AF 447 Thread No. 5

[john_tullamarine]

To make things a little easier to navigate, we'll include a number of links to various spots in the complete thread.

For no reason other than it's a tidy number, we'll try and contain each part thread to around 1000 posts from now given that it is obvious that the thread is going to end up being of epic proportion.

Thread part -

(a) #1 starts here (http://www.pprune.org/tech-log/395105-af-447-search-resume.html#post5303737) and finishes here (http://www.pprune.org/tech-log/395105-af-447-search-resume-195.html#post6408432). Posts = 3890
(b) #2 starts here (http://www.pprune.org/tech-log/449639-af-447-search-resume-part2.html#post6408428) and finishes here (http://www.pprune.org/tech-log/449639-af-447-search-resume-part2-127.html#post6476460). Posts = 2537
(c) #3 starts here (http://www.pprune.org/tech-log/452836-af447-thread-no-3-a.html#post6476336) and finishes here (http://www.pprune.org/tech-log/452836-af447-thread-no-3-a-104.html#post6515428). Posts = 2071
(d) #4 starts here (http://www.pprune.org/tech-log/454653-af-447-thread-no-4-a.html#post6515515) and finishes here (http://www.pprune.org/6561320-post1061.html). Posts = 1061


Links to the various BEA reports are given below with additional links to the spot in the complete thread where the particular BEA report was issued. If I have missed any of the useful papers, please PM me with the URL and I can include it.

(a) BEA site - French (http://www.bea.aero/fr/index.php), English (http://www.bea.aero/en/index.php)
- Report link page - French (http://www.bea.aero/fr/enquetes/vol.af.447/vol.af.447.php), English (http://www.bea.aero/en/enquetes/flight.af.447/flight.af.447.php)

(b) Interim Report (No, 1) Jul 2, 2009 - English (http://www.bea.aero/docspa/2009/f-cp090601e1.en/pdf/f-cp090601e1.en.pdf)

(b) Interim Report No. 2 Dec 17, 2009 - English (http://www.bea.aero/docspa/2009/f-cp090601e2.en/pdf/f-cp090601e2.en.pdf)
- Update Dec 17, 2009 - French (http://www.bea.aero/fr/enquetes/vol.af.447/point.enquete.af447.17.12.2009.pdf), English (http://www.bea.aero/fr/enquetes/vol.af.447/update.on.the.investigation.af447.17.12.2009.en.pdf)

(c) Estimating the wreckage location Jun 30, 2010 (http://www.bea.aero/en/enquetes/flight.af.447/phase3.search.zone.determination.working.group.report.pdf)

(d) Wreckage search analysis Jan 20, 2011 (http://www.bea.aero/fr/enquetes/vol.af.447/metron.search.analysis.pdf)

(e) Briefing and associated update May 27, 2011
- Briefing (http://www.bea.aero/fr/enquetes/vol.af.447/info27mai2011.fr.php) - update French (http://www.bea.aero/fr/enquetes/vol.af.447/point.enquete.af447.27mai2011.fr.pdf)
- Briefing (http://www.bea.aero/fr/enquetes/vol.af.447/info27mai2011.en.php) - update English (http://www.bea.aero/fr/enquetes/vol.af.447/point.enquete.af447.27mai2011.en.pdf)
- Briefing (http://www.bea.aero/fr/enquetes/vol.af.447/info27mai2011.de.php) - update German (http://www.bea.aero/fr/enquetes/vol.af.447/point.enquete.af447.27mai2011.de.pdf)
- Briefing (http://www.bea.aero/fr/enquetes/vol.af.447/info27mai2011.br.php) - update Portugese (http://www.bea.aero/fr/enquetes/vol.af.447/point.enquete.af447.27mai2011.br.pdf)

(f) Third Interim Report July 2011 - French (http://www.bea.aero/docspa/2009/f-cp090601e3/pdf/f-cp090601e3.pdf), English (http://www.bea.aero/docspa/2009/f-cp090601e3.en/pdf/f-cp090601e3.en.pdf)


Miscellaneous pertinent links -

(a) Airbus Operations Golden Rules (http://www.airbus.com/fileadmin/media_gallery/files/safety_library_items/AirbusSafetyLib_-FLT_OPS-SOP-SEQ03.pdf)
(b) ALPA FBW Primer (http://cf.alpa.org/internet/alp/2000/febfbw.htm)
(c) C* and Civil Transports - Cranfield (https://dspace.lib.cranfield.ac.uk/bitstream/1826/186/2/coareport9303.pdf)
(d) Longitudinal Flight Control Design - RAeS (http://www.raes.org.uk/pdfs/2989.pdf)
(e) Longitudinal Stability: Effect of High Altitude and CG - Boeing (http://boeing.com/commercial/aeromagazine/aero_02/textonly/fo01txt.html)
(f) pitot static system performance - USN (Pax River) FTM (http://www.aviation.org.uk/docs/flighttest.navair.navy.milunrestricted-FTM108/c2.pdf)

Search hint: You can search PPRuNe threads with a filter in Google by using the following search string example -

ths af447 site:http://www.pprune.org/tech-log/

This will search for mentions of THS in the AF447 threads of tech log only.

Just change the THS in the string to whatever you want to look for. This allows one to search for any term or phrase of interest throughout the threads.

Adding the site:URL end part is the magic that restricts Google to only searching in Tech Log.

This filter technique is absolutely wonderful and can be used generically to find things of interest in PPRuNe - appears to work OK in the PPRuNe search function as well.

[BOAC]

Excellent work, thanks John - hope you wake up good looking:D

[PJ2]

John, first class moderator work, thank you. These threads are now a research tool as well as a "trace of the dialogue". The search tool created by a PPRuNe'r is especially appreciated.

(John, just getting up here on the west coast of N.A. (the 'beauty sleep' didn't work here...better luck!) and I would like to supply the following links to the first thread, (although the real first one (in R&N) got shut down almost immediately and is at http://www.pprune.org/rumours-news/375937-air-france-a330-200-missing.html. This first thread begins June 1, 2009 and ends on June 4 2009, is 952 posts long and ends at this posting, http://www.pprune.org/rumours-news/375937-air-france-a330-200-missing-47.html#post4974651.)

The "first" substantive thread, (really the second due the above), is 4598 posts long and was moved to Tech Log some time back and is here: http://www.pprune.org/tech-log/376433-af447.html. It begins June 4th 2009 and ends April 9th 2011.

The first post in that thread is at: http://www.pprune.org/tech-log/376433-af447.html#post4974708
Last post in that thread is at: http://www.pprune.org/tech-log/376433-af447-229.html#post6359812

For the archivists and historians among us! The thread contains some very prescient work.

[PJ2]

Reply to Chris Scott, from thread #4 (http://www.pprune.org/tech-log/454653-af-447-thread-no-4-a-53.html#post6561309):

Chris;
I don’t think much would happen to the THS during the initial rotation from level flight, as it would have required little up-elevator to enter the climb. Once the 7000ft/min had been achieved, the trajectory would be maintained by the EFCS even with no back-stick. As the speed started to drop, more up-elevator would need to be introduced by the EFCS to maintain 1g, and it would then start to trim the THS a bit to retain full elevator authority. Once the aircraft got on to the back end of the drag curve, however, this process would proceed rapidly.
Your previous post on the THS on thread #4, here (http://www.pprune.org/tech-log/454653-af-447-thread-no-4-a-50.html#post6559268), explains the THS operation very well and this one connects that explanation with how the THS likely functioned with AF 447. I think its a reasonable explanation of what occurred to the THS and how, after the initial pitch-up.

[Diversification]

Hi All!

This thread has been most interesting to me. Especially on points where the opinions among "experts" differ.
I am still surprised by the fact that BEA gave no hints in the short list explaning where the various ACARS were coming from. One of the last was about faults in Prim 1 and Sec 1, which were earlier assumed to be either showing serious faults of caused by pilot shut-downs of these systems.
Very often it has been assumed in this thread that there was 5 computers involved on AF447, however each of the three ADIRUs also contain at least one each and perhaps also one in each of the Air Data Modules. I am making this conclusion from the australian report about sporadic AoA signals, where it is stated a software update for the ADIRU uncovered an old bug.
I am also thinking about a fixation of the pilots on a single phenomenon as part of the causes, somewhat similar to TMI-II operators failed behaviour.

Regards

[hetfield]

Sorry,
but I lost track.

Concerning the "zoom climb", could have A/P and/ or pilots received an "overspeed condition", which in turn traded speed to height, according relevant law?

[ChristiaanJ]

John T,
Not sure a No.5 link is really the answer....

Unfortunately this is just a forum... without a way to index the various posts into categories like "THS", "Pitots", "Software", "SideStick", "FDR", etc. which would make them easier to "exploit".

Personally just looking forward to the next BEA report... and the way that will put the fox among the chickens, once again.

[takata]

Hi Diversification,

I am still surprised by the fact that BEA gave no hints in the short list explaning where the various ACARS were coming from.
Please, read again BEA interim reports 1 & 2 and specific ACARS chapters. Those reports, including the last note, are all completing each others and what could be explained with all informations on hand at the time each report was printed... was explained.
ACARS is designed for aircraft maintenance, not for aircrash investigations. Hence, some informations in ACARS sequence can not be acertained without access to other sources (CVR, DFDR, or by recovering avionics memories). Nonetheless, at this point, most is already explained or very narrowly conscripted.
What is much more disturbing on the subject is in fact this thread's noise/information ratio around some of the ACARS already explained from day 1 (see Bearfoil's posts still denying pitot and subsequent airspeed issues and consequences on flight systems!).

One of the last was about faults in Prim 1 and Sec 1, which were earlier assumed to be either showing serious faults of caused by pilot shut-downs of these systems.
PRIM 1 and SEC 1 ACARS are only ECAM messages (cockpit effects). There was no "fault" correlated with them that was sent by ACARS.
It could be due either to simple manual reset, or an auto-reset if some fault was detected, by its built-in test equipment (BITE); a single function affected may do that. There is no way to know more without looking into other system memories. If it was due to a manual reset, the CVR won't tell anything if nobody was talking about reseting the PRIM/SEC... The seriousness of this fault is quite improbable as there is 2 other PRIMs and another SEC.

Very often it has been assumed in this thread that there was 5 computers involved on AF447
There is effectively five Flight_Control_Computers": PRIM 1, 2, 3 + SEC 1 & 2. They very specific task is to manage pitch, roll, yaw, etc. depending on the various Flight Control Laws, which depend on other imputs (like Air Data, Inertial References, etc.)

however each of the three ADIRUs also contain at least one each and perhaps also one in each of the Air Data Modules.
Most avionic part of the system may be considered as a "computer". But they are very dedicated "computers" performing some straitforward tasks: ie. An ADM (Air Data Module) task is to digitalise the pneumatic source of a sensor for an ADR unit ; the ADR (Air Data Reference) role is simply to compute the various functions derived from those sensors (Speed, Mach, AoA, barometric altitude) for other "computers" like the FMGC, FADEC, PRIM, SEC, FWC...

I am making this conclusion from the australian report about sporadic AoA signals, where it is stated a software update for the ADIRU uncovered an old bug.
I have read the same report and the conclusion was that no "bug" was found on this ADIRU. Nonetheless, something went wrong, twice, with the same unit, but they did not found what it was. AoA spikes filtering was suspected but they could not reproduce it into the lab. Hence, what could have caused it? Was it internal or external? In fact, nobody knows.

[Mr Optimistic]

At 2 h 10 min 51.......Around fifteen seconds later...........altitude reached its maximum of about 38,000 ft, its pitch attitude and angle of attack being 16 degrees

The recordings stopped at 2 h 14 min 28.

The last recorded values were a pitch attitude of 16.2 degrees nose-up.

So from 10:51 +0:15=11:05 to 14:28, ie 3 minutes +, all the efforts of the crew seem to have had no net effect on NU, but the heading changed. Is this plausible ?

[HazelNuts39]

Diversification;

Just to add another observation to takata's post - at 2h13min the aircraft was descending through FL175, deeply stalled, making uncontrollable roll oscillations left/right.

A similar temporary 'computing' condition may have occurred during the uncommanded pitch-down of QF72 - from the ATSB interim report on QF72: In summary, the PRIM PITCH FAULTs and PRIM 3 FAULTs that occurred during the flight were consistent with the system design. They were consequences of the pitch-down events and not the initiators of those events.

[HazelNuts39]

So from 10:51 +0:15=11:05 to 14:28, ie 3 minutes +, all the efforts of the crew seem to have had no net effect on NU, but the heading changed. Is this plausible ?Based on the released information on the crew actions, it is entirely plausible. The great mystery is why the crew did not take decisive action to unstall the airplane. According to BEA's "3d" depiction of the flight path, the heading changed after point 6, when the airplane descended through FL350 at around 2:11:40. No further information on the heading change is available in the Update. I think the explanation must be sought in the difficulty of controlling the bank angle in a deep stall.

[Mr Optimistic]

Yes, I understand. But I struggle with it. The clearest interpretaion is that the crew sat for 3 minutes asking for NU and the a/c held its stalled attitude more or less constant through the descent for all those minutes. There are some who may wish to argue that the crew in fact wanted ND but the 'system' frustrated their attempt, but I see no evidence for that intent or that obstruction. Could it be that they just gave up ?

Edit: perhaps as an SLF I should wind my neck in, as they say, but the upshot is the a/c was stalled - clearly and obviously to the a/c systems- but it failed to convey that one vital piece of information to the crew despite all its cleverness and left them guessing for 3 minutes of descent in the turbulent darkness.

[john_tullamarine]

without a way to index the various posts into categories like "THS", "Pitots", "Software", "SideStick", "FDR", etc. which would make them easier to "exploit".

I have yet to figure out an easy way to do this. However, the filtered search query will do just this for a given term - not quite as convenient but achieves the aim.

[bearfoil]

Mr. O

Clearly, BEA believe that what they have witheld holds no danger in current A330 flights, or there would be mitigation; it would be difficult to hide any substantive change to the control system or airframe.

They allowed Airbus to make a statement, and one believes its accuracy, for it will harm the builder greatly if they are found to tell lies. BEA have no duty to "correct" public speculation, for they are comfortable that the information they provided is sound, and no corporate or gvernmental harm lurks.

It is not entirely wise to label what they have done as damage control. Typically, history teaches us that bad news is less disruptive if it is released slowly, and the public has the time both to soften, and go on to other things, (forget).

From the timetable itself, the a/c was in Alternate Law as she climbed. This provides no protection for Roll limiting, but includes AoA protection and direct control for both roll and pitch, aiui.

Right along with doubts about the climb whilst the PF is represented as commanding it, one must suitably indict the a/c for trimming for maximum Pitch UP. What was he THINKING.......

What was she DOING? Certification is mainly a mystery to me; I trust the system to certify a/c to be safe and reliable.

One understands the need for emphatic NU at TO and landing, but in the arena 447 found herself, why doesn't the THS have a LAW LOCK on it similar to the RTLU?

Your question is not so mysterious to me, The PF held back stick because he thought it the correct play. At 10k, his pard thought otherwise, and overrode the PF. "Your Airplane".

The Fourth ACT awaits us later this month?


EDIT. For Mr. O. The a/c systems did NOT know the a/c was stalled, no one did, Why would it protect itself from goofy feet (RTL), and let the Powered slab in back demolish everyone?

Trim is for comfort, when I learned how to use it. Giving any control surface the power to doom the a/c is so............unlike AirBus.

"She did everything asked of her....." Reminds me of what they said post Perpignan.......

[Mr Optimistic]

Bear, all I can say is that they have my blessing: they were intelligent, trained and wanted to get home.

[bearfoil]

It is so reassuring to hear you say that, it is in short supply here.

best wishes.

[Mr Optimistic]

Yes, but my sympathy can't help them. If they did the wrong thing I would be reluctant to hold it to their account with so much software, and so many 'protections', standing guard over them.

[bearfoil]

"Protections".

The nugget at the core of the Grand discussion. Keep in mind the Protections are to protect the a/c.

Loss of Autopilot in this fbw a/c is not an everyday or mundane thing. It should not be dangerous, and likely was not in this case.

From even the few scraps we were thrown with BEA's note, the first inputs by PF post a/p drop seem innocent enough. They morphed into ever more serious states of flight in very few seconds.

The AB flies "different" out of automatic, not fundamentally, though, and as I see it, the challenge is mounting the horse in full stride with gentle hands. Would this accident have happened if THS "TRIM" was disabled? Doesn't a certified a/c have to demonstrate recovery without trim? What in the World is so much control authority doing in STALL recovery? So much authority that the a/c cannot recover......it says so in the FCOM!!

Simplistically, why does this a/c have anything in addition to NORMAL LAW except bowing out gracefully to let the boys and girls fly it?

Such a needy, dependent, and conflicted aircraft is this one. Has a hard time "Letting Go". Or was it those who programmed her who can't give it up. Control Freaks?

[Graybeard]

HN39: Agreed, and everybody seems to think of the pitots misreading at high AoA, forgetting that airspeed is derived from the difference between two pressures: pitot and static. Sometime ago someone posted a drawing showing the static ports on the bottom of the front fuselage. At these AoA's the misreading of the static pressures may be more important than that of the pitot pressures. EDIT:: Particularly when "The airplane was subject to roll oscillations that sometimes reached 40 degrees" (Thx to an anonymous reader of the thread).

Thanks also to A337 for the refresher pix of the static ports.

The A330 has an apparent up to 300 ft static port correction at low airspeeds. This is not unusual, but at a greater AOA than stall warning, the static pressure is sure to increase to the point the static ports nearly become pitot ports.

Rather than, "What's it doing now?", the more I read the more I question, Why did they design it that way?"

[Mr Optimistic]

Well there is the question as to why the crew commanded a climb when 'pitch and power' was what was needed, unless you contend this wasn't wanted. UAS alone shouldn't have caused this loss.

[bearfoil]

Mr Optimistic.

They commanded a climb because it was proper to do, at the time, airspeeds were fine. They noted "ALTERNATE LAW" eleven seconds AFTER the a/p quit. BEA haven't said where the THS was positioned at loss of a/p. They do say, however, that the a/c was slow to respond to PF's climb input. "At PITCH +10, the a/c began to climb." If the climb had established at AL snatch, what is the protocol for LAW change?

I do NOT believe the PF intended a climb rate at 7kfpm. Nor do I think he wanted necessarily to climb. He pulled back because what he saw and took in told him a roll left and NU was indicated......let's give them that.

At that point, the 340 zoom might or might not be instructive.

Bottom Line? My feeling is that if at a/p drop and then UAS the pilots were expecting, and given Direct Law, there would be no need to be cautious with the stick, to worry about Protections (or depend on them, falsely).

STALLSTALL at his initial pull? Probably a chirp due his unfamiliarity with the a/c response to his hand, and if he relaxed it, (I think he must have) this was the cause of the a/c lagging in climb response.

[syseng68k]

Greybeard, #18

The A330 has an apparent up to 300 ft static port correction at low airspeeds. This is not unusual, but at a greater AOA than stall warning, the static pressure is sure to increase to the point the static ports nearly become pitot ports.
Interesting point, The higher static pressure would be translated to a decrease in altitude on the display.

However, if the a/c were stalled, the alt would have been unwinding
pretty fast anyway...

[BOAC]

They commanded a climb because it was proper to do, - can you support that statement of fact? I would suggest, that having discussed their 'inability' to climb due to the thermal structures of the atmosphere it would have been quite 'improper'?

[GarageYears]

BOAC +1 ^ :D

How was a "climb" the *proper* thing to do? At all?

Please educate me... given the situation (UAS) surely we ALL agree the proper thing to do is "more or less nothing" (stabilize the aircraft, fly pitch and power, figure out what is going on in a methodical structured manner).

[bearfoil]

Garage Years and BOAC'

My bad. "climb". "proper". I should have included the quotes, or parents.

The PF at a/p drop ("I have the controls"), Input back pressure.

BEA does not use "climb", nor should I. They state "INPUT".

We do not know the state (assiete) of the airframe at a/p quit, only that it was followed by PF's control ip.

"The a/c at PITCH UP of ten degrees, began to climb."

Did the pilots know at drop they were in UAS? NO. PNF states eleven seconds later, "So we have lost the Speeds, .....ALTERNATE LAW".

We can conclude PNF is reminding PF, or we can conclude he is stating something that has just been noticed.

We can also say that PF may have been trying to capture PITCH and POWER with his movements.

If the a/c had dropped ND a bit, and rolled right a bit in turb, he could have been establishing S/L then intending to P/P.

Remember, the a/c was in weather of some description, if PF had sussed immediately UAS, his first order was to regain S/L. P/P may have been needing an input of Left, NU. He may have been waiting to set N1, until after S/L was attained. Can't do everything at once.

I don't accept that PF ("I have the controls") started hand flying with an utter misunderstanding of the situation. I think his initial assessment was of loss of A/P and then A/T, things happen fast when the wheels are coming off.

My post was not meant to confuse; instead, I think I fell to what is present here, assumptions of events by mutation and groupthink reinforcement.



edit; Anticipating a release in some weeks, I am personally trying to prepare for more data. To start with, there is an embarrassing dearth of evidence to claim anything with confidence.

I still have on open mind, I think stasis in the findings will surprise, and favor a rather standard accident: Too many unusual and unanticipated events happen too quickly, and the a/c and pilot cease a mutually beneficial and safe rapprochement.

No virgins left at the end.

[bearfoil]

Deep bow, cap off.

Big fan of the F27.

[ChristiaanJ]

I do have the impression that too many people here are 'parsing' all the 'subtleties' of the English-language translation of the BEA report, trying to 'tease out' information which isn't really there, and isn't there in the original French either.

Being an ancient, and lazy by nature, I haven't bothered yet to put the French and English versions next to each other, except to solve a couple of obvious misunderstandings...

I expect the same thing to happen when the next mid/end July BEA Interim Report is coming out.

As an engineer, I would like to see all the FDR traces - and it's unlikely they will all be put into the report, leave alone on the net....

The CVR might help with a few clues, but I'm not putting the same degree of reliance on it, that some people here seem to do.
"Oh, merde" may be perfectly obvious to the pilots in the cockpit, with one pointing to something visible to all, but no longer comprehensible to those trying to reconstitute the happenings up there, more than two years later.....

Give those people at BEA a chance, and try not to attempt to outguess them too much.

[bearfoil]

ChristiaanJ

I agree. The essential outcome of this two year ordeal could have been solved (and explained) with the discovery of the Boxes. Witholding data that is in and of itself innocent of bias is traditional, and creates a stage for politics and corporate competition. Except for ass covering and proprietary damage control, I fail to see the need for endless time given to "the Report".

Perpignan, and Habsheim have the stink of controversy yet, as does AA587. The offered report is puffed up and sold as the Truth. The saving grace here, with AF447, is a new vector, extensive and passionate commentary in a very wide audience.

In the last, and for not nefarious purpose, this "Investigative Process" has served to smooth the certain impacts on the commerce that would happen with instant access to the vulnerability of Air Travel to disaster.

Ignorance can be bliss, it can also augment the bottom line.

[KBPsen]

...trying to 'tease out' information which isn't really there...You mean like attributing made up quotes to the BEA such as
"The aircraft, at 10 degrees Pitch up, finally began to climb." Or
"At PITCH +10, the a/c began to climb."Or continually making wrong statements about the control laws such as
...the a/c was in Alternate Law... This provides no protection for Roll limiting, but includes AoA protection and direct control for both roll and pitch.Or just making stuff up such as
So much authority that the a/c cannot recover......it says so in the FCOM!!Or is it just the general smothering of posts with generalities and ambiguities at a level that normally isn't found outside of the horoscope section of a woman's magazine?

[bearfoil]

Please continue, but can you back up some of your nay saying?

Start with ALTERNATE LAW?

[HazelNuts39]

They do say, however, that the a/c was slow to respond to PF's climb input. "At PITCH +10, the a/c began to climb."They didn't quite say that, but it may be a literal interpretation of what they wrote in the Update. I have a slightly different interpretation that I would like to throw up for debate. As I read it, one investigator has listened to the CVR and notes the words spoken at 2:10:16 and 2:10:50. Another investigator has studied the DFDR data and gives an account of various observations he has made between 2:10:05 and 2:10:51. He places those observations in a 'logical' order, more or less but not necessarily exactly in the correct time-sequence. For example: The PF made nose-down control inputs and alternately left and right roll inputs. The vertical speed, which had reached 7,000 ft/min, dropped to 700 ft/min and the roll varied between 12 degrees right and 10 degrees left. Was the nose-down input before or after V/S reached 7,000 ft/min? The reason I'm raising this is not that sentence, but the preceding one: The airplane’s pitch attitude increased progressively beyond 10 degrees and the plane started to climb.I don't believe these two events occurred in that sequence. If they had, the airplane would be in level flight with pitch at 10 degrees and therefore AoA 10 degrees. At M=0.8 stall warning begins at 4.2 degrees, alpha-max is 5.25 degrees, and the airplane stalls at about 8 degrees. Furthermore, pitch angle does not jump instantaneously from the initial 2.5 degrees to 10 degrees. As soon as pitch angle starts to increase 'progressively', AoA and hence lift increases also, and the airplane starts to climb (give or take small g-variations due to 'chop'). Just can't wait for the real DFDR traces to look for myself ...

[bearfoil]

Obviously, and especially after reading your last, I am struggling mightily to get a handle on the initial events. You say it so well, and I am ironically satisfied that anyone would single out my struggle for flame.

At some point after origination of PITCH UP, (not the command, the actual), the a/c "began to climb". Does this indicate a gaining of altitude, or arrival at, or transition through, sufficient AoA to enable altitude increase? It enters into question the lack of STALL wrn, but, due Cavalry Charge and MASTER CAUTION, (A/P loss), was a STALLSTALL missed? Logically no, for BEA say the WARNING was "two" in number. implying a cessation of the original WARN at PF's first inputs?

(HN39. Is it at all possible that PF's Right and Left roll commands were in pursuit of an angle steep enough to cause the Nose to fall? It seems too early for such a "desperate step"?)

[grity]

Thanks also to A337 for the refresher pix of the static ports.

The A330 has an apparent up to 300 ft static port correction at low airspeeds. This is not unusual, but at a greater AOA than stall warning, the static pressure is sure to increase to the point the static ports nearly become pitot ports.

Rather than, "What's it doing now?", the more I read the more I question, Why did they design it that way?" http://walter.bislins.ch/aviatik/media/Verteilung%20des%20statischen%20Drucks.jpg
the place of the pitots is even sensible, the "static" pressure is not constant over the different places of the fuselage.....the selected place for the pitot is the first place with a static pressure near zero for "normal flight" .....up front is the static pressure higher, behind he is lower, this place is a very good place because the different between the mesured static- and the pitot-pressure shows(indicates) good the airspeed,

with higher AoA the pressure in the static port will get up, (and the correction for the speed) with higher AoA s converted into very difficult.....or impossible

but this is also a chance for an alternativ speed indicating system.....the fuselage itself works like an half-pitot probe...the flow accelerates at the side of the fuselage, and with the different static presure between to different points over the front of the fuselage it must be possible to indicate the speed without a pitot probe!, and the static probe will be not so delicate against ice or ash or insects like a pitot-probe.....

[hetfield]

Sorry to say,

PEANUTS.

[bearfoil]

grity

In a similar discussion earlier, a combination Pitot/Static was suggested in the form of a "Tympanum", a membrane that resembles the skin of a drumhead, flexible, but impervious to water, Ice, or Hornet Nest. The Statics would be arranged about the perimeter, where least deflection of the membrane, and the "Pitot" portion would read at the center, where deflection is greatest. It would take a computer to weight the deltaP by geography, but it is feasible.

[HazelNuts39]

Is it at all possible that PF's Right and Left roll commands were in pursuit of an angle steep enough to cause the Nose to fall? It seems too early for such a "desperate step"?I think you answered your question. At that point there wasn't any need for a "desperate step". If they'd wanted the "Nose to fall" they'd pushed the stick forward not pulled back, wouldn't they?

[bearfoil]

HazelNuts39

I think you are correct, it seems too early. We do not know the situation the PF found himself in. I myself cannot eliminate some form of counter-intuitive aspect of the a/c that baffled the PF's experience and actions.

I cannot accept that the a/c was performing "as designed" whilst the Pilot initiates a radical climb into altitudes that were previously rejected by consensus, a climb that saw 7kfpm, and roll oscillations of plus/minus 12 degrees.

It is possible that all prompts, or most, were not to be trusted (whether they were or not is not relevant),

From a position of balance, given PF's level of skill (high), and the a/c's track record, (impeccable), the two were at odds almost from the outset.

I think the answer will be found in the twenty seconds that bracket the loss of the autopilot.

thanks for your comments, it is an honor to be in conversation with you.

[Machinbird]

I've been thinking about where BEA is likely to be going in their investigations of the human factors aspect of this accident.

I suspect the words 'cognitive fixation' will factor significantly into their report. (In French of course.:})

In the course of reading up on the subject, I found that there are some simulation tools for predicting this type of problem and quantifying it.
Here is a 6 year old paper on aviation related work in this direction.
http://www.humanfactors.illinois.edu/Reports&PapersPDFs/humfac05/foyhoobyrcordeulebleiwic.pdf
Now if they were to take this set of models and apply it to the piloting tasks faced by the crew of AF447 that night there might be some clarity to the perplexing question of how they let the aircraft get away from them.

Of course with the CVR, DFDR and possibly ?? the high resolution recorder yielding information, that may be overkill. I think we have teased all the information from the initial BEA note that can be extracted at this point.

[ChristiaanJ]

ChristiaanJ
I agree. The essential outcome of this two year ordeal could have been solved (and explained) with the discovery of the Boxes.Judging by your comments, I take it you've never been involved in an accident investigation, nor have been involved in 'reading' and fully interpreting an FDR recordng. Witholding data that is in and of itself innocent of bias is traditional, and creates a stage for politics and corporate competition. Except for ass covering and proprietary damage control, I fail to see the need for endless time given to "the Report". The bias is all yours, I'm afraid....
Perpignan, and Habsheim have the stink of controversy yet...Perpignan doesn't (company pilots playing "test-pilot" at low altitude without really seriously knowing what they let themselves in for).
Neither does Habsheim which had a pilot with no serious knowledge of the aircraft, getting himself somewhere in the envelope where he shouldn't have been, while switching off some of the systems, then blaming the aircraft and the systems, rather than his own incompetence.
Me262 and Meteor pilots were well aware, that a jet engine at idle needs time to 'spool up'. this jerk obviously didn't....

[infrequentflyer789]

Right along with doubts about the climb whilst the PF is represented as commanding it, one must suitably indict the a/c for trimming for maximum Pitch UP. What was he THINKING.......

What was she DOING? Certification is mainly a mystery to me; I trust the system to certify a/c to be safe and reliable.

One understands the need for emphatic NU at TO and landing, but in the arena 447 found herself, why doesn't the THS have a LAW LOCK on it similar to the RTLU?


Curious, what would that achieve exactly ? Based on the info we have (and see the helpful timelines previously posted by others) elevator authority alone was sufficient to get 16deg pitch up and fully stalled. THS simply relieved the elevators.

Had THS not moved, and elevators held 16deg nose up instead, what benefit results ? Only (as far as I can see) perhaps quicker recovery - but THS trims for neutral elevator, so they should, and it appears did, still work if ND is attempted. Unless of course we are into deep stall situation (I would say we don't know if that was the case yet), but in that case THS position quite possibly doesn't matter.

It seems that what you really want is more an attitude-protection law - 10deg pitch up in cruise is silly so sorry dave I can't do that.

But we already have that, in a better way, with AOA & speed protections, but these are lost here - because the planes sensors (or at least some of them) are lying and it doesn't know what is happening with sufficient confidence to apply protections.

Should AOA protections degrade to attitude protections of some sort ? More laws / sub-laws ? More variables combinations to learn and find time to actually be trained on. Does that really help ?

[bearfoil]

infrequentflyer789

Thanks for your response. Help me to understand how "relieving the elevators" does not acquire a massive amount of PITCH Authority in one or the other direction? The HS is acting as a lever to "neutralize" the effort required to deflect the elevators, ever producing more baseline AOI. Angle of Incidence in this sense is an artificial "neutrality". The FCOM alerts the operator to the THS preventing some PITCH authority above 180 knots? How is this alert benign to the efforts of PF447 recovering the a/c?

Yes, I think elevators alone would have been preferred. Once above a certain angle, and at >180 knots, with All Trim Fuel aft, recovering seems a tall challenge? In this sense, the elevators are "Trim Tabs", ineffectual at "boosting" the control surface (THS), to allow maneuvering. Instead, they have a range of effect that traps the a/c in fluctuating PITCH excursions. Neither direction is satisfying, to the extent that AoA is "never below" 30 degrees (BEA).

Not even Flare should top 17 degrees, yet here the a/c is at "cruise" and 16 degrees! Do we set out to castigate the pilot ("Je ne comprends rien").
Do we attack the machine? Why do either? The a/c in some way got away from her pilot. Some random misfortune is trying to tell us something. To the extent we make up our minds, we lose the opportunity to learn.

As an aside, you say "Elevators alone were sufficient to get her to 16 degrees and fully STALLED." In ALTERNATE LAW, isn't the airframe protected from such a thing?

[Graybeard]

grity: the place of the pitots is even sensible, the "static" pressure is not constant over the different places of the fuselage.....the selected place for the pitot is the first place with a static pressure near zero for "normal flight" .....up front is the static pressure higher, behind he is lower, this place is a very good place because the different between the mesured static- and the pitot-pressure shows(indicates) good the airspeed,

with higher AoA the pressure in the static port will get up, (and the correction for the speed) with higher AoA s converted into very difficult.....or impossible

Interesting graph, Grity; thanks.

I should have explained that my surprise was not at the fore-aft placement of the static ports on the A330, but their placement so low on the fuselage, maybe only 30-40 degrees off vertical centerline.

By comparison, the DC-10 static ports are at least 60 degrees off the vertical. FWIW, they are also about 47 feet aft of the nose, beneath the mid-cabin doors. The low speed static correction is less than the 300 feet of the A330; more like 240 feet, IIRC.

Also noteworthy is the lack of an airspeed input to the Stall Warning on the DC-10. It is based on AOA sensor, modified by flap discretes.

[PJ2]

CJ;
I do have the impression that too many people here are 'parsing' all the 'subtleties' of the English-language translation of the BEA report, trying to 'tease out' information which isn't really there, and isn't there in the original French either.
FWIW, I agree CJ - it is a mistake to read too much into each word in an attempt to squeeze this or that interpretation, (ours!), from it. Finding agreement when far more is known is going to be equally difficult as well.


Interesting post and link Machinbird, thank you. I don't disagree that a form of cognitive overload may have occurred. In keeping with this discussion, I would like to broach a human factors aspect about which thus far nothing has been noted or asked. The observation concerns SOPs, CRM and cockpit discipline in the handling of this event.

The creation, implementation, training and checking of SOPs, CRM processes and their outcomes, cockpit discipline, are intended to avoid or delay cognitive overload, or cognitive dissonance.

While cockpit design, cockpit displays, ergonomics, and aircraft/system drill and checklist design will influence outcomes, a "Standard" way of accomplishing complex tasks under both time and operational pressures reduces the potential for error. I know very well that it doesn't always work that way despite best efforts.

I would like to preface this observation by stating that this is not just about "the crew", but it is a question which will arise in every airline pilot's mind because SOPs, CRM and cockpit discipline are heavily emphasized in recurrent training and line checking.

This is not about finding blame because that is not what the investigative process is about. The investigative process is about "finding things out" and must be free to ask all questions regardless of how uncomfortable they may be. In other words, the investigative process is unlike ordinary discussion in that when a question is asked, it does not imply anything other than a need to know.

So asking a question about training does not imply that "training is under suspicion" nor does asking questions about the crew's actions imply that such are under "special scrutiny".

I would like that distinction to be as clear as possible. This has nothing to do with complementing or criticizing the crew. The notions of "defending the crew" or "criticizing the crew" don't apply in the investigative discourse. Criticizing or defending the aircraft may have a place in other venues and so may such an examination of the crew have a place, but that would be a legal, political, economic discourse, not the investigative discourse.

I make this distinction partly for the reason CJ posted his comments on parsing language - the same words will mean different things, depending upon the discourse. "Investigate" means different things in politics and law than it does in safety work.

That said...

The question of SOPs and standard responses to abnormalities arises out of the almost-immediate response just after 02:10:05 by the PF to the autopilot and autothrust disconnect and the ECAM messages. We know that the BEA Update states that almost immediately there was a left and nose-up SS input and pitch increased beyond 10 degrees.

Abnormal and Emergency SOPs are created and trained to:

a) ensure control of the aircraft is firmly in hand and that stable flight was being maintained and to ensure the flight path (track and altitude) was being maintained as needed;

b) ensure that all crew members on deck were alerted to the problem, and to who was in control of the aircraft and who was to execute drills and/or checklists - ATC would be notified when there was time;

c) ensure that all crew actions are predictable and understood by all cockpit crew members and to avoid "individual variations" leading to unexpected responses and confusion.

This is the standard Aviate, Navigate, Communicate rule that we have seen mentioned.

In terms of CRM and responding to abnormals and emergencies, no action, no drills, no checklists are started until the aircraft is under control and stable.

Most of the time that is a quick assessment and emergency drills are done without delay. For an abnormal such as this one, there is no hurry. The airplane was stable before the event and other than minor variations perhaps due to turbulence, would continue that way in the absence of input.

The pilot flying always initiates a drill or checklist by announcing the drill being executed or the requesting the appropriate checklist. This communication alerts everyone in the cockpit (usually just the two), to what is coming next and to prepare for response, as trained.

If a memorized drill (such as the Rapid Depressurization, Emergency Descent), the PNF monitors the drill for accuracy and correctness while the PF flies the manoeuver and where necessary calls out any deviations. If required (in a EGPWS manoeuvre for example or Stall Recovery), the PNF may call out primary parameters such as pitch, altitude, speed, rate of climb and so on. Here, such feedback would be of critical importance to help avoid "tunnel vision" and increase situational awareness for both crew members, and to help the PF who would be concentrating on flying the aircraft with a possibly-reduced scan.

As I have said, this wasn't an emergency such as a depressurization, an engine failure or fire or a GPWS event which requires timely, immediate action but it did have two memory components to the drill, (as shown in the BEA Interim Report #1), before the UAS QRH Checklist was to be called for. I have discussed this memorized drill and checklist a number of times on previous threads.

The next step in the SOPs for handling an abnormal is to execute and clear the ECAM messages. There are SOPs for this process. Once clearing all the ECAM messages is accomplished, the STATUS page is checked for equipment and capability lost. The ECAM is then cleared. Then, if still necessary, the "paper" checklist, (QRH) is called for by the PF and brought out by the PNF and referenced. Usually the QRH checklist most commonly used are the Landing Config/Approach Spd/Landing Distance Following Failures and Landing Distance Without Autobrake CONF 3 or CONFIG FULL checklists. These kinds of items might be delayed until closer to destination - I'm just using this as one example.

When all ECAM actions and Status reviews are complete and when the required QRH checklists are completed and when the aircraft is considered secured the process of communicating to ATC any problems with capability in terms of maintaining flight and navigation, then communicating with the Flight Attendants, then, where necessary, the company. Any diversions, changes in altitudes are considered at this time.

This is one example of how it's done and there will be variatons, slightly different priorities and more or less memorization of drills depending upon the airline.

The key point here is, this process must be thoroughly trained and checked during recurrent simulator and line checks. SOPs, CRM and cockpit discipline are for those times when things start come unglued in a hurry. The training focuses one and gives a structure to the inevitable initial chaos which can unfold rapidly as we have seen here; - at 02:08 they were talking about deviating to the left of course, and just over six minutes later they were gone.

The question of SOPs goes beyond the crew and must be asked "upstream" of just this crew. What support for these areas was there and how robustly was it carried out?

A more complete update from the BEA will hopefully shed some light on this aspect of this accident because it may be related to the reason for the pitch-up and stall.

The "Airbus Golden Rules (http://www.airbus.com/fileadmin/media_gallery/files/safety_library_items/AirbusSafetyLib_-FLT_OPS-SOP-SEQ03.pdf)" came out a very long time ago - around 1998 IIRC. The later 2004 document discusses the above process in greater detail and is well worth examining.

[Turbine D]

Hi Bear,

See you are back and posting once again. There was a very interesting post awhile back on the other AF447 thread in R&N. Take a look at it, would like your thoughts. You can find it at: Post #1222, Pg.62 by The Shadow.

I would sure like to know what was happening in the two minutes or so before AP/AT disconnect. If the pitots were beginning to clog, what was the autos doing to adjust for sensing slower speed that really wasn't slower.

[bearfoil]

Hi TD!

I've read the shadow, and more than once. As to a gradual packing up of the Pitots (and three apace), the a/c would trim ND/NU with ThrottleUp and/or THS/N/U/D. This would satisfy the computer, and completely bollox up the actuals. At some stage, and not necessarily due ICE, the a/p would quit (cannot hold 'Altitude'), or for any of a number of easily understood reasons. If so, and prior to "Disagree", the a/c may simply handover the goods and continue in NORMAL LAW. If agreement then degraded to the extent of AD needing "Timeouts", there is a separate kettle of fish, eh? That is UAS, certainly, but as a follow on, not as a priori. I am not sure if this mode is represented in the prior incidents of UAS, but I also do not know if our crew had experienced an actual UAS of the garden variety either.

I am amazed that so distinguished a group as this one hasn't thought the PF was indeed acting on bad data (not his "fault"), and was doomed to a guessing game either way, No?

nice to meet up again, my friend.


Can we call this mode: "Triply redundant bogus airspeed, but who knew?"

TRBA/bwk........

[PJ2]

bearfoil;
I am amazed that so distinguished a group as this one hasn't thought the PF was indeed acting on bad data (not his "fault"), and was doomed to a guessing game either way, No?Where is the guessing game here? It was an airspeed indication failure. Engine thrust including all engine indications, the altitude indication, the IVSI, the aircraft attitude indicator and the ship's GPS (for groundspeed and actual altitude) were all functioning and available, and the use of these indications is guided by the UAS memorized drill and checklist. There was no need to do anything but wait.

There is no guessing game which is probably the reason that it hasn't been brought up for serious discussion. It can be brought up I suppose but where is the evidence and what is the defence for the notion that this was a guessing game?

[bearfoil]

"Je ne comprends riens." From a pilot flying a wide body with 280 souls on Board. "No valid indications". "We have no indications".

Absent anything of value to rely on, my 'guess' is that "guessing game" is a kind sort of way to describe epic fail.

[bearfoil]

"There was no need to do anything but wait". The Pilot flying thought differently, and acted accordingly. You have evidence to prove he was mistaken?

If The Shadow is correct, and he makes a compelling case, the a/c was guessing too. Acting on bogus data might be a fair way to frame it. It passed along its blunder to the flightcrew.

[takata]

Hi Bearfoil,
The FCOM alerts the operator to the THS preventing some PITCH authority above 180 knots? How is this alert benign to the efforts of PF447 recovering the a/c?
In fact, the FCOM is underlining that the aircraft "PITCH authorithy" is better than in "conventional aircraft". What is mentioned is about a very remote case: a fully "jammed" THS - without any manual or electrical trim available. Above 8 deg NU, elevators will still be effective below 180 knots: this is the limit speed mentioned for safe flying in this case.
But now, do you think that AF447 had a jammed THS? Should I remember you that autotrim and manual trim were both very likely available. In fact, it seems that the main flight-control issue about AF447 "recovery" attempt, so far, was rather the complete lack of PF sustained nose down imputs...

Yes, I think elevators alone would have been preferred. Once above a certain angle, and at >180 knots, with All Trim Fuel aft, recovering seems a tall challenge?
By itself, "All Trim Fuel aft" means nothing... there is a variation from 0 to +0.5% aft of the target CG due to central tank fuel use which is completed by transfer from the THS to the central tank during cruise; add also a 2% safe margin below certification aft limits (if target is at max) and a push-button for forward fuel transfer, just in case.
Recovering from a stall without sustained nose down imputs seems rather quite more challenging than any "all trim fuel aft".

[bearfoil]

bon soir, takata.

"Better" Pitch authority than conventional a/c? Describe Better? More powerful (Stubborn)? More "Travel" (~14 degrees)? Impossible to recover at certain speed and exaggerated deflection? Jammed or not, The THS is a formidable force. Pitch Authority is more complicated than mere power, though admittedly Airbus has that ground covered. How quickly is it available? If it transits to its NU limit, are elevators enough to recover from some unusual attitudes? I think the answer is patently NO.

Without assigning a responsible, the THS can prevent a predictable planform. yes?

I think there is a working theory that has fossilised into a narrow ledge for some.

I doubt seriously the pilots will be found to have handled this a/c correctly at every turn. Likewise, the a/c itself became a riddle....... "Je ne comprends riens"............

Airbus once again must confront: What is it doing? It seems the THS happily wormed its way to near Full NU, and remained there. Likewise, the a/c climbed careeringly to STALL.

Regardless the upshot of the piloting, A330 has a legacy of explanation of its own, imo.

[takata]

"Je ne comprends riens." From a pilot flying a wide body with 280 souls on Board. "No valid indications". "We have no indications".
Absent anything of value to rely on, my 'guess' is that "guessing game" is a kind sort of way to describe epic fail.
Absent anything of value to say/add in your many posts, you'll better refrain from bolding quotes out of your FANTASY LAW universe.
"Je ne comprends rien" is not part of the tanscript, neither in French or English. (Beside, you dramatically added 52 "souls" on board).
"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".
Here is the good quote from the note in English.
And some part of your answer (about what indication was lacking) is certainly to be find in the following sentences:
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, fifteen seconds before this point, the speeds were invalid (AoA was above 40° and the PF was applying full back stick for 30 seconds)... then, maybe no speed at all were displayed on either PFD, nor Stand-by gauge...

[JD-EE]

I took a break. Several things are obvious upon reading to catch up. So I've caught up and herewith deliver this word bomb.

Nothing's changed, at least through the morning of the 6th.

(wordy annecdote)
There seems to be a lot of oversimplification in fields I work or have worked. For example, in some systems you cannot use "voting" type redundancy. The GPS satellite FSDU, Frequency Synthesizer and Distribution Unit, that takes the Rb and Cs clock 10.23MHz signals and applies carefully modifications before distributing the system clock to the two independant clock busses on the bird. There was a passive frequency distribution network from the clocks to the frequency synthesizer inputs. It combined all clock outputs into the three synthesizers' inputs. Since a 10.23 MHz sinewave is not something you can vote about only one clock and one synthesizer is powered at a time. (Otherwise you would get unacceptable spurious signals even with very high quality electronic relays to select clock signals.) I had to design for about 120dB isolation hoping to get at least 100dB. That's a 1 trillion to one isolation ratio as the target and 10 billion to one as a target. Trust me, clocks and synthesizers not needed were turned off. The outputs were all in parallel with a circuit designed to not short out the output bus if a transistor failed short circuit or open circuit. So that was, in essence, a passive voting system. The powered synthesizer drove the bus. With two busses a failure on one bus let the other survive and take over the full job. (/wordy)

PJ2 likes the first step of the UAS scenario concept. It fits very well when you consider it's claiming coincidence for all three pitots to fail the same way at the same time. If the PF side, which we do not see, showed even a brief overspeed just as the aircraft disconnected that would be the last thing the PF saw and he might have over trusted it. The off-again-on-again-finnigan stall alerts certainly could foster the view that they were spurious when overspeed actions fix what stall actions seem to bring back.

bearfoil wants and "easy" switch. It appears AirBus has patented such an idea. Way back in the June 2009 "era" of this discussion the idea of using the INS and GPS as a backup to the pitot tubes was broached. It was denied. Everyone figured long term, for which it cannot work. For short term, say a couple minutes, it should work just fine as an extrapolation tool. ABI seems to be planning to use this or is using it, likely on the A380. That's as "easy" as it gets. Warn the pilots to be on their toes and more attentive than usual. But fly through the mess, AoA, Thust, and GPS/INS. If at least one of the pitot tube readings does not become "sane" within 2 or 3 minutes or of altitude hold is too difficult then let the pilot ease into control. He's had a couple minutes to become well aware of what has been going on.

(By the way, the "easy switch" is the path towards a fully robotic plane, you know.)

BOAC seems to still desipise the glass cockpit and FBW. Right or wrong it is not going to go away no matter how much he rails about it. On a per million miles basis the glass cockpit in the A330 line shows half the accident rate and hull loss rate of the Boeing competitor he loves so much. Those are VERY loud words in mute bare statistics. I'd have more sympathy for him if the statistics were reversed. I suspect he will see a two person "executive" cockpit before he sees a return to cables or direct control. (The executive makes executive decisions about where the plane goes, never "files it", and is there rather than on the end of a long string of satellite relays away from Nevada. The other person is the relief executive. Both are trained with three special skills, giving the executive direction to the aircraft if something odd happens, telling the world about these changes, and reading the radars. He might even be trained to push a button to switch from one set of computers to another if something extraordinary were to happen.) It seems to me that is the direction it is all moving. And when the electonics can handle a hole blown in a plane with the plane still marginally flyable it will happen. "Get over it."

Confiture is remarking about the pilots seeming unawareness of what each was doing. If the quiet cockpit the BEA release conjures as a vision is real, at least one new feature must be trained into pilots: thinking out loud. Announce what you see and what you are doing about it. And acknowledge what the other has said. If that oddball scenario I mentioned above with PF seeing something quite different from PNF and recorded left seat only data then such an announcement of observation and intended action could have saved the plane.

PJ2 reposted (this time), for the Nth time, the schematic of where the various sensor signals go. I guess after RR_NDB's comments about redundancy it's time to wonder what makes the pitots redundant with only one going to any given ADIRU? I hope somebody did the numbers and decided this was better than feeding all three to all three ADIRUs. Or else there are data feeds between ADIRUs that are not shown. Anyway, I'll run an idea up a flagpole. Display all three to give speed with an error band with special displays for lost channels. Then there would be no chance PF would see something different from PNF. (I'd add a fourth channel to the picture, the consolidated GPS/INS report corrected for the last known calculated air speed.)

And we have the bozos who setup the cirriculum for AB330 pilots teaching them to keep their grubby paws off the trim wheels at all times and the designers who told the software people to never resume autotrim once the pilots mess with the trim wheels. Oy vey!

Detail regarding Captain seeing over shoulders of the PF and PNF: Note that he was found floating. The others were found belted in. He was probably standing observing closely.

As a hint for people who have a new thought it would be smart to revisit the BEA release and work it into the last 6 minutes and 21 seconds of the plane's flight. Ask, "How does this fit?" It might prevent your looking like a bonehead. (bearfoil continues his attempts at this proof.)

bearfoil, "Certification is mainly a mystery to me; I trust the system to certify a/c to be safe and reliable."
Sir, there is no such thing if you mean "never fails". The only way to achive "never fails" is to "never try." Stay on the ground and never fly. Then something other than an airplane will kill you.

Bear, all I can say is that they have my blessing: they were intelligent, trained and wanted to get home.
It is so reassuring to hear you say that, it is in short supply here.
Certainly not intentionally from me, bf. That is why I concentrate so hard on why they performed the damnfool stunt looking in training for the answer.

It's clear "what" killed the plane and the people aboard it. What is not at all clear is "why?"

Mr. O and bf mentioned "protections". They are NOT protections. They are limits. Calling then protections gives a false sense of security. I sense this all through this discussion, by the way. There is too much, "It can't fail." Can't is a very very big short contracted pair of words.

While cockpit design, cockpit displays, ergonomics, and aircraft/system drill and checklist design will influence outcomes, a "Standard" way of accomplishing complex tasks under both time and operational pressures reduces the potential for error. I know very well that it doesn't always work that way despite best efforts.
I remember asking WAY WAY WAY back in the June 4 2009 thread about some of this. If there is a standard drill for handling a plane in an unusual condition why does the plane not do it itself rather than expect the under informed (for instance no AoA) humans to take the load? There should be a better way.

This is the standard Aviate, Navigate, Communicate rule that we have seen mentioned.
Please forgive me here if I "bitch" about this a littlte. You have a TEAM in the cockpit. They are not telepathic. As you aviate tell your partner what and why. Think out loud, as I said above.

I am amazed that so distinguished a group as this one hasn't thought the PF was indeed acting on bad data (not his "fault"), and was doomed to a guessing game either way, No?Do you read more than you post or do you post more than you read? (As it happens I rementioned this above.)

Quoth ChristianJ, "Personally just looking forward to the next BEA report... and the way that will put the fox among the chickens, once again."

Amen.

[Machinbird]

There was a very interesting post awhile back on the other AF447 thread in R&N. Take a look at it, would like your thoughts. You can find it at: Post #1222, Pg.62 by The Shadow.

For those interested, The Shadow's post is on pg 61, #1218 R&N thread. We have discussed similar issues on the Tech Log threads, although not in such a concentrated manner.
It is pretty obvious that no one on the AF447 flight deck saw the trim indication in time. If they had, there should have been an understanding of what the problem was.

[bearfoil]

JD-EE

Thanks for the gentle treatment, ma'am. Guilty. I think you referred to BUSS (BackUpSpeedSystem), not fitted to 447. I do not advocate a robot of any description, it is (will always be), a potential lethal comeuppance for the Hubris of those who have more education than brains.

Machinbird. If that alone is the upshot of this tragic accident, everyone on several continents who had a hand in 447's demise deserves a flogging.

(ie: Not "noticing" Trim). For the record, may I opine that calling that THS a Trim device is abundantly fantastic? Like comparing a haircut to a decapitation.

[mm43]

The following graphic is a compilation of work done by HazelNuts39 and updated to include modifications suggested by A33Zab. It covers a period of 2 minutes from just prior to AP/ATHR disconnect to about one minute after the aircraft actually stalled.

http://oi51.tinypic.com/dbr05u.jpg (http://oi56.tinypic.com/9pt3ds.jpg)

The time the stall actually occurred is shown as 2:10:59 and observation will show that the aircraft gained a small amount of height by ballistic momentum over the next 6 seconds.

I'm sure that HN39 will assist with explanations should they arise.

The graphic above is 785 x 500 pixels so as not to stretch the page when being viewed on displays of 1024 pixels horizontal resolution. Clicking on the graphic will link to a full size image (1100 x 700) displayed in a separate window.

[takata]

Hi Machinbird,
For those interested, The Shadow's post is on pg 61, #1218 R&N thread. We have discussed similar issues on the Tech Log threads, although not in such a concentrated manner.
I've read it and, quite frankly, it is full of obvious misunderstanding of the very basic systems. Hence, beside very plausible description of some likely crew reactions, the theory developped is completely confusing with such a mix about flight control laws including their related sub-systems monitoring.

I wonder how he may think that the initial PF pitch-up described by the BEA was certainly commanded by the "flight system" and was not due to any manual side stick imput?
If the flight system needs to move a control surface, if possible within the current flight law, it will do it directly without making some side-stick imputs! But if the recorded side-stick channel is showing an imput, this is evidently a PF action... Why would one have a single doubt about that?

Hence, what such post is mostly showing, is that many people simply do not understand the basic logic behind the flight controls but still are furiously patching up some theories that will contradict most of the investigators work... (see Bearfoil's sustained daily efforts to continuously stall this thread into the deep-deep!)

It is pretty obvious that no one on the AF447 flight deck saw the trim indication in time. If they had, there should have been an understanding of what the problem was.
What would be the problem with the trim, beside the initial roll tendency after AP disconnection?

[Machinbird]

And we have the bozos who setup the cirriculum for AB330 pilots teaching them to keep their grubby paws off the trim wheels at all times and the designers who told the software people to never resume autotrim once the pilots mess with the trim wheels. Oy vey!
JD-EE, we were temporarily lead astray by forum members who apparently believed that autotrim would not resume control once you made a manual trim input. PJ-2 has kindly set us straight (with technical references) and explained that autotrim will resume once you take your paws off the trim wheel. I strongly suspect there is some misinformation adrift in the Airbus community that needs correction. I wonder how BEA will address that?

[grity]

Graybeard I should have explained that my surprise was not at the fore-aft placement of the static ports on the A330, but their placement so low on the fuselage, maybe only 30-40 degrees off vertical centerline.mayby the different positions of the static ports also generate a different sensibility in case of icing.....

dolphins have their sensors at the forehead under the blowhole!
http://onderwijs1.amc.nl/medfysica/doc/Echolocation%20by%20marine%20mammals_files/image004.jpg

[Machinbird]

What would be the problem with the trim, beside the initial roll tendency after AP disconnection?


Takata,
The problem with the trim is that it moved to a high aircraft nose up setting without crew awareness.
It appears that a FBW aircraft requires the pilot to know exactly what mode the aircraft is operating in or else the question arises, "What's it doing now?" In the case of the AF447 crew, they had no attention to spare to consider what the trim might be doing, thus the nose up demands caused the trim to run silently to a high setting without the knowledge or anticipation of the crew.

Once at a high setting, the trim acted to stabilize the aircraft in the deep stall that they eventually achieved. When the Captain arrived on the flight deck, he had to puzzle out what he was seeing. From the jump seat, the indications were essentially hidden by the wheels themselves.

The THS autotrim system has virtually eliminated the problem of trim-runaway, but it has replaced that problem with a new set of problems.

With regard to The Shadow's post, I merely pointed to its location. It was a pretty good post considering the date of posting and the breadth of coverage, particularly the human factors. I did not agree with all his points however.

[jcjeant]

Hi,

JD_EE
Detail regarding Captain seeing over shoulders of the PF and PNF: Note that he was found floating. The others were found belted in. He was probably standing observing closely.Another Pprune scoop ...
Better than Le Figaro there ...
JD_EE .. you also been a "person close to the investigation" .. a "reliable source" ?
Can you show your reliable source confirming the text in bold ?

[BOAC]

BOAC seems to still desipise the glass cockpit and FBW the glass cockpit and FBW the glass cockpit and FBW. Right or wrong it is not going to go away no matter how much he rails about it. - I'm afraid, that like many other inputs from many 'experts' on this huge sequence of threads, that is a complete mis-representation. If you read the other thread (Safety forum) you will discover that it is the attitude to the implementation of "the glass cockpit and FBW" and its interface with the pink and fleshy bits that operate it that I "despise" - if that is your chosen approach.

Even PJ's 'Golden Rules' from Airbus (how concerning is it that this needed to be published? Where have we 'arrived'?) make no mention I could find of 'Direct Law' handling, merely 'manual flight' - ie 'protected'. It makes no mention of that fact that the 'protection' we 'sell you' with the aeroplane may not. The mindset that needs to be broken is that all this is going to 'look after you'. It will until it doesn't. That, if anything. must be the key message. BA tried hard a few years back (following a worrying spate of loss of 'SA' and common-sense induced by the mesmerising glass) with a far-seeing course for pilots called 'EOI' - 'Enhancing Operational Integrity'.

One further comment - I am concerned that these 'graphs' produced after hours of hard work by folk like MM and A33 will pass rapidly into the 'factual' world - as pseudo FDR traces - when in fact they are supposition - guess-work - based on extremely limited information. We just do not know enough at this time.

[cwatters]

I'm no expert but I've been trying to follow the AF447 tech thread with the aid of the Flight Crew Operating Manual here..

http://www.mercadodaaviacao.com.br/arquivos/14_04_2010_11_14_20_flight_controls.pdf

In the section on Alternate Law it says..

Quote:
Low speed stability
At low speed, a nose down demand is introduced in reference to IAS, instead of angle of attack and alternate law changes to direct law.

Won't going to Direct Law remove the nose down demand that it just tried to apply? It says in Direct Law all protections are inoperative.

Have I missunderstood?

[takata]

The problem with the trim is that it moved to a high aircraft nose up setting without crew awareness.
Any pilot flying an aircraft with autotrim should know that his trim will follow his stick imputs, shouldn't he?
It appears that a FBW aircraft requires the pilot to know exactly what mode the aircraft is operating in or else the question arises, "What's it doing now?"
Isn't it one of the basic skill needed for one wanting to be rated for a specific type? What makes you think that many FBW pilots don't know exactly in what mode their aircraft is operating?
In the case of the AF447 crew, they had no attention to spare to consider what the trim might be doing
Well, considering that the trim was doing what a type rated PF asked, and what it is always supposed to do in such a case, what would be the point to consider that it would take more "attention" than usually?
thus the nose up demands caused the trim to run silently to a high setting
Hence, as usual when imputs ask for a lot of nose up, what is wrong with that?
without the knowledge or anticipation of the crew.
What make you believe that a type rated crew would not anticipate it or lacked the knowledge that it will do exactly that? Do you think that it wasn't what they wanted, nose up?
Once at a high setting, the trim acted to stabilize the aircraft in the deep stall that they eventually achieved.
Right, the PF achieved a full stall with the help of the side stick, thrust and THS trim. Hence, what's wrong with the side stick, the thrust lever and the THS trim?
When the Captain arrived on the flight deck, he had to puzzle out what he was seeing. From the jump seat, the indications were essentially hidden by the wheels themselves.
Beside hindsight, what makes you believe that the Captain would have immediately recovered the situation with all the trim settings displayed under his nose? He wasn't there from the begining of the crisis and still possibly far behind the other pilots. He also might have seen the Flight Control page, where the THS trim setting is displayed, right in front of him...
The THS autotrim system has virtually eliminated the problem of trim-runaway, but it has replaced that problem with a new set of problems.
I still can see the problem with the THS trim. If they had acknowlegded their stalled situation in time, they would have immediately applied full and sustained nose down imputs, hence, THS trim would very likely follow that. If, for whatever reason, THS trim would not follow those imputs, not enough elvators authority should have attracted PF attention about considering that trimming nose down could help him... at least, theoretically if his training level wasn't the issue.

[rudderrudderrat]

Hi BOAC,
... it is the attitude to the implementation of "the glass cockpit and FBW" and its interface with the pink and fleshy bits that operate it that I "despise"..
I tend to agree with you. If you keep taking tactile feed back away from a pilot, then you reduce him/her to a visual clues only input processor. If the FBW computers couldn't cope without valid airspeed information, is it a bit too much to expect a human to do a better job without the benefit of a "conventional aircraft's elevator feel"?

[jcjeant]

Hi,

takata whrote
Quote:
Originally Posted by Machinbird
The problem with the trim is that it moved to a high aircraft nose up setting without crew awareness.

Any pilot flying an aircraft with autotrim should know that his trim will follow his stick imputs, shouldn't he?
Quote:
Originally Posted by Machinbird
It appears that a FBW aircraft requires the pilot to know exactly what mode the aircraft is operating in or else the question arises, "What's it doing now?"

Isn't it one of the basic skill needed for one wanting to be rated for a specific type? What makes you think that many FBW pilots don't know exactly in what mode their aircraft is operating?
Blah .. blah ...
So .. when read all this .. my feeling is:
The pilots were rated on type ... but nevertheless were not qualified for the situation of AF447 was
They had not knowledge of basic flying skills
They don't know how the Airbus systems work
So we can conclude that:
The formation and training of those pilots is very low
So Air France bear all the responsibility for this accident by not providing adequate training to their pilots or not detecting by exams (simulator) that those pilots were not qualified for fly a Airbus A330
At least and even if this above is not entirely true .. Air France stay bear the responsibility of this accident as the contract between Air France and their passengers was to transport them from A to B and they failed....
Are my feelings good ?

[JD-EE]

Machinbird re trim wheels - thank you for clarifying that. I must have missed that even though I make a point of reading PJ2's postings extra carefully. Alzheimers must be setting in.

[JD-EE]

jcjeant, the PF and PNF were brought up belted to their seats according to BEA press releases.

The releases declared:
* They pulled up two bodies.
* They pulled up the two pilots seats.
* They DNA identified the pilots.

Ergo, if the two bodies were not in the seats or very near them, who was and why were they dumped from the seats? (And if they were not in the seats I wonder how they came out considering how they are strapped in. It's not a passenger style seat belt. The pilots use full harnesses.)

[JD-EE]

BOAC, on the graphs I am in agreement with you. And I believe we are in agreement with gums about the word "protections." The word sets up the wrong mindset leading to people getting reckless and cavalier about deadly serious subjects.

Re FBW - you could have (and did) fool me. You seem dead set against AirBus despite its superior safety record. And as far as I know for transport aircraft though the A340 that AirBus has embraced the automation more than other airlines. So I drew the conclusion you rather disliked FBW and software anywhere on the plane, except perhaps in the inoperative laptops the SLF carried on board. You have been busy ripping software engineers a new set of orifices it seems.

[BOAC]

You have been busy ripping software engineers a new set of orifices it seems - not quite sure w t f that means but it sounds like something my mum would not like me to do. I suspect we move in different social circles.

I see you have not contributed to my thread at all so I suspect the Alzheimers has prevented you from reading the opening post too, or maybe you forgot you read it?

[mmciau]

This video on the loss of the X31 back in the nineties - it was suggested a disconnected probe (and ice) was the fault!

It too went straight up!!


YouTube - ‪X-31 Crash Segment from "Destroyed in Seconds"‬‏

[CONF iture]

AirBus superior safety record
I am not aware of anything like it ... ?
The pilots use full harnesses
Anywhere below 10000 feet but rarely at cruise level.


Right, the PF achieved a full stall with the help of the side stick, thrust and THS trim. Hence, what's wrong with the side stick, the thrust lever and the THS trim?

Takata, if you are asked to fully stall your aircraft for exercice, would you still trim up past the early signal of the approaching stall ?
Why automation has been doing something you would not ever do yourself ?
IF ... the pilots were confused enough to maitain NU inputs, was it necessary for the automation to help them in their confusion ?
Leave on their shoulders that kind of initiative.


As I have said, this wasn't an emergency such as a depressurization, an engine failure or fire or a GPWS event which requires timely, immediate action but it did have two memory components to the drill, (as shown in the BEA Interim Report #1), before the UAS QRH Checklist was to be called for. I have discussed this memorized drill and checklist a number of times on previous threads.

PJ2, I am unconfortable with your view here.
You have not adressed my concerns (http://www.pprune.org/tech-log/454653-af-447-thread-no-4-a-30.html#post6545287).


If you hate the Airbus FBW flightdeck so much ...
You are WAY out DW, and should know better ...

[HazelNuts39]

mm43;

Thanks for your superb graphics work enhancing the crude EXCEL graphs I posted here (http://www.pprune.org/tech-log/454653-af-447-thread-no-4-a-40.html#post6553124), and for posting your graph on this thread.

One further comment - I am concerned that these 'graphs' produced after hours of hard work by folk like MM and A33 will pass rapidly into the 'factual' world - as pseudo FDR traces - when in fact they are supposition - guess-work - based on extremely limited information. We just do not know enough at this time. Of course you are quite right. My 'pseudo FDR traces' are to some extent 'supposition - guesswork', but I don't understand your concern. I thought that, while we're waiting for the publication of the real FDR traces and many posters discuss AoA's, pitch angles, airspeeds etc., this was better than nothing.

Perhaps it would help to explain in some detail how the data shown on these graphs have been derived. In this 'computer simulation' (an EXCEL spreadsheet) the airplane manoeuvre is driven entirely by an assumed variation of acceleration (az/g) along the earth vertical that is shown here (https://docs.google.com/leaf?id=0B0CqniOzW0rjNTIwZDI2ZWYtY2ExZi00ZjE0LTkyNDItNDA2MDY zZDI3YWE2&sort=name&layout=list&num=50). At first, that driver function is just a wild guess. But then the resulting v/s, altitude, airspeeds, AoA, etc., is compared to the data in the BEA Update, including the time line, and the input function is 'massaged' to improve the goodness of fit, and the same process is repeated. After a large number of iterations I felt that 'version 4' is as good as it will ever get until we get the real data.

The calculated parameters are derived from the 'driver' function az/g by strict application of flight mechanics (i.e. Newton's laws) and A330 aero data published by Airbus (where available(*)). (**). The calculation then goes as follows: V/S is calculated from (by integration of) az/g. Altitude is then calculated similarly from V/S. Subtracting altitude from total energy yields kinetic energy and hence TAS, CAS and Mach. V/S and TAS together yield FPA. Next lift coefficient CL is calculated from weight, normal load factor n, Mach and altitude. CL and Mach yield AoA from the aerodynamic data (*). Finally, pitch angle is calculated as the sum of AoA and FPA.

For what it's worth, until we get the real FDR traces ...

(*) The available data cover the operating envelope between Mmo and buffet boundary. There are no data close to the stall and beyond. For these conditions I have assumed a pitch angle of between 15 - 16 degrees and calculated AoA from Pitch-FPA. Whenever I quote a stall-AoA, it is based on what I think is a reasonable extrapolation of the available data.

(**) This means that, if the airplane is subject to the assumed az/g, then it must follow the derived data shown on these graphs. In other words, the data shown are mutually consistent.

[CONF iture]

Are you sure the sidesticks are not visible from the P3 seat, even if you lean forwards? They are on the A320.
You are correct Chris, but you still need favorable conditions :

P3 not in the usual aft position
Tray table stowed
Adequate luminosity


http://i45.servimg.com/u/f45/11/75/17/84/af447_12.png (http://www.servimg.com/image_preview.php?i=101&u=11751784)

http://i45.servimg.com/u/f45/11/75/17/84/af447_13.png (http://www.servimg.com/image_preview.php?i=102&u=11751784)

What I'd like to emphasize on is the following :
IMO, fully visible control columns are a natural and easy Gold mine of valuable information. That free information is lost with the sidestick philosophy as implemented by Airbus.

People here pretend that one sidestick was maintained full NU for 30 seconds ... Were the PM and Captain aware of that situation ?
Never with fully visible control columns, such critical information could have been missed.


Disagree, the THS indication will be covered by the trim wheels from P3 seat.
...
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?
As stated by Chris Scott and PJ2, I can confirm that it is possible to get that information from P3, and so without P1 or P2 concourse :

http://i45.servimg.com/u/f45/11/75/17/84/af447_14.png (http://www.servimg.com/image_preview.php?i=103&u=11751784)

http://i45.servimg.com/u/f45/11/75/17/84/af447_10.jpg (http://www.servimg.com/image_preview.php?i=104&u=11751784)

http://i45.servimg.com/u/f45/11/75/17/84/af447_15.png (http://www.servimg.com/image_preview.php?i=105&u=11751784)

[BOAC]

but I don't understand your concern. - I obviously did not express my 'concerns' simply enough. I have no issue with the hours of work folk have done on these images and they are 'interesting'. My concern is that they will inevitably become 'fact' and we will be again be plastered in posts similar to those resulting from the Meteosat images '"See - they flew straight in to a big red thunderstorm"etc etc. As long as everyone remembers that these 'graphs' are NOT from the FDR we will be ok.

However, it won't be long before we see- "since they had xxxx at 02:xx:xx (from the FDR trace) then surely yyy"

mmciau - interesting clip I had not seen before - secondary cause of accident - ?
"pilot ignorance of an option to override computer control". No, I mustn't.

[Turbine D]

@ Machinbird,

Thanks for the post and page correction on The Shadow's post. I guess a couple of posts were removed after I made a note of it, leading to my error.

[rudderrudderrat]

Hi BOAC,

"pilot ignorance of an option to override computer control". No, I mustn't.
I just wish AB had fitted such a switch.

[GerardC]

Originally postted by Confiture :
would you still trim up past the early signal of the approaching stall ?
Why automation has been doing something you would not ever do yourself ?
IF ... the pilots were confused enough to maitain NU inputs, was it necessary for the automation to help them in their confusion ?
+1

1) how on earth can a "system" allow the THS to go to full 13° up in cruise at 35.000' ?

2) how on earth can a stall warning be disabaled below 60 Kts to just kick in again when control is being regained (and completely confuse the poor crew) ?

[Lonewolf_50]

A couple of comments that call for a rejoinder.
The problem with the trim is that it moved to a high aircraft nose up setting without crew awareness.
Crew awareness of nose attitude begins, in instrument conditions, with the artificial horizon/attitude indicator. If that was working as advertised (no data to date suggests it was not) then the primay scan instrument should have given PF and PNF (and later Captain) indications of where the nose was relative to "level flight." Instrument Flying 101.
It appears that a FBW aircraft requires the pilot to know exactly what mode the aircraft is operating in or else the question arises, "What's it doing now?"
True of most modern aircraft (to include modern helicopters that aren't FBW, but do have a lot of redundant and overlapping flight control systems and related degraded modes)
Example is the SH-60 Seahawk:
From all things (and A/P such as it is) on (AFCS on) you go to AFCS off, then Trim Off, then SAS off (SAS 1 and / or SAS 2) then Boost off. You are still flying, but in each case you can do some things, and can't do others. The aircraft also gets a bit more "touchy" to handle, and pilot workload goes up. The last puzzle piece (which means you are having a very bad day) would be if your Boost was off and you then got a horizontal stab miscompare, which forces you into manual control of the stab. When working in fully functional mode, it is that aircraft's sole FBW control surface.
Graceful degradation? I guess so.

The Control Laws of A330 may or may not be as graceful in degradation, but the aircraft itself is a bit more complex, not the least due to the requirement to manage fuel and CG via various fuel transfer protocols.
Also there are more A/P functions and, more FBW involved. I have once again walked my way through the degraded modes. They make sense.

I guess that they make sense to A330 pilots, particularly if you get to practice them in suitable training environment. Nothing like some practice and a few "hell sessions" in a sim to get you to know your systems. :cool:

Regardless of which bird you fly, you really have to know your systems.

The more systems, and the more they interact, the more you have to know. Enter your company, and the manufacturer, and their training material, and the training programs.

Those last are critical elements in how well any crew understands their aircraft.
In the case of the AF447 crew, they had no attention to spare to consider what the trim might be doing, thus the nose up demands caused the trim to run silently to a high setting without the knowledge or anticipation of the crew.
Crew awareness of nose attitude begins, in instrument conditions, with the artificial horizon/attitude indicator. If that was working as advertised (no data to date suggests it was not) then the primay scan instrument should have given PF and PNF (and later Captain) indications of where the nose was. Instrument Flying 101.

jcjeant:
So Air France bear all the responsibility for this accident by not providing adequate training to their pilots or not detecting by exams (simulator) that those pilots were not qualified for fly a Airbus A330

All? Outside of the cockpit, there are three non trivial and overlapping bodies who influence how well prepared a crew is for their missions.
The airline
The aircraft manufacturer
Regulating bodies

The rule sets and information each of these bodies issues to guide, restrict, limit or otherwise influence expected pilot behavior is subject to omission or error. AF has a share of responsibility, but for you to say "all" is an overstatement.
At least and even if this above is not entirely true .. Air France stay bear the responsibility of this accident as the contract between Air France and their passengers was to transport them from A to B and they failed.... Are my feelings good
I suppose that from a "strict liability" point of view, that's one way to look at the accident: breach of contract to carry from point A to point B.

Looking at it that way doesn't get one any closer to addressing the sysetmic issues that are under the conginzance of

The airline
The aircraft manufacturer
Regulating bodies

Therein lies the remedy to avoiding such a mishap in the future.

[bearfoil]

TD good morning,

More than shifting the (at the time) fascination with sea bottom debris arrangement to AD disagree precursors, Shadow's post is illuminating. Airdata that became discrepant is assumed to be the cause of the accident, how did it come about? He introduces the concept that this phenomenon may have an actual beginning, and it may not be the "So, we have lost the Speeds"...

It has been addressed before, but not to the extent that people may include it in their concept of the progression of failures that brought 447 down. The direct cause of ICE in Pitots is considered to be microcrystalline particles. If in the area of some well distributed solid particles, it is reasonable to conclude the tubes may ingest these at some conforming rate. The Three tubes were "identical" in nature, differing perhaps in the degree of corrosion the drain holes had experienced in service. Dependent on the concentration and rate of uptake, it is logical to assume the Air Pressure differential migrated lower over time, indicating an airspeed that was progressively lower than actual value.

As the speeds declined, the ship would accommodate the "loss" of speed by increasing power, since energy needs to be added and altitude needs to remain the same, but as the a/c climbed anyway, (the energy was actually just right, the computer found it to be low because of ICE), the Nose would be lowered. This might continue until the a/c was zipping along at its assigned cruise level carrying too much power and actual velocity. Depending again on the rate of uptake, this false trimming would last until the a/c autopilot checked out, unable to control the Nose "hunting for a satisfactory Pitch". (AutoPhugoid?)

That is merely a hypothesis, BEA have not addressed through their data any such thing. Neither have they favored ICE as the reason for UAS, to my knowledge.

Autotrim. Takata is correct, of course. Except for one thing. The THS is a very large surface and can control Pitch without as much steady pressure as required by elevators alone. For this, the a/c pays a price in Response.
The Horizontal surface is powerful because it is large. Large things move more slowly than smaller things. To think that it is desirable that when a pilot needs response, he is awarded Power instead, and that lagging the possible cycles of deflection necessary, misses the point. By the time TRIM has "helped" it is not needed, and it becomes a handicap in the ability to maneuver. (AutoPhugoid?) At a/p loss, was it dropped because the Pitch oscillations were too great? Did the PF "chase" the THS all the way up to STALL, trying to get the nose down while still in the aft area of the BackStick? Unable to see THS deflection, would he be able to sense the lack of ND he wanted, thinking that at "neutral" stick, it was no such thing, just a steady increase NU? Who wants to chase TRIM all the way up to ballistic? Bottom line. Why Autotrim in dire circumstances. Obviously available, even mandatory, who needs it?

Needless to say, given the size of the THS, quick movement puts large mechanical demands on the surface, and the jackscrew that accomplishes the deflection. For the pilot to have considered that the THS was "AutoHelping" he would also need to determine that it was also a hindrance. Operating an airbus with the certain knowledge that the a/c was creating a problem is not perhaps in the cerebral databank of its operator. Likewise, the Manual Trim as safety device. The airbus needs a safety device? This may be too subtle for normal flight, but in the tall weeds it may have been a factor.

At the risk of parsing too closely, In the audio where the pilots are noticing "No indications", is it surprise one senses? Or Betrayal?

[Lonewolf_50]

Dependent on the concentration and rate of uptake, it is logical to assume the Air Pressure differential migrated lower over time, indicating an airspeed that was progressively lower than actual value.

As the speeds declined, the ship would accommodate the "loss" of speed by increasing power, since energy needs to be added and altitude needs to remain the same, but as the a/c climbed anyway, (the energy was actually just right, the computer found it to be low because of ICE), the Nose would be lowered. This might continue until the a/c was zipping along at its assigned cruise level carrying too much power and actual velocity. Depending again on the rate of uptake, this false trimming would last until the a/c autopilot checked out, unable to control the Nose "hunting for a satisfactory Pitch".

One hopes that some more research (NASA still working on this?) will shed light on the degradation rate, or mode. (Then again, there are those Goodrich probes ... :8 )

Bear, in a curious way, the elevator and THS work together like Charlie Kaman's servo flap/rotor blade lashup in the old SH-2, and the current KMAX, helicopter. What you end up doing is using a small airfoil to change the pitch of a larger airfoil until equilibrium is reached.
Take a look at this picture.
http://upload.wikimedia.org/wikipedia/commons/thumb/e/e6/N267KA.JPG/220px-N267KA.JPG

That little tab near the end of the rotor blade is the servo flap. The pilot's inputs via cyclic (stick/sidestick analogue) moves the servo flap, which changes camber of airfoil (blade) which aerodynamic forces then resolve into a new pitch angle. (The difference in actual function, and where the two are not the same, is in the moveable THS in an airliner being internally adjusted (motors and hydraulics) to a new position to reach the new stabilized position based on the change induced by elevator movement, rather than how the KMAX does its thing by harnessing fluid flow effects).

[bearfoil]

And in so doing establish a commitment to a particular, and artificial, Angle of Incidence. This is fine in cruise, but maneuvering an a/c which has cranked in a preference for one (Pitch)or the other (never both), becomes a challenge in adapting to the response of one airplane depending on a very important factor.

Changing the characteristics of an airfoil has dangers inherent in its "benefits". Neutral stick is no such thing when 16 degrees NU, it only "Logs" neutral, and when the deflection cannot be read, there is your guessing game.


I'll stick with swash, and internals. Maybe a particle separator. For the motor, not the pitot.

In the Traces, I'll be looking for gee. Just like Perpignan, but this time at the beginning of the crash.

[Lonewolf_50]

Bear, take a look at page 5 here. http://www.kamanaero.com/images/PDFs/K-MAX%20brochure%20PF%2020050727.pdf

I flew for a few years with Kaman's servo flap system. It's very responsive to pilot inputs. You don't need hydraulics(though they are handy, and with hydraulics gone, the collective is tiring to move and hold in position).

I personally prefer it, stick and rudder wise, to the swashplate that needs 3000 lbs of hydraulics to change pitch on rotor blades. (Down side, of course, is more parts and thus more maintenance worries ... so it goes, no free lunch ... )

As to the A330 THS and its teaming with the elevator, is there something to be learned from the UH-60?

In that cockpit, you will always know where your Horizontal Stab is (a FBW surface that moves) because there is a guage that tells you its deflection from the horizontal, on the center console. (That gauge is pretty important, since if you are flying above certain speeds, full down Horizontal Stab will kill you due to a nose pitch that the rotor system can't overcome).

From the various material I have access to, on the A330 can all up your THS on a standard ECAMS page. I am not sure if that display is the default or not.

Food for thought, in re knowing what your airfoils are doing while you are flying. Did the crew know where it's THS was? Interesting question, but the more critical question, beginning with the initial LW/NU move on the side stick, is

Did the crew know where their nose was relative to the horizon? (Particularly before apogee was reached).

[Zorin_75]

I don't quite understand the obsession with the autotrim - clearly this would be a concern if they had gone down with sustained full ND input, fighting a hopeless battle against the evil THS. From what we know this was neither the case nor do they seem to have lost all pitch authority...

[Lonewolf_50]

The concern seems to be in sussing out whether the trim functions in ALT-2 (or in AA Law, which some still suspect was in effect at some point) had an influence on nose pitch attitude in the first half of the event. If no, then solution is in one direction, if yes, then it goes in another direction.

After that, the problem seems to be one of pitch authority: was there enough?

[Chris Scott]

Quote from PJ2:
Your previous post on the THS on thread #4, here (http://www.pprune.org/tech-log/454653-af-447-thread-no-4-a-50.html#post6559268), explains the THS operation very well and this one connects that explanation with how the THS likely functioned with AF 447. I think its a reasonable explanation of what occurred to the THS and how, after the initial pitch-up.

Thanks for your kind acknowledgement of my recent beginners' guide to "Primary and Secondary Pitch Control" on the previous AF447 thread, which also attempts to describe very briefly how the basic concepts are applied on Airbus FBW, and their relevance to AF447.

The key to the THS movements are, of course, how much elevator the EFCS is using: you explained that here before I ever did.

In a couple of follow-up posts, including the one you have quoted in your post, I tried to develop the argument to describe part of what may have been happening with pitch control as the aircraft reached its apogee, and immediately after:
http://www.pprune.org/tech-log/454653-af-447-thread-no-4-a-50.html#post6559334[/URL]
http://www.pprune.org/tech-log/454653-af-447-thread-no-4-a-53.html#post6560444 (http://www.pprune.org/tech-log/454653-af-447-thread-no-4-a-50.html#post6559268)

Finally, I offered a partial explanation of the problems the PF seems to have been having with roll and pitch control using the sidestick, and how the EFCS may have interpreted what it thought he wanted in pitch.
[URL]http://www.pprune.org/tech-log/454653-af-447-thread-no-4-a-53.html#post6561309

Quite how the aeroplane eventually established itself in – as others have commented – a remarkably stable descent at AoA > +40 and pitch ~ +15 remains mysterious, partly because this is uncharted territory in terms of the aerodynamic performance of the fuselage and THS, as well as the wing. The resulting pitch-moments are therefore unclear. In that context, I recommend a look at Meikleour's contributions, the first of which is here (http://www.pprune.org/tech-log/454653-af-447-thread-no-4-a-50.html#post6559424), which relate to a simulator exercise many of us have not done.

The other unclear factor is how the C* pitch-function of the EFCS would treat the invalidation of CAS (IAS) data, when determining the crossover from g-control to pitch-control. As I understand it, that crossover is normally a gradual transition as the airspeed falls below a certain figure in routine flight. Understanding how the UAS affected this will be the other key step in solving the relationship between sidestick position, elevator/THS position, and the achieved trajectory.

As these pieces are on the previous thread, the links provided will enable you to reach them more easily, and I look forward to any comments or objections. If none should be forthcoming, I shall infer that even the most erudite of our contributors find nothing to disagree with in my proposals... ;)

[bearfoil]

Did the PF know his Pitch (attitude) at a/p loss? Of course he did.
It was ND, and needed NU. The a/p quits at ND-9 degrees. That much? Either way, the PF input NU, there is no call to question the decision?

[rudderrudderrat]

Hi Chris,
But this aircraft was degraded to ALT 2 law: a combination of Direct law for roll (stick-to-aileron/spoiler) and Alternate law for pitch, the latter without any high-AoA protection.
In trying to cope with the roll-control problems described (but not yet explained) by the BEA, it is almost inevitable that the PF was making continuous roll inputs, and probably had the stick in the palm of his hand. This would have made accurate pitch control difficult.
I agree.
It would only have needed a small amount of rudder trim to have levelled the wings (a technique forgotten / not learned by FBW crews). The stick could then have been released and used more normally to control the attitude. I suspect PF was struggling somewhat to maintain wings level (Meikleour previously described how "twitchy" it was in roll in ALT LAW during his loss of airspeed event).

[BOAC]

Chris - I understood that the C* in the AB switched at around 210 kts so I would expect the FCS to be pitch rate driven during the 'climb' and not Nz, especially given the supposed low IAS readings?

Bear - how on earth do you arrive at pitch -9? Is that what you are proposing now?

[Chris Scott]

CONF_iture,

Many thanks for going to the trouble of obtaining and posting excellent photos of the view from the P3 seat in daylight. They confirm my A320 recollections, after a gap of nearly ten years. If in its stowed position, it should be safe to roll the P3 seat forward to the position the photos were taken from, although the pitch of +15 might have made it difficult. Was the captain merely standing?

As you say: although the sidestick can be seen, provided the PF's table is stowed, the console lighting would preclude this at night – unless the dome floodlight was on. In any case, its position would be unclear if it was in the palm of his hand.

THS position should not be a problem, provided the observer's eyes were adapted to low-light conditions.

[A33Zab]

Quote:
Originally postted by Confiture :
would you still trim up past the early signal of the approaching stall ?
Why automation has been doing something you would not ever do yourself ?
IF ... the pilots were confused enough to maitain NU inputs, was it necessary for the automation to help them in their confusion ?

+1

1) how on earth can a "system" allow the THS to go to full 13° up in cruise at 35.000' ?


Because 1 hand on 1 stick, connected to 3 xdcers commanded the 3 FCPC - in ALt 2 - to do so.
(In the absence of ss xdcr, FCPC or pitch system faults, it wasn't a 'flaw' order generated by the system itself.)

2) how on earth can a stall warning be disabaled below 60 Kts to just kick in again when control is being regained (and completely confuse the poor crew) ?


Maybe because flying at 60 kts, 15° pitch and 40° alpha was not accounted for?
Ask B. they quit all the signals at 30Kts, so between 30 and 60 flight seems to be possible with that one!?

[Chris Scott]

rudderrudderrat,
Yes. That the PF was struggling with roll-control may have overloaded him. Later, at very high AoA, resultant sideslip would add to probe problems, as has been said. At that stage, was the use of aileron/spoiler productive, counter-productive, or irrelevant?
I'm interested in your rudder-trim argument, but don't see how it would counter wing-drop if the latter was caused by turbulence.

BOAC,
The 210kt crossover seems to be a popular figure. I think there must be a gradual blending-out/blending-in process, to make it seamless to the pilot (which it is). But, as I said, what logic is applied when/while airspeeds have been declared invalid?

[bearfoil]

BOAC

Steady on. -9 degrees is the a/p limit, the a/c Pitch has not been supplied by BEA. Except in + range........ (perhaps ND does not concern?)

:ok:

[Turbine D]

Good morning Bear,

I do believe one has to look at the two minutes before AP/AT disconnect and at the moment there is no information from time of 2 h 08 min 07 and 2 h 10 min 05. The speed was reduced to about Mach 0.80 and the turn to the left was initiated at the start of this time period. Although the BEA never specifically has said the pitots became clogged with ice crystals (nor should they at this stage of the investigation), it is apparent they are strongly looking at this as the starting point of the total event. I also think the clogging was not one where in one-second the pitots were clear and then poof, in another second they were clogged. It probably happened on a gradual but ever increasing basis over these couple of minutes or so.

Speed
So as the pitots began to clog, the sensed airspeed by the computers began to go down. Now I can't imagine the computers observing this degrade in speed sat there and did nothing, but perhaps Takata can provide the computer reasoning and logic in this situation while in AP/AT. I would think they would signal the engines to spool-up and increase the speed to maintain level flight the AP was attempting to do at that time. Unfortunately, the sensed speed degrade was wrong and the aircraft was gaining speed it didn't probably require in level flight. I would assume that when the AT dropped and thrust lock occurred, the thrust was locked at a higher N1 setting than perhaps the PF thought it was at?

Pitch
I am not going to comment on this aspect as to what the computers were doing or not doing. But rather, some questions about an observation I noted in reading the reports regarding aircraft balance. In the very first BEA Interim Report, dated June 1, 2009, at the time of the beginning of the incident, the aircraft weight was estimated and reported at 205 t and an aft balance between 37.3% & 37.8%, controlled within 0.5% of MAC. The second BEA Interim Report mentioned nothing in this respect.
However, in the BEA Update, dated May 27, 2011, The weight of the aircraft was again reported at around 205 t, but the balance was changed to 29%, or in other words moved forward 8% or so. I thought the aft balance (37.3% - 37.8% reduced drag and improved overall efficiency.
So my questions are: How did this happen? Why did this change happen? Does this have any effect on maintaining pitch either by the automatics or in a manual fly mode?

Just curious...

[rudderrudderrat]

Hi Chris,

Correct - it wouldn't work for random turbulence, but only if it was mis-trimmed to begin with (rudder + or slight fuel imbalance + or thrust asymmetry).

"From 2 h 10 min 05 , the autopilot then auto-thrust disengaged and the PF said "I have the controls". The airplane began to roll to the right and the PF made a left nose-up input."

[bearfoil]

TD

A change of 8 per cent in Weight would be 33,000 pounds. So the 8 percent of CG is a whopper. Unfashionable to change such heavy horses in mid stream. It may represent the entire aft fuel load, as if it were foreward, which it was not. Cheating Fuel is an old trick, and it saves a significant amount of fuel burn? The cost is Stability, orienting the Cl to the Cg is hazardous. The a/c becomes more sensitive in Pitch, obviously.

If, for instance the Cg fell behind enough, Up becomes down, and down Up. PF did hold aft stick all the way down, after all. hmmm..........


I am not real clear on the a/p's authority in Pitch, Roll, and keeping the two in line with each other. To me, if Pitch transits got out of phase with Power, their could be trouble? Insofar as rate, I think Power up when Nose down would be problematic, as would the reverse. If the THS is in there, what is the calculated rate for stopping speed and Pitch excursions that are (or have become) unnecessary?

If it is a rate thing, do the a/p's limits constrict? As in, "Keeping Up"? I still think it is a toss-up which came first, the 'slows', or the 'unreliables'.

I lean to the slows.......:confused: leading to hand flight.

Now, will there be some clarity from BEA?

[infrequentflyer789]

As the speeds declined, the ship would accommodate the "loss" of speed by increasing power, since energy needs to be added and altitude needs to remain the same, but as the a/c climbed anyway, (the energy was actually just right, the computer found it to be low because of ICE), the Nose would be lowered. This might continue until the a/c was zipping along at its assigned cruise level carrying too much power and actual velocity. Depending again on the rate of uptake, this false trimming would last until the a/c autopilot checked out, unable to control the Nose "hunting for a satisfactory Pitch". (AutoPhugoid?)


Maybe not impossible, but I think the theory falls at the same test as the idea that updrafts caused or accelerated the climb - namely that the kinetic-potential energy then doesn't add up. Those (not me) that did the maths and posted however many pages back, showed clearly that the BEA figures match the a/c trading KE for PE. Your theory has the a/c carrying additional KE over and above what BEA says (real AS > IAS) before the climb - which would give a higher apogee, I believe.


Bottom line. Why Autotrim in dire circumstances. Obviously available, even mandatory, who needs it?


Yet in several other crashes and incidents, loss of autotrim has lead to LOC (and deaths) as pilots failed to manage the trim along with everything else they were handed at short notice.

Autotrim on or off - no right answer. Whichever you choose as a designer, sooner or later someone is going to die in part because it wasn't the other way round.


At the risk of parsing too closely, In the audio where the pilots are noticing "No indications", is it surprise one senses? Or Betrayal?

Given we've only got a transcript and that through translation - who knows.

I also keep coming back to that line though, and wondering what other indications they lost. Did they lose attitude, distrust it, or just not see it ?

[bearfoil]

infrequentflyer789

Perhaps not a smooth climb, then, but one with rolling and porpoising? Both eat up energy quickly. The Rolling we know, and the Pitching we can infer from BEA?

[takata]

Hi Bearfoil,
I really think that you are chasing your own tail all around this thread.
Steady on. -9 degrees is the a/p limit, the a/c Pitch has not been supplied by BEA. Except in + range........ (perhaps ND does not concern?)
The BEA supplied some informations in its narative. Those they considered relevant in order to understand roughly the sequence of events, mostly because there is still many data they would have to check further in detail or to derive from those rough recorded data. But, be sure that it should not cover the flight parameters while she was still flying in auto-mode as it would be very easy for them to verify immediately if everything was ok until the point autopilot disconnected (cross-checking all speed, altitude, position, parameters from the various sources will tell you straight away if it is right or not).

At AP disconnection, the only thing they considered worth mentioning was that the aircraft started rolling (meaning she was wings level before), we don't know the rate or amplitude; but, do you really think that they would hide to us something very unusual, just before this point?
More likely, don't you think that she was flying as expected at FL350, 275 kt, wings level, +2.5 deg pitch, THS should be about ~2-3 deg NU?

Some of this is already part of the narative:
At ORARO : flight level 350, Mach 0.82, pitch attitude about 2.5 degrees; airplane around 205 tonnes and 29% MAC; Autopilot 2 and auto-thrust engaged...
Further change is noted:
2 h 08 min 07: slight turn about 12 degrees to the left; turbulence level increased slightly; speed reduced to about Mach 0.80.
2 h 10 min 05 : autopilot then auto-thrust disengaged; airplane began to roll to the right...

Beside, AP disconnection, one not due to protections kicking (High AoA or High Speed) or Failures in relevant systems, then due to AP limits are:
- Aircraft attitude :
* Pitch > +25° or < -13°
* Bank > 45°

[HazelNuts39]

I also think the clogging was not one where in one-second the pitots were clear and then poof, in another second they were clogged. It probably happened on a gradual but ever increasing basis over these couple of minutes or so.I wonder on what consideration you base that assumption. On the basis of how a pitot tube 'works', it is not plausible at all. The BEA Update speaks of 'a sharp fall from about 275 kt to 60 knots in the speed displayed on the left PFD, then a few moments later on the ISIS'. The Air Caraibes Memo speaks of 'une diminution tres rapide de la CAS'. On the basis of the ACARS Fault message PROBE PITOT, BEA's Interim no.1 attributes the initiating event to 'a decrease of more than 30 kt in one second of the polled speed value'.

[DozyWannabe]

JD-EE, we were temporarily lead astray by forum members who apparently believed that autotrim would not resume control once you made a manual trim input.

That would be me, having misread the documentation I had.

I strongly suspect there is some misinformation adrift in the Airbus community that needs correction. I wonder how BEA will address that?

Again, it was just me - the "Airbus community" were the ones who kindly corrected me via PM.

The problem with the trim is that it moved to a high aircraft nose up setting without crew awareness.

But all indications suggest that the PF was commanding the elevator and by extension the THS to do just that - it didn't do it on it's own.

It appears that a FBW aircraft requires the pilot to know exactly what mode the aircraft is operating in or else the question arises, "What's it doing now?"

Not true. "What's it doing now" usually applies to modern autopilots (i.e. FMS/FMC), which are not restricted to FBW aircraft (the 757, 767, Classic and NG 737 and 744 have them for starters), nor indeed Airbus. As far as trim goes, all you need to have in the back of your mind regarding modes/laws is that in anything other than Direct Law and below, autotrim is active, so one needs to be wary of large, sustained inputs.

You are WAY out DW, and should know better ...

Really? How else am I to interpret at least 5 years of posts demanding that Airbus return to interconnected yokes and introduce a big red "Direct Law" button (as in the 777), not to mention continued belief in a conspiracy surrounding AF296 @ Habsheim?

If you keep taking tactile feed back away from a pilot, then you reduce him/her to a visual clues only input processor. If the FBW computers couldn't cope without valid airspeed information, is it a bit too much to expect a human to do a better job without the benefit of a "conventional aircraft's elevator feel"?

But "tactile feedback" has been artificially driven in every major airliner designed since the late '60s, and indeed is computer-driven in the case of the 777 - so if you're in a situation where you don't trust the aircraft, who's to say that the feedback you're getting is accurate?

Also, the FBW computers coped just fine with the loss of airspeed information. The A/P and A/THR kicked out, and some protections were lost but ultimately the pilots had a controllable aircraft.

And I believe we are in agreement with gums about the word "protections." The word sets up the wrong mindset leading to people getting reckless and cavalier about deadly serious subjects.

The problem is that "limits" (gums' suggested term) does not adequately describe what the system will do for you - for example, the Alpha Max/AoA protection will spool the engines to full thrust in the case of a sudden nose-up input - that's not a limit, it is - for want of a better term - a "protection". Also, your comment suggests that you believe some consider the existence of protections and their description as such might lead to a false sense of security - but from what I've learned from this thread, conscientious FBW Airbus pilots seem well aware of the limitations of said protections and the modes/situations in which they will not function.

[HazelNuts39]

Dozy;

While I agree with the entire post, just a minor semantic correction in your last paragraph to avoid confusion:

The protection that commands TO/GA (the EEC controls the spooling up) is named alpha-floor. IIRC it is activated in normal law when the AoA exceeds the corresponding threshold (between alpha-prot and alpha-max), sudden or not.

[rudderrudderrat]

Hi Dozywannabe,

But "tactile feedback" has been artificially driven in every major airliner designed since the late '60s,....
Correct. When manually flying I could "feel" the aircraft getting slow because the elevator would feel heavy in order to maintain altitude (until I manually trimmed the elevator). No so with AB FBW.

Also, the FBW computers coped just fine with the loss of airspeed information. The A/P and A/THR kicked out,.... I wouldn't call that "coped" - I'd call that given up!
Even my old Boeing 707 A/P would have remained engaged, all that would have been required would have been manual thrust adjustment.

[OK465]

Even my old Boeing 707 A/P would have remained engaged, all that would have been required would have been manual thrust adjustment.

If I recall, those old 707/727 autopilots would also remain engaged with a complete hydraulic failure (A&B) even though they couldn't "fly" the aircraft from that point.

I think they put in a special red light for that.

[takata]

To me, if Pitch transits got out of phase with Power, their could be trouble? Insofar as rate, I think Power up when Nose down would be problematic, as would the reverse. If the THS is in there, what is the calculated rate for stopping speed and Pitch excursions that are (or have become) unnecessary?
First, you should try to put those events into the right sequence, then your questions should be answered by themselves.

Autotrim large change took place past 0210:51 : "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." [BEA]

Why would you put absolutely this aircraft out of pitch trim before this point, beside trying to fit something squared into your rounded mind?
If THS trim, for whatever reason, was something else than 3 deg NU before 0210:51, it reverted to this setting, then reached 13 deg NU between 0210:51 and 0211:50.

How does it fit now with your question?
Ask yourself.

[jcjeant]

Hi,

At the risk of parsing too closely, In the audio where the pilots are noticing "No indications", is it surprise one senses? Or Betrayal? There is a subtle difference between the French and English about this conversation
In the French text is "indication" (singular form) and in the English version is "indications" .. ( plural form)
This is very different :eek:
I wonder how it's possible to make a difference of plural or singular form .. when a french tell "indication" as it's no difference for mark (voiced) the plural !!
So why make a difference between the versions :confused:

[Turbine D]

Originally posted by HazelNuts39
I wonder on what consideration you base that assumption. On the basis of how a pitot tube 'works', it is not plausible at all.

From Airbus Abnormal Procedures 2.05.80:
Drain Holes Free:
The IAS may fluctuate or drop quickly towards the sticker shaker speed. The IAS behavior depends on the condition of the pitot tube drain holes.
The sensed Pt drops quickly towards static pressure (Ps).

[DozyWannabe]

Correct. When manually flying I could "feel" the aircraft getting slow because the elevator would feel heavy in order to maintain altitude (until I manually trimmed the elevator). No so with AB FBW.

Thus far we have not had a serious UAS incident on the 777 to see what the latest generation of "artificial feel" will do when a significant data source is compromised.

I wouldn't call that "coped" - I'd call that given up!
Even my old Boeing 707 A/P would have remained engaged, all that would have been required would have been manual thrust adjustment.

I think you're misunderstanding the point I was making - the FBW system is distinct and separate from the Autopilot/FMC system. They pass data back and forth where necessary, but they are entirely different in terms of purpose, hardware and software. Now, as to what you're saying about old-school autopilots, IIRC in the 707 we're not talking much more than a wing leveller and altitude hold with a turn function. It didn't have an autothrottle or try to manage your speeds, ergo pitot information had no bearing on the design of the thing. Modern aircraft are very different in that respect and autopilot/FMS functionality much more all-encompassing.

Personally I think Airbus made the correct decision to disengage A/P upon confirmed ADR DISAGREE, and yet again we're back to Birgenair, where the A/P did continue to try flying the aircraft with blocked pitot and an erroneous overspeed warning. The result was that the aircraft had a very high pitch angle and it was only the massive amounts of thrust and a hard limit on FMC authority that kept the thing in the air. For all the stick Airbus come in for due to supposedly "encroaching on pilots' authority", their systems are designed to put the pilot in charge very early on in the failure sequence.

[HazelNuts39]

jcjeant,

I suppose you didn't notice the other difference, the Special Foreword To English Note?

To me, the noticeable element in this exchange is that the PNF acknowledges the PF's announcement, but at the same time corrects it, by adding the word 'valid'. IOW, there were indications but they were not considered valid.

[takata]

Hi jcjeant
There is a subtle difference between the French and English about this conversation
In the French text is "indication" (singular form) and in the English version is "indications" .. ( plural form)
This is very different
Agree... and it is not the only one.
The reference text is the French version, in any case, the English one being a hurried translation (as to your "why?").
Another point very badly translated, where Bearfoil's is driven to interpret it as a non-sense, is this one:
English: "The airplane’s pitch attitude increased progressively beyond 10 degrees and the plane started to climb" -- here was also the error with angle-of-attack.
Bearfoilly's : "At PITCH +10, the a/c began to climb."
French : "L’assiette de l’avion augmente progressivement au-delà de 10 degrés et il prend une trajectoire ascendante."

In fact, the poor French syntaxe (in context) was badly translated in English, and Bearfoil's reading was, at the end, completely wrong ("only when pitch reached +10°, the aircraft started to climb").

What it means basically was :
"pitch attitude increased progressively (above +10°) while the aircraft trajectory was starting to climb".
As, of course, the climb did not start only when the pitch was above +10 (plane attitude changed smoothly), despite all those inertial forces involved.

[rudderrudderrat]

Hi Dozy,
Thus far we have not had a serious UAS incident on the 777 to see what the latest generation of "artificial feel" will do when a significant data source is compromised.
I'm not qualified on 777 - but I am led to believe Boeing have fitted the "big red button" - so that it would fly just like a very large 737. (with all the tactile feed back one could want aka Direct Law).

[HazelNuts39]

According to the Update, between 2:10:16 and 2:10:50 'the speed displayed on the left side increased sharply to 215 kt (Mach 0.68)'. At 2:11:06 the speed on the ISIS increased sharply towards 185 kt, and was then consistent with the other recorded speed.

If one of the PFD's had been switched to ADR3, would that be recorded on the DFDR?

[DozyWannabe]

I'm not qualified on 777 - but I am led to believe Boeing have fitted the "big red button" - so that it would fly just like a very large 737. (with all the tactile feed back one could want aka Direct Law).

I'm no expert on the 777, but as I understand it there are no "laws" to the system design akin to those of the Airbus system. Now - you've got your "tactile feedback", but it's computer controlled, based on the inputs the flight computers are receiving from the various sensor systems. Take those inputs away and I'm not sure what the back-driven system will do in response.

[takata]

my feeling is:
The pilots were rated on type ... but nevertheless were not qualified for the situation of AF447 was
They had not knowledge of basic flying skills
They don't know how the Airbus systems work

So we can conclude that:
The formation and training of those pilots is very low
So Air France bear all the responsibility for this accident by not providing adequate training to their pilots or not detecting by exams (simulator) that those pilots were not qualified for fly a Airbus A330
At least and even if this above is not entirely true .. Air France stay bear the responsibility of this accident as the contract between Air France and their passengers was to transport them from A to B and they failed....
Are my feelings good ?
Certainly not.
Placed on the very same situation, but with hindsight about the outcome, most pilots, including any member of AF447 crew would certainly not make the same errors : basically, they would understand quickly that they will stall, or that they are already stalling, then certainly they will act properly to recover. Nonetheless, everything is pointing that this did not happen during this night.
Maybe, this very same scenario, played in the simulator (up to the point it could play it), with the same crew could have ended differently... who knows? Maybe the PF records during his sim checks was also near perfect? So the basic question of the investigation is to address the real security issues, not to find who seems "guilty" of what.
As for the level of civil responsability to be shared between the manufacturer, the company or the crew, honestly, this should be left to the court to decide. In the future, we'll be certainly allowed to comment its conclusion to the death. As a matter of fact, for me so far, any actor involved is possibly responsible of something wrong in the process leading to this catastrophe. But then, I need first to understand what it was exactly and why he was acting like that.


Hi HazelNuts,
I wonder on what consideration you base that assumption. On the basis of how a pitot tube 'works', it is not plausible at all. The BEA Update speaks of 'a sharp fall from about 275 kt to 60 knots in the speed displayed on the left PFD, then a few moments later on the ISIS'. The Air Caraibes Memo speaks of 'une diminution tres rapide de la CAS'. On the basis of the ACARS Fault message PROBE PITOT, BEA's Interim no.1 attributes the initiating event to 'a decrease of more than 30 kt in one second of the polled speed value'.
Spot on!
Now that everything is showing that stuff involving AP & THS fantasy laws are not worth the bandwith, we should go back to the basics of Unreliable Airpseed Events... if we really want to understand what kind of situation was faced by AF447 crew, and possibly discuss what could have confused the PF and crew. PJ2, Chris Scott and few others have already tried (more than once) to bring back this thread on the cockpit confusion (hence, ergonomics and interface issues) but it looks much less sexy than talking about any Airbus Systems getting confused.

According to the Update, between 2:10:16 and 2:10:50 'the speed displayed on the left side increased sharply to 215 kt (Mach 0.86)'. At 2:11:06 the speed on the ISIS increased sharply towards 185 kt, and was then consistent with the other recorded speed.
If one of the PFD's had been switched to ADR3, would that be recorded on the DFDR?
I guess that what is recorded is ADR1 & 3 airspeed channel, independently from where it is displayed (hence the choice of ADR3 instead of 2 as it could be displayed to Captain's PFD). Note, your typo about 215 kt (Mach 0.86)?!

[bearfoil]

I await the news of BEA next report as everyone does.

Perhaps it will clear up this confusion. When autopilot dropped out, the PF made immediate inputs, and heard the STALL Warning, two times.

What could the autoflight have done to get this aircraft to so obviously be nibbling at aerodynamic STALL? If dropping a/s reads, would the ap have increased power to such an extent that both engines were blazing away, and altitude still was dropping?

By definition, this is UPSET. At some point later, the onset of zoom climb qualifies technically as Loss of Control (LOC).

We hear the PF "I have the controls". So after the uncontrolled zoom climb starts, we will certainly hear PNF on the radio reporting "Out of...."

Will there be a MayDay in there as well? I believe we will hear at least one.

takata, you are wishful thinking. I know the feeling, and you have it.

[ChristiaanJ]

....In the French text is "indication" (singular form) and in the English version is "indications" .. ( plural form)
This is very different :eek:Obviously you do not know any spoken French, or you wouldn't have posted this.
Spoken French tends to elide the last letter of most words.
In 99% of cases that's not a problem, since the meaning is obvious from context.
In this case it isn't... but please stop playing Sherlock Holmes, when you have no significant clues, and English is clearly not your mother tongue either.

[DozyWannabe]

takata, you are wishful thinking. I know the feeling, and you have it.

Pot, meet kettle.

Seriously - takata's going on the evidence we have so far and you're still working on the supposition that the aircraft must have done something on it's own despite everything that we've been told - because, as you said before, you don't want to believe that the PF made a basic error and then compounded it.

We don't have anywhere enough information to make a call yet, but if you expect us to take your input seriously then you must also equally consider the possibility that - aside from the pitot issue - there was nothing wrong with the aircraft and that the upset was pilot-induced.

[bearfoil]

Doze. But which pilot?

Dazzle me with a theory of a Near STALL widebody at handoff. Because if you cannot, I will continue and suggest that the unreliable airspeeds were caused by the Rolling moment of a fast widebody in chop, and that the discrepant reads were made so by the airstream losing its integrity at the lower nose, while she mushed on full of gusto and KE. Not to mention plenty of NU. Hopefully BEA will fill the void they created between 2:08:07 and 2:10:05. Then I'll buy you an adult beverage of your choosing. My soul is ready, how's yours?

Lily White Auto?

[takata]

Hi Christiaan,

Obviously you do not know any spoken French, or you wouldn't have posted this.
Spoken French tends to elide the last letter of most words.
In 99% of cases that's not a problem, since the meaning is obvious from context.
In this case it isn't... but please stop playing Sherlock Holmes, when you have no significant clues, and English is clearly not your mother tongue either.
You are of course totally right concerning the CVR transcript but let me complete the explanation for people who don't know that, in French, the pronounciation of such sentences would be phonetically exactly the same :
« je n’ai plus aucune indication » <=> « je n’ai plus aucune indication(s) »
« on n’a aucune indication qui soit valable » <=> « on n’a aucune indication(s) qui soi(en)t valable(s) »
Nonetheless, in both case, the plural form is incorrect ; the correct written form would be a singular "aucune indication" (not a single indication)... which, in turn, could also mean that they have lost "all indications"... go figure!!
This would be a problem with most transcript when spoken and written forms could have different meanings as this is really ambiguous to be sure what exactly "indication(s)" is aimed at.
It could be : "je n'ai plus aucune indication [de vitesse] => lost all speed indications, or anything else lacking on his instruments pannel as it is "undefined". This could be addressed with context as it could be about whatever "indications" they were talking about before, or after. Beside, I also believe that jcjeant is also fluently speaking his mother tongue.

[henra]

Dazzle me with a theory of a Near STALL widebody at handoff.


bearfoil,

please bear in mind that the gap betwen Alpha = 2,5° (Cruise AoA) and Alpha = 4° (Stall Warning) is not really much if you are forcing the aircraft from level flight to a RoC of 7000fpm within seconds.

A Pull- Up sufficient to achieve this RoC in a short time would be easily sufficient to briefly exceed the STALL WARNING threshold (which is btw not the real stall AoA), especially when some turbulence contributes to it.

[Zorin_75]

What could the autoflight have done to get this aircraft to so obviously be nibbling at aerodynamic STALL?
How's an a/c "nibbling at stall" supposed to do that 3000 ft climb?

[jcjeant]

Hi,

So the basic question of the investigation is to address the real security issues, not to find who seems "guilty" of what.
As for the level of civil responsability to be shared between the manufacturer, the company or the crew, honestly, this should be left to the court to decideAcademic blah blah :)
I have not to learn you the fact that the real security issues will point to some actors
And the court will point exactly the same actors with some nuances ... that's a lawyers game to be performed .. for the spectators we are :)
Rarely a court of justice will point responsibilities to actors not already involved in the security issues
It's granted that the pilots will take the most of the weight .. and so by consequence .. AF for many negligence
Placed on the very same situation, but with hindsight about the outcome, most pilots, including any member of AF447 crew would certainly not make the same errorsYourself have already the verdict !
All this will be confirmed in some loooong years ... when all the smoke is settled :)

[henra]

Hi,

Academic blah blah :)
I have not to learn you the fact that the real security issues will point to some actors
And the court will point exactly the same actors with some nuances ... that's a lawyers game to be performed


But being on an aviation forum I find it waaaay more relevant and interesting to find out what went wrong and why than assigning blame to any of the involved parties. There are other professions who are paid to to the latter and I'm more than happy to leave that part (which I find not very pleasing) to them.
Therefore count me in for the academic blah blah as well.

[Turbine D]

@ takata
Now that everything is showing that stuff involving AP & THS fantasy laws are not worth the bandwith, we should go back to the basics of Unreliable Airpseed Events... if we really want to understand what kind of situation was faced by AF447 crew, and possibly discuss what could have confused the PF and crew. PJ2, Chris Scott and few others have already tried (more than once) to bring back this thread on the cockpit confusion (hence, ergonomics and interface issues) but it looks much less sexy than talking about any Airbus Systems getting confused.


So far this thread plus the previous four total 9677 posts and counting. Apparently, questioning, probing and trying to understand technical and engineering "stuff", as you put it, regarding the aircraft and its FBW controls seems to be not the thing to do in your mind. The conclusion seemingly has been reached by you, ergonomics and interface issues were the cause, end of discussion. It will be interesting to see if in the final BEA report if they are in agreement with your conclusion. Hopefully, they will have a more "in depth" examination that goes beyond your present "bandwidth."

[gums]

Hard to keep up, and I am a very fast reader.

- Zorin asked about the autotrim, and others have tried to figure it out. From what I see of the tech manuals and inputs from other contributors, it looks like a basic way of providing the elevator the most authority and reducing the drag of an elevator that is "x" degrees deflected to maintain the current gee or AoA command.

Bear in mind that my primitive FBW system did not have an elevator at the rear of a horizontal stabilizer ( HS). The whole HS moved for pitch commands.

As with the 'bus, HAL "auto trimmed" to our gee command trim setting. Unlike the 'bus, we could trim for a gee, and not be limited to a one gee command.

- Gerard asked a great question, and it is one of mine.

What was the "stall warning" all about after the pilot pushed over a bit?

- Chris brought up the relatively benign deep stall characteristics. It's what got me joining this august grope of "experts", wannabe's and actual 'bus drivers. And others.

All who have flown a delta wing raise your hands! Concorde counts. Mirage variants count. The one I flew as a yute was so deceptive that it was scary - F102. Very slight "buzz", but no real buffet or burble. Great directional stability and lateral stability. But the altimeter was pegged at 10,000 feet per minute going down.

The modern commercial heavies have really great aero characteristics that can make a stall insidious. And the stall is not like the Airbus manuals depict on the lift versus AoA curve. There is no sharp break in the curve at "x" AoA. It's a very gentle curve and one can fly at fairly extreme AoA's without the sharp pitch excursion we all saw when checking out in a Chipmunk or Cessna or T-28 or......

The problem occurs when the jet reaches a certain AoA and c.g. and speed combination that prevents normal pitch down commands from being effective. It's that pitch moment graph I posted years ago ( heh heh).

The test pilot maneuver resulting in a deep stall that I posted was not the classic entry to a deep stall in the Viper. The classic entry was a fairly steep pitch, low gee, rapidly slowing speed, and running outta air molecules for that HS or THS to use to get the nose back down. Does that sound relevant here?

I gotta admit, that from this old fossil's FBW experience and perspective, that there are too many autopilot functions embedded in all the 'laws". The jet seems perfectly capable of flying to the basic limits that all the heavies, if any, can match. And my problem is the "basic" limits seem to take short shrift behind roll angles, autotrim, mach warnings, etc. etc. ad nauseum. Then I read here that one reversion law commands the motors!! BEAM ME UP!! If not in some autopilot mode, let the plane fly. Sheesh.

I thank all here for allowing a "lite" pilot with some FBW experience back when the Earth was still cooling to participate. I am now SLF, and I wanna feel comfortable about the jets I ride in.

[takata]

Placed on the very same situation, but with hindsight about the outcome, most pilots, including any member of AF447 crew would certainly not make the same errors
Yourself have already the verdict !
All this will be confirmed in some loooong years ... when all the smoke is settled
If you were not such a :mad:, you would understand that anybody, including pilots, may be induced in error, even by serious Air France or Airbus shortcomings. So first step is to understand what goes wrong.
Stop trolling, please.

[bearfoil]

Honestly, my picture of the accident includes everything I read here. I don't reject anything, you may notice my input has to do with proposing some things, some perhaps a bit bizarre, but what about this accident is NOT unusual? I do intend to embrace the Truth when it arrives, my perspective may not project that, but questions cause thought, unless rejected, and I think that is too bad.

This thread exemplifies what I think is a solid plus in analysis. There is no boardroom with a coffee maker and sandwiches which instill a faux civil atmosphere. It is a rare pilot who can be scrupulously objective. There are plenty here, and I admire all the people who post here.

As of now, it looks rather bad for the pilots, all three. I cannot figure out why in the world BEA would accede to pressure to release such an unsatisfying Note. It has made the adversarial nature of the discussion ever more polarized, not that it has any relevance on their Report.

[takata]

Hi Turbine,
So far this thread plus the previous four total 9677 posts and counting. Apparently, questioning, probing and trying to understand technical and engineering "stuff", as you put it, regarding the aircraft and its FBW controls seems to be not the thing to do in your mind. The conclusion seemingly has been reached by you, ergonomics and interface issues were the cause, end of discussion.
Certainly not. Discussing systems and engineering "stuff" is very fine with my bandwith allocation. What I'm very less interested is about such fallacious and circular argumentations based on nothing but greviances, which discards investigation work in order to insert some supposed hidden informations, revealing the cover up of imaginatory supposed "facts".

I'll give you an example:
Bearfoil's point is that the aircraft attitude at AP disconnection was in some abnormal attitude (pitched down below -13°) and slow, but fast - such fact, of course is hidden by the BEA - then UAS was immediately due to "turbulent airflow" while she zoomed 3000 ft due to crazy THS systems triming her to the max because of some nose down roll tendency, but Pilots fought the roll and nose up pitch, but were few seconds later back to 3NU which was now increasing to 13NU while applying full back stick during half a minute, and so on...

Here, let me tell you that it is in fact a huge waste of bandwith, in my book.

[GarageYears]

I have followed this thread since Day 1 and contributed occasionally and asked questions when my personal knowledge ran out. It seems a great pity that we have to persistently wade our way through piles of cr*p to get to the 'good stuff', and most recently I have to take issue with bearfoil. With the exception of little green men from the planet Zog, it seems that any kooky idea with a shred of Airbus-itus (definition: anything built by Airbus must be implicitly designed to screw with the crew in some nefarious and more convoluted manner than it did in the previous post) must be somehow to blame, and blow me down with a feather, the crew must have been overtaken by HAL as it went increasingly 'nuts' (obviously hell bent on dashing the airplane into the ocean despite the heroic efforts of the crew).

The last post I bothered to read by bear involved some absentmindedly forgotten-by-BEA nose-down pitch (of -9 degrees!) and overspeed (I think it was), that the PF fought against resulting in the zoom-climb of doom....blah, blah, blah.

Look I'm all for theories, but let's face it - this imaginary world belongs firmly over in Rumors and News. Please take this lala-land and post it where it belongs. Please.

I have learned so much over here in the relative sanity of the Tech Log - massive :ok: to mm43, gums, Chris Scott, Turbine D, takata, henra, PJ2, DW, '33' and others. The sanity you have brought here is greatly appreciated.

I'm not sure what this post itself contributes other than allowing me to vent some... :{

[A33Zab]

Quote:
What could the autoflight have done to get this aircraft to so obviously be nibbling at aerodynamic STALL?
How's an a/c "nibbling at stall" supposed to do that 3000 ft climb?


Just before!

In NORMAL law αsw = 23° (fixed value for all flight phases)
In ALT & DIRECT Law αsw = function of M and S/F config.
S/F is not applicable, in this flight phase αsw = function of M only.

αsw---- MACH
10.8°-- <= 0.28
9.9°--- <= 0.35
7.6°--- <= 0.53
5.2°--- <= 0.75

3.8°--- <= 0.866

-Inhibited M >0.866
-Inhibited on GND (if not in test)

[takata]

But which pilot?
Dazzle me with a theory of a Near STALL widebody at handoff. Because if you cannot, I will continue and suggest that the unreliable airspeeds were caused by the Rolling moment of a fast widebody in chop, and that the discrepant reads were made so by the airstream losing its integrity at the lower nose, while she mushed on full of gusto and KE. Not to mention plenty of NU. Hopefully BEA will fill the void they created between 2:08:07 and 2:10:05. Then I'll buy you an adult beverage of your choosing. My soul is ready, how's yours?
Well, it seems I'm the one making wishful thinking while an endless Bearboiling of circular points seems to make your own days. Obviously, what makes you think that she was near STALL at handoff, when AP kicked off, is that the STALL WARNINGS sounded twice, then stopped. On the other hand, in many UAS case, without changing anything about the flight parameters, this happened exactly the same.

From here come your insistence that she could not have been in "controled flight", no matter if everything else is pointing that she was, except a starting roll to the right.

On the other hand, I have already underlined many other cases of UAS events recorded that are obviously pointing at exactly the same "suspect" stall warnings when the FLIGHT LAW is switched from NORMAL to ALTERNATE. For me, this is certainly a major issue (if confirmed) of the Warning System because I really think that it could have played a major role during the following sequence leading to the total loss of control by the crew.

In fact, there is a VERY simple BASIC rule in the system :

* NORMAL LAW -> COMPLETE SAFE FLIGHT ENVELOPE USED BY ELECTRONIC FLIGHT CONTROL SYSTEM
* ALTERNATE LAW -> REDUCED SAFE FLIGHT ENVELOPE USED BY ELECTRONIC FLIGHT CONTROL SYSTEM

Hence, any switch from NORMAL to ALTERNATE LAW should be immediately followed by a reduction of the safe flight envelope at both ends : in clear, the safe margin should be expanded concerning both the overspeed warning and the stall warning (nonetheless, the aircraft real "flight envelope" is still the same, but its defined "safe limits" are changed due to some certification concerns about its systems state and possible manual flight).

1) In our case, the high speed limit warning would be reduced from Mach 0.86 to Mach 0.82. Also, the low speed warning (alpha-prot) could be rised (I did not find the relevant data about it, then, if wrong, see point 2).

Nonetheless, neither overspeed nor stall protections could be applied because of the current declared airspeed monitoring by EFCS : ALT2 is immediately applied, no protection could kick without a valid airspeed ; After this point, the PFD function displayed (overspeed and stall warning speed limits) will disapear from both PFD.

Next, following an UAS confirmed in ALTERNATE LAW, the calculation mode of this stall warning limit will change again from one function using an AOA corrected by a Mach value supplied by those ADRs to another one using a default Mach parameter. This would change the granularity of the AOA measured and subsequently will increase the margin for the stall warnings.

My explanation (so far) is that, when UAS is declared, there is a small time window where the limitation of the safe flight envelope is applied to the stall warning limit which last during the resolution of an UAS monitoring : it takes 10 seconds for the system in order to confirm ALT2 (after that, the system could not subsequently revert to NORMAL LAW without a full ground reset).

So in fact, the aircraft, during those 10 seconds window, without changing any flight parameter, will fly at speed closer -or below- the threshold of the STALL WARNING speed. But, following the UAS confirmation, the new function will apply another AOA warning limit. Then, this would stop the WARNINGS... if the reduced threshold has been overshot during those 10 seconds. So my bet is that the STALL WARNINGS stopped at 0210:14 and would have sounded during the 0210:05-0210:14 time window.

2) If alpha-prot calculated speed do not rise when switching to ALTERNATE, another simple explanation is that a drop of the polled speed, due to unreliable airspeed situation, is not filtered by the stall warnings during the same defined 10 seconds time window. Hence, if the polled (unreliable) speed goes below alpha-prot speed, this alarm is sounding. Once UAS is confirmed, as precedently, the new UAS STALL WARNING function is declared and the alarm is stopped.

Those 2 points are based on the history of published UAS events :
Here are the tables of the 36 UAS events declared before the publication of 2nd BEA report; one may see that 12 cases of "suspect" STALL WARNINGS were reported (33%). Moreover, those stall warnings do not let any trace outside the CVR or crew reports (they are not part of the maintenance post flight reports), and this survey was mostly incomplete about many cases listed. So it may be assumed that more cases of "suspect stall warnings" were not recorded.
http://takata1940.free.fr/list.jpg

http://takata1940.free.fr/stall.jpg

[Machinbird]

Dozy, multiple quotes:
Originally Posted by Machinbird http://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/buttons/viewpost.gif (http://www.pprune.org/tech-log/456874-af-447-thread-no-5-a-post6563886.html#post6563886)
JD-EE, we were temporarily lead astray by forum members who apparently believed that autotrim would not resume control once you made a manual trim input.

That would be me, having misread the documentation I had.

Quote:
I strongly suspect there is some misinformation adrift in the Airbus community that needs correction. I wonder how BEA will address that?
Again, it was just me - the "Airbus community" were the ones who kindly corrected me via PM.

Dozy, you can't take all the responsibility, there were others as well putting out this misinformation.

[takata]

Dozy, you can't take all the responsibility, there were others as well putting out this misinformation.
To be fair with Dozy, this "misinformation" comes from Airbus itself, as the manual states in one page that the use of manual trim will "freeze" autotrim, and somewhere else that the PRIMs do not fault when manual imputs are applied, but that the PRIMS will re-synchronize with the manual trim imputs, which have the priority over autotrim.

[Machinbird]

Takata,
Quote:
Originally Posted by Machinbird
The problem with the trim is that it moved to a high aircraft nose up setting without crew awareness.
Takata
Any pilot flying an aircraft with autotrim should know that his trim will follow his stick imputs, shouldn't he?Yes, assuming he knows he made the stick inputs.
Quote:
Originally Posted by Machinbird
It appears that a FBW aircraft requires the pilot to know exactly what mode the aircraft is operating in or else the question arises, "What's it doing now?"

TakataIsn't it one of the basic skill needed for one wanting to be rated for a specific type? What makes you think that many FBW pilots don't know exactly in what mode their aircraft is operating? Takata, suppose we sat a pilot down and hit him with a fire hose stream. Do you think he can remember his birthday while this is going on?

Perhaps a couple of recent accidents make me think that way.


Quote:
Originally Posted by Machinbird
In the case of the AF447 crew, they had no attention to spare to consider what the trim might be doing

Well, considering that the trim was doing what a type rated PF asked, and what it is always supposed to do in such a case, what would be the point to consider that it would take more "attention" than usually?Takata, have you ever been in a really stressful situation while flying? From your comments, it appears that you have not. That is fortunate for you, if so, but it gives you a blind spot with respect to the effects of in flight stress. You seem to be assuming that the initial pitch up to FL375 was deliberate.
Quote:
Originally Posted by Machinbird
thus the nose up demands caused the trim to run silently to a high setting

Hence, as usual when imputs ask for a lot of nose up, what is wrong with that? Nothing down low when setting up for a landing, a whole lot is wrong when it happens at cruising altitudes. The problem is the silent motion of the trim. They needed to know it was moving so that they could monitor it.
Quote:
Originally Posted by Machinbird
without the knowledge or anticipation of the crew.

What make you believe that a type rated crew would not anticipate it or lacked the knowledge that it will do exactly that? Do you think that it wasn't what they wanted, nose up?Yes, I think that they didn't want all that nose up initially. Later, after the stall, who knows?
Quote:
Originally Posted by Machinbird
Once at a high setting, the trim acted to stabilize the aircraft in the deep stall that they eventually achieved.

Right, the PF achieved a full stall with the help of the side stick, thrust and THS trim. Hence, what's wrong with the side stick, the thrust lever and the THS trim?Just an opinion at this point, but the addition of TOGA thrust coinciding with the second stall warning is too reminiscent of an airline approach to stall procedure as recently taught, except pitch control was improper/clueless as it had been since PF said"I have the controls."
Once in the stall, it was imperative that stall recognition occur, but it seems, it didn't. Without AOA indicatiors, without stall warning, without comprehending that the decreasing altitude was real, there was one final item that could have explained the situation and that was the THS trim position.
Quote:
Originally Posted by Machinbird
When the Captain arrived on the flight deck, he had to puzzle out what he was seeing. From the jump seat, the indications were essentially hidden by the wheels themselves.

Beside hindsight, what makes you believe that the Captain would have immediately recovered the situation with all the trim settings displayed under his nose? He wasn't there from the begining of the crisis and still possibly far behind the other pilots. He also might have seen the Flight Control page, where the THS trim setting is displayed, right in front of him... There is no surety that the Captain would have been able to puzzle out the situation in time if he had seen the THS trim, but if he had noted its very abnormal position, there is a logical thought process that should follow that would lead to stall recognition. For him to check the THS position, he would almost certainly have to form the thought to check it and then lean over for a peek.
Quote:
Originally Posted by Machinbird
The THS autotrim system has virtually eliminated the problem of trim-runaway, but it has replaced that problem with a new set of problems.

I still can see the problem with the THS trim. If they had acknowlegded their stalled situation in time, they would have immediately applied full and sustained nose down imputs, hence, THS trim would very likely follow that. If, for whatever reason, THS trim would not follow those imputs, not enough elvators authority should have attracted PF attention about considering that trimming nose down could help him... at least, theoretically if his training level wasn't the issue. We seem to agree that they likely never tumbled to the fact they were in a stall. The recent Perpignan trim related accident combined with the AF447 accident seem to indicate that there are issues in trim position awareness in Airbus land.
My apologies for a rather cursory reply, unfortunately I have limited time during the week.

[CONF iture]

However, in the BEA Update, dated May 27, 2011, The weight of the aircraft was again reported at around 205 t, but the balance was changed to 29%, or in other words moved forward 8% or so.

TD, I have partially addressed your question here (http://www.pprune.org/tech-log/454653-af-447-thread-no-4-a.html#post6516330).
As the take off CG was very much forward (23.3%), and despite the aft fuel transfer, I figure the ideal target of around 38% for fuel saving could have been approached only toward the late stage of the cruise phase, not after 3 hours of level off.

To have a CG more fwd than aft should help for the handling, and stall recovery as well ...


Really? How else am I to interpret at least 5 years of posts demanding that Airbus return to interconnected yokes and introduce a big red "Direct Law" button (as in the 777), not to mention continued belief in a conspiracy surrounding AF296 @ Habsheim?

I don't demand much, just criticize what, IMO, deserves such.
You, obviously, do not tolerate such critics to be made. Fine with me.

As you're not willing to publicly discuss Habsheim, despite my invitation, why can't you quit mentioning it ... ?

[takata]

Hi Machinbird,
Any pilot flying an aircraft with autotrim should know that his trim will follow his stick imputs, shouldn't he?
- Yes, assuming he knows he made the stick inputs.
- You seem to be assuming that the initial pitch up to FL375 was deliberate.
- They needed to know it was moving so that they could monitor it.
- Yes, I think that they didn't want all that nose up initially. Later, after the stall, who knows?

Well, I would say that what the PF really wanted during his initial imput is quite irrelevant concerning the "THS issue". You should read again the BEA note as you seem to be the one assuming that the THS was trimmed during the initial climb to FL375 (please, don't trust everything Bearfoil is posting!). You'll discover that everything started a while later: this THS was trimmed from 3NU to 13NU between 0210:51 and 0211:50, therefore, until this point, everything seems about right about its behavior:

"0210:51, the stall warning was triggered again. The thrust levers were positioned in the TO/GA detent and the PF maintained nose-up inputs. [...] Around fifteen seconds later, [...] The PF continued to make nose-up inputs."

What would make you believe then that the PF maintained (at this stage) all those nose-up imputs without knowing it?

Once in the stall, it was imperative that stall recognition occur, but it seems, it didn't. Without AOA indicatiors, without stall warning, without comprehending that the decreasing altitude was real, there was one final item that could have explained the situation and that was the THS trim position.
In fact, stall warnings seems to have sounded correctly at this point (see above) while the PF was trimming his THS near its max by applying sustained NU orders! Hence, this THS was fully trimmed during the stall sequence, not before it!
Without puting the sequence in the correct order, this will be fairly useless to discuss its usefulness as to alert you that you are going to stall, when you are fully stalled, but still trimming it the other way!

Beside, I also believe that there is a great deal of chance that the initial PF nose-up order, and following climb, was not voluntary but rather the result of an overcontrol of the roll tendency. Nonetheless, this is absolutely not the issue discussed about this THS setting. When THS goes there, it is quite hard to believe that the PF wanted something else than those sustained nose-up orders... Consequently, what more could he have learned from his THS setting that he already didn't knew while pulling up?

Your concern about it is only understandable with hindsight. Should they have tried to recover from a stall, at some point, this certainly would not help... but then, he put it here at the first place when it was certainly not the right thing to do at all...
My point stop here on this subject.

[Machinbird]

Hi Takata,
Just a brief note, my assumption is that the trim initially traveled slowly nose up and began to really move as the aircraft approached the stall. I do not attribute the nose up attitude to the trim as some are wont to do, it was merely the result of more nose up input than nose down input from the SS, averaged over time-that and what must have been a completely fouled up scan.

Is there any sort of pitch indication adjust function on the PFD? The PF's control inputs act like he had an erroneous level flight pitch setting. I am strictly a steam gauge guy so I've never had the opportunity to see how the other side currently lives.

[Machinbird]

In fact, stall warnings seems to have sounded correctly at this point (see above) while the PF was trimming his THS near its max by applying sustained NU orders! Hence, this THS was fully trimmed during the stall sequence, not before it!Yes it did, but look at it from the standpoint of the PF. He got a stall warning and applied what to him seemed like an approach to stall recovery, and the stall warning eventually extinguished (because he was deeply stalled). The aircraft attitude changed very little. Why should he think he was stalled. He just didn't have airspeed indications, and now the aircraft is acting really strange, dropping wings and things like that, and the altimeter is doing the digital equivalent of unwinding.:eek:

[rudderrudderrat]

Hi Machinbird,
He got a stall warning and applied what to him seemed like an approach to stall recovery....
I agree & in 2009, there was no stall warning procedure in the QRH.
The guidance was buried in FCOM, Supplementary Techniques, Flight Controls which describes the initial actions which the PF took.

"An aural "STALL, STALL, STALL" warning sounds at low speeds. Upon hearing it, the pilot must return to the normal operating speeds by taking conventional actions with the controls:
Thrust Levers...TOGA
At the same time:
Pitch Attitude...Reduce
Bank Angle...Roll Wings Level"

Unfortunately he then lost the reference power setting he had before the UAS event. I would guess that he recalled the power and pitch attitudes he learned during his conversion course for unreliable speeds and remembered the TOGA + 15 degs pitch ... (but that doesn't work at FL 375.)
The next bit reads "Thrust/Pitch .... CL/5degs Above FL 100"
but by then they were so very deep into the stall they would have needed at least 10 degs nose down to accelerate.

[HazelNuts39]

Here are the tables of the 36 UAS events declared before the publication of 2nd BEA report; one may see that 12 cases of "suspect" STALL WARNINGS were reported (33%). Why do you label these stall warnings 'suspect'? BEA has investigated several of these cases and writes in its Interim Report No.2: Stall warning. Nine cases of triggering of the stall warning were observed. (...) All of these warnings are explicable by the fact that the airplane is in alternate law at cruise mach and in turbulent zones. Only one case of triggering was caused by clear inputs on the controls.
Note: At high altitude, the stall warning triggers in alternate law on approach to the stall. The stall manifests itself particularly through vibrations.I think there are number of other statements in your post that you may wish to rethink. Alpha-prot is the AoA at which Normal Law changes from an Nz law to an alpha-law. In this connection you are several times referring to speed where the reference should really be to AoA (*). Alpha-prot is only relevant in Normal Law and I doubt it is even calculated in Alternate Law since it has no significance in that law. In Alternate(1) there is a protection called 'Low Speed Stability' that is driven by IAS instead of AoA, and changes alternate law to direct law. It is active from about 5 kt up to about 10 kt above the stall warning speed (*), depending on weight and slats/flaps configuration. Low Speed Stability is lost in Alternate (2) Law.

P.S.:: (*) For given configuration, weight, c.g., and altitude, AoA is a function of Mach and load factor. V-alphaprot and V-alphamax shown on the speed scale of the PFD are calculated for 1 g from alpha-prot and alpha-max, respectively. V-S/W is calculated for the actual "gee" and the stall warning threshold AoA.

[DJ77]

The other unclear factor is how the C* pitch-function of the EFCS would treat the invalidation of CAS (IAS) data, when determining the crossover from g-control to pitch-control. As I understand it, that crossover is normally a gradual transition as the airspeed falls below a certain figure in routine flight.

Please, what is this transition from g-control to pitch-control you are talking about and where is it described in the FCOM? Does it apply to A-330?

[Turbine D]

CONF iture

Thanks for the CG explanation. That was something I was trying to understand, and I missed it in your previous posts.

[jcjeant]

Hi,

takata
If you were not such a http://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/smilies/censored.gif, you would understand that anybody, including pilots, may be induced in error, even by serious Air France or Airbus shortcomings. So first step is to understand what goes wrong.
Stop trolling, please. takata I will tell you what goes wrong and will be wrong in the next decades
During the next ten to twenty years .. forecasts show that companies will grow very quickly (especially those of the Persian Gulf region)
The demand for pilots and other personnel will be huge
The consequences of these expansions will be reduced formation and training while the aircraft are becoming more complicated
Ironic indeed ....
The result of all this is easy to predict
The planes will start dropping like flies killed by insecticide
This is what's wrong (and already present)

serious Air FranceSerious .. Air France ? ... I disagree (see audit results and stats)

[HarryMann]

So...

Have some airlines really been training NU inputs and HITHRUST for stall recoveries when this seems to produce further (and usually unwanted) NU trimming?

Has there really been a history of excessive ND Stall recoveries creating ground proximity incidents - forcing this re-evaluatiobn of traditional stall recovery methods?

Or... has this type of recovery procedure stemmed from 'The Devil makes work for Idle Hands'..

e.g there has been no specific events creating a need for high power, NU recovereies, other than that modern fan-engined aircraft are (nominally) capable of such recoveries.

[BOAC]

One area of confusion in my mind Chris S may be able to clear up. What I think I see here and from BEA is that the THS did not move from its cruise angle until the top of the zoom climb? Given that it is supposed that PF held a nose-up demand most of the way up, why not? There must have been a good 40 seconds or more of 'demand'.

[GarageYears]

BOAC: More 'imaginative thinking?'....

One area of confusion in my mind Chris S may be able to clear up. What I think I see here and from BEA is that the THS did not move from its cruise angle until the top of the zoom climb? Given that it is supposed that PF held a nose-up demand most of the way up, why not? There must have been a good 40 seconds or more of 'demand'.


Where the heck do you SEE that written?

From 2 h 10 min 05 , the autopilot then auto-thrust disengaged and the PF said "I have the controls". The airplane began to roll to the right and the PF made a left nose-up input. The stall warning sounded twice in a row. The recorded parameters show a sharp fall from about 275 kt to 60 kt in the speed displayed on the left primary flight display (PFD), then a few moments later in the speed displayed on the integrated standby instrument system (ISIS).

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

The airplane’s pitch attitude increased progressively beyond 10 degrees and the plane started to climb. The PF made nose-down control inputs and alternately left and right roll inputs. The vertical speed, which had reached 7,000 ft/min, dropped to 700 ft/min and the roll varied between 12 degrees right and 10 degrees left. The speed displayed on the left side increased sharply to 215 kt (Mach 0.68). The airplane was then at an altitude of about 37,500 ft and the recorded angle of attack was around 4 degrees.

From 2 h 10 min 50, the PNF tried several times to call the Captain back.

So where are the "held nose up inputs"??? It's just NOT there. Why invent this?

The comment regarding the THS comes later. Read the note.

[JD-EE]

Takata and others, Zorin_75 asked a very pertinent question about the persistent fixation on the autotrim. Why IS everybody so fixated on it?

Surely nobody here thinks that turning autotrim off or simply coupling the elevator to the stick would have made a difference, I hope. The elevator jack screw runs too slowly for the pilot to use it for primary control. So the dual action, a quick action partial solution and a chugging along slower action is derived as the best way to handle it all. But the real problem is the full to the stops NU input that persisted until the plane was in an attitude from which recovery was problematic.

Hadn't it gotten into a condition such that the elevator authority was sharply limited by it's being fully stalled? By the time they made the final ND input there was no way to pull out of their stall. (I mentioned the thought of breaking out of it with unequal thrust to introduce an asymmetry to break out of the stable stall. And, yes, I can see no sane pilot wanting to do that. I vaguely wonder if it could have led to breaking the stall before it hit.)

The plane was crashed, essentially, by the persistent NU command not the THS. I've talked about training to use the trim wheels. But on thinking it over and too vaguely remembering the stall characteristics of the aircraft vis a vis position of the elevator I suspect all the elevator would do is slightly modify the NU forces on the aircraft. Are you worrying about something that appears to make a huge difference yet makes no real difference at all when the AOA of the aircraft is some 60 degrees?

Just askin....

[BOAC]

The comment regarding the THS comes later. Read the note. - Hmm I thought that is what I posted, never mind! Specsavers?

The 'Nose-up demand' certainly does not fit with my 'understanding' of events (which again you MIGHT have noticed (Specsavers?)) but does appear frequently here as a mantra so I was looking to see if it was possible, actually. I'm sure there are those here who think PF made the a/c climb, or am I imagining that? Anyone own up or can we eliminate that 'theory??

JD-EE - indeed , and I have discussed this with my tame AB expert - we both agree that after 40 + years of 'doing aviation' neither of us had ever contemplated a situation where a tailplane could be so stalled that a nose down elevator command could be a nose up.

[bearfoil]

JD-EE Great minds think alike, wish mine were one. There is very little to go on from the investigators, and that partially explains the breadth of comment here re: the most important phase of flight. Induction of Fail.

Too many shiny objects to harrumph about, and the meat of the matter in abject darkness. For ten seconds before A/P drop, and ten after, 447's fate was being sealed.

Either one believes the PF (and auto before him), created the stage for an absurd and fatal climb, or one believes they did not, and the hand of Satan slapped them silly at 2:10:00.

In between, (and in the belly of the only important data, that which is missing), this flight was lost.

Who is to say the airframe did NOT actually STALL after the very first WRN? Was the fatal parabola initiated at the beginning of ACARS, or some time before?

Maybe it's me, but I sense that most here assign controlled flight to this a/c until the apogee of the zoom. By definition, one thinks, LOC happened at the "the aircraft began to climb...." Whether or not the PF "caused" the event, is not as important as what caused the event that "caused the event".

Snapshot thinking? a/p dropped for a reason, so in strict terms, can one absolve the a/c?

Of course not. This was a continuum, and I truly believe that when the data is complete, and in the fullness of time, there will be still some adversarial and parochial gripes to be had.

In the meantime, Shadow is most intriguing. With the chronic and slow loss of "Read Speed", wouldn't the a/c Trim Power UP and NU also?

Why hasn't anyone addressed what the a/c might do with the need to "Maintain Speed and Altitude" when in autoflight? Because BEA have ignored it? It is "off limits"?

It occurs to this nomex clad cattle prod wielding ex-pilot that some one should at least attempt it?

Could the a/c have been at max power and NU somewhat at drop? Enough nose up to chirp the STALL and Cricket at 'one' NU left input?

The precise data in this bracket of unaddressed time is seductive.....

[PJ2]

BOAC;
What I think I see here and from BEA is that the THS did not move from its cruise angle until the top of the zoom climb? Given that it is supposed that PF held a nose-up demand most of the way up, why not? There must have been a good 40 seconds or more of 'demand'. While it may be an impression on the part of some, the reference for any of this is not here but the BEA Update, and it does not state that NU SS was held most of the way up. It states that after the plane started to climb the PF made ND control inputs and alternately left hand right roll inputs.

We see a this best in the Excel graph which A33Zab provided, (post #691) (http://www.pprune.org/tech-log/454653-af-447-thread-no-4-a-35.html#post6549447)in the previous thread - He has shown, and I think accurately so, that the THS does not begin to move from its 3° position until the aircraft is almost at the apogee. The SS was not NU most of the way up but was NU briefly which initiated the pitch-up then ND which began a slight level-off though the aircraft kept climbing. The stall warning occurred @02:10:51 according to A33Zab's graph and a continuous NU SS and application of TOGA thrust is coincidental with that event, and the THS begins to roll towards NU. The aircraft actually stalls at about 02:11 as the descent begins, while the SS is continuously held in the NU position with the pitch attitude at 16deg and thrust set at TOGA. According to the graph, the THS reaches 13NU at around 35,000ft in the descent at about the same time the captain enters the cockpit.

I suspect that while the THS position moves to continuously neutralize elevator forces just as any trim does, the movement is a "follow-up", the rate of change being governed by the pitch basic control loop which has a number of discrete inputs but primarily the sidesticks and the accelerometers. A long discussion has already taken place on Nz law and trimming to 1gee. Manual control of the THS can be taken any time by rolling the trim wheel forward or back. The following is a schematic of the THS general arrangement:


http://www.smugmug.com/photos/i-NdwnjLk/0/XL/i-NdwnjLk-XL.jpg

I'm sure there are those here who think PF made the a/c climb, or am I imagining that? Anyone own up or can we eliminate that 'theory??Again, the BEA Update states that the PF made "a left nose-up input". It isn't a "theory". Back-stick was later held during the stall, and for 30 seconds during the descent. Also, ND SS was briefly held after the initial pitch-up and briefly again during the descent. Knowledge of all other times will have to wait for the next Interim Report.

[JD-EE]

BOAC, I "think" what I meant was that a ND input would still come out NU and an NU input would also be an NU input. Whether they reversed as gums has said can happen, I don't know. I don't THINK the charts showed a full reversal even to the level that ND was more NU than an NU input. All I remember is that it looked like both resulted in NU type motion.

And I think rudderrat (http://www.pprune.org/tech-log/456874-af-447-thread-no-5-a-7.html#post6566210) hit the nail on the head for why the PF pulled nose up even though he was above FL100. The big (well trained) print buried in the FCOM called for TOGA and NU. (If it really is presented as quoted or as I remember seeing it in the past with smaller print for the above FL100 part it was presented poorly. It should break right at the beginning for above FL100 and below FL100 so the decision is made early and then procedure can be followed logically and linearly. (And thank you thank you for that post rudderrat.)

[JD-EE]

bearfoil, logically the airspeed loss cannot be slow. If it was the heaters would be effective. For the icing to happen it would have to take place very quickly in a fashion to overrun the heater's capacity on an instantaneous or nearly instantaneous basis.

It took awhile for that coin to drop, too. The original statement bothered me. I just figured out why.

[JD-EE]

PJ2, would the original NU command be a persistent, albeit moderate, command or would be a short one to establish the increased AoA and then returned to neutral? I got the impression from choices of wording that the original NU command was transient.

[PJ2]

JD-EE, transient and then neutral, then with slight ND, then NU more continuously, is my impression.

[BOAC]

PJ - that fits with my understanding, so where the *** does 7000fpm come from? That is one hell of a r o c for a 'transient nose-up followed by nose down'. To take your words "but was NU briefly which initiated the pitch-up" - I am still having difficulty in envisaging 7000fpm in a 200t a/c at FL350 from that - are you content? I am, by the way, quite aware of what BEA are saying about when the THS moved and I have assumed it was to compensate for the increasing NU demand on the elevator from PF's 'stall recovery'.

[takata]

Hi JD-EE,
And I think rudderrat (http://www.pprune.org/tech-log/456874-af-447-thread-no-5-a-7.html#post6566210) hit the nail on the head for why the PF pulled nose up even though he was above FL100. The big (well trained) print buried in the FCOM called for TOGA and NU. (If it really is presented as quoted or as I remember seeing it in the past with smaller print for the above FL100 part it was presented poorly. It should break right at the beginning for above FL100 and below FL100 so the decision is made early and then procedure can be followed logically and linearly. (And thank you thank you for that post rudderrat.)
Respectfully, the procedure recalled by rudderrat is to apply Nose-Down (reduce pitch attitude) at the same time as TOGA... while, in our case, the pilot apply Nose-Up (increase pitch attitude) at the same time as TOGA... Then, this is quite hard to conclude that he was following this procedure!

This is what (below) he is talking about; you may also notice the relevant part about the aural stall warning sounding at "altitude":
"... it warms that the aicraft is approaching the angle-of-attack for the onset of buffet. To recover, the pilot must relax the back pressure on the sidestick..."

http://takata1940.free.fr/A330_ALT%280%29.jpg
http://takata1940.free.fr/A330_ALT%281%29.jpg

[JD-EE]

takata, that is correct if you are not reading in a hurry.

This is what rudderrat quoted:

"An aural "STALL, STALL, STALL" warning sounds at low speeds. Upon hearing it, the pilot must return to the normal operating speeds by taking conventional actions with the controls:
Thrust Levers...TOGA
At the same time:
Pitch Attitude...Reduce
Bank Angle...Roll Wings Level"
So this is what the pilot was doing. He never got down to the other part.

The next bit reads "Thrust/Pitch .... CL/5degs Above FL 100"And note that this is from the FCOM not the QRH. Rudderrat remarked that in June 2009 the QRH had nothing to say about stall....

Is what you quoted from 2009 or a current manual. It was noted in some incarnation of this thread that the procedures had been altered and something had been added to the QRH regarding stalls.

[bearfoil]

Assuming the PF was sane and coherent, (I do), NU would be input to counterract ND, or a descent of some sort. After his correction, neutral stick. If the slight rotation he commanded (NU) then appeared too much, he would input ND (he did). Wait, that did not work, she still climbs. A bit more ND, and what is that pesky Roll? More Roll? compensated. More Roll still? and continued Climb? Increasing climb rate?? More ND and More.

BEA tells the Truth, and I see it this way. By BEA's data alone, where is PF screwing anyone's pooch on the way up? On the way down, with gobs of AoA, the Pitch can reverse with a Stalled Tail Plane. Remember this is not so much a Tail as a variable incidence wing.

JD-EE. Chronic and slow enough to allow the TailPlane to trim for it. And engines to develop max thrust (or close to it).

[PJ2]

BOAC - we don't know the details of the SS movement so it isn't possible to correlate such movement with rate of climb. The aircraft would have had a nominal pitch attitude of around 2.8deg roughly - SS movement aft of 3 - 4cm (previously said 2 - 3cm), as measured at the top of the stick would produce an enormous but clearly brief rate of climb of the kind we see here - it would be the equivalent I suspect, of about a six-inch rearward movement of the control column on the B737, just to try to equate a sense of the large changes involved in pitch and climb.

"Two-hundred tonnes" I believe is immaterial here as the wings produce commensurate lift for the design. It is a matter of mass, momentum and available energy (far more than 200T worth) from the wings at the initial CAS, which, given the eventual pitch attitude of 15deg clearly would be quickly unsustainable but in the short term, achievable. The BEA Update states that the VSI reduced to 700fpm and it is easy to understand/imagine the ballistic trajectory which resulted prior to the start of the descent.

Aside from my original thoughts of responding to the UAS drill instead of "doing nothing" while getting out the QRH for pitch-and-power settings, this almost looks like this was a reversion to original training where the approach to the stall is taught in transition or initial courses at lower altitudes in which the goals have traditionally been minimum loss of altitude, (much discussed in earlier threads) and "powering out of the stall" using TOGA thrust. The initial pitch attitude just may be some over-controlling which resulted in checking the stick forward a bit before responding again to the stall warning with back-stick, (driving the THS up, as we see). As I mentioned a number of times before, once the aircraft departed level flight, the "knowns and cues" for stable, level flight were gone and situational awareness, (what pitch? what power?) became problematic. The simulator exercise required a lot of nose down and I don't recall seeing what the THS actually did during the exercise and didn't look at the THS indiction. The descent rate was 7500fpm and the stick had to be held full forward. This was a stall from a pitch-up and the PFD looked like this in the recovery:


http://www.smugmug.com/photos/i-6svsRpq/0/X2/i-6svsRpq-X2.jpg

[takata]

So this is what the pilot was doing. He never got down to the other part.
Obviously, it isn't what the pilot was doing as he applied sustained nose-up, no? Otherwise, every single procedure calling for TOGA would fit with your definition of what he was doing. It would better fit with WINDSHEAR procedure in this case.
As the BEA did not provide any hint about any manual change of N1 rate during the first part of the climb (between 0210:05 and 0210:50), we may also think that the PF realised he climbed to 37,500 ft without adding any thrust from 35,000 ft and was trying to compensate for it. Maximum N1 is about 115%, but I don't know if such level could be reached in current conditions... at 35,000 ft, he was flying at about 95% N1.
And note that this is from the FCOM not the QRH. Rudderrat remarked that in June 2009 the QRH had nothing to say about stall....
Is what you quoted from 2009 or a current manual. It was noted in some incarnation of this thread that the procedures had been altered and something had been added to the QRH regarding stalls.
This FCOM quote is dated March 2003 (Rev 18). Most people did not look at the FCOM 3 which is providing "supplementary techniques" (3.04.27).

[bearfoil]

PJ2 "Once the aircraft 'departed' level flight". Other than level is not a 'departure', yes? Departure means a loss of aerodynamic flight, no?

Per BEA, how is the a/c known to be at S/L flight at dropout? PF obviously corrected for a ND or descent (or overspeed) of some sort, right? Assuming his NU input was a stupid or inadvertent blunder is not supported by the Data, surely? He could have pulled NU to correct an overspeed whilst NU already, yes? This would fit with such an unusual roc so quickly. Would the a/p have trimmed the NU to control speed with added power it had applied to "correct" a "slow" IAS due particle ICE plugging?

I do not mean to nitpick here, but your commentary is the Gold Standard here, and am I missing your drift? Maneuvering to retreat from STALL WARNING is not a STALL recovery, that is why the book allows for back pressure. I cannot find where it allows NU? Only back pressure, to minimize altitude loss? In fact, it advises lowering Pitch at this point, which is not the same as ND. This is parsable, but I read it as "non-negative" 'Target Pitch', to maintain altitude. I find nowhere a direction for PITCH UP.

Situational Awareness is the key, of course. Strictly speaking, loss of autopilot, for whatever reason, is a loss of SA machine-wise? Whether for UAS or inability to maintain programmed flight envelope limits?

[BOAC]

PJ - having never handled a side-stick I have no idea what a 'normal' manual input would be to maintain level flight, but 3-4 cm seems excessive to me, and certainly 6" on a Boeing yoke would raise my eyebrows as PNF. Would you expect that as a 'corrective' input?

I disagree on the 200t being immaterial - you speak of momentum - yes, 200t of it to get moving upwards. It does not matter what the steady state S&L match is, you still have to start the elephant moving upwards from his seat!

The more times I read the interim, the more unlikely the whole scenario becomes - at some indeterminate time after 2:10:16 a climb begins. The next 'fix' we have is at :51 with a stall warning AFTER the climb has been 'killed', so we assume that around 30 seconds or less of 7000fpm happened (probably about right for the height gain) during which NOSE_DOWN inputs are the only ones mentioned. So, the a/c must have pitched fairly rapidly to climb pitch to do what it did (and equally 'fallen out' or bunted over equally rapidly at the top) and can we assume then that it was pitching nose-down in response to the elevator input for several seconds?. Do we have any idea of the 'g' required for this pitch up into the climb? I see 1.75g quoted as an over-speed FCS 'increase' in applied PF input. Are we close?

[GarageYears]

JD-EE:

I "think" what I meant was that a ND input would still come out NU and an NU input would also be an NU input. Whether they reversed as gums has said can happen, I don't know. I don't THINK the charts showed a full reversal even to the level that ND was more NU than an NU input. All I remember is that it looked like both resulted in NU type motion.Then stop THINKING and read.

Look, the damn text from BEA states that pitch authority was STILL working well in the descent:

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.The only real information we have is in the ?BEA note, so stop making up fantasy land la-la imaginary stuff. I don't understand the need or necessity to be doing this.

Seriously, making up cr@p doesn't make it real.

The aircraft RESPONDED to ND with ND. In the stall. OK....?

Sorry for the hard language, but this is becoming increasingly frustrating.

:confused:

[bearfoil]

BOAC

Would the Pitchup to that roc be easier to entertain if the a/c had begun the rotation in NU (but level) flight to begin with? Were the PF's inputs in any way additive to an existing state? We do not know what the attitude was at 2:10:16. Or is BEA's "Ten Degrees" a clue? For me, the dynamic nature of this twenty second picture is difficult to grasp. It will help immensely, I trust, when BEA releases all the Data.

[roulishollandais]

So long as the BEA refuses to deliver the contents of the CVR, we will only lead us astray in trying to understand what has happened.

Il is urgent that the BEA make public the whoole raw CVR and DFDR .

Aviation safety is a requirement for an modern aviation.

Transparency is essential to improve flight safety.

Thank you for supporting my request.

[HeavyMetallist]

Look, the damn text from BEA states that pitch authority was STILL working well in the descentThere's ample evidence in reports linked to in the previous thread to support the facts reported so far by the BEA that nose-down pitch control would remain effective even when the mainplane/tailplane were stalled. Why some people persist in believing that stalled == totally ineffective is a mystery.

[rudderrudderrat]

Hi HeavyMetallist,

Why some people persist in believing that stalled == totally ineffective is a mystery.
Please could you explain the forces acting on the tail during the stall for me?

Normally, the elevator and stab produce a down force at the tail. (to balance the nose down couple with the c of G being forward of the Centre of Lift).
During the stall, with an angle of attack of about 45 degs on the elevator and Stab, the forces on the tail must have been upwards. If not - then I don't understand why.

Please explain how holding full back side stick kept the attitude at around 15 degs until impact.

[DozyWannabe]

So long as the BEA refuses to deliver the contents of the CVR, we will only lead us astray in trying to understand what has happened.

Il is urgent that the BEA make public the whoole raw CVR and DFDR.

Why should they? No other accident investigator has this demand made of them. Are you another of Norbert's disciples?

[bearfoil]

Both of you are wrong, imho.

Any data gathered in an investigation into commercial carriage that involves Death or substantial commercial Loss must be made available to those involved, and to those who are affected, either directly or indirectly.

Some discretion with personal grief must be allowed for, when it is not directly appurtenant to the accident.

Commercial Carriage (Travel) is a CONTRACT. A CONTRACT that disallows disclosure of material bearing on the CONTRACT is not a legal CONTRACT.

Witholding pertinent material of any description that bears on the ability to perform, is a species of FRAUD. I purchase a Ticket (Contract) and I am not aware of the dangers inherent therein, by design, violates the DUTY of CARE implicit therein. This can be waived, by me, a right that is alienable, (removed). Disclosure is the foundation on which the contract reposes. Secrecy is for subjects, not citizens.

[RetiredF4]

GarageYears
Look, the damn text from BEA states that pitch authority was STILL working well in the descent

BEA
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

HeavyMetallist
There's ample evidence in reports linked to in the previous thread to support the facts reported so far by the BEA that nose-down pitch control would remain effective even when the mainplane/tailplane were stalled. Why some people persist in believing that stalled == totally ineffective is a mystery.

To say the truth, we dont know or at least nobody can know from the BEA stuff. I f BEA was sure at the moment of the statement that the reduction of the AOA and the validation of the speeds was a direct outcome of the former ND input, the wording could be clearer like

----Around fifteen seconds later, the PF made pitch-down inputs, the angle of attack decreased, the speeds became valid again and the stall warning sounded again.------- my wording

The wording " in the following moments" needs also to be noted as non standard expression to describe an event, which based on an preceeding one and was immidiately following. I see hesitation and time delay in this expression like saying ------- that was happening,, but we dont´t know yet how it is connected----. Why is no time mentioned, it would be available on the second.

The amount of reduction of angle of attack was not mentioned, but we know that it was not below 35°, as BEA stated that AOA never was better than 35AOA until impact. The triggering of the stall warning therefore has to be caused by the speed increase to above 60kts, if i remember the numbers correctly. But the speed was subjected to erroneous indications before, at the beginning ice (at least most of us agree on that) and later on due to disturbed airflow due to high AOA, yawing and banking and maybe even WX input. In the descent the ship might have entered the bad WX zone again, which could cause speed changes as well. AOA did decrease, BEA does not say how much, it might only have been some few degrees. It might have been caused by other movement of the aircraft, like rolling from much bank through the zero bank to the other side. There also AOA would decrease and later increase again.

And we have three pilots in the pointy end, who for sure contributed to the tragic outcome somehow, but wouldn´t they have made the conclusion that their ND input was successfull und therefore should have been maintained? They deliberately made ND input and reduced power out of TOGA, so we can assume that 3 pairs of eyes tried to see an improvement of the situation. Instead they gave up on it and tried something else? Why? Did they not recognize the AOA change and the increase in speed or did they not relate it to there former ND input? Maybe they discontinued their ND input and at that time the aircraft responded due to outside factors.

I dont know, i think it is to early and founded on meager information, on just one sentence with uncommon wording (or is that my language barrier) to say ND was effective and the crew just didn´t notice it.

Lots of options and possibilities, and sure, one of them is also that there was a ND input and it had an effect, which the crew did not recognize.

[bearfoil]

The AoA could have been decreasing due to the mass itself, not its controls. At the top of a ballistic climb, the nose comes down naturally, with controls or without. Drag. Sharp end has less. What is left of energy.

[PJ2]

Hello BOAC;
Would you expect that as a 'corrective' input?No, I would not - my reaction would be the same as your own, for sure. But that doesn't mean it didn't happen. But even a smaller SS deflection is going to have quite an effect - I suspect that the two stall warning "blips" occurred as a result of momentarily exceeding the Stall AoA threshold.
I disagree on the 200t being immaterial - you speak of momentum - yes, 200t of it to get moving upwards. It does not matter what the steady state S&L match is, you still have to start the elephant moving upwards from his seat!My thought was, relatively speaking, the airplane is, in terms of available lift against weight, able to respond to small control inputs and climb very rapidly. It doesn't take more than a couple of seconds to start the change pitch, and my guess is it took less than 10" to get to >10deg from a nominal 2.8deg[/I]), given the amount of excess energy (in forward momentum) available (and spent) in the trade for altitude.
The more times I read the interim, the more unlikely the whole scenario becomes -

. . . .

I see 1.75g quoted as an over-speed FCS 'increase' in applied PF input. Are we close?On your first comment, yes, agree. We need the data. Hopefully it will come soon, and with as much completeness as possible. One your second re gee, I suspect fairly gentle...1.3g's, perhaps, for the pitch-up?


Bearfoil;
Re S&L flight, I am partially inferring from reading in the BEA Reports and partly drawing from experience. At 02:08:07 the PNF suggest going, "a little left." There was no hint of any changes in altitude and I suspect and infer but do not know, that whatever turbulence that may have been encountered was light, possibly slightly more with no material effect upon altitude or pitch attitude. At 02:10:05 the event began, with an AP/AT disconnect and moments later the ECAM messages were displayed, (we infer from the existence of the ACARS messages - I doubt if the the ECAM messages were recorded). There are no strong reasons to consider that the aircraft was not in stable, level flight and that the pitch up left (departed) FL350 in a climb. Remember, the altitude parameters were available and valid until, (as I know some have suggested), both roll and AoA will likely have affected altitude readings somewhat). There are no suggestions in the BEA Update of any change in altitude (downwards) which the PF was reacting against. That would have been material to the update and it was not said.

My sense of it is we will see stable, level flight in the data when it comes out. If the A330's sidesticks are the same as the A320's, the fore-and-aft movement is +/-20°, the lateral movement +/- 25°. I think we will see a five-to-seven degree, (out of a maximum deflection of 20 degrees), aft movement of the sidestick followed a neutralizing of the SS, then a strong (perhaps 10deg) forward ND movement and at 02:10:51 likely a 15-20deg aft movement of the stick, continuing for some time. I think the next ND movement will be mild, less than 10deg ND where the speed begins to pick up.

Please bear in mind that I am not "predicting" values so much as conveying a sense, from experience in the airplane, of what these movements may have been. I'm not interested in "getting it right" but I think there is some legitimacy in providing a sense, a "metric" so to speak, from experience, of what is likely and what is not likely in these various notions. It is not a matter of being right or wrong because very soon we will know. As with others, this is being assessed with the available data and so, as with all extrapolations, must be viewed with great caution.

Regarding pitch up, you are correct in stating that SOPs generally require a reduction in pitch attitude, (and TOGA thrust), if a stall warning occurs. The pitch-up may be explained in a few ways. One scenario is already discussed, (UAS drill response), the other is a "startle" reaction which would not be a sustained back-SS. Other than those scenarios which we either know about or have discussed, I can't explain the pitch-up or the back-SS in the descent.

[kiwiandrew]

@ bearfoil. As far as I am aware your contract of carriage is between you and the airline. So far as I am aware the regulatory body responsible for investigating a crash is not party to that contract. Perhaps you have discovered something in the contract of carriage that the rest of us have missed? If so, please feel free to share.

[Zorin_75]

Bearfoil, did you ever actually read the BEA report or are you just randomly making stuff up? :confused:

[bearfoil]

kiwiandrew

In US Law and NZ, I warrant, (both based on Queen's Bench), A contract must be a legally binding agreement. It is enforceable at Court, once juris and standing are established, (not difficult). So yes, it is founded in the Law, and the Law is a Lady, one who must not be teased.

At Court, the Judge is the Law, and he may issue a subpoena to those he deems may have pertinent information. These beneficiaries of his invitation do not have the luxury to deny, save for declaring a personal and biased interest, founded in their rights at Court. At which time they are subject to indictment as accessories to defraud the Court. In America, any individual, any one, may request a document be divulged. Save for Government security, this request must be honored. To avoid delivery of the document constitutes a felony subject to punishment by the Law.

amica populi, the other side of the coin.

[bearfoil]

Zorin_75

Of course I read it. More than once. I give it the credence it deserves, which is not very much.

Here's why:

In the Note, (I assume you are referring to this last missive to the masses), They State the PF says "I have the controls". They state then, The pilot input a NoseUp Roll left command. Fine, so far, except........


Was the pilot himself responsible for the Nose Down Roll Right he was chasing with the SS? It does not say, so we have two possibilities.

To wit: The aircraft was ND, descending, Rolling right prior to the Pilot Flying adding his stick?

As above, in 'carpe baton', did he instill a nudge down, a nudge right?

Worse yet, they go on such that the esteemed group here present vomits
such...............

"When I was in kneepants, Stall meant Nose Down....FOOL"

"He held backstick instead of ND? What a moron!" ETC.

The best here were convinced the PF SINGLE NURL was actually back pressure up to, and over the top.

So, BEA either unwittingly and/or innocently, advantaged the Manufacturer in an ongoing investigation. Or, with curious timing as to said manufacturer's Day at the FAIR........they allowed themselves to be manipulated into writing a laughable document that erodes their credibility in their mission quest.

BEA deserves neither abject guessing nor unquestioning allegiance, EH?

They deserve nothing, perhaps except for Airbus' debt of gratitude. A case of Guinness, then? Bus Badges for all? Favored seating at the Oktoberfest?

A Half Truth is a Whole Lie.

[Owain Glyndwr]

RRT

Please could you explain the forces acting on the tail during the stall for me?

Normally, the elevator and stab produce a down force at the tail. (to balance the nose down couple with the c of G being forward of the Centre of Lift).
During the stall, with an angle of attack of about 45 degs on the elevator and Stab, the forces on the tail must have been upwards. If not - then I don't understand why.

Please explain how holding full back side stick kept the attitude at around 15 degs until impact.

Since you ask ....

First thing is that MM43's excellent graphic of THS flow (Thread 4 #1042) is missing one important parameter. A lifting wing, even a stalled wing, produces downwash at the tail. A ballpark range for this would be between 0.4 and 0.5 times body AoA. So at 60 deg AoA as in the graphic, the THS AoA would have been around 17 or 18 deg. With zero elevator this would have been on the point of stalling - but it would have been stalling with UPWARDS lift.

That means that without any elevator the THS would have been giving a substantial ND moment. The centre of lift of a fully stalled wing is probably fairly close to the centre of area, which on the A330 is slightly aft of the CG given for AF447. So both of these are ND. What could hold the nose up then?

The forward fuselage has roughly the same moment arm about the CG as the THS, but nobody would pretend that it has the same aerodynamic lift efficiency, so that cannot balance the THS ND moment. Thrust? sure, but do the sums and you will find that the NU moment even with both at TOP won't come anywhere near what is needed.

What's left? Up elevator! Enough of it to make the THS plus elevator force downwards and give enough NU moment to balance the AoA at (in this case) 60 deg. Up elevator would also take the THS away from upwards stall.

For lower AoAs the THS would be even further from upwards stall.

Full back sidestick put the aircraft at 60 deg AoA - the FPA was 45 deg downwards, so the pitch was 15 deg. OK?

[bearfoil]

I think FPA of 45 degrees was a construct, here, to allow for ease of computing the velocity through air.

In the sense of the word Stall at the tail (upwards), you do mean that when the Tail Stalls the Nose goes down right?

bear

There is no STALLSTALL for Tailplane afaik.

[Owain Glyndwr]

FPA of 45 degrees is what you get from the BEA stated impact conditions with zero surface wind.

No, if the tail stalls when giving upwards lift the loss of that lift would give a nose up pitch increment.

[bearfoil]

Upwards lift at the tail creates downforce on the fuselage, and prevents the Nose from falling to make a big hole.

"Upwards" to the tail is the opposite of UP to the wing. Its camber is on the bottom surface, no?

[gums]

Owain seems to have a decent description of some of the factor involving the THS and its effects upon all the moment arms.

I refer all to my graph of the Viper pitch moments ( will find the post later, as on slow landline connect now). Granted, we flew at a very aft c.g. compared to the 'bus. But the fact that the jet could settle into a fairly benign condition at 50 deg AoA with no violent pitch changes and a very good directional condition ( no spin), and only small roll change was a surprise to all of us.

http://i120.photobucket.com/albums/o196/gatlingums/pitch-moment.jpg

Our HAL cut out all pilot pitch inputs via the stick once AoA was above 30 deg or so. HAL also took over rudder to help prevent a spin. In short, once in the deep stall we were observers. But we still had NU capability if we could only gain direct control of the HS. So they gave us the "manual pitch override" doofer. It only worked if AoA was above 30 deg, but it allowed us to "rock" the jet outta the deep stall.

Show us the pitch moment graph!!!! And I realize that BA did not get a 'bus into a deep stall to get the data. But it would seem to me that they could calculate all the moments and control surface effects.

I have a feeling that the THS could have helped the pilots if they had manually moved the doofer to the nose down angle. I don't have the control logic for the THS, but looks to me from reading all the manuals that it simply moves the HS to minimize deflections of the elevator. A neat idea, and doesn't need AoA or airspeed or ..... So a constant pitch input could result in moving the HS to the limits, especially if speed was slow.

On a personal note, and being a pilot, I feel sorry that the crew was presented a condition that just didn't "compute". I think that if any had seen films of the Viper deep stall that they would have tried something after about a minute, anything, do something different fer chrissakes. Would love to find film of our deep stall, and you would be surprised how easily the jet settled into the stall.

[Owain Glyndwr]

"Upwards" to the tail is the opposite of UP to the wing

Maybe in your world, not in mine. If you start mixing definitions according to what part of the aircraft you are talking about you can get confused very quickly!

Positive lift is upwards (anywhere) positive attitude is nose up, positive angle of attack is nose up, positive THS setting is nose up, positive elevator is TE down (i.e. nose up) etc.

[ChristiaanJ]

"Upwards" to the tail is the opposite of UP to the wing. Its camber is on the bottom surface, no?Bear, do you have any aeronautical engineering background at all? Your statement/question seems to indicate you don't.

[bearfoil]

So.. if the tail falls off, the a/c climbs?

It seems to me that rather than trying to find fault with others, and instead donated some knowledge to the thread in one's specialty, one could help everyone in their desire for understanding.

I have never been accused of being an engineer, they do most everything by proxy.


let's see, press tail down for up.........

[takata]

Hi PJ2,
If the A330's sidesticks are the same as the A320's, the fore-and-aft movement is +/-20°, the lateral movement +/- 25°...
A330 sidestick travel limits are : +/-16° in pitch, +/-20° in roll.

[Owain Glyndwr]

So.. if the tail falls off, the a/c climbs?

Now you are just being silly!

It seems to me that rather than trying to find fault with others, instead of donating some knowledge to the thread in one's specialty one could help everyone in their desire for understanding.

I thought that was what I was trying to do, but when the response one gets is similar to that above it seems hardly worth while :ugh:

[mm43]

With the ongoing debate over the when, why and how of the initial climb, perhaps a few links to graphics posted earlier may help you all with your musings. If you are using a decent tabbed browser, e.g. Firefox, Chrome or Opera, then opening each link will open it in a new window. This will allow for easily jumping between the thread tab and the reference graphic tab.

Descent Angle of Attack Values (http://oi56.tinypic.com/52lv5t.jpg)

THS - Configuration plus Elevator NU/ND (http://oi54.tinypic.com/pp2sz.jpg)

Initial Stall Analysis - small (http://oi51.tinypic.com/dbr05u.jpg)

Initial Stall Analysis - large (http://oi56.tinypic.com/9pt3ds.jpg)

The salient points named in the BEA Note were left off for clarity but can be added if you think they will be helpful.

Why not just leave the BEA Note (http://www.bea.aero/fr/enquetes/vol.af.447/point.enquete.af447.27mai2011.en.pdf) open in another tab for easy reference.

[rudderrudderrat]

Thanks Owain,

Your explanation makes sense.

[airtren]

Several posters made reference to "stable/level flight" before AF 447 "a/p disconnect"....

If my understanding is correct, for the same trajectory, the controls/adjustments performed by the "a/p" during a flight through "turbulent air" are quite different in certain aspects, from those made during a flight through "non-turbulent air".

Assuming a straight line "overall" trajectory:

a) in "non-turbulent air", the flight is "a straight line", with almost an "inertial", no significant controls/actions from the "a/p".

b) while in "turbulent air", the trajectory under the effect of the turbulences is a concatenation of a sequence of "up" "down", "left" "right" "level" segments, with a distribution as a consequence of the "a/p controls" of "up/down", "down/up", "right/left", "left/right", and "level" in between, which is at best ONLY an "approximation" of "a straight line", and thus of course NOT "a straight line".

The segments are shorter, or longer, depending on the degree of turbulence, and "a/p actions".

In terms of actions, the "a/p" "actions/controls" continuously try to counter the "up", "down", "left", "right" a/c motion driven by the turbulence, in an attempt to keep the flight level/straight.

It seems clear that before the "a/p disconnect" the "a/c" was in "turbulent air".

The trajectory the "a/c" followed immediately after the "a/p disconnect" depends on which type of segment and which position were the control surfaces of the "a/c" at the very moment of the "a/p disconnect".

My understanding is that the "a/c" would continue "level" under inertia and position of control surfaces as left after the "a/p disconnect", ONLY and ONLY if the "a/c" were on a "level" segment.

But the probability of being on a "level" segment is 1/5, which is 20%, which is quite low (maximum probability is 100%).

The probability of being on a "NON-level" segment - "up" or "down" or "left" or "right" - is 4/5, that is 80%. That is quite high!!!

[airtren]

mm43:

> With the ongoing debate over the when,....


Illustrative graphs - thanks!

Question: it is unclear what the "Stall Warning" curve is. Would you please clarify? Thanks in advance.

It seems obvious it is not the "Stall Warning" message given to the pilots, as that was, afaik, not permanent/continuous.

[bearfoil]

Hello Garage Years. Script is an unfortunate term. It infers a drama, a fiction, something crafted from whole cloth by someone to gain interest or commercial advantage. Wait..........wasn't AB pleased to trumpet it?

It is simply not possible to know where the NU part of RL derived. In not giving up some data, by way of explanation, BEA have encouraged a result not in evidence. Or, it could be treated as you did, absence of evidence is evidence of absence. I choose to assume the input was correct as stated, and derived as one would who had some confidence in the PF. You choose another way, variety is the spice of........

Take your pick, both are conjecture. Do you not see this? OR, in seeing it, do you choose to ignore/deny it?

Can you try playing the Ball, and not the Player? Your emoticons are starting to fade from exposure to the ether.

[EMIT]

Gums #179

Thanks for that pitching moment graphic, I had it in my head, of course, but didn't have a physical copy of it anymore.
For people who can interpret such a graph, it is extremely enlightening, but of course, they must be able to appreciate the differences between an F-16 and an A-330 to get to the right conclusions.

Thanks again for the picture.

[DJ77]

Originany posted by Owain Glyndwr about the downwash angle:


A ballpark range for this would be between 0.4 and 0.5 times body AoA.


Ordinarily, the downwash angle at the tail is related to the lift coefficient more than to the wing/body AoA. Would your values be more specific to a stalled swept wing?

PS: Welcome aboard!

[bubbers44]

Bear is correct about the airfoil of the horizontal stabilizer causing downward thrust making the aircraft stable. Soon after the Wright Flyer this was incorporated into most aircraft. Using the term upward lift confuses the issue because an increase of airspeed in stable flight will cause a downward force on the horizontal stabilizer bringing the nose up to stable flight. This negative lift or what ever you want to call it requires the wing to supply more lift to compensate for that effective extra weight.

Airbus used fuel transfer to get the CG as far aft as possible to eliminate some of the effective weight the wings had to carry. I have seen race planes lose their tails and they immediately dive into the ground because of the loss of down force on the tail.

[GarageYears]

Bear, all this is fun, but we have a 'limited' (and on that I think we agree) set of data that BEA have deigned to bestow upon us - clearly it is not the full story, CVR or flight data wise, but I think we can be pretty confident that the important stuff is in there. Or do you think they are holding back on some surprise? Otherwise all hell breaks loose when they DO release the rest.

I used the word "script" with purpose, because so far that is all we have - in my world a script is used to instigate a more complex set of actions "below the surface". So I meant that we have the keywords, the triggers if you like, those things that the BEA fell worth reporting at the top level, without which presumably this accident would not have occurred. There may be other less significant issues that were not so evident from a couple of weeks of looking at the CVR/FDR, but will there be great revelations from here on out....? Somehow I think all we will see is joining the dots, and those are to the majority already in front of us. That is my position. Yours appears to one that needs many other dots, simply because you don't like the picture. Your musing don't seem to achieve much aside divert useful thought on the information that is known.

[takata]

Hi BOAC,
Do we have any idea of the 'g' required for this pitch up into the climb? I see 1.75g quoted as an over-speed FCS 'increase' in applied PF input. Are we close?
Assuming that this aircraft overshoot Mach 0.86 (Normal Law), after an overspeed warning, with speed still increasing, an overspeed protection could have been ordered by the FMGC and could have added up to 1.75 g pitch load while disconnecting the autopilot, hence, this would happen at 0210:05.

The main issue with such case is that the BEA/AIB/NTSB/etc. would perfectly know it from the beginning, right after the first CVR (warnings) and DFDR tracks (speed, etc.) lectures ; then they will voluntarily hide that to us...

Another issue is that it doesn't fit either with all the known flight conditions (~Mach 0.81 = 275 kt), neither with all the known (and clearly acertained) system faults at 0210:05 which are all linked with an Unreliable Airspeed event.

In fact, there is not a single doubt that this aircraft entered ALTERNATE 2 at 0210:05, right after an UAS check took place during the previous second (airspeed incoherence detected). It is acertained that the system confirmed the already applied ALT2 ten seconds later -> 0210:14/15; hence, it is also proved that it was not a transient fault, meaning that NORMAL LAW was lost for the remainder of the flight.

Consequently, from 0210:05, autopilot, autothrust, several systems/functions, and all the flight envelope protections were lost, excepted the envelope g-load factor protection that will limit the PF imputs into the range of -1 g to 2.5 g in clean configuration.

[bearfoil]

thanks bub.

Fuel cheat was a hidden art in the olden days, when wings were fat and safety came first. At the outset, if the chief found you squirreling fuel away aft of cg you caught Hell. Then the beanbags caught on, even that long ago, when fuel saved was minute, they said "hold on, what's this tail loading thang"

Whether negative lift or no, I always looked at it as a drag nullifier. To load the tail aft means some of net lift to carry the a/c is shifted to the tail. A heavy tail, carrying some weight, "flies" with less induced drag, which instead converts to lift, to obvious advantage in fuel savings. win/win, except when you lose. And when the cg is too far aft, to lose is to die.

This is from a non-engineer, maybe I should drag it across Chris' desk before posting.....

not now, nor have I ever been an engineer. Quick question for

takata. You say PF input is limited to 2.5 g with inertially derived g envelope prot in ALT 2. Is that separate from what the a/c will bear, or a total. As in. the Pilot can not ask for/get more than 2.5g? Does the a/c compute a "g" at all in AL2? Except for its limits? G is not "damped"?

[PJ2]

Thanks very much takata, IIRC those are familiar numbers from the A320 as well...how quickly one forgets. PJ

[henra]

The trajectory the "a/c" followed immediately after the "a/p disconnect" depends on which type of segment and which position were the control surfaces of the "a/c" at the very moment of the "a/p disconnect".

My understanding is that the "a/c" would continue "level" under inertia and position of control surfaces as left after the "a/p disconnect", ONLY and ONLY if the "a/c" were on a "level" segment.


The Question is not so much what the positon of the control surface are upon AP disconnect but rather how the change from Roll Normal Law (Rate command) to Roll Direct Law (Deflection) is handled in that regard. I haven't found any reference to that but would assume that control surfaces return to normal at that point.
If Roll Normal Law was compensating for a constant Air Mass movement (vertical? lateral?) that could lead to a certain amount of roll in that case.
Anyone here knowing how this is done exactly?

[A33Zab]

IMO there was an escape from this stall but it did require the THS.

From the events (BAE) and *not official* but excellent calculations by HN39 (http://www.pprune.org/tech-log/454653-af-447-thread-no-4-a-40.html#post6553124), the A/C needed TOGA + Full Elevator Up + THS 6° (ANU) to increase the pitch from 6° to 15°.
More THS (ANU) travel didn't had any influence on the pitch axis, it seems to be stabilised at this value.

Later in the sequence (after 2:12:00), engines at idle '55% N1' + THS in 13° (ANU) the brief ND elevator input reduced the pitch to ~ 5° (ANU).
thereafter pitch went to stabilize @ 15° again.

With a travel of 15° THS (13° + 2°) available and the ND elevator authority (10° Pitch AND in this stalled situation) it should be theoretically possible to get the nose down and regain speed.

But then again, I do most 'everything' by 'proxy'.

@mm43:

It's a pity this is not visible in your very enlighten graph, would it be possible to extend the timeframe to 02:13:00 at the least?

[bearfoil]

A33Zab

Just a poor jab, Sir. Not meant in malice at all.

takata has entered into the log the g envelope protection which is the "only" protection left in AL2 (?).

So the same question to you sir. Is this Limit actively monitored by the accels? And if so, when the a/c reached her zenith (perhaps even more than -1), would the a/c activate NU to regain some g? IOW, if essentially weightless for a short time, would 447 runup the THS to gain some "G"?

Hope it is not a stupid question. If any, what would be PF's authority over such a command by the a/c?

[bearfoil]

I suppose another way to put it would be, that if THS remained +/- 3 degrees all the way up, would the a/c have started THS NU to counterract the -g the a/c "felt"(up to, through, and beyond the apogee?). Aren't the accels in charge of this protection? Would the PF know that the THS was trying to reweight the airframe, not retain the Stall? If this is what happened, the THS would articulate NU to the stop, since positive g at that point would be unrelated to THS position (all the way down), Yes? Is the 'g' protection active, then? Or just preventive?

Does this question have anything to do with Perpignan at all? Was Test pilot #1 trying to exceed 2.5 gees? To Pull up and away from the water?
Was the a/c actively prevented from more than +2.5 gee? Was 447 actively prevented from recovery from Stall because the PF did not know the THS had migrated all the way UP to regain +g? At 10,000 feet, was 1g regained, and the Tail became responsive again?

thanks, and much respect, Sir.

[takata]

Hi Bear,
takata has entered into the log the g envelope protection which is the "only" protection left in AL2 (?).
Without valid airspeed, yes.

So the same question to you sir. Is this Limit actively monitored by the accels? And if so, when the a/c reached her zenith (perhaps even more than -1), would the a/c activate NU to regain some g? IOW, if essentially weightless for a short time, would 447 runup the THS to gain some "G"?
It doesn't work like that: PF imputs, on flight control surfaces, are filtered by a function that would not allow excessives g-forces to be pulled out, even in direct law with an abrupt full deflection order.
http://takata1940.free.fr/Limits.jpg

[A33Zab]

I'm not sure if I understand your questions in total.
Load Factor Protection is the same in NORMAL as ALTERNATE.

Maybe you other questions become more clear with this general concept of G demand, if not we have to wait on Takata or any other to reply.

Note: (* added by me.

Flight Mode

In pitch, when an input is made on the sidestick, the flight control computers
interpret this input as a “g” demand/pitch rate. Consequently, elevator deflection
is not directly related to sidestick input. The aircraft responds to a sidestick order
with a pitch rate at low speed and a flight path rate or “g” at high speed. When no
input is made on the sidestick, the computers maintain a 1g flight path. Pitch
changes due to changes in speed, thrust and/or configuration, which in a
conventional aircraft would require the pilot to re-trim the aircraft, are
compensated for by the computers repositioning the THS. The pitch trim wheel
moves as the control law compensates for these changes. Sometimes, changes
of trim due to changes in thrust may 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 has stabilised after the trim change.
Due to its neutral static stability, the aircraft maintains the selected flight path.
Should it deviate however, only small sidestick inputs are required to regain the
desired flight path.

http://i474.photobucket.com/albums/rr101/Zab999/GeeA330.jpg




Load Factor Protection


On most commercial aircraft, the maximum load factor range is 2.5g/
-1g clean

and 2g/0g with slats and/or flaps extended. The load factor protection is

designed to maintain the aircraft within these limits while allowing the crew to

consistently achieve the best achievable aircraft performance, if required.
On commercial aircraft, high load factors are most likely to be encountered when
the pilot responds to a GPWS warning. Airline pilots are not accustomed to using
"g" as a flying parameter and experience has shown that, in emergency
situations, the application of "g" is initially hesitant and then aggressive. If a
GPWS alert is generated which requires an immediate pull-up, full back stick
should be applied and maintained. The load factor protection will allow maximum
"g" to be achieved in the shortest time while preventing the aircraft from being
overstressed.








http://i474.photobucket.com/albums/rr101/Zab999/GeeA3302.jpg




Protected/Non-Protected Aircraft Climb Angle Comparison


If the pilot maintains full aft stick because the danger still exists, the high AOA

protection will eventually take over. This is one instance where load factor

protection is enhanced by the high angle of attack protection. (* Hi AOA Prot. NOT in ALT)

[bearfoil]

In "Flight Mode": "when no input is made on the sidestick, the computers maintain a 1g flight path."

In the zoom, we are in uncharted territory, so my questions may seem "thick". The Approach to STALL was through the back door of the Drag curve.

The Pilots and pax experienced a climb, one that when it came to an end, engendered up to or even more than -1g. As she decelerated, g was diminishing, the SS may have not been active, even if it was, it was likely ineffective, and at -g the computer will try to regain +g, Yes? Of course at this point they are aerodynamiclly STALLED, but the computers would still roll in THS (NU) to regain g? No other protection is available, and AoA would be an iffy way to regain aerodynamic flight.

From the dark side of the drag curve, STALL warn would not recognize the attitude re: STALL anyway, and the THS is the preferred method for reloading the airframe. The computers would have no interest in stopping the Stall, or recovering Flight, in AL2 they do not speak STALL RECOVERY.

When the PF made his ND inputs, the a/c reacquired sensible Warnings, but the a/c would sense ND as reacquiring -g, and keep rolling in more THS. So when the final STALL activated, the elevators may have signalled to PF a climb, rather than a ND, and he relaxed ND to think of something else.

I'll stipulate that the PF may have elevated the a/c into the climb, but once STALLED and even before, would not the computers be "protecting" "g"?

You know, after two years, I have to put on a serious thinking cap to prep for this thread, and PF PNF and Captain had seconds.

What was she doing? My understanding of the last seconds of Perpignan have the PF pulling everything to gain gee, and miss the sea. The computer would not allow >2.5. She kept her slippers on, right into the drink.

[takata]

I suppose another way to put it would be, that if THS remained +/- 3 degrees all the way up, would the a/c have started THS NU to counterract the -g the a/c "felt"(up to, through, and beyond the apogee?). Aren't the accels in charge of this protection? Would the PF know that the THS was trying to reweight the airframe, not retain the Stall? If this is what happened, the THS would articulate NU to the stop, since positive g at that point would be unrelated to THS position (all the way down), Yes? Is the 'g' protection active, then? Or just preventive?

Does this question have anything to do with Perpignan at all? Was Test pilot #1 trying to exceed 2.5 gees? To Pull up and away from the water?
Was the a/c actively prevented from more than +2.5 gee? Was 447 actively prevented from recovery from Stall because the PF did not know the THS had migrated all the way UP to regain +g? At 10,000 feet, was 1g regained, and the Tail became responsive again?
Bearfoil, you should stop dreaming that you will be able, any day soon, to rewrite the history of every "Airbus" already resolved crash without having a single idea of what you are talking about.

This is something I really don't understand about you... Those basic things are mandatory to understand how those aircraft are flying and most of this stuff, about Airbus FBW systems, is available nearly everywhere.

Why don't you take a little time to read it, all by yourself, instead of posting daily, from two years now on this thread, such a load of cr*ap about a subject you never bothered to study a minimum?

[bearfoil]

No problem. Adios.

[Chris Scott]

Quote from DJ77:
"Please, what is this transition from g-control to pitch-control you are talking about and where is it described in the FCOM? Does it apply to A-330?"

Sorry for the sluggish response. If you thought you detected some hesitance or vagueness in my glossed-over references to C* (PITCH) law, you were right. The reason is quite simple: my only source of information is an extract from an A320 FCOM dated August 1987, six months before A320 type-certification, headed "British Caledonian" (joint launch-customer with Air France), which I obtained a few months later for my type conversion. That admitted, I doubt the fundamentals of C* law will have changed much in the meantime. But it amounts only to a brief introduction for us line pilots.

To answer the second part of your question first, Airbus have deliberately provided all their FBW aircraft with similar handling characteristics. A330 and A320 speeds are, I think, broadly similar. For example, on the A320, 210kt IAS is a typical "clean" holding speed below FL200, which has to be increased by 10kt or so at maximum landing weight. I doubt the A330 is greatly different. So the speed criteria used in C* are likely also to be similar.

My old FCOM says that C* law uses "normal acceleration as the basic parameter. At low speed, pitch rate is mixed with load factor [i.e., normal acceleration] 'G' such that at less than 150kt the effect of both G and pitch rate is [sic] equal. Above 210kt pitch-rate effect on the flight path is zero."

Later, it continues: "The overall effect of the law is that with the [sidestick] controller at neutral, the aircraft will maintain 1G and zero pitch-rate at low speed and 1G at high speed. As a result the aircraft is short-term attitude-stable."
[my hyphens, and my comments in square brackets]

In relation to AF447, I commented yesterday (http://www.pprune.org/tech-log/456874-af-447-thread-no-5-a-5.html#post6564953):
"The other unclear factor is how the C* pitch-function of the EFCS would treat the invalidation of CAS (IAS) data, when determining the crossover from g-control to pitch-control. As I understand it, that crossover is normally a gradual transition as the airspeed falls below a certain figure in routine flight. Understanding how the UAS affected this will be the other key step in solving the relationship between sidestick position, elevator/THS position, and the achieved trajectory."

[andianjul]

Takata doesn't speak for me when he tells you to get lost.:{
This is not big brother so he doesn't get to vote you off.:=
JT has that right yet has chosen not to do so.:D
So, please, bear, keep probing, asking, seeking truth. I for one enjoy your contributions.:ok:
Sorry if I overdid the smileys.;)

[jcjeant]

Hi,

bearfoil
My understanding of the last seconds of Perpignan have the PF pulling everything to gain gee, and miss the sea. The computer would not allow >2.5. She kept her slippers on, right into the drink. Unfortunately you can't refer to the Perpignan final report about gee
They released a bunch of graphics and tables but no one about the "gee" :*

http://www.bea.aero/docspa/2008/d-la081127.en/pdf/d-la081127.en.pdf

If anyone find one .. post here .......

[GarageYears]

Unfortunately you can't refer to the Perpignan final report about gee
They released a bunch of graphics and tables but no one about the "gee" http://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/smilies/bah.gif

Please "andianjul" don't encourage bear... see above. Yet MORE imaginary b/s from bear. There's a limit to what makes meaningful sense to extrapolate - but to simply make sh!t up seems shamefully self-fulfilling. We have facts, we have holes between those facts, but they mostly line-up to tell the story. There are those that want to believe that "the plane did it", but the facts (limited as they are) don't seem to tell that tale. That doesn't mean there can't be improvements related to the aircraft - every accident is an opportunity to learn and change things (if warranted) - but that also applies to pilot training, company procedures, etc.

:}

[PJ2]

Hi Chris;

I'm not sure this helps but there are two documents, (rare) on C-star laws and fbw - they can be found at:

https://dspace.lib.cranfield.ac.uk/bitstream/1826/186/2/coareport9303.pdf
and,
http://www.raes.org.uk/pdfs/2989.pdf

They're really technical and I found them difficult but there were a few nuggets in there for a non-engineer retired Airbus pilot!

[EMIT]

Bearfoil 13 july 00:09
Quote
The Pilots and pax experienced a climb, one that when it came to an end, engendered up to or even more than -1g. As she decelerated, g was diminishing, the SS may have not been active, even if it was, it was likely ineffective, and at -g the computer will try to regain +g, Yes? Of course at this point they are aerodynamiclly STALLED, but the computers would still roll in THS (NU) to regain g? No other protection is available, and AoA would be an iffy way to regain aerodynamic flight.
Unquote

Bearfoil, please get some education on flying before you spout more of this nonsense.
A zoom climb is not any uncharted territory.

In the most extreme case, when you decelerate to zero airspeed, you will have no more lift, so you will enter a free fall. How many G do you encounter in a free fall? Zero!

The minus 1 G that you conjure up could only be achieved by PUSHING FORWARD a large amount on the sidestick, yoke, steering wheel or whatever pitch control your aircraft has, while it still had enough airspeed to generate minus one G with a negative angle of attack.

I hope that this minus one G story of you, so that the computer would definitely roll in max THS up, yes? will make it clear to all how far off the mark you are. Please pay attention when people are politely trying to educate you.

As far as the lack of information from BEA is concerned - didn't they convey clearly that they have just put out a note:
"The BEA has decided to publish a note with information on the first facts established, based on analysis of the data from the flight recorders."

This note is not yet a final report, they need more time to analyse information.
Just imagine, they might first want to run a number of wind tunnel tests to check whether at 60 degrees of AOA there is enough nose down authority available to unstall the wing and recover the aircraft to normal flight. If they would not present proof about that in the final report, PPRUNErs would forever keep discussing about the point whether the a/c was recoverable or not.

[PJ2]

airtren;
My understanding is that the "a/c" would continue "level" under inertia and position of control surfaces as left after the "a/p disconnect", ONLY and ONLY if the "a/c" were on a "level" segment.

But the probability of being on a "level" segment is 1/5, which is 20%, which is quite low (maximum probability is 100%).

The probability of being on a "NON-level" segment - "up" or "down" or "left" or "right" - is 4/5, that is 80%. That is quite high!!!I think there are different meanings of the term "level" at work here - one for an engineer and one for a pilot, :) . Yes, the chances of it not "being on a "level" segment may be 4/5 or 80%, especially if nobody takes over the aircraft after the autopilot and autothrust has disconnected. But as you say, it is going to remain more or less level out of it's own inertia and the position of the control surfaces, etc. The pilot takes over and maintains cruise level and speed, (pitch and power), as I know you know.

By "stable, level flight" is meant maintaining an altitude while accepting small excursions above and below the exact altitude to maintain and not climbing or descending. It's never going to be "level" in the exact sense.

Is this what you meant? Tx...

[jcjeant]

Hi,

GarageYears
Please "andianjul" don't encourage bear... see above.Maybe .. but why not encourage the BEA to release a graphic of the "gee" for the Perpignan case :ok:
Maybe it can be interesting.

[takata]

Hi andianjul,
Takata doesn't speak for me when he tells you to get lost.http://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/smilies/boohoo.gif
I'm speaking for nobody else than myself. I'm just feeling now like I'm feeding the troll for too long. If you are a member of the same fanclub, here is a good place to start reading about the aircraft: SmartCockpit - Airbus 330 (http://www.smartcockpit.com/plane/airbus/A330/)
and another good place to post and discuss whatever theory your imagination can elaborate without the need to read anything remotedly well documented on the subject: http://www.pprune.org/rumours-news/447730-af447-wreckage-found.html
Now, my personal opinion is that a "technical" thread is not the best place for a conspiracy theorist (see above), but I may be wrong.

[mm43]

Originally posted by airtren ...
Question: it is unclear what the "Stall Warning" curve is. Would you please clarify? Thanks in advance.

It seems obvious it is not the "Stall Warning" message given to the pilots, as that was, afaik, not permanent/continuous.Have a look at HN39's post #70 (http://www.pprune.org/tech-log/456874-af-447-thread-no-5-a-4.html#post6564645) where he explains the how the data was constructed.

With regard to the stall warning, it is designed to warn of an approaching stall and works on the basis that a stall is then avoided. When in ALT2 LAW the AoA value and the CAS must be within prescribed limits for the system to calculate, and when they fall outside, e.g. AoA > 30° and/or CAS < 60 KTS, the system determines there is No Calculated Data (NCD). No valid data has resulted in the SW turning off, and it appears that when the data became valid the SW resumed, but the application of NU commands to the SS has resulted in the SW stopping again. Result is an inappropriate action was rewarded.

Looking at the AoA curve in the graphic (http://oi56.tinypic.com/9pt3ds.jpg), it bounces along the SW line as the aircraft pitches up into the climb, briefly triggering the SW. The Stall Warning sounds at 2:10:51 and continues sounding until shortly after the Capt. enters the FD. Though not shown on the graphic, it later sounds when the aircraft is established in the stall and the data is once more valid following ND inputs to the sidestick. NU inputs stopped it!

[john_tullamarine]

A little in the way of personality clashes creeping in, folks.

If you or I, as in individual, disagree with what someone else is saying, then we should just ignore the detail or the post as you prefer. I will only censor if a post is blatantly outside our reasonable expectations.

Please don't get into the gutter and engage in tit for tat - not becoming for this forum and just moves the individual combatants down the respect ladder a rung or two.

[DJ77]

Thanks Chris Scott for your detailed answer about C*. I wil take some time trying to uderstand it better.

Thanks also PJ2 for the references to C* docs.

[HazelNuts39]

Question: it is unclear what the "Stall Warning" curve is. Would you please clarify? Thanks in advance.The curve shows the stall warning threshold. It varies with Mach number according to a schedule that has been posted by A33Zab a few weeks ago. Except for the NCD condition explained by mm43, stall warning begins when AoA exceeds the stall warning threshold, and continues until the AoA has decreased below that threshold.

[rudderrudderrat]

Hi Takata,

I think Bear was asking something like:
During the apogee when sensed g is less than 1, and stick free, will the FBW logic increase pitch in an attempt to hold 1 g?

Some of my students use the term "g" when they meant to say "delta g".

[BOAC]

I'll chuck this (2000) paper in too if it helps.

Fly-By-Wire A Primer for Aviation Accident Investigators (http://cf.alpa.org/internet/alp/2000/febfbw.htm)

[rudderrudderrat]

Hi BOAC,

Your paper sums up in one sentence, what I've tried to say.
Now for the bad news. While FBW technology could make an aerodynamically unstable aircraft flyable, it can also destabilize an otherwise stable airframe.
Once stall "protection", "limit" in Normal Law is lost - PLEASE return my "elevator feel" with Direct Law.

[BOAC]

It might be a good idea to return this thread 'to earth' with a brief summary of what we know.

Leaving aside what happened after the climb, what about the climb?

1) There is nothing in the BEA report to suggest that the aircraft caused it itself. The only 'query' here is the track record of system reaction to 'events', like the QF pitch anomaly and the 2001 North Atlantic altitude excursion with TC-JDN. It is worth noting that in this the crew did not trigger a climb. (There is some confusion (for me) in the AAIB report where the FDR traces suggest the TCAS RA occurred BEFORE the a/c left its cruise level). Had this crew been in the ITCZ at night and not in clear air in daylight it is worth contemplating what might have occurred.

2) There is nothing in the BEA report to suggest that the pilots caused the climb either.

Until the BEA provide the full CVR transcript AND RHSS trace from the FDR for the period 2:10:05 to 2:10:51 we are all guessing. Why they have not is a mystery to me.

[Owain Glyndwr]

Ordinarily, the downwash angle at the tail is related to the lift coefficient more than to the wing/body AoA. Would your values be more specific to a stalled swept wing?

If you ignore the slight complication of no-lift angles and wing body settings (which change the zero body angle downwash), then lift coefficient is just AoA times lift curve slope, so they move together. Almost all textbooks and reports use the AoA format as this makes the equations a bit easier to handle. I guess I just stuck with it from force of habithttp://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/smilies/smile.gif

The numbers I quoted are pretty good for an aircraft like the A330, at least up to stalling AoA. When lift curves go nonlinear then I would agree with you that lift coefficient would be a better handle. I don't think anyone knows exactly what the downwash would be at 60 deg AoA, but I was using it in an argument about THS stall and as the later bit of my argument took the THS away from stall I didn't worry too much about ithttp://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/smilies/smile.gif

Thanks for the welcome!

[syseng68k]

Takata, #204


This is something I really don't understand about you... Those basic
things are mandatory to understand how those aircraft are flying and
most of this stuff, about Airbus FBW systems, is available nearly
everywhere.
I'm afraid not. The voluminous fcom looks to me like a user guide,
rather than a serious technical manual and the logic that drives the
transitions between the various laws is not available anywhere, afaics.
Perhaps you could provide pointers ?. Sure, the fcom has bits and pieces
dotted around all over the place, but nowhere can I find a flowchart or
logic diagram that describes the whole process. The fact that, ergo, ab
seem to think that this is not important to crew is one of the most
worrying things about the whole episode. Fly the computers, not the a/c,
seem to be the modern mantra and you don't need to know about the
detail :eek:.


Why don't you take a little time to read it, all by yourself, instead of
posting daily, from two years now on this thread, such a load of cr*ap
about a subject you never bothered to study a minimum?
Are the personal, ad hominem attacks really necessary ?. If you don't
like a post, then don't read it. It's not as though you had anything
constructive to say in rebuttal anyway. It's not the way that it's done
here, so please, let's keep it civil...

[Loerie]

Sorry,but I find that takata`s outbursts are unpleasant and confrontational and not really required.Everyone is doing a fantastic job here with lots of team effort to try to discover what caused the death of so many innocent people,and that includes bearfoil.Some are more qualified than others and some have other agenda`s that are not easy to see.Sometimes those from without Looking In have better vision that those inside who may not see the Wood for the Trees......pull together guys and girls.Works much better.

[syseng68k]

BOAC, #222


2) There is nothing in the BEA report to suggest that the pilots caused the climb either.
Other than the sidestick input, yes ?.

Something that occurred to me is the fact that the sidestick transducer,
which translates physical input to electrical signal, could have failed
in such a way as to provide a bias in it's output. Don't have enough
info to know if it uses a synchro, resolver, potentiometer or optical
encoder, but any but the last of those could in theory degrade to
provide a bias away from zero, (ie: nose up) depending on failure mode.

Probably a long shot, but it is a possibility...

[KBPsen]

It is completely understandable that frustration surfaces when repeatedly confronted with fantasies, ignorance of facts, invention of facts, rewriting of facts and then attempting to mask it by consistent use of gobbledygook.

Loerie,

What you have here is a bunch of people running in circles and they have done so for quite a while. Some have even resorted to just spin around them selves.

Try this little experiment; Select at random five people who regularly posts on AF447 threads 1-5, select at random five posts from each, compare the five posts. If you can spot any difference let me know.

[DozyWannabe]

Sorry,but I find that takata`s outbursts are unpleasant and confrontational and not really required.

Maybe, but I'd say that they were fairly understandable.

Everyone is doing a fantastic job here with lots of team effort to try to discover what caused the death of so many innocent people,and that includes bearfoil.

Actually, I'd say that Bear has been deliberately trying to obfuscate and make things unclear in order to push his own agenda - the fact that he elected to do it so prolifically in the last few days does not help his case.

some have other agenda`s that are not easy to see.

One of whom is Bear. I'm all for getting as many heads around the table as possible, but what he was doing was tantamount to spamming the thread - not just with questions, but with statements that were (based on the information given) demonstrably untrue.

(I hope this won't be construed as being "personal", this is just my observations from the last day or so)

@rudderrudderrat : There has been no such thing as real "elevator feel" since the '60s, and Direct Law does not provide it. The only difference between Normal/Alternate and Direct Law when it comes to tail surfaces is that the trim movement becomes manual-only in the latter, and the elevator command directly affects deflection rather than commanding a rate.

@KBPsen - some of us have been effectively forced to repeat ourselves because of the drip-feeding of misinformation that you are describing - in fact quite a few genuinely knowledgeable people have got fed up and only pop in occasionally, if at all. That's probably a major source of the frustration right there, because if some of us don't fight to keep the discussion to the facts then we could end up with some of the misinformation quoted in a newspaper somewhere, and that's how fallacies like "The plane thought it was trying to land and overrode the pilot" get spread around.

[Diversification]

BOAC posted an intressant link; Fly-By-Wire A Primer for Aviation Accident Investigators (http://cf.alpa.org/internet/alp/2000/febfbw.htm)
I have enjoyed reading the short description of how FBW systems operate and about C, C*, and G*U. In principle it looks almost like normal PI controllers and not PID ones. What strikes me is that all is written with the assumption that the controllers are analog and not digital. From my own experience - writing well performing digital controllers and their real-time performance is a very different story.

Regards

[A33Zab]

2 Xdcrs(contains 4x triple potentiometers per axis).

FCPC1 & FCSC1 driven by separate linkage. (Dual Channel output 4 potentiometers, 2 unused) per axis.
FCPC2 & 3; FCSC2 driven by the other linkage (Dual Channel output 6 potentiometers) per axis.

The sidestick is placed in a polycarbonate container to prevent entrance of foreign matter.
The sidestick design is such that rupture, disconnection or jamming of any of the parts can't cause the loss of total A/F loads on one axis or block free movement of a set of a potentiometer group related to one axis.
Transducer output is monitored and compared, if any difference F/CTL L(R) SIDESTICK FAULT ECAM message is triggered.

Schematic:

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

[airtren]

Thanks for your clarifications


Have a look at HN39's post #70 (http://www.pprune.org/tech-log/456874-af-447-thread-no-5-a-4.html#post6564645) where he explains the how the data was constructed.


The curve shows the stall warning threshold. .... Except for the NCD condition explained by mm43, stall warning begins when AoA exceeds the stall warning threshold, and continues until the AoA has decreased below that threshold


Then it would seem that naming of that curve "SW threshold" would make the graph clearer/self explanatory. A "SW" curve (could be non-contiguous) could be the curve representing on the time scale the intervals when the Stall Warning was (should have been) active.

As I looked again at the graph, I thought it would be helpful to see the corresponding curves/data that were available to the "a/c systems" and "a/c pilots" in the context of "loss of data", and showing the discontinuity in the SWT (stall warning threshold) curve, due to NCD - was there such a graph already made available?


No valid data has resulted in the SW turning off, .... but the application of NU commands to the SS has resulted in the SW stopping again. Result is an inappropriate action was rewarded.

The Stall Warning ON->OFF->ON->OFF transitioning during the Stall is one of the several elements that seem to be in the most troubling category. Would this qualify the SW during the event in a different type than "lack of info"? Would it be, the "FALSE info" type?

Is the calculation/equation used for determining the providing of the Stall Warning relying on too few parameters?

"Vertical acceleration", or "vertical speed", perhaps "no lift"? Is any of the existing sensors, and parameters available on the "a/c" able to provide info, so that a Stall Warning could have been clearly brought to the knowledge of the pilots for the entire duration of the Stall?

[PJ2]

syseng68k;

Re your post #224, good observation. The FCOM is a need-to-know user's manual and indeed does not explain the aircraft. I think this is one of the underlying issues. FBW and C-star law are not in and of themselves problematic but unlike complex hydraulic or electrical systems, the differences in "the how" of control are materially different and require understanding, as do the more bread-and-butter areas of high altitude, high Mach number flight and even some jet transport aerodynamics. I did not know and did not understand until a lengthy and patient exchange with HN39 that the stall AoA for my aircraft was much lower at high Mach numbers in cruise flight than what Davies had expressed in his wonderful book, which was the approach and landing case with high-lift devices extended. Big, big difference and, even in retirement, I learned some fundamentals.

These are not taught very thoroughly in initial ground schools at least in my experience, and if one wasn't in the air force one's knowledge was increased largely through one's own efforts.

The frustrations of not knowing and not being able to find things out easily have been endemic - while easy to fly and a joy to hand-fly, "automation" has become as much a marketing tool as it has a way of solving the problems of flight. The resistance to knowing more than the "NTK". need-to-know, ground-school curriculum requires, comes first from how expensive it is to train well, and next from a lack of knowledge in those who must do the teaching, always of course, with wonderful exceptions from those memorable instructors who's passion takes them, and their students beyond NTK.

Learning is expensive and NTK and automation are assumed to "solve" that "problem" for a cash-strapped, (de-regulated) industry.

This isn't "THE" problem, because clearly the aircraft and the design's record is no worse in terms of fatal accident rates than conventional types - in short, the airplane and the design work extremely well but one should never be in a position to not understand and not anticipate what his airplane is doing.

Below is a nuts-and-bolts schematic of the pitch-basic loop. I hope it is of some service in understanding the pitch control of the A330.


http://www.smugmug.com/photos/i-RvKWdbv/0/XL/i-RvKWdbv-XL.jpg

[Meikleour]

Takata: When the g load is less than 0.5g then the THS is frozen. Perhaps this is not known to Bearfoil?

[bearfoil]

Meikleour

It was not known to me, and I appreciate rudderrat's rephrase. I'll be brief with my next question. Of course it may (is) in the FCOM, but may I see any answer in the thread?

If frozen, the THS would be unavailable for Trimming, (or Pitch changes), until what point? When does it become available again?

So the original question remains: If less than one g, does the THS move independently of Pilot's inputs? Does it try to regain 1g or satisfy itself that anything greater than -1g is acceptable?

Does it "Unfreeze" if the g becomes <-1g? And then input NU?

The limits are intriguing to me, until I have a better picture of what the THS may have been doing in <1g, who can say what the a/c's behaviour was?

To expand on BOAC's #2, BEA have not assigned the climb to the pilots, that is true, and they affirm that by specifically stating, "ONE" (a) Noseup, left roll input. That apparently happened prior to the "climb", as I read it.

[takata]

Hi BOAC,
Leaving aside what happened after the climb, what about the climb?
1) There is nothing in the BEA report to suggest that the aircraft caused it itself. The only 'query' here is the track record of system reaction to 'events', like the QF pitch anomaly and the 2001 North Atlantic altitude excursion with TC-JDN. It is worth noting that in this the crew did not trigger a climb.
There is another way to change pitch attitude than pulling up on the sidestick as simply applying thrust could do the job if the ammount is large enough.
While I agree that QF event remains a mystery, TC-JDN case is showing that, right after autothrust disconnection, manual thrust was applied and increased from N1 below 70% to 100%. Sidestick (ND?!) imputs were not applied until the top of the climb 30 seconds later, hence nothing contraried TC-JDN to change its level flight. Someone also posted a revised chart of DFDR control imputs but, as far as I remember, it did not include any thrust track.

(There is some confusion (for me) in the AAIB report where the FDR traces suggest the TCAS RA occurred BEFORE the a/c left its cruise level). Had this crew been in the ITCZ at night and not in clear air in daylight it is worth contemplating what might have occurred.
There is some more confusion (for me) in the AAIB report and in the cockpit. Had this crew been in the ITCZ (or anywhere else at night) it would be certainly dangerous, but they still were in NORMAL LAW and the flight envelope, contrary to AF447, was still fully protected as airspeed was valid all the time.

2) There is nothing in the BEA report to suggest that the pilots caused the climb either.
Well, I should have read another "report" as in mine, a nose up order was (almost immdediately) given by the pilot... the later nose down orders that were applied only reduced the climb rate from 7,000 ft to 700 ft/mn (which is not enough to start a descent). So here, we effectively need to see the tracks in order to understand what the PF really wanted to do. It is not like this initial climb looked like uncommanded, but the report doesn't tell much about how it was controled and what could have prevented this high climb rate control by the PF.

[HazelNuts39]

naming of that curve "SW threshold" would make the graph clearer/self explanatory, while adding a "SW" curve (non-contiguous curve) would be the curve representing on the time scale the intervals when the Stall Warning was (should have been) active.To start with just a reminder of BOAC's justified concern that these curves should not be mistaken for real DFDR data. What you are asking is problematic because the curves assume still air, and one should be aware that turbulence would superimpose "grass"-like fluctuations on most parameters. IMO that is the reason that the two brief activations of S/W after 2:10:05 are not shown as threshold exceedances on mm43's graph. May I suggest that you just make a note that the AoA was 'invalid' between 2:11:40 plus 'a few seconds' and 2:12:17?

... and showing the discontinuity in the SWT (stall warning threshold) curve, due to NCD ... The systems consider the signals coming from the AoA vanes invalid, there is no discontinuity in the SWT.

You pose more valid questions, but I regret not being in a position to answer them.

[JD-EE]

HeavyMetallist, "Why some people persist in believing that stalled == totally ineffective is a mystery."

gums has posted some graphs that show an actual inversion of control for a totally different kind of aircraft when in a bad enough AoA configuration. Somebody else posted a graph I believed was for the A330 produced by calculations that indicated an AoA of 61 was sufficient to put the A330 into a realm where the tail was not particularly effective.

That said, it appears from the release, in a part I'd forgotten (take your own advice, Joanne), that there still was some authority from the tail surface. Unless the PF pulled up again after the stall warning the tail surface did not have enough authority to pull them out in the remaining 2 minutes. So it was basically ineffective or marginally effective.

[Diversification]

A33Zab
Thanks for a nice and illustrative picture of the stick mechanism.
I wonder if a very strong force on the stick to the left could force some undesired nose-up if the enclosing structure is not sturdy enough.
I am also a little surprised that potentiometers are used - even with two (or more) in parallell for each axis.

Regards

[JD-EE]

bearfoil, you'd best concentrate on something you know somewhat better than law. I can think of several instances off the top of my head wherein people who are not parties to a contract or any other record do not have access to the data.

One is when a settlement is reached and both parties insist it be kept secret as a part of the settlement.

[syseng68k]

A33Zab, #230

Thanks for the excellent diagram. Not quite clear on the following:

2 Xdcrs(contains 4x triple potentiometers per axis).

FCPC1 & FCSC1 driven by separate linkage. (Dual Channel output 4 potentiometers, 2 unused) per axis.
FCPC2 & 3; FCSC2 driven by the other linkage (Dual Channel output 6 potentiometers) per axis
So what you are saying is that:

The system has a total of (4 x 3) 12 pots per pitch and roll axis, total 24

FCPC1 and FCSC1 each get pitch and roll, triple redundant, 12 pots (minus 2 ?)

FCPC2 and FCSC2 each get pitch and toll, triple redundant, 12 pots

Question: Why are two pots unused ?.

Looks like a clever design though, in that the redundancy even extends
to the mechanical linkages. In the unlikely event that one linkage
disconnects or breaks, the second linkage and potentiometer set would continue to
function.

Question: What is the function of the solenoid and does that lock the
stick at any point (zero ?) in it's travel ?.

[airtren]

By "stable, level flight" is meant maintaining an altitude while accepting small excursions above and below the exact altitude to maintain and not climbing or descending. It's never going to be "level" in the exact sense.

Is this what you meant? Tx...



Indeed, the "a/c" trajectory is never really a "perfect" "straight line". It is rather a series of segments of the type I've mentioned - "up", "down", "left", "right", "level" - with the length of these segments depending on the degree of air turbulence, and how fine the control of the "a/c" is.

In non turbulent air, the 4 "non-level" segments are very short, while the "level" segments are long, or very long, and predominant.

That is different in turbulent air: the length of the 4 "non-level" type segments is a lot more significant, while the length of the "level" segments a lot shorter, possibly down to "zero", with a predominance of the "non-level" segments, versus "level" segments.

That implies more drastic or significant actions of the "a/c controls", that react to the change and transition from one type of segment, to the next, to keep the "a/c level".


But as you say, it is going to remain more or less level out of it's own inertia and the position of the control surfaces, etc.
My understanding is that that would be the case if there is no, or little turbulence.

However in turbulent air, at an "a/p and a/thr disconnect", which can be coincidental with a change of law, and loss of certain protections, the "inertia" and the "a/c control surfaces at normal position" would keep the "a/c" level, ONLY and ONLY if the segment is "level".

Otherwise, as I understand it, if the segment is "non-level", there is a good chance/probability that "inertia" and "control surfaces" as left after the disconnect, and lack of protections, can bring the "a/c" way out of being "level" - "up", or "down", or "left" or "right". The degree of how off from "level" depends also on the time interval between the "automation disconnect" and the taking of the controls by the pilot, as well as a correct control correction coming from the pilot.

The probability of 20% and 80% I've referred to implies an equal distribution and length of the 5 types of segments, which is a stretch, for the sake of an easier explaining/understanding .

But it is a stretch in both directions!!!

Which means that for a very active turbulence, for the duration of that turbulence, the segments might be only "non-level", in which case in that time interval the "probability" goes from 80% to 100% - which makes it "a sure thing".

[JD-EE]

syseng68k, the SS probably did not fail. The PF was able to achieve ND type inputs on several occasions. And if the PF pulled the stick and got NU he'd no doubt announce it and turn control over to the PNF whose stick would presumably work.

And I'd be tempted to look into "springs" and strain gauges. (The sticks gums cites very probably were based on strain gauges since they had so little movement.) Strain gauges have nothing to get dirty, noisy, or erratic. So they're a little more reliable.

[BOAC]

takata - post #235 - you accuse Bear of posting "such a load of cr*ap about a subject" and then do it yourself. I repeat - there is NOTHING in the BEA report to tell you that the pilots caused the climb. A 'nose up' input of unspecified size or duration does NOT prove that and may well have been of short duration - you do not know. As for your bit about "There is another way to change pitch attitude than pulling up on the sidestick as simply applying thrust could do the job if the amount is large enough." - you don't say? Now show me where the report tells you they increased thrust. You are making this up!

Now to TC-JDN - have another look at the trace. The a/c began pitching while the engines were throttled back, the side stick did not move but the THS did.

I note you come 'from Toulouse'.

[airtren]

Thanks for your clarifications...

Hm.... Perhaps I've missed this.... are the variables/parameters determining the values of the Stall Warning Threshold function and thus the shape of the curve valid, for the entire time (X) axle in the graph?

If NOT, then, "invalid", or "non-defined values" for the variables determining the values of the function/curve, means "invalid" or "non-defined function values", which means segments of curve which would be "invalid", or "non-defined". This means that the "non-defined" portions of the curve can be represented accurately only as a discontinuity - gap - on the non-contiguous curve.

Ultimately, it does not matter much, as these curves are just an illustration to help the understanding and communications of info on this thread.


The systems consider the signals coming from the AoA vanes invalid, there is no discontinuity in the SWT.

[bearfoil]

Would the Throttle setting be cruise detent? Could the actual thrust of the engines be somewhat higher than "normal" due a/p increases to maintain straight and level? If so, at handoff, the Throttles would lock? An assumption could be that with high N1, a change in Pitch (up) might be aided by thrustline? (These are rephrasing of my earlier question, so if they seem repetitive, they pretty much are just that).

:p (no offense)

[foster23]

hi everyone. could some one please explain the g loading on a aircraft in laymans terms. many thanks

[Lonewolf_50]

Short explanation of g loading:

G is an expression of acceleration.

If you or I simply sit in our chair, we feel the normal 1 g load on our body. That is due to earth's gravity acting down toward the center of the earth.

If we are in a roller coaster car, and go racing down an incline, when we reach the bottom, and then race up the next incline, we feel more than 1 g acceleration as we go through that arc on the bottom of the track. (we feel pushed down into our seat a bit). This is like a pitch rate change in an aircraft, pitching the nose up.)

If we are in a plane flying along straight and level, we should feel 1 g.

If the plane goes into a 60 degree angle of bank turn, straight and level, the vector forces sum up to 2 g's. You'll feel that in your seat. (You'll feel a bit heavy).

If you are flying with the Red Arrows, or Blue Angels, or Snow Geese flight demonstration teams, you may do a high G turn over the field to show how maneuverable your jet is. You can induce g's up to 5, 6, 7 ... depends on which aircraft you fly. While doing such a maneuver, if you try to raise your arm, it will feel heavier to lift than when under 1 G. Under 5 g turn, your arm feels about 4 times more heavy than just sitting in your seat. (You can usually still lift it, but it feels strange to do so, much effort).

If you are in level flight, and you push the stick forward, you will tend to feel light in your seat: you are feeling < 1 g. If you fly the plane in a particular manner, beginning nose up, you can push over into a parabola shaped flight path that will induce a zero G condition, temporarily: if not strapped in, you can float a bit in the aircraft cabin. (Astronaut training used to include such events. Not sure if it still does).

If you choose to roll the aircraft inverted, and fly level, you will feel 1 G acting in the opposite direction to your sitting down: you will feel pushed OUT of your seat, not held into it. (Keep those harness straps on nice and tight). That G is typically referred to as negative G. It makes the blood rush to your head. The earth pulls on you the same, but your orientation made you experience that force differently.

A vigorous nose down push on the stick from level flight can induce negative G, and you will fall "up" toward the aircraft's cabin ceiling if you are not strapped in.

For much smaller changes, you can induce a 1.2 g or 1.1 g, or slightly less than 1.0 G (0.9, 0.8) via small pitch changes, as a result of control inputs that you choose.

G onset tends to be rate sensitive. If I make a very slow input, nose up or nose down, I induce a small acceleration, so the "g" of that maneuver, or the "change in G force" is small.

If I make a rapid input, the G tends to increase, and it is readily felt.

Does that help?

If you like a fuller article, this one is OK, more detail.
g-force - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/G-force)

[foster23]

thanks very much for your time sir:ok:

[HazelNuts39]

.... are the variables/parameters determining the values of the Stall Warning Threshold function and thus the shape of the curve valid, for the entire time (X) axle in the graph?As I said, in a given configuration SWT depends only on Mach. I have explained in a recent post how Mach etc. are calculated. The calculated speeds are the speeds that the airplane physically has in the simulation, and do not reflect any erroneous or 'invalid' speed that the systems may have 'thought' the airplane had. You have to consult the BEA Note for those. The SWT shown on the graph is valid for the 'simulation' Mach.

It is not entirely clear how the system calculates SWT in the event of erroneous or invalid airspeed. BEA#2 says that the system then sets it at the low speed value of 10 degrees. But several UAS incidents show that that does not occur. Maybe we just need to have better understanding of 'erroneous' and 'invalid'. For the NCD condition it doesn't matter where SWT is, or does it?