 2011, 00:59

JCJEANT (POST #840

Hi,

Quote:
"When the autopilot and autothrust disconnect in cruise, one takes over and manually flies the aircraft. With no speed information, the last thing one should do is change anything...pitch or power.The airplane was stable just before the loss of airspeed data. "

Why always repost this speculation ?
By myself I read (and it's not a speculation .. but a fact!) the aircraft was stable because he was in a cruise flight stabilized by the autopilot and auto throttle
When autopilot and auto throttle go out of the loop .. we don't know if the airplane stay "stable"
So maybe .. instead of touch nothing (hands off) the pilot had to act immediately for stabilize the plane
Remind .. the plane immediately banked to right (unfortunately no clue about the bank angle from BEA note ....)
So will the pilot wait the aircraft go in a 30° or more bank angle before react ?

JC

Totally Agree

At the point when 447 entered "something", ALL HELL BROKE LOOSE!

Pitots iced up. Airspeed lost. A/P and A/t kicked off. 32 or more error messages sent. The Pilot warned of "a bumpy ride".
And soon after the plane entered it's ride of doom into a deep stall.
And to me the likelihood of severe turbulance and strong up and downdrafts.
If there is reluctance to "hand-fly" the plane at altitude at all, what happens to a pilot who has never done so in turbulent air.

Are all those things happening at once sheer coincidence? Not to me.

bearfoil

7th Jul 2011, 01:25

Chris - I do apologize to you and to takata for scrambling my post. My underlying post meant to establish the cognizance of lost speeds and degradation to ALTERNATE LAW at a TIME certain, and not subject to ACARS delays, routes, and signal.

It was at eleven seconds after a/p dropped ( @2:10:05 ), and PF (RHS, In this I agree with takata ) assuming even a three second recognition and speech delay, the CVR establishes that the Cockpit has been made aware by one of the PILOTs that LAW change has occurred eleven seconds after a/p loss.

Could you comment on the idea that involuntary loss of the A/P due control limits exceedance means a drop not to ALTERNATE, but to retention of NORMAL LAW?

For at least two reasons the CVR is the key to a final reconcile of this accident. First, it is TIME perfect, and exceedingly capable witnesses will be heard commenting on the source and progress of the tragic crash?

bubbers44 For my money, your approach is the best I see. Incorporating as it does a connection with the flying Pilots and high altitude hazard, I think you may be very close.

Hopefully BEA will give up a bit more soon

SaturnV

7th Jul 2011, 01:29

Just a note. The BEA retrieved the fourth seat, but no mention of their retrieving the third seat. This was during the first recovery. (The other two cockpit seats were retrieved with their occupants, and it was the DNA analysis on these two bodies that led the French court to proceed with recovery of other bodies.) One can surmise the BEA may have had an interest in the straps on the fourth seat.

After Ile de Sein swapped crews at Dakar and returned, the second recovery seems to have been dedicated to retrieval of bodies. Looking back, the crew swap may have been to bring on board a team experienced with traumatic death. And it may have been representatives of the French court that were directing the second recovery phase, with the BEA more of an observer.

PuraVidaTransport

7th Jul 2011, 02:43

When the PF made the "left-nose up input" (notice singular), it seemed to solve the (small) problem he had at AP cutout. The next time we are given is 11 seconds later and no further inputs have been made on the SS (that we know of) and the aircraft seems to have been in stable and level flight for that 11 seconds.

Question 1: So if it was such a drastic input to initiate a 7K/ft/mn 'zoom climb' wouldn't it have begun much quicker especially with the speed and altitude they were at?

At that 11 second point into the incident, the note is clear that "the pitch attitude increased and the plane began to climb" keeping in mind this is 11 seconds after the only known control input. Also, the wording (the pitch and the plane did X) leads me to think the aircraft did this as no other control inputs are mentioned.

Question 2: With the different protections removed in Alt law, how would the aircraft increase pitch to such a degree with no inputs? Could turbulence/updrafts be sufficient to induce such a pitch up?

About 15 seconds into the incident, "the PF made nose down inputs" (notice plural). This seems to indicate he made more nose down than up however, these multiple inputs only reduced the climb rate but did not end it. Keep in mind, the THS had not moved at this point, that comes later. The roll left and right indicate to me there was turbulence involved at this time.

Question 3: If one left nose-up input starts such a climb why were multiple nose down inputs not enough to completely arrest it? And since the PF noticed the climb and tried to correct it, why did he let it continue at 700ft/mn for the next 35 seconds?

At 45 seconds into the incident, the aircraft ran out of energy and the AoA increased, setting off the stall alarm. Thankfully, the speeds had returned to over 60K or that might not have happened either (see later on). "The thrust levers were positioned in the TO/GA detent and the PF maintained nose-up inputs."

Question 4: Is it possible, despite the PNF telling PF Alt Law, the PF (whose speeds may have been valid at this time) thought he was back in Normal Law?

That to me is the chain of events that led to the stall with PF holding nose-up and THS moving to max due to those commands. The note is so vague on the fall, almost impossible to raise questions as of yet. My pet theory is the Captain got back in the LHS and took over the last minute but no real evidence except not sure senior PF would have given the stick over to junior PNF.

Thanks to any/all that can shed any light on what I see as the chain of events that all have to happen to lead to an accident of this nature.

mm43

7th Jul 2011, 03:09

From page 13 post #260 - AF447 Thread No.3 (http://www.pprune.org/tech-log/452836-af447-thread-no-3-a-13.html#post6478009) and 2725 posts ago.
At 2 h 12 min 02, the PF said "I don’t have any more indications", and the PNF said "we have no valid indications". At that moment, the thrust levers were in the IDLE detent and the engines’ N1’s were at 55% the angle of attack decreased, the speeds became valid again and the stall warning sounded again.
My interpretation is that the aircraft was in a deep stall and passing through FL250 with RoD about 10,000 feet/min, and even though both engines N1's were 55%, the pitch-down inputs decreased the AoA and the airspeed data became valid. However, that IAS was low and the stall warning activated again but ceased with further pitch-up commands as the data again became invalid.

Without AoA information, neither pilot had any idea in what part of the stall regime they were, and seemed to react as if a return of the SW was indicating Vmo, hence the continuing pitch-up command. So failure at this time to persist with the pitch-down command effectively left them doomed, as even then with the time taken for the THS to readjust (if it was going to) and for the wings to start flying, meant that the chance of reducing the RoD to zero before FL0 was marginal.

It strikes me that no-one on the flight deck realized that the AoA data was only valid when IAS was greater than 60KTS. Even though they went looking for the FPV, it seems it was only after the SW stopped at 2:11:40 plus a few seconds, and therefore to no avail - see ACARS FPV messages timed 0212z. Their final chance to grab the FPV page was missed shortly after 2:12:02 when the stall warning sounded again - meaning valid airspeed!
Since the post above, A33Zab has provided information on the No Calculated Data (NCD) and PJ2 has provided a possible PFD image as a help to interpreting what the pilots were seeing at this time.

I have previously provided some updated timing for when the FPV page data was selected (between 02:11:55 and 02:11:59) and A33Zab has posited that the Capt ordered the thrust to idle. I also suspect that the Capt didn't know that the aircraft had been to FL380 and was in no better position than those in the front seats in understanding the reason for the SW following ND commands.

All were confused by the continuing NU eliminating the SW, and the PF most of all as he apparently didn't realize that the initial couple of stall warnings were short excursions into high AOA.

A system designed to provide warning of an approach to a stall has implemented that warning on the basis that the normal means of avoiding the stall will be taken. If as part of the design criteria an increasing AoA and decreasing IAS were further considered, then the NCD case would have resulted in "STALLED" in large red letters on the PFD.

Now stalling an Air Transport aircraft is what the SW set out to avoid, and the (NCD) lack of data on the PFDs resulted in the, "No valid indications" comment rather than, "We are stalled!"

If it is now possible to rationally explain some unforeseen bi-product of switching to ALT 2 LAW (following loss of airspeed data) that contributed to the "zoom climb" and inability of the crew to get the nose down, then all the A332 series aircraft could be at risk. I don't think that, and I guess that neither does Airbus Industries or the BEA. An aviation psychologist may provide an answer, but the simplistic approach is "action = reward", and that false reward needs to be addressed in the software logic associated with the Stall Warning.

I am not advocating that the FD crew become the servants of computers, though if those same computers had been programed to "save" the aircraft from the "crew", then IMHO none of what we are second guessing would have happened. The crew are given the right to have the final say, and sadly in this accident their interpretation of events turned out to be wrong.

EDIT :: It is worth noting that no control surface systems fault warnings entered the the CMC and resulted in ACARS messages. There was plenty of time for them to be transmitted, and due to the manner in which the BEA produced their Note, it may be safe to assume that there were no control faults recorded by the FDR.

BOAC

7th Jul 2011, 07:14

The system compensates almost 100% for trim changes, due to speed and configuration changes. - can you tell us please where that unattributed quote is from? If this relates to the 330, I would also appreciate an explanation of how the trim compensates for 'speed' (and which 'speed') ie is its response a direct function of 'neutralising' the resulting elevator input required for speed change or is there a direct 'speed' function for the THS?

The last para regarding 'lock' at 8+ is particularly alarming.

A33Zab

7th Jul 2011, 07:50

Its stated in FCOM Vol 3, Supplementary Techniques, Flight Controls, Flight Mode. (3.04.27 P3).

I think you understand but for the ones which do not:

Pls don't consider the THS being locked but read as:

"If THS > 8 up (and no autotrim available), full elevator pitch down authority may be insufficient for speeds above 180 knots."

This also from FCOM 3 and mentioned several times in the 'Abnormal and Emergency' section.

BOAC

7th Jul 2011, 07:57

Thanks A33 - I have to admit the word 'locked' (ie no 'autotrim') does not sit easy with me, especially with what I understand to be a not unusual training policy on AB a/c regarding 'use' of the trim wheel..

So, what are the 'speed' inputs, if any?

Chris Scott

7th Jul 2011, 08:43

Turbine_D and A33Zab,
Thanks for your responses. The view in the photo is exactly what I have in mind and memory, and could easily be mistaken for an A320 centre-console. (I presume, however, it is an A330?)

Each pilot has a THS trim wheel. (Unlike the sidesticks, they are interconnected.) There is a THS-position indicator on the outside of each wheel. From the P3 seat, one or the other can easily be seen by moving your head and shoulders laterally to left or right. Do you now agree, A33Zab?

I cannot be completely sure in relation to the A330, but on the A320 you can also observe either sidestick, provided you lean forward slightly. This enables a training or check pilot to monitor the PF's handling of the sidestick, which is impossible from the PNF's seat. This is less easy, however, at night, because side-console illumination is low.

The clear view of the whole operation obtainable from the P3 seat is one of the arguments in favour of conducting line checks from that seat.

takata

7th Jul 2011, 09:11

Hi Lonewolf,

I wonder why you call it tunnel vision instead of a conditioned response to procedural training, pattern mapping, or learned behavior."

So far, there is no such "conditioned response" measured behavior, including several other AF crews, as those many previous cases won't show any pattern of similar behaviors.

With respect, takata, I don't think you understood what I was talking about.
With all due respect, Your Smartiness should be right. It seems to be all about "conditioned response" and I can't understand what you are talking about.

It would be useful to consider what the reaction to stall warning training is and how it is done. (Or was). Some pages back, a very useful description of the 2005 vintage of that procedure was linked to.

The condition/response set isn't the same issue to address as "reaction to UAS training," which is a malfunction of a lesser order.

Nonetheless, if your Smartiness did his homework, he should have also noticed that most recorded UAS events included the same STALL warnings (ie. see Air CARAIBES report) and none resulted to such zoom-climb until AF447 case.

Then talking about "conditioned response" doesn't fit with the case on hand as the previous pilot reactions ranged from "no stick imput" to "emergency descent".

The fact is that the STALL warnings was already identified as the main factor of early confusion during an UAS event BEFORE AF447 case. It was where the procedure seemed already weak (some concern about it was discussed with Airbus) as it was also the first information displayed before the UAS issue was identified, then it was potentially known as dangerous.

I'll post further data later tonight about those previous cases.

A33Zab

7th Jul 2011, 09:17

Sorry Chris, still not convinced, maybe (for A330) if you ask P1 or P2 to move to the side and lean forward L or R from P3 seat?

Below A330 for sure!

http://i474.photobucket.com/albums/rr101/Zab999/TWA333rdSeat.jpg

Below A320 (not sure i'm not familiar)

http://i474.photobucket.com/albums/rr101/Zab999/A320TW.jpg

Chris Scott

7th Jul 2011, 09:40

Hi A33Zab,
Love your photos – thanks. But am at a loss to understand your visibility problem. Could we be misunderstanding one another?
Quote:
Sorry Chris, still not convinced, maybe (for A330) if you ask P1 or P2 to move to the side and lean forward L or R from P3 seat?

P1 and P2 do not block your view of the centre console. No problem!

Chris Scott

7th Jul 2011, 10:13

A33Zab,
Without affecting my previous, I now notice from your two centre-console photos that there is a difference in the THS-position indicators between the A320 and the A330. The A320's are inboard of each wheel; the A330's outboard. (Refer again to PJ2's photo (http://www.pprune.org/tech-log/454653-af-447-thread-no-4-a-41.html#post6554443).) This should improve visibility for the P1 and P2. The P3 would, as I said, need to move head and shoulders left or right to observe one or the other.

Otherwise, the two aircraft seem virtually identical, although the thrust-reverser levers look to be different.

HarryMann

7th Jul 2011, 10:18

With much discussion - some verging on serious disagreement though perhaps that is mainly in emphasis and tone rather than on facts - the following points seem to be featuring strongly where tentative agreement exists:-

1) A stall warning system that has (more than) raised eyebrows before, could be at the centre of cockpit crew confusion once the event had 'matured'
2) A THS trim system, has possibly (or effectively) 'run away' to an extreme setting, that would not be expected at high Mach and cruise Altitude. Said THS system's manual trim wheels do not light up, flash, shout or scream, nor display messages on PFD when at such an extreme setting, even when at that Mach, Alt and Config which surely must be considered a bizarre combination - so why not?
3) An AoA sensor, that whilst likely more immune from debris and/or environmental contaminants than pitot-static AS sensors, and an essential last-ditch safety device (feeding SW system), as well as providing a valuable singular (& independent) item of air data in its own right:
a) did not have its own dedicated display (matching its singular discrete origin and across-the board usefulness)
b) had its feed into the SW system inhibited/constrained in a fairly predicably dangerous fashion (that is creating a fait a complit, should a full (deep sic) stall actually occur)

It appears from reading all the above posts, that their only chance was the Captain, who fought back to the cockpit upon call ASAP, like as not assessed the situation correctly despite not having even half the history & information at his fingertips, and had begun to take pro-active steps along the right lines when old father TIME just ran out for him - I cannot help but feel fustrated even now that we have learnt so much over the last 100 years, and forgotten half of it..

That half is...

We are in WING-BORNE FLIGHT through a fairly decent & consistent layer of air and very few things matter most of the time:
other than AoA and a modicum of speed and thrust, even the latter can be dispensed with for quite a long time in most aircraft, subject to some altitude.

But AoA, not even pitch, is everything with wings and air. Both the THS system and Incidence vanes are major player in AoA matters.

Goodness - even a bit of string (albeit kevlar with a luminescent tracer in it) alongside each side-screen could have jerked someone back into the real world in this instance, no?

Ok, hand-up to hindsight... but having flown sailplanes & hang-gliders, still find it strange that the basic origins and roots of flight are ignored... even the Space Shuttle is an AoA device when back in the atmosphere, indeed, most crucially when re-entering at the very outer limits!

Chris Scott

7th Jul 2011, 11:18

HarryMann,
That was a most thoughtful and relevant post.

Just a few thoughts of my own, based first on your numbered ones:
1) The inhibition of the stall-warning when the sensed airspeed falls below a certain value needs to be addressed. I suspect the problem is that the present generation of AoA sensors cannot operate accurately at very low TAS, which is what they experience every time an aircraft vacates the runway after landing. Ground/flight detection remains, unfortunately, less than 100% reliable. That may sound ridiculous in the context of AF447, but it's part of the problem for the designers.
2) Agree as far as configuration is concerned. There is no way that you would ever want a THS setting of 13NU on a clean aeroplane. Even half that value is a frightening thought.
3a) Rightly or wrongly, this is standard industry practice: not an Airbus-ism.
3b) The constraint is an attempt to avoid false stall warnings, which themselves are dangerous, but it failed the crew in this instance.

Re some of your other points.

The captain had an impossible task on his return to the cockpit. In any case, the "ride" would have made any activity/observation extremely difficult, unless and until he managed to get into the P3 or P4 seat and attach seat-belt or full harness. (The view from the P4 seat is likely to be poor.)
Regarding your other comments, I think the emphasis on AoA would involve revolutionary changes in civil pilot training; starting ab-initio. To justify that, we would need to consider how much a lack of AoA awareness may have contributed to other accidents, not only the obvious ones like G-ARPI, which also involved an unawareness of wing configuration.

In the case of AF447 the bottom line remains, however: why did the PF demonstrably embark upon and maintain a clearly unsustainable climb from level flight?

Lonewolf_50

7th Jul 2011, 12:22

takata: your tone is unappreciated. I am trying to be cordial here. You might notice that I used the ;) smile to indicate humor in the Brenner Pass jest. You respond with snotty sarcasm.

"Tunnel vision" is a particular kind of congnitive problem to overcome in a cockpit. (Also known as target fixation in tactical jets, and a non trivial factor in numerous CFIT mishaps). I find it an utterly unsatisfactory diagnosis for the crew's performance in AF447.

Please go back to the post you have chosen to respond to with such sarcasm, and note my edit for clarity. Compound emergencies versus malfunctions: what are you trained to do, and how are you trained?

LATER EDIT: you may not realize that we are in violent agreement. ;)
The fact is that the STALL warnings was already identified as the main factor of early confusion during an UAS event BEFORE AF447 case. It was where the procedure seemed already weak (some concern about it was discussed with Airbus) as it was also the first information displayed before the UAS issue was identified, then it was potentially known as dangerous.

I ask you in all seriousness, again, how do you, takata, train people to do tasks? Do you? The point is to connect to your own personal experience, not to talk down to you.

Your pretense that all that is needed to address is previous UAS incidents is at odds with the problem set confronting the crew, and the non-trivial problem to how the crew reacted to stall warning, at altitude. (As noted earlier, whether they should have needed to respond to stall warning is a good question, but once you are presented with stall warning, what do you do?)

mm43 makes an important point about timing, descent rate, and the chances of recovery (via nose lowering and subsequent pull out once the wing is unstalled) that points to the odds of recovery as _low_ once the high AoA, stalled descent had become a more or less stable flight condition.

For my money, he's very close to the mark.

This makes response to the initial stall warning a critical action in the chain of events. Response to stall warning ... trained response ... NOT tunnel vision.

Yet again, the difference between dealing with a malfunction versus dealing with an emergency, or approach to an emergency, and multiple malfunctions at once.

Back to the Swiss Cheese. (Hence the Brenner Pass, more humor). Even with the admonitions from the Pitch and Power Chorus, even with PJ2's well reasoned point that patient, gentle, response to UAS and Alt law flying at altitude, there are still cheese slices to pull out of the stack in how one responds to both malfunctions and more serious inflight problems: stall, or approach to a stall. Again, as I point out, and others more experienced than me have as well, this points to a training issue.

Stall response, and stall training response is linked to the AoA display question.

The industry generally (not just Airbus) chooses not to add AoA gages into airliner cockpits. Sound arguments for and against can be made. One should not be surprised that many pilots would prefer that a flying parameter, AoA, is available on the display, but simply adding a gauge isn't enough.

How do you train? (This question is not now directed at you, takata, but perhaps better said as "how does an organization train its people?" )

How do you habitually incorporate an AoA gauge into your scan? The answer to that question would be a component of the answer in whether or not AoA display is a chosen feature.

If the aircraft monitors the AoA for you (which most passenger planes seem to do), AoA going absent for a while leaves you blind. You can look all you want, and the information you seek isn't there.

This goes back to a question which may never be answered: what did the PF see? What did the nose pitch attitude tell him? The BEA is pretty clear about where the nose was, and how long it stayed there. The largest flight instrument in the cockpit is usually the artificial horizon (attitude indicator) on the PFD. A330 cockpit layout looks to be no exception.

GarageYears

7th Jul 2011, 13:09

I have a very nice poster from Airbus of the cockpits of the A320/A330/A340 and A380 all together. In reality you can hardly notice the differences.

Below I have tried to post a photo I took of the poster for the A320/A330 cockpits. The perspective is probably a little higher than the 3rd occupant seat, but my take is you COULD see the sidestick from this position. You make up your own mind...

http://i1116.photobucket.com/albums/k579/GarageYears/AirbusPoster.jpg

Apols if the pic screws the page width...

Lonewolf_50

7th Jul 2011, 13:29

GY:

If the sidestick is being held in a pilot's hand, and manipulated, what useful information would you see if you looked at the side stick to inform you of what is going on, other than the movements of the pilot's hand?

GarageYears

7th Jul 2011, 13:40

If the sidestick is being held in a pilot's hand, and manipulated, what useful information would you see if you looked at the side stick to inform you of what is going on, other than the movements of the pilot's hand?

Beats me. :bored:

I was simply providing the picture, in support of a discussion between A33Zab and Chris Scott, I believe....

Actually I think the pic is pertinent to the on-going discussion anyway. :ok:

HazelNuts39

7th Jul 2011, 13:52

Recovery - (from FL 350, M.4/130 kCAS, 10,000 fpm at 2:11:40) - a few 'ballpark' figures:

1. First you have to reduce AoA to unstall. Let's say pitch down 30 degrees from 15 NU to 15 ND, 20 seconds?? at 10000 fpm that's 3333 feet down, FL317.
2. Then you need to recover to an airspeed that lets you pull say 1.5 g without stall warning, say M.59/235 kCAS/362 kTAS, that's another 3622 ft down, you're now at FL 280.
3. Pull 1.5 g during 10 seconds, 863 ft down, and you're level at about FL270.

Comments welcome.

Lonewolf_50

7th Jul 2011, 14:01

HazelNuts39

Is your estimate based on the idea of performing the recovery from stall with no usable airspeed reference during the recovery?

Or

Is the idea that, at some point in the recovery, the airspeed indications become valid again?

hetfield

7th Jul 2011, 14:03

@HazelNuts39

Your computation may be right. Anyhow I have the impression that all three pilots didn't know what the :mad: was going on until too late.

And this is a clear issue of aircraft design.

HazelNuts39

7th Jul 2011, 14:07

Lonewolf 50;

No, I've no ideas about that, it's just physics. But why would airspeed not become usable while pitching down?

Lonewolf_50

7th Jul 2011, 14:12

If the initial icing issue had cleared itself up, seems to me at some point they would, as the points BEA presents indicate that they did.

At what point the pilots see the info on the tapes, trust it, and use it remains open, but I suspect that if the speeds "came back" they'd be more likely to trust the info than not.

BOAC

7th Jul 2011, 14:19

The system compensates almost 100% for trim changes, due to speed and configuration changes. - still hoping someone can enlarge on this please? Anyone?

HN - I suspect you have been somewhat optimistic in your height loss for achieving manoeuvre speed and pulling out at "1.5g", not forgetting you are starting at 10,000fpm down and this will increase dramatically during your 'recovery'..

HazelNuts39

7th Jul 2011, 14:30

... not forgetting you are starting at 10,000fpm down and this will increase dramatically during your 'recovery'...So what? Level at 250?

EMIT

7th Jul 2011, 14:34

Garage Years, # 926

The pictures are nice, but they show a misleading perspective. The photos are taken using a very wide angle lens, in order to capture the whole cockpit in one view. The downside of such a view is that objects seem to be much further away than they really are: you would think it is about a mile to the instrument panel, actually the observers knees are pressed against the pedestal, the view towards the sidestick is obstructed by the broad shoulders of the pilot, etcetera. If the pictures had been taken by a lens more closely resembling the acute field of view of the human eye, about four pictures had been necessary across from left to right and three rows from top to bottom.
Unfortunately, the pictures that I have to demonstrate this, contain recognizable pilots in view, so I will not post them here.

Chriss Scott, # 924

Well said, although I would change your statement
"why did the PF demonstrably embark upon and maintain a clearly unsustainable climb from level flight? "
into "a clearly unsustainable pitch attitude"

I know it runs into semantics, because you can reply that clearly they managed to sustain the pitch attitude all the way down into the ocean, didn't they, but is was the unrealistic pitch attitude that caused the speed loss and subsequently the stalled condition.

PJ2

7th Jul 2011, 14:54

Chris, A33Zab, the photo below, taken from the Right Seat, is of an A330 pedestal/trim wheel/trim indication. The trim indication is smaller than the A320 and is on the outside of the trimwheel. I recall it being highly visible from the front seats but it seems not visible from the Observers seat where the captain likely would have sat down, (cockpit arrangement diagram below).

http://www.smugmug.com/photos/i-9czgPfz/0/L/i-9czgPfz-L.jpg

http://www.smugmug.com/photos/i-QNCjZ2G/0/L/i-QNCjZ2G-L.jpg

OK465

7th Jul 2011, 15:19

Having an AOA indicator in the cockpit doesn't necessarily imply that it be used as a control instrument or even incorporated in one's scan...

But it would be the first place I would look if I heard, "Stall, Stall".

The digital/analog indicator on the PFD in "some" 737 NG's is very unobtrusive...and in the aircraft without it, it's even more unobtrusive.

DJ77

7th Jul 2011, 15:22

Does the trimwheel move when autotrim is active ?

Chris Scott

7th Jul 2011, 15:52

Garage Years,
Thanks for the photos and yes, EMIT, there is a perspective problem with that wide-angle lens. Both pilots' seats look to be well-aft of their normal in-flight positions, particularly on the A320 photo. When I sat on the P3 seat in its central position, my knees were almost touching the back of the centre console. The A320 P3 seat is adjustable sideways (but see below).

Lonewolf_50,
In daylight it would be possible to see if the stick was being pushed or pulled, but it would be difficult at night due to the low illumination of the side console.

PJ2,
Thanks for that better photo of the A330 centre console, and the seat plan. When sitting in harness in the P3 seat, it is still possible to move your torso to the left or right – provided the inertia-reel shoulder harness is not locked. I think that should enable enough sideways head movement to see the left or right THS-position scale, but you may well know better! Do you have access to a sim?

In the seat-plan diagram, do you agree that both P1 and P2 seats are in the full-aft position, provided for ease of entry and exit?
And is the P3 seat moveable sideways, while remaining attached to the rear bulkhead? If so, it looks further aft than on the A320, so viewing the sidestick across the lap of a pilot may not be possible. Is it capable of being locked in more than one position, like the A320?

Chris Scott

7th Jul 2011, 15:55

Quote from mm43:
It is worth noting that no control surface systems fault warnings entered the the CMC and resulted in ACARS messages. There was plenty of time for them to be transmitted, and due to the manner in which the BEA produced their Note, it may be safe to assume that there were no control faults recorded by the FDR.

Yes, and I agree with the rest of your analysis.

PA 18 151

7th Jul 2011, 15:57

Lonewolf_50

7th Jul 2011, 16:05

Doesn't the "what" depend on if you are up high or down low with the gear down? ;)

BOAC

7th Jul 2011, 16:21

HN - whatever - it is really irrelevant since we understand NO effective recovery action was taken. Far more interesting (for me) is the answer to my query on #902 which I guess no-one knows? Very reassuring.

PJ2

7th Jul 2011, 16:34

DJ77;
Does the trimwheel move when autotrim is active ?
Yes. Like the Boeings (although I can't recall the B767's arrangement), the trim wheel moves with trim changes in either manual or auto flight. It is in motion, quite frequently, with the small speed/pitch changes that normally occur.

Chris;
Thanks for that better photo of the A330 centre console, and the seat plan. When sitting in harness in the P3 seat, it is still possible to move your torso to the left or right – provided the inertia-reel shoulder harness is not locked. I think that should enable enough sideways head movement to see the left or right THS-position scale, but you may well know better! Do you have access to a sim?

In the seat-plan diagram do you agree that both P1 and P2 seats are in the full-aft position, provided for ease of entry and exit?
And is the P3 seat moveable sideways, while remaining attached to the rear bulkhead? If so, it looks further aft than on the A320, so viewing the sidestick across the lap of a pilot may not be possible. Is it capable of being locked in more than one position, like the A320?
Sitting in the center seat it is entirely possible to move sideways slightly and observe the trim position. Other considerations in reading the trim setting would be turbulence, the fact that the indication and pointer are on the top of the indicator and one is viewing from the rear, (there is no parallax however).

Yes, the forward seats appear to be in the full-aft position - the rails take each seat slightly outboard for more room - still, it is a bit of a step across the inboard part of the seat to get in.

The third (center) seat in the A330/A340 is on rails, well ahead of the rear bulkhead and cockpit entrance. The rails take the seat from the full forward position, which is about eight to ten inches behind the aft edge of the pedestal, rearwards about two feet behind the pedestal and thence to starboard about two feet, maybe a bit more. The fourth observers seat is well to starboard, behind, and to the right of the F/O position, and fixed to the bulkhead.

In my opinion one cannot adequately see or judge what movements on the stick are occurring. Most movements are tiny - a pitch-up such as this one might take a two, maybe three centimeter movement aft.

When I first checked out on the A320 I really liked the "Iron Cross" feature because it told me what the other stick was doing. On my first takeoff, the symbol disappeared at lift-off and I distinctly recall being surprised because I thought it was a natural and needed bit of information. Over the years I grew used to using many other cues as to what the other stick was doing and the Iron Cross would not indicate the tiny movements referenced above, but the airplane would. Communication between crew members on this type is vital where any possibility of confusion exists - it is a "cerebral" airplane in that sense, displacing physical cues with digital cues which must go through an interpretive process first. That was "the veil" that I felt when I first sat in the A320's cockpit. The "interpretive process" becomes natural and as swift as in a conventional cockpit after a while and one can get very good at it, all subconsciously of course.

I don't know the arrangement of controls in fighters, so let me ask those who flew them - do fbw fighter aircraft have a way of conveying to the pilot in the front or the back seat, what control inputs the other pilot is making or do both sticks move, (via mechanical connection, etc)? Are there back-driven autothrottles in any types - how is thrust control arranged? Is it standard to display AoA in every fighter?

syseng68k

7th Jul 2011, 16:38

Svarin, #848

Do you mean subsystems inside one given computer/unit, inside one PRIM or
inside one ADR for example ?
I'm thinking about something that has one function. An adr is probably a
good example, as it's function is simply to measure air data parameters
and send the results elsewhere. It's functionality is quite limited and
the only thing the internal software must do is produce accurate results
when the inputs are within range and an error message when it finds that
the inputs exceed the limits of the measurement hardware. That may be a
little oversimplified, but it's basically a box that converts barometric
pressures to electrical signals that other parts of the system can
understand. Because of the limited functionality, it's not too difficult
to devise tests that provide a high degree of confidence that the thing
is working to spec.

The complexity problem arise when many of these individually reliable
boxes are connected together, as you then have time as an added variable
thrown into the mix. Depending on conditions, the various boxes send
their messages with slight variation in timing, so that, for example a
data or error message may arrive at one box before, or after, a message
from a third, or fourth. The testing and validation problem is one of
how to model or prove the system correct when timing variation, together
with all possible system operating and failure modes, probably gives
millions of possible combinations / sequences to test against.

You might compare an adr to a fiddler in the local pub, while a complex
interconnected system is more akin to a symphony orchestra. If the
orchestra is playing Bach, then you're probably ok, so long as everyone
is in tune and in sync. Jazz, and you might be in big trouble :-)...

rudderrudderrat

7th Jul 2011, 17:20

Hi BOAC,
Originally Posted by BOAC
Originally Posted by A33Z #902
The system compensates almost 100% for trim changes, due to speed and configuration changes.
- still hoping someone can enlarge on this please? Anyone?
Far more interesting (for me) is the answer to my query on #902 which I guess no-one knows? Very reassuring.

What is it you don't understand about maintaining a pitch attitude (modified for 1g) by auto-trimming out the load due to changes in air speed?

BOAC

7th Jul 2011, 18:49

Well, rrat - it is to see HOW exactly it does it, do you see? More to the point, do you know? Are there ADC inputs to THS setting? Do I assume you know?

Thanks for replying, by the way.

EMIT

7th Jul 2011, 18:57

PJ 2 #944

In F-16, no feedback from one sidestick to the other.
Even more, in the F-16 the sidestick cannot be moved like in the Airbus. The signal is the FORCE that is exerted on the stick, not the angular displacement.
In the original, F-16 the stick was really as rock solid as an iron pipe, it turned out that that configuration was not so nice for finer control, so a little bit of play was built into the versions from Block-10 onwards (maybe 2 or 3 millimeters of movement at the top of the stick).
Philosophy for the non-moving stick is as follows: there is a "perfect" relaxed steering attitude for your hand, the stick is built in that attitude. If the stick had to be displaced angularly for generating steering signals, that would mean rotating your hand out of the perfect steering attitude - would be a painful exercise under a 9 g load.
In the Rafale, the French originally built a sidestick akin to the Airbus setup. It took some rough remarks from an F-16 pilot to get the factory to switch to an F-16 type stick, after that the Rafale was a fine flying machine.
Info on what the other guy is doing comes from aircraft response. No such thing as "Dual Input" calls as in Airbus. Does it always work out fine that way? No, there has been a case in F-16 history when a non F-16 rated backseater kept his feet well away from the rudder pedals; unfortunately that brought his knees very close to his sidestick. When his G-suit inflated during a dive pull-out, the expanding suit pushed the sidestick sidewards, unexplained sudden roll, didn't work out well.

Autothrust in a fighter, no, everything is done manually. Exception, I believe, Saab Viggen, for landings on short runway strips.

Angle of Attack indicators in fighters? YES.
And, yes, they are actively used.

AOA in civil airplanes - unfortunately, mostly in disguised form: the red minimum speed indication on the speed tape is actually AOA driven, ever notice how it moves up as you increase g-load? (OK, that is observed mostly in the SIM, e.g. during unusual attitude recoveries). Too bad, that when the speed tape is taken away because of system errors, you also loose your disguised AOA indication.
So yes, I would like an AOA indicator in civvie aircraft.

EMIT

7th Jul 2011, 19:07

PJ 2 #944

In the 767, there is no trim wheel and no trim actuation noise. Trim position is indicated on a tape style indicator on the pedestal, approximately next to the throttle quadrant. Only time you really use it, is for setting of take-off trim, after that, trim more or less disappears from your conscious memory.

(PJ 2 knows, but info for others)
When flying manually, you trim as needed. A/P trim works without pilot involvement.
Tricky thing is, autopilot may trim very much nose up without your conscious knowledge. Results are not only awkward in this AF447 case, but also in the B-737 Turkish 1951 stall accident in Amsterdam, and in many stall incidents.

henra

7th Jul 2011, 19:09

The last para regarding 'lock' at 8+ is particularly alarming.

May I point you to the fact that similar statements would have to be made for most if not all types of airliners ?

Full NU Trim will overpower the elevator not only in the A330.

And please don't assume it can only happen in an Airbus that you are handed an Aircraft with Full NU trim. AP commanding full NU Trim quitting and handing over a plane with 10° + NU Trim.
Has happened on different types.

I would also appreciate an explanation of how the trim compensates for 'speed' (and which 'speed') ie is its response a direct function of 'neutralising' the resulting elevator input required for speed change or is there a direct 'speed' function for the THS?

Although I don't know for sure how it is technically solved in the A330 the system behaviour strongly points to an inertia based (read IR) system rather than anything ADR.
As always happy to stand corrected.

Chris Scott

7th Jul 2011, 19:12

PJ2,
Thanks for confirming that the THS-position indicator is visible from the P3 seat, as I expected. However, I should admit that, on entering the low-lit cockpit from the front vestibule (or galley?) area, there is a potential problem of adjustment to night vision. (I know that the vestibule lights probably dim automatically when the cockpit door is opened, but that only serves to protect the night vision of those already in the cockpit.)

Quote:
In my opinion one cannot adequately see or judge what movements on the stick are occurring. Most movements are tiny - a pitch-up such as this one might take a two, maybe three centimeter movement aft.

You are right, particularly in the case of pilots who prefer to hold the stick continuously in the palm of the hand, rather than making inputs and then releasing. With the roll problems the PF was experiencing, and the reversion to Roll-Direct law, he may well have been holding it in the palm of the hand. As I've previously commented, the low illumination of the side console at night would also make it very difficult to see the stick.

[EDIT] There is another slight possibility re cockpit illumination. Being in a remote area, and in the vicinity of thunderstorms, the crew might have elected to put the dome light on. This would not be my choice, but I've seen it done. It floods the whole cockpit with light.

jcjeant

7th Jul 2011, 19:22

Hi,

Sitting in the center seat it is entirely possible to move sideways slightly and observe the trim position. Other considerations in reading the trim setting would be turbulence, the fact that the indication and pointer are on the top of the indicator and one is viewing from the rear, (there is no parallax however). Well .. as the THS was in full deflection .. honestly .. regarding any error of interpretation .. we can put the eventual parallax out of the game.
I assume if one check the pointer of the THS wheel .. it will see immediately that the pointer indicate a full deflection .... :ok:

rudderrudderrat

7th Jul 2011, 19:32

Hi BOAC,

In Direct Law it's like a Boeing, you don't need any ADC input to manually trim the elevator stick load out.
In Normal or ALT LAW the autotrim works in a similar way to maintain the (modified) pitch attitude. I can't see why it would need any ADC input either.

OK465

7th Jul 2011, 19:47

And what would be the next thing you would do?

Is this a trick question? :)

mm43

7th Jul 2011, 19:58

The position of the sidestick(s) and its view from seat #3 appears to becoming an issue judging by posts in the last couple of pages. As previously noted many posts ago, the sidestick position is displayed on the PFDs when in the WoW mode.

If displaying the the sidestick position following an AP disconnect is adding too much clutter to the display, then displaying it when loss of airspeed data due to NCD occurs might be a good get me home option.

In the same situation displaying the mean AoA value plus the THS position would save one from making the, "No valid indications" comment.

BOAC

7th Jul 2011, 20:06

OK - that's one vote for a 'sort of inertial' system and one that appears to not understand what the question means.I offer the instruction free of charge. - I'll take you up on that - do you perchance have a system diagram showing inputs to the THS system that I might learn from?

May I point you to the fact that similar statements would have to be made for most if not all types of airliners ? - no you may not since you do not understand the significance of the word 'lock'. I'm not sure whether that is a language problem or if you fly the a/c but do not understand it properly (as fantom said in his now 'disappeared' post). In English 'lock' means to secure something so that it CANNOT EASILY BE MOVED - as in the Airbus.

If I could have a definitive answer that will not be challenged two pages later by someone else I can move along.

henra

7th Jul 2011, 20:19

- no you may not since you do not understand the significance of the word 'lock'. I'm not sure whether that is a language problem or if you fly the a/c but do not understand it properly (as fantom said in his now 'disappeared' post). In English 'lock' means to secure something so that it CANNOT EASILY BE MOVED - as in the Airbus.

That may indeed be a language problem being not a native speaker although I generally do understand what 'Locked' means.

However I did not take it literally as 'locked' in that paragraph, more along the lines the THS being at +8° (e.g. due to Auto Trim deactivated, so unless manually moved it will simply stay there but not being mechanically arrested in any way).
Bear in mind Airbus is a Company with a lot of French influence/origin, thus English documents may deviate slightly from the original French ones from time to time. My feeling is you might be over- interpreting something in their Language.
Do we have any indication that there is a possibility to literally lock the THS (in the sense you took it) ?

rudderrudderrat

7th Jul 2011, 20:42

Hi BOAC,

and one that appears to not understand what the question means.

I think you'd enjoy the course.

The ADC input will modify the elevator movement. The stab will be autotrimmed so the elevators return to their neutral position.

http://www.merrowresidents.org/pprune/Stabtrim.jpg

BOAC

7th Jul 2011, 20:51

Thank you rrat - I'll wait a couple of pages and see if anyone else interprets the 'ADIRU' input differently. Are you saying, then, that a low 'detected' IAS will increase effective elevator 'gearing' which will produce a greater THS follow-up movement?

henra - it has been stated that the THS locks in one of the failure modes - ie autotrim ceases to function. Regarding 'translation', I feel that if FCOM Vol 3, Supplementary Techniques, Flight Controls, Flight Mode. (3.04.27 P3) did not mean 'locked' (in English) then it should say so?.

mm43

7th Jul 2011, 20:55

BOAC;

Could I put it this way -

The only known method of locking the THS position is to hold on to the trim wheel. So if the THS is > 8 degrees and held, the elevator may not be effective at more than 180 KTS.

rudderrudderrat

7th Jul 2011, 20:59

Hi BOAC,

The "gearing" "Q pot" etc. is now done via the ADIRU input. It would probably feel "twitchy" if the real airspeed was greater than sensed. However, the elevator position to hold a given attitude would be the same and hence so would the trim position.

henra

7th Jul 2011, 21:01

henra - it has been stated that the THS locks in one of the failure modes - ie autotrim ceases to function. Regarding 'translation', I feel that if FCOM Vol 3, Supplementary Techniques, Flight Controls, Flight Mode. (3.04.27 P3) did not mean 'locked' (in English) then it should say so?.

Hmm maybe we still have a different notion of the word 'locked'.

I understand that in Abnormal law as well as in Direct law Auto Trim is lost/disabled and the THS will stay in the last position unless manually manipulated by the Trim wheel.
However, I'm not aware that there is any kind of blockage/hindrance against manual operation of the Trim. Just the system won't do it for you any more automatically. Effectively you change plane from A to B.
Also the schematics which have been posted point in that direction.

KBPsen

7th Jul 2011, 21:34

You are trying really hard not to fall off the outrage express, aren't you BOAC.

As any other mechanical system a stabilizer can become locked, blocked, jammed, immovable, seized up........Should I continue?

http://img219.imageshack.us/img219/9991/fctlstabctlfault.jpg

BOAC

7th Jul 2011, 21:37

Just remember I did not write the word 'locked' in the FCOM please.

KBP - many expresses do not stop until they reach destination. So, for 'lock' we now read 'jammed'? Nothing to do with the cessation of removal of autotrim function. My goodness me, that took a while, but I think I saw a train approaching the station.

PJ2

7th Jul 2011, 22:06

FWIW, wrt the visibility of the THS indication and the F/O's sidestick, two views of the cockpit - Daytime, A330, night-time, A340:

http://www.smugmug.com/photos/i-bJvfTcP/1/L/i-bJvfTcP-L.jpg

http://www.smugmug.com/photos/i-WJNxHQf/0/L/i-WJNxHQf-L.jpg

A33Zab

7th Jul 2011, 22:20

I did try to clarify to prevent discussion:

I think you understand but for the ones which do not:

Pls don't consider the THS being locked but read as:

"If THS > 8 up (and no autotrim available), full elevator pitch down authority may be insufficient for speeds above 180 knots."

But I get the impression I failed..........

This remark is given in the mentioned FCOM 3.....when a FCTL STAB CTL FAULT is present. This was for sure NOTthe case here. The THS was free (NOT locked) to move Airplane Nose Down.

What it will say is that full elevator authority alone is not sufficient to counteract the PITCH UP THS position if this is > 8 ANU and if Speed > 180 Knots.
If THS <=8 ANU the elevator deflection alone can counteract a THS 8 (or less) ANU position.

If SS input was FWD the THS would have followed the command as designed.

@ BOAC:

The FCPC gets ADR & IR information to compensate for speed.
The IR part can't be compared to the old INU systems, this is very precise accelerometers and 3 axis ring laser gyros equipment and yes the crew is allowed to have a peek on the same signals through its PFD.

There is an interface with ATA 76 (engine controls) but these are discrete signals only and used for ground spoiler logic(T/L position), for 3rd T/R lock release and for limitation of the green servo control speed in case of a dual engine failure.

@CS:

Maybe you have better eyes then me, I need periscopic glasses to do it without interfering the guys on P1 or P2.

DJ77

7th Jul 2011, 22:30

PJ2,

the trim wheel moves with trim changes in either manual or auto flight. It is in motion, quite frequently, with the small speed/pitch changes that normally occur

Thanks for your answer. Then, there is perhaps a (remote) possibility that a PNF could suspect inadequate pitch inputs by the PF by noticing from the corner of an eye the trimwheel moving in an unexpected way. This is probably irrelevant, however, in a tight situation.

Mr Optimistic

7th Jul 2011, 22:41

What factors do the designers consider when setting out how far the THS can travel ? Would it have mattered much in real life if it had been limited to less than 8 degrees NU ?

A33Zab

7th Jul 2011, 22:43

One stroke on the Trimwheel ~0.65° THS movement. (2 hydr. motors B+Y available)

PJ2

7th Jul 2011, 22:58

DJ77;
Then, there is perhaps a (remote) possibility that a PNF could suspect inadequate pitch inputs by the PF by noticing from the corner of an eye the trimwheel moving in an unexpected way. This is probably irrelevant, however, in a tight situation. Re your first statement, in a word, yes, I think it is possible to put together a THS wheel rolling aft out of the corner of one's eye while observing the pitch increase and the inappropriately high vertical speed but it requires a calm eye in the face of the unfamiliar and a habit of not focussing on the same thing as the other crew member. I think there's more than that: Listening to that "sixth sense" would be part of it... the fact that the air noise begins to go a LOT quieter when the pitch is still high, one begins to slowly, gently feel lighter in the seat and one can begin to actually hear the engines, as well as paying attention to whatever it is in one's belly that says things aren't good. But I think your second statement applies as well.

Machinbird

8th Jul 2011, 04:11

One stroke on the Trimwheel ~0.65° THS movement. (2 hydr. motors B+Y available) So if trim is sitting at 13 degrees aircraft nose up direction and you need to get it down to around 4 degrees ANU to recover, it would take 13-14 strokes on the trimwheel.

Anyone have an idea how long that might take to execute? Does trim wheel motion keep pace with the THS position on its way down to reduced trim or can it get out in front of it and let the tail catch up?

gums

8th Jul 2011, 06:00

Salute!

Thanks to EMIT, thanks.....

- The transition from a big stick or yoke to the "force" transducers was very easy. Like about 3 or 4 seconds on first flight. Put some pressure on the stick and the jet moved ( rolled or pitched). I flew with many fossils and newbies in the family model, and that was my experience when letting them fly.

- The family model sticks "added" the command for roll and pitch, and we could not see the other guy's inputs, nor would it have made any difference. as the stick didn't move more than a few millimeters. So I could 'help" the newbie, but if I let go he would wonder why the jet was trying to climb a bit on final approach.

- I flew three jets with the AoA indicators. The two that counted were the SLUF and the Viper. The SLUF was a Navy variant and had the "indexer" lights up on the glareshield, or on one side of the Head Up Display. This allowed us to fly the optimum AoA on approach without calculating weight versus speed. AoA is AoA, regardless of your weight.... duuuuuh. We still had to do a rough, rule-of-thumb, correlation of our indicator with the airspeed we expected. This was due to leading edge flaps that allowed a higher speed for the same AoA and other factors. Nevertheless, the Navy folks here can tell ya about the AoA "indexer" lights.

- The Hornet has an "autothrust" feature. Only did a few approaches in the sim, but I basically used pitch for AoA , and let the motors handle the vertical velocity part of the function. Not sure how this works for the heavies, and I really didn't find the feature all that neat. I preferred to trim for the AoA and use throttle for descent. I also had the neat HUD flight path doofer to see where I would impact if I didn't change anything. Saw it first in 1971 when checking out in the SLUF, and it was a real treat.

As another contributor has stated, wings provide lift according to AoA and "q". It's the same for a 'bus as for a Cessna or an F-22. I do not advocate yet another indicator in the cockpit, but for approaches an AoA indicator could be very useful. OTOH, when near a stall or actually in a stall, the AoA indicator is of extreme value.

One of these days I can digitize my HUD video of the leading edge failure episode. The flight path marker really helped me, as the bird was yawing quite a bit, reacting funny with roll inputs ( all 1 -2 pounds of available command authority) and you can see my goal - 1,000 feet down the runway!

from the high mountains in Colorado, I comment, read, and learn from my fellow pilots flying vastly different aircraft.......

jcjeant

8th Jul 2011, 06:03

Hi,

So if trim is sitting at 13 degrees aircraft nose up direction and you need to get it down to around 4 degrees ANU to recover, it would take 13-14 strokes on the trimwheel.From the Rumours and News:

BEA
"At 2 h 12 min 02, the PF said "I don’t have any more indications", and the PNF said "we have no valid indications". At that moment, the thrust levers were in the IDLE detent and the engines’ N1’s were at 55%. Around fifteen seconds later, the PF made pitch-down inputs. In the following moments, the angle of attack decreased, the speeds became valid again and the stall warning sounded again."So there is no evidence that the PF did not in fact maintain the nosedown inputs?

Typically of the BEA (on this occasion) the note later mentions both pilots applying simultaneous inputs - but it doesn't indicate whether those inputs were up or down......

On the other hand, the BEA DOES say without equivocation that the THS remained in the same 'full up' position that it had adopted (for whatever reason) at the onset of the accident "until the end of the flight." And, as the BEA said in the earlier Perpignan report which I quoted above, this would likely have left the pilots in a situation which they "could not manage to counter, even with the sidestick at the nose-down stop"?http://www.pprune.org/rumours-news/447730-af447-wreckage-found-98.html#post6558788

When PF make nose up stick inputs the THS follow .. and when PF made nose down inputs the THS don't follow
Why :confused:

rudderrudderrat

8th Jul 2011, 07:15

Hi jcjeant,

when PF made nose down inputs the THS don't follow. Why?

Because they didn't keep the ND input in for long enough.

They had not diagnosed their problem correctly, and attempted to arrest their ROD with NU side stick inputs.

BOAC

8th Jul 2011, 07:25

But I get the impression I failed.......... - yes, you did. By 'omitting' the vital part "This remark is given in the mentioned FCOM 3.....when a FCTL STAB CTL FAULT is present." which others have now posted you in fact 'raised more questions than you answered'.

Your line "The FCPC gets ADR & IR information to The FCPC gets ADR & IR information to compensate for speed.." makes me again 'board the train' and ask exactly what ADR info the FCPC gets.to 'compensate for speed.'. You see what bothers me is that I don't think anyone here, and I include the software and system designers, can possibly (or do) understand the intricate processes that system failures can inject. There are simply too may variables and too little 'beta testing' time. It would be a breeze for some clever software writer to give the THS access to a IAS/angle/alt/c of g table and have it automatically adjust its datum concept. He/she might then go away thinking, 'Haven't I done well? One less stream of THS follow-up signals associated with speed change. Look - it KNOWS exactly where it should be for 1g at 230kts, 190kts, etc'

Now, once you 'inject' a speed input into the THS setting you begin to open 'maybe' doors onto the behaviour of the mid-Atlantic 340 and possibly 447 and others. I note the evident resistance in the AB community to accept that anything could be wrong but I do not admire it.

To pick up on MR Optimistic's post #968 - indeed, I did suggest that following a spate of BOEING (everyone see that?) and then the AB PGF THS triggered accident/incidents there should be some physical intervention (a 'wake-up call', if you like) required by a crew to permit THS settings beyond a certain value. This could well have saved 447.

I appears that autotrim, whether it be A/P driven in the 737 or in manual flight, has a lot of fatalities to answer for.

rudderrudderrat

8th Jul 2011, 07:55

Hi BOAC,

Sorry - but you are beginning to confuse me now. Have you started the conversion course already?

Now, once you 'inject' a speed input into the THS setting you begin to open 'maybe' doors onto the behaviour of the mid-Atlantic 340 and possibly 447 and others. I note the evident resistance in the AB community to accept that anything could be wrong but I do not admire it.

No one would design a system like you seem to suggest with It would be a breeze for some clever software writer to give the THS access to a IAS/angle/alt/c of g table and have it automatically adjust its datum concept. He/she might then go away thinking, 'Haven't I done well? One less stream of THS follow-up signals associated with speed change. Look - it KNOWS exactly where it should be for 1g at 230kts, 190kts, etc'

How would it know where the C of G was with a full plane load of passengers doing the Conga from the front to the back? (e.g. Last TriStar flight from Dublin)

It might be controlled by FBW - but it's still physically a conventional aircraft obeying the same aerodynamic laws as your Boeing.

BOAC

8th Jul 2011, 09:05

How would it know where the C of G was with a full plane load of passengers doing the Conga from the front to the back - we are talking datums, sir. If it don't know that, you are 'dead in the water' as they say.

Anyway, I'd like to move this thread back to a piloting perspective if you would all be patient?

This is what I understand (*? inserted where I am not sure, ? is a normal query). I refer to the point at which the Captain is roused from his bunk and re-enters the flight deck, and my puzzle lies with the fact that for the next *?3 minutes *? the attitude and flight profile of the a/c remains effectively *?unchanged*?

Let's start with the assumption that he arrives on the f/d with a possible sensory awareness of a climb and speed reduction. He *?sees a low or non-existent airspeed indication across the panels*? He *?sees 3 pitch attitudes of 15 degrees*?. He *? sees altimeters at 350 and a VS of 10,000fpm down*? He sees *?TOGA*?. He is otherwise 'untainted' by the excursion of the a/c in the preceding minutes. Why *?does he not recognise it is stalled*?. Does he? Is he then thrown completely off track by the resumption of the stall warning as 'recovery' begins to take effect (throttles to idle etc)? If so, does the *?rapidly unwinding altimeter and VS reading*? not prompt some further attempts?

There are many puzzles in this accident, this is another. NB I hope you all notice that 'software' and 'AB' are excluded from the above.

A33Zab

8th Jul 2011, 09:06

Quote:
Originally Posted by A33Zab
But I get the impression I failed..........

- yes, you did. By 'omitting' the vital part "This remark is given in the mentioned FCOM 3.....when a FCTL STAB CTL FAULT is present." which others have now posted you in fact 'raised more questions than you answered'.

Don't think so because the remark has nothing to do with the FCTL STAB CTL FAULT but with elevator authority to counteract a certain THS position.

I failed here:

I think you understand but for the ones which do not:
Pls don't consider the THS being locked ....

---

ask exactly what ADR info the FCPC gets.to 'compensate for speed.'

What do you need for speed calculation? These signals are fed into the FCPCs.
Input the accelerometer and rate information from ADIRU, weight and CG from FMGEC, SS input and you will have all ingredients to position the THS.

There are simply too may variables and too little 'beta testing' time

To little time?........Iron bird... 24-7?

IRON BIRD:
Since all aircraft systems are controlled from the flight deck, the Iron Bird requires a cockpit for its control, provided by three Airbus Fixed Based Simulators (FBS) along with a mobile visual system – which can be connected to either simulator.
From the flight deck, the Iron Bird can be flown like a standard aircraft, with a computer generating the aerodynamic model and such environmental conditions as air density, air temperature, airspeed and Mach number.

CONTINUED BENEFITS

The team of engineers and pilots who have worked many years with Airbus’ various Iron Birds have a rich backlog of experience, which is valuable when making testing technologies for the safety, efficiency and comfort of the company’s next jetliner products.
Airbus’ previous Iron Birds – which were utilised beginning with the milestone A300B2/B4 and A310 programmes, and followed by the A319/A320/A321, A330/A340 and A380 – are still operational. When called upon, they are used to replay scenarios with the actual hardware and software, providing insights on the situation or to try new enhancements before they are introduced as a modification on the aircraft type.
One such development is the study of electro-hydraulic actuators (EHAs), which could lead to a more-electric aircraft, and already have been tested both on the Iron Bird and in flight.

RetiredF4

8th Jul 2011, 09:18

BOAC
Your line "The FCPC gets ADR & IR information to The FCPC gets ADR & IR information to compensate for speed.." makes me again 'board the train' and ask exactly what ADR info the FCPC gets.to 'compensate for speed.'

Long time ago i asked a similar question and got no definite respose, therfore let me jump in again here.

When a pilot operates the stick in an aircraft where flight control deflection is not influenced by computers, he will do it by training and habit dependent on the aerodynamic state (TAS) of the aircraft. Going fast, small inputs and small onset rates, slower speeds greater input and maybe faster onset rates. In the F4 in approach configuration and speed the stick could be jerked around without causing any flightpath change, if you did it fast enough. At high mach we needed to be very sensitive with control input not do over g or even get an accellerated stall. The artificial feel produced by a separate pitot system and some weight (bellows and bobweight) helped us with that.

That said i´m not in the clear, on what data the FBW system is doing its job in that area, changing the output to the flightcontrols in relation to different TAS. As there is no artificial feel on the stick, there must be an implemented computer logic to modulate the input to the system to get the correct amount of deflection onset and total deflection in different TAS regimes. Where does this speed value come from or is the system using a logic not depending on speed?

BOAC

8th Jul 2011, 09:18

A33 - I cannot see any point in carrying on this direction since we seem to have a language issue and I do not speak 'anywhere'.

You said
"This remark is given in the mentioned FCOM 3.....when a FCTL STAB CTL FAULT is present."
Now you say
"Don't think so because the remark has nothing to do with the FCTL STAB CTL FAULT"??

As for "What do you need for speed calculation?" my point is I do NOT need a 'speed calculation' and nor should the THS.

rrat "No one would design a system like you seem to suggest with" - your confidence is most impressive. Does it extend to knowing that no-one would design a system to shut off the stall warning in flight whilst the a/c is still stalled?

rudderrudderrat

8th Jul 2011, 09:37

Hi BOAC,

we are talking datums, sir. If it don't know that, you are 'dead in the water' as they say.
It doesn't need to know the C of G. We need to prove the C of G is within limits for TO & Landing and to estimate the stab trim setting for take off.

When it's airborne, the FMGC will estimate the VLS using config, fuel distribution and previously entered ZFW C of G. However the FAC will display the real VLS using measured Angle of Attack.

Does it extend to knowing that no-one would design a system to shut off the stall warning in flight whilst the a/c is still stalled?
No - it certainly doesn't extend that far and there is no mention in FCOM either. With hindsight, I hope AB change that logic on the stall warning inhibit and include WoW, Radio Alt logic etc. instead.

With "Stall Stall" blaring at them as the Captain entered the Flight Deck at FL 350, I believe we would not be having this dialogue.

jcjeant

8th Jul 2011, 09:38

Hi,

rudderrudderrat
Because they didn't keep the ND input in for long enough.

They had not diagnosed their problem correctly, and attempted to arrest their ROD with NU side stick inputs. I'm in complete disagreement with your statement.
This is no need of long ND input fot change the THS deflection.
Any input (up or down) is followed (a response) by a movement of the THS ..up or down (in the flight law they were)
But the BEA note .. tell that the "THS remained in a full up position to the end of the event" ...

So despite nose down inputs ..

BEA again:
"At 2 h 12 min 02, the PF said "I don’t have any more indications", and the PNF said "we have no valid indications". At that moment, the thrust levers were in the IDLE detent and the engines’ N1’s were at 55%. Around fifteen seconds later, the PF made pitch-down inputs. In the following moments, the angle of attack decreased, the speeds became valid again and the stall warning sounded again."

So the aircraft was responding to the nose down inputs orders .. but the THS not !
It's something not right there !

rudderrudderrat

8th Jul 2011, 09:52

Hi jcjeant,

"After the autopilot disengagement:
„„the airplane climbed to 38,000 ft,
„„the stall warning was triggered and the airplane stalled,
„„the inputs made by the PF were mainly nose-up,
„„the descent lasted 3 min 30, during which the airplane remained stalled. The angle of
attack increased and remained above 35 degrees,
„„the engines were operating and always responded to crew commands."

They lowered the nose at some stage but then received the stall warning again. The report doesn't say that they continued to inject nose down inputs after that event. All it says is that they were mostly nose-up.

Do you think they were still pushing down hard at impact? The last recorded values were a pitch attitude of 16.2 degrees nose-up, a roll angle of
5.3 degrees left and a vertical speed of -10,912 ft/min.

A33Zab

8th Jul 2011, 09:53

As for "What do you need for speed calculation?" my point is I do NOT need a 'speed calculation' and nor should the THS

A330 apparently requires a speed signal.

Excuse me for not writing 'the perfectly english' which you only understand, next posts - if any - will be adressed to all but you. I can only write 'anywheres'.

PA 18 151

8th Jul 2011, 10:02

Re: Asking what would the the second thing to do after looking at AoA value when hearing STALL STALL.

Is this a trick question? :)

Nope :). So you have your AoA value, lets say it's Seven.

If that's the first thing you look at it must be key to the subsequent process that you plan to apply. So what do you do next? What is so important about the AoA number that the aircraft is telling you in your subsequent decision process. If you need to question the stall warning then why do you believe the actual AoA, it's coming from the same system....

Me, the first thing I'd look at is a horizon (an AoA indicator of sorts of course, but which also tells me whether my wings are level. Two birds with one stone....)

BOAC's attitude is interesting, a remarkable desire to blame the aircraft with zero evidence to go down that track. One wonders if this is relevant to this accident, the CVR should be key to working out the contributing factors, one wonders what else was said. Perhaps a "What's it doing now" ???

BOAC

8th Jul 2011, 10:10

a remarkable desire to blame the aircraft with zero evidence to go down that track. - just a million biased miles off track - avoiding CB's perhaps?

No-one ready to answer my poser with a serious response?

rudderrudderrat

8th Jul 2011, 10:28

Hi BOAC,
No-one ready to answer my poser with a serious response?
Amongst the 13,630 + posers you've made, which one is the serious one?

Chris Scott

8th Jul 2011, 10:31

In case anyone is getting the wrong impression, let me chip-in an important point to this THS discussion.

BOAC is focussed on discussing the THS as if it is used as a primary flight control. This is not the case on FBW Airbuses, just as it is not the case on an A300 or A310, or on B707 through B777. They are not like Gums's Viper, which uses the whole horizontal stabiliser (tailplane) as an elevator.

On all these jet transports, primary pitch control is provided by the elevator, as per DHC-1 Chipmunk or Cessna 150. On those aircraft, the pilot then adjusts a trim tab on the elevator itself, which provides an aerodynamic load to hold the elevator at the position the pilot wants. This position is reflected by the control stick.

On large jet transports, speeds, CG and high-lift devices are so much more variable that, on the approach, the elevator would be in a very high position. In other words, the primary control of pitch would be already near the limit of its travel. This is plainly unsatisfactory. The solution is to provide a secondary pitch control, in the form of the all-moving horizontal stabiliser, which trims the aircraft in pitch to enable the elevators to return to neutral. The control column will also return to neutral. On Airbuses, FBW or not, this is referred to as the THS.

When hand-flying an A310 or B767, the PF makes pitch commands with the control column. The elevators move. When the PF achieves the pitch effect he/she wants, he trims the THS to enable himself to relax pressure on the column. All jet transports have an autopilot (AP) which uses the same technique as the pilot. When it trims the THS, we call that auto-trim.

On a FBW Airbus, the AP works much the same, using auto-trim. When hand-flying, the PF does not need to trim the THS manually: the auto-trim does it. (Several American jets had a crude version of this 40 years ago, called control-wheel steering [CWS]). This only applies in Pitch-Normal and Pitch-Alternate laws. In Pitch-Direct law, the PF does his own THS-trimming.

AF447 left its cruise altitude in Pitch-Alternate law, and most of us think that this was retained for the rest of the flight (but lacking any high-AoA protections). The EFCS interpreted the PF's stick commands in pitch according to its C* terms of reference, applied the appropriate elevator when necessary, and then trimmed the THS to enable the elevators to return to neutral. The reason it trimmed the THS all the way to minus 13 degrees (13NU), was to avoid reaching full-travel UP on the elevators.

At any stage during that up-trimming process, or even after it, what would have happened if the PF had pushed the stick fully forward? The EFCS would have selected full down-elevator, and started trimming the THS in the nose-down-trim direction.