IF789

If the descent was transient, and chronic, why shouldn't the THS react with 13 degrees nose up?

Transient as in intermittent, and Chronic as in trend. Both. Pilots do this often, tweak, wait, tweak, wait ad ab. Another term could be: Hunting.

BEA report the THS moved from 3 - 13 degrees. Three degrees could mean sometime before the a/p is lost. This fits in with one excursion only, and could include both a/p and PF inputs, separated by the drop.

"...So they were trained not only not to touch the trim wheel, but also that if they concentrated hard enough, it would actually disappear ?

To me, some of the scariest comments on these threads have been on training practices. Was PFs only training for stall warning "pull up" (to minimize alt loss) ? That is all it would take..."

The pullup at STALL may mimic an artifact in training (not changed til after 447 went in) where the "Recovery" is w/o excessive altitude loss.Where was the added Thrust?

you say

and indeed they don't specify a duration, however the next mention of inputs is nose down after the (first) climb.

During that first climb PF gets stall warning. At 37500ft he gets stall warning again and "maintains" NU input in response. If the response to the SW is consistent, then the conclusion is chronic PF NU.

If the THS had some excess NU, and PF added more NU at handover, what is to say he was not attempting his trained recovery. At STALLSTALL he would NOT immediately input ND but per SOP he would maintain "pull" to minimize altitude loss, not knowing his meager ND, (relaxed back pressure) was way insufficient to keep from Stalling.

He may have actually input Nose down, but it was not beyond neutral and was "READ" as NU by the FMC? He may have been trying to fly with elevators "Only", (not knowing NU/ND would react completely different in response) that would be his set from Stall Training? He certainly didn't train approach to STALL with 13 degrees of THS NU.

At this point, would he become a little unnerved at the reaction to seemingly "appropriate inputs. He would be getting large (and variable and delayed) actions from his hybrid elevator, Tail Plane mongrel. Once again, was his continuous back pressure on the way down his stubborn insistence on his reaction to the a/c at this point (Pull Back, Nose drops, Push, Nose raise?)

If so, at what point was the "feel" of the a/c so foreign to him that he acted in "unpredictable" ways?

thanks for the response :ok:

You're getting things a little muddled, bear. A/P disconnect appears to be caused by the loss of air data, not the position of the THS.

Read the article that PJ2 linked to, it contains some very useful information - including the fact that the ADR disagree lasted for 45 seconds, which means that return to Normal Law is unlikely to have happened (Svarin should find that interesting).

Doze

You're getting things a little muddled, bear. A/P disconnect appears to be caused by the loss of air data, not the position of the THS.

No. A/P disconnected via unreliable air data OR it limited out. Not loss. It is the cause of the discrepancies that is important, and unknown. The a/c was being trimmed at handover. It was descending and rolling OUT of A/P. This suggests to me that the cause may have been severe turbulence AND/OR an autopilot that could not keep up.

Either way, these are two distinct possibilities. With Ice, we are stuck with only one. The timing of the faults suggests a/p dropped before the reads became unreliable. This means it is possible the a/c remained in Normal Law for a short term, until the discrepant reads instigated the Law change. I have not seen a proof against this. Only some "assurances".

Zorin_75:

Full text of the paragraph from the BEA.

Your version:

Not saying the same thing are they. You are interpreting a version that assumes completion of THS movement at 2:10:51 (which is only 46 seconds and quite short of "about 1 minute" and since they have exact times, why not state 46 seconds?), my read is that starting around 2:10:51 the THS moved from 3 degrees NU to achieve 13 degrees about minute later.

You pick? Either is possible from the given text. Note the PF NU inputs (maintained) at and beyond 2:10:51... what would they do to the THS?

@bear - The article also states that the turbulence was moderate, not severe. The A/P is likely to have disengaged at the first sign of pitot blockage, which was some seconds before the computers confirmed ADR DISAGREE.

That initial pitch-up
 

I am still not convinced by most theories posted here on why there was a nose-up input as soon as the autopilot dropped out due to unreliable speed data. The most rational so far:

1. it was an involuntary action, an unwanted side effect of putting in a left roll demand to counteract a right wing low tendency, or
2. It was the response to a false indicated speed increase,

I find (1) unconvincing because it was one hell of an input, sufficient to cause a 7000 fpm climb and, apparently, two stall warnings, sounds sort of deliberate to me.

similarly (2) sounds wrong because, while we don't know for sure what the indications were on the PF's panel, due to the lack of recorded data, we do know that the other two systems showed abrupt speed decreases, and the previous high altitude pitot icing incidents, including the Air Caraibes precursor, also only registered speed decreases. So it would be extraordinary for the unforunate AF co-pilot to be the only one to have been presented with the opposite.

That same Air Caraibes report also said that at the time of the beginning of the anomalous air data, the indicated altitude rapidly dropped 300 ft (presumably due the lack of a vaild Mach number to correct the static pressure (? ) the BEA has already told us that with no vaild M, the stall warning system uses a value near zero...) Maybe the PF was reacting to that, admittedly 300 ft isn't much, but I suspect it looks a lot on the tape, and it would have been rapid. Perhaps this is the trigger we've been looking for.

BEA. The first two statements, by BEA, describe a recovery from APPROACH TO STALL.

The next Statement describes a good picture of the THS after its position at a/p loss plus PF's additive, created the climb. If PF was unaware of THS postion at handover, he is figuring, hmmm. three degrees. His attempted recovery from APPROACH TO STALL, instead of being from three degrees, was from SIX, which he appears to have held.

If he had captured TOGA, (such as it was), the absence of the STALLWARNING means he is a success. Unfortunately, the TRIM is helping him maintain back pressure up to thirteen degrees.

SO. Two recoveries from APPROACH TO STALL. Holding back pressure all the way. With the eager help of THS.

garageyears:
Actually I absolutely agree with you. Please read again, what I was saying is that even when read that unreasonable way, you can't get the report to align with bear's theory of the a/p disconnecting as the THS reached its end stop (which is also completely ignoring that we have already quite a good reason for the a/p disconnecting in the UAS).

Zorin

Your turn to read again. I say no such thing. THS at 3 degrees, at drop. With the a/c descending and rolling right. AT STALLSTALL, PF selects back pressure to escape the Warning this is not the same as NOSE UP. It is agee thing, to which the THS responds. The only training he had re: APPROACH TO STALL was certainly without the THS involved? PITCH is protected in A1 and NL.

yep.

Uhm, I did:

@bear - in anything other than Normal Law, protections can be overridden with sufficient control input. If you're now suggesting that he pulled hard backstick expecting the protections to have his back, then he either failed to hear the call "Alternate Law" from the PNF or there was something wrong with his training. All this supposes that your theory is correct - for which, of course, we have no evidence.

The THS "reaching its stops or limits at "2deg (ND) or -14deg (NU)" will not cause the a/p to disengage.

I doubt if there is overly much difference between the initial FDR printouts of the Jetstar VH-EBA UAS incident and those recorded by AF447. Have a close look at what happened to the TAT, SAT and CAS traces and similarly to the altitude when the Mach correction wasn't available.

Probably worthwhile bearing those traces in mind when discussing the initial upset. How LOC came about is another matter.

PJ2;

A nagging thought has been, why wouldn't/didn't the THS move the additional degree to 14° NU with what appears to have been fairly constant NU inputs?

bear:

Where do YOU get this stuff from? Nowhere does anything state the aircraft was DESCENDING at the start of event, except in your posts - I honestly think the BEA might have mentioned such a condition. And now you are imagining some kind of AP drop off at THS authority limit.... This is bunkum and the worst kind of dramatic imaginings, solely it seems an attempt to fit some other version of reality to the BEA framework in a twisted fashion.

Zorin_75: :ok:

(re-read your post... got it third time round :ugh:)

stalls, OODA, THS "laws"
 

Salute!

- First of all, there are "stalls". Then "deep stalls". Then "deep" stalls. So despite my posts describing a true "deep stall" in another jet, I can't say for sure if the Bus will do the same thing. I brought it up because the other jet was FBW and it was not a T-tail ( the config normally associated with a "deep stall"). My only valid comparison is the FBW system tried to do its best to no avail. In our case we had a large aft c.g. and a demonstrated pitch moment at a certain AoA that allowed the jet to settle into a true "deep stall".

Then there are "deep" stalls. Way beyond C-sub-ell max, but basic static stability and nose down stab/elevator usually allows recovery.

- I can't think of any pilot that does not employ the OODA principle, especially when making an instrument approach. Further, if it had not been for Boyd, Moody Suter, Sprey, et al, I would never had the chance to fly the first operational 100% FBW jet ( and no trim wheel for the THS, just our last-ditch manual pitch override doofer).

- PJ and another one or two agreed with my view of the THS trim law, but another pilot has implied that under certain conditions or reversions that the pitch control trim becomes more of an "attitude" command versus a gee command, and then an AoA command when certain limits are reached.

My point is that from the manuals' description, the HS is trimmed so that a stick command is always a gee when the gear is up or some AoA limits are reached or .... Gets confusing, don't it? So pull back a bit, then relax and the jet climbs at 1 gee corrected for pitch. So at a 30 deg attitude, it would trim the jet hands-off for a 0.87 gee normal force on your body, at 45 degrees 0.707, and the beat goes on. This makes sense for a heavy, as a continuos 1 gee would result in ever-increasing pitch, wouldn't it?

So the jet might appear to be in an attitude control mode, but damned if I can find that in the descriptions.

The potential problem that may deserve attention in this accident and with respect to the Airbus control laws is what does the THS do if the pilot has a small, but constant back stick when the jet is already at 1 gee , or even a bit less ???

more later.....

mm43;

I believe the slightly higher limits are the mechanical trim stop limits.

gums, when I first checked out on the A320, a really sharp friend (also doing the same) observed that the one-gee law would actually cause a slight increase in the rate of climb as the aircraft got further away from earth... ;-)

Awwww maaaan.....
 

Salute!

Gee, PJ, I thought I was losing it....

Unlike our little jet with different operational requirements, that's what we saw when we relaxed pressure on the stick in a slight climb. Hmmmmm......

So I was pleasantly surprised when I read the Airbus pitch correction for the "gee input" by the stick. Made sense to me for a heavy.

One of my dreams is to have all the heavy pilots fly a system that commands gee until the jet reaches a certain AoA, then follows the AoA limit ( I don't like the term "protection"). Upon releasing the stick the system tries to establish the last gee command, whether a trim gee by the confusers or a manually set gee. I know for a fact what my jet's laws did.

I have a bad feeling that the Bus may not re-trim the stab real quick after a prolonged maneuver at the AoA limit, then just relaxing on the stick.

respectfully,

Funny what goes around when no one knows...never saw the "slight increase"! Funny what still goes around...

I think the term "protections" conveys a prophylactic sense which speaks to some airline folk who want to reduce training, hire cheap and claim that commonality means one-for-all training. You can always tell a salesman but not very much.

The A332 trim rate is 0.2deg/sec on AP and I believe the rate is the same for manual flight using the sidestick. The same 3 electric motors, (only one operating at a time, IIRC) drive the THS. Manual/mechanical trim is meant to be used and employs two hydraulic motors. The mechanical stops are part of both systems. A pawl and ratchet system prevents back-movement under air loads. From what I have been able to learn, I don't believe that the THS would return to a previous setting after a prolonged manoeuvre if the stick is merely relaxed, (neutral, no orders to the FMGEC > FCPCs). I believe the THS would remain "as is" in manual flight and the airplane would "settle" into the setting just as any airplane would. In autoflight it would of course, trim.

RetiredF4 and HeavyMetallist
 

Not disagreeing at all with RetiredF4's detailed post, and in fact building on it, I would like to ask a question concerning the situation once the a/c had established an AoA of about 61°.

http://pickyperkins.home.infionline....roundSpeed.jpg

Using the graphs in HeavyMetall's reference for the lowest aspect ratio (6), isn't it the case that stick forward, elevator down, would lead to a decrease in the lift on the THS, and hence a more nose-up attitude of the a/c?

http://pickyperkins.home.infionline.net/PostStallCL.bmp

So for a pilot getting to the bottom of his barrel of options, might that inhibit further stick forward experiments, and strongly encourage a stick back tendency?

http://pickyperkins.home.infionline.net/PostStallCD.bmp

It is true that drag on the THS would also increase and that would tend to act in opposition, but by how much?

PJ2, Actually I did put a link for this one, but I certainly wouldn’t blame you for not noticing …
I don’t really want to comment further about it, but I take that opportunity to admit one more time, if needed, how little respect I have for my beloved BEA :
Their note is nothing else than that : partial and approximate

I know you don't agree, I know how people want to trust their Institutions, but all I need is the full data, nothing more, but nothing less.

Goodnight to all !

Re RetiredF4 and HeavyMetallist
 

@ PickyPerkins

Thank you for doing the handywork posting the graphs i referenced to. I´m too dumb on computers to do it:).
You visualized my point of view.

I ask again - why is it you're asking this of the BEA and no other accident investigation bureau/institution? Is one incident forever going to preclude acceptance of any finding of theirs that includes "pilot error" as a factor?

Also, you're a pilot, I'm an engineer - but I wouldn't trust myself to derive a correct conclusion from the raw data. What makes you so sure you could?

THS
 

PJ2:

I’ve got these figures of THS rate.

If they stated: "there's only 1 motor in control" they mean the ELECTRICAL motors (P1,P2 & P3) whichs drives the control sleeve. Control sleeve position will be overriden by mechanical input (from handwheels)


The THS itself (the ballscrew) is driven by 2 hydraulic (B & Y) motors.

Max. Operating Load and Max. Speed (2 motors)

18940 daN (42578.81 lbf) ----- 0.4°/s
16950 daN (38105.11 lbf) ----- 1.0°/s
6770 daN (15219.56 lbf) ---- 1.2°/s

Half speed for 1 motor (1 hydr. B or Y system failure) operation.

Since the hinges are on the trailing edge and therefore the aerodynamic load on the drive spindle is in the AND (stab. Nose Up) direction (see diagram by Tailspin Turtle) it would take 12 sec. to travel from 13° back to 3° ANU. Or is that a too simple conclusion?

The rate for the BEA mentioned 1 minute to go from 3 to 13 ANU was 10°/60 = 0.16°/s.

Limit load (both compression as tension) is 32500 daN (73062.9 lbf).
I assume this limit load is mentioned as being the limit for the Hydr. motors to drive the THS.

Aerodynamic authority / sensing the flux
 

Hi there,
Just wondering about the opportunity to provide to the pilots additional flight parameters such as the AoA and beyond: wouldn't it be possible to measure the efforts generated by all the control surface actuators (in response to the flight control loop orders), to estimate directly/specifically their aerodynamic authorities and display them ? (roughtly, the harder to actuate the control surface, the more aerodynamic authority it has ? or an estimation performed through more sophisticated aerodynamical models for each control surface and the airframe ?).

gonebutnotforgotten
Man-machine interface. Is the unreliable M related only to airspeed/pressure sensing, or is it also related to a TAT sensing anomaly?
mm43
How can BEA confirm or determine if the ice and pitot tube interaction was accompanied by an ice TAT probe interaction?

I will guess that a trend line from "X" minutes prior to the event could show where Temp anomalies are or aren't likely. The recorded cockpit briefing about temperature not developing as planned/forecasts may be of no moment ... or maybe a clue pointing to TAT readings sensing beginning to degrade as Airspeed sensing began to go wrong?

Full download of thread - available?
 

Given the intense interest from the piloting community in this baffling event, and my previous decision to refrain from posting in case this ancient showed how out of touch she was, is there any way to bulk download this series (1-4) of threads, so that one might search previous posts on a specific topic?

(This after skimming over a post which I can't now find, which seemed to suggest that the standby instruments (ICUS, I believe they/it are called) are not fundamental, steam-driven devices, but take their data input from some branch of the computed data stream.)

I can find the printable area, but 40 posts only. I'd like to be able search any discussion point. Anyone?

Was it 'one hell of an input'? 7000 fpm is achieved after 18 seconds of 0.2 g; 12 seconds of 0.3 g, or 9 seconds of 0.4 g.

BEA Interim Report #2:
This explanation is either in error, or we are misinterpreting it (The BEA Update adds a new meaning to 'invalid airspeed'). In the case of the UAS incident documented in the Air Caraibes Memo, stall warning occurred at 4.2 degrees, with ADR DISAGREE. In the case of AF447, the stall warning must have been at a similar value, because the low-speed value of 10 degrees is well beyond stall AoA.

@JenCluse:

I think you're talking about ISIS (shown here)

http://www.samtel-hal.com/cache/isis.pdf

It's a digital display, and yes air data will still come from the pitot tubes and static vents (as would be the case with "steam gauge" hardware too), but the data is taken from standby units as I understand it - it is intended to be independent of the main systems. At present there's no evidence that any data on either the main PFDs or the ISIS display was incorrect - other than airspeed data, which was anomalous for a duration of approximately 45 seconds.

Hi JenCluse,
I'm also feeling your pain as I'm trying to catch-up with this thread after a while.
I understand that you are refering to ISIS and what you think is, in some way, both right and wrong. Stand-by instruments are supplied by analogic pnematic sources: probe pitot 3 and static probe 3. However, both probes are used for direct sensing and/or connected to numerical Air Data Module (ADM). In this case, those ADMs are feeding ADR3 which may replace either ADR1 (Captain probes) and ADR2 (FO probes) while the stand-by gauges (ISIS) are displaying the direct measures from the same probes.

You can also refer to the BEA first report which have a detailed diagram with usefull explanation about Airdata, page 22:
http://takata1940.free.fr/Airdata.jpg

LW50:
I missed the implications of the briefing on temps not developing as expected before now but this fits well with my (just a)theory that almost every item included in the BEA note will in hindsight appear to be relevant to the final determination of the event chain.

As I have said before they (BEA) have a much better picture of what happened than outsiders so the note would have been written with the likely ultimatly signinificant factors in mind.

Also possibly significant is that the final item in the note is the mention of dual control inputs (no hint if matching) and the transfer of control.

My take on this is that beyond this point there was still (at the time the note was created) discussion/uncertainty within BEA as to whether the situation was (even theoretically) recoverable and the level of understanding of the situation in the cockpit.

finding stuff in past threads
 

JenCluse

Although it isn't a download, you can achieve a search of only the 4 threads by using the following search string in Googlethis 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. Adding the site:URL end part is the magic that restricts Google to only searching in the tech log on here

Copied to post #1 for general dissemination

THS Rates & Trim terminology
 

A33Zab,
That explanation is invaluable, thanks. So it's only too easy to get confused between the electric (control) motors and the hydraulic (actuation) motors...

From the auto-trim point of view, the movement from 3NU to 13NU (after FL375) was very nearly continuous? I guess it only uses the one speed of 0.2deg/sec, as quoted by PJ2. Although you state a 2-motor speed of 0.4deg/sec, perhaps limiting the speed to 0.2 would avoid any slow-down if either the blue or yellow hydraulic motor failed?

On the face of it, those who have advocated use of manual trim-wheel in stall recovery seem to be vindicated, as its 1deg/sec might be needed. The argument probably only applies in Pitch-Alternate Law. We still have no idea what the effect of full down-elevator is when the THS is at 13NU. (That is: what would be the equivalent THS setting with neutral elevators?) Sadly, the answer does not seem to be pertinent to this accident.

Quote:
Since the hinges are on the trailing edge and therefore the aerodynamic load on the drive spindle is in the AND (stab. Nose Up) direction...

Please forgive me for offering readers a warning on terminology here, from my experience of various jet transports with THS under one name or another. "Nose-up" is a term normally used to indicate the trim-effect on the aircraft, not the physical position of the THS. Because the THS is hinged at its aft spar, it's easy to think of "nose-up" as meaning that the leading-edge of the THS is up. Not so.

For maximum nose-up trim, a THS is at its fullest NEGATIVE incidence, with its leading-edge fully down. The A330's mechanical limit seems to be -14 (see PJ2/mm43 discussion). We call that "14 degrees nose-up" (14NU). For a typical take-off, the THS setting calculated on the trim-sheet by load-control might be 3NU. This requires the incidence of the THS to be -3 deg. However, load control and most pilots refer to it as "+3". Confusing, perhaps, but that's the way it is.

In fact the A320 system does something very similar when it compares the gross weight calculated from air data and inertial data to the gross weight calculated in the FMS from loadsheet and fuel used. In case of a discrepancy, a CHECK GW message is generated. (See Perpignan Final report). I don't know if that function is available in the A330. Using that same logic in reverse the airspeed could be calculated from the FMS weight. The BUSS presumably does something similar.

Murphy, about misunderstanding in the cockpit, it might get curiouser and curiouser ...

IF
you lose airspeed, or it becomes unreliable
AND
You are an A330 Pilot who is already reasonably familiar with previous incidents in your model aircraft ... since the manufacturer and your company put out bulletins and findings of previous UAS incidents
AND
You are in a UAS incident yourself

You do X, Y, and Z in response. (Comments in the cockpit on loss or lack of indications, which I presume it means airspeed, is what I am working with here ...)

At what point can you determine that the airspeed has stopped acting up and become reliable again?

The forensic analysis points toward about 45 seconds worth of bad airspeed, and then a return to reliable state ... how does the crew know that it has returned to reliable? Did they ever have a cue (problems with stall AoA's on pitot tubes considered) that AS was telling them good information again?

What is dwell time (human observation and perception not being a step function) between "it's bad" and "it looks good again" in a

Benign cockpit environment?
High task load cockpit environment?

Do the training pamphlets or the sim sessions devoted to UAS training address what symptoms tell you that your airspeed tapes are once again reilable?

You aren't using the old style circle gages, where the needle might stop agitating and then return to a more normal looking state. You are looking at the vertical strip. What discrete cues do you have? From the air data diagram that takata so kindly posted, it seems that the ISIS display might be the first cue, depending upon which pitot tube got itself back in order first.

I apologize for asking what might be an idiotic question, but I've not flown an A330, nor been exposed to A330 UAS malfunction/emergency training.

Hazelnuts39:
Do you mean 1.2, 1.3 and 1.4g? (I am guessing that you meant a delta from a "stable" 1 g reference.)

Aerodynamic authority / sensing the flux
 

Hi,

Hyperveloce @ Post #105

Sounds a very good idea. And with a good approach: To provide extra and (redundant) important info

Considering the computational capabilities in these "advanced planes" it seems it would be quite easy to do this "pattern recognition" in real time.

Question:

What kind of sensors you imagine in order to provide the data to the System? Some are yet available?

Hyperveloce, 105

Have been thinking about something similar, but in relation to wing loading
as an extra parameter input for the calculation of lift. For the control
surface case, this could be instrumented via strain gauge type transducers,
one would think, near the control surface root.

In the wing loading case, deriving lift force is complicated by acceleration
forces, but since other areas of the system (adirs) already measure this, the
acceleration could be subtracted out to derive actual lift on the wing. How
usefull any of this might be, I don't know, but there are times when the more
cross check type data that there is available, makes it easier for dumb logic
to determine what is really happening....

Lonewolf50;

Yes, your interpretation is correct. Added to the acceleration due to gravity, the 'sensed' acceleration values are 1.2, 1.3 and 1.4 g. The values of rate of change of velocity (dV/dt) are 0.2, 0.3 and 0.4 g. Sorry for being somewhat pedantic, couldn't help it.

Return Of Reliable Airspeed
 

LW50: When all of your speed indications are again the same and are consistent with the pitch and power that you have been flying to prevent upset.