rudderrat and takata, when rudderrat said or quoted "The elevator orders are progressively transferred to the THS through a low-speed integrator to decrease the drag." was this necessarily correct? Is that from documentation or a presumption?

If I think about the apparent intent of the THS it aims to keep the elevator's mean position at neutral. So it's really integrating the elevator's position not the stick input commands. It will continue to drive the THS downwards as long as the PF does not push the stick hard enough for the elevator to go nose down, at which time THS would move. One comment I received suggests it would move nose down faster than it had moved to full nose up.

So I see your position from flying. Nevermind my question.

Pilot 'sees Nose Down, and right drop. First thing he thinks is, not does. "I might need to stop that." Stop only, not reverse. That is next, maybe. He is too much the big picture, not enough, gentle, and patient.

He is trying for UP UP UP, if he sees this bird, and sees the bird UP UP UP, he thinks, 'more is wrong than at first I thought'? He is not the one to be flying, a new picture makes him more confused and more stubborn, some one else please to fly, maybe the one who asks, can we go down, now?

When "everything" wrong, the "right" thing can only make this worse, new pilot please. Time later for apologies and courtesy. And perhaps to be fired? get new job.

Computers in cockpits....
 

As a thought experiment I started looking at the data available to the computers that inform the pilot (and autopilot system component) with information about the plane's position, velocity, acceleration, orientation, rate of orientation change, and the rate at which the orientation rate is changing in three dimensional space.

They have GPS.
They have at least one very good ring gyro system and perhaps several more prosaic inertial reference units.
They have pitot tubes.
They have air pressure sensors for altitude.
They have AoA sensors.

And I'm tired enough just now I am probably forgetting something. Modern computational techniques (Kalman filters) can take all these inputs, known data about their goodness for measuring the data about the qualities for various aspects of their data. GPS measures the position (and time) the plane had in three dimensional space at some point in time relatively recent depending on the time scale involved, closer to milliseconds than seconds. It says nothing about velocity without considering the differences of at least two readings and ideally a string of readings for averaging. Accelerometers are good with the rate of change for the plane's three dimensional velocity. And so forth.

Presume some information is lost. That Kalman filter can adjust its parameters to reject or at least partially disregard data that is not present. This degrades the solution; but, you still have a pretty darned good idea of what the plane is doing.

Take the data and work back to extract more data, specifically wind speeds acting on the plane in three dimensions. (An AoA vane on the top of the plane might be handy for deriving a cross-wind data independent of calculated guesswork, by the way.)

Now we step off the cliff. What is the largest wind speed change a plane in normal (non-hurricane) conditions likely to encounter translated to a change in airspeed as measured and corrected? Is it 60kts, 75kts, what? This number gives you a wind velocity change range in which to look for a solution. The plane is without airspeed indication it is willing to accept. But it still knows its orientation and inertial velocity with cross checks from GPS. If flying pitch and power is sufficient to keep the plane flying I suspect AoA and power is even better. The plane knows the AoA. It knows the power. It knows attitude. It knows position. It can work backwards from the pitch/power figures to figure out what airspeed, actually what air velocity set, could have the plane moving the way it is with the pitch and power settings it also knows. It calculates a substitute airspeed of quite remarkable accuracy. (I'd then judiciously feed this back into the Kalman filter for a quality check on pitot readings.)

Presuming no CPU cycle limitations there is no reason for the plane's computers to decouple from most of the automation control of the plane. In fact I am willing to assert that the plane could actually have continued on to Paris and even landed on the mark under computer control with aggressive enough software.

At the very least that suggests even a modest '386 class machine should have been able to guess airspeed well enough to be able to issue a quite adequate stall warning at all times.

I am somewhat bemused by the APPARENT fact that the flight displays only relied on a very small subset of the sensors available. I'm sitting here idly wondering why these computers did not make use of the full suite of adequately accurate instrumentation available on the plane.

(And I suspect I ignited a stink bomb with this observation here among a batch of pilots, mostly good ones at that.)

It drives the same speed in both directions, but from it's zero point it's got further to go nose up than it does down.
One of the tests we do on the THS involves testing it's auto function as well as that it'll stop auto-functioning when the wheel up front is held. We position a man in the tail to verify a valve moves to close and the THS actuator stops.

Flying A0A and Power
 

JE EE: Except AoA isn't very useful at cruise airspeeds. At cruise speeds, AoA varies much less per knot of airspeed than at approach speeds. Trying to fly AoA at cruise speeds is like trying to balance on top of a bowling ball. Not easy.

On the other hand, when trying to prevent, or recover from a stall, AoA is exactly what you need.

Which Way To Trim?
 

Tyro: Without any feedback in the stick, it makes it hard doesn't it? The only thing you can do is to try it one way or the other and see what happens, but I sure don't want the system changing what I had set. If I'm trimmed in pitch and have the power set right in cruise, I really don't want to change anything. All I want to do is make very gentle changes to hold altitude but I don't want to change the trim.

Why not leave the stick alone and fly with trim?

Fly Only With Trim?
 

Because in turbulence you want to preserve that trim setting which will cause the aricraft's positive longitudinal stability to get you back to a correct AoA. Several pilots here have said that simply letting go is the classic way to get out of a difficult situation, and that is true, but once the trim is changed, letting go is no longer an option. In fact, with the neutral longitudinal stability brought about by the autotrim (when hand flying) if you let go, the airplane will hold the existing pitch at one Gee and if it is nose up, you will either mush along or stall when you run out of kinetic energy. Several posters here have commented that the Bus has wonderful positive longitudinal stability. We should take advantage of it.

Interesting as personal preferences as to what autotrim should do or not do may be, I fail to understand what relevance to AF447 these have. Between 02:11:40 and 02:12:10 the PF pulled the sidestick fully back. If at any time in the descent he had pushed the SS fully forward 30 seconds and the THS had not moved, then it would have been an issue in AF447.

HN39,

At time 02:11:40 was already mainly full NU.
The relevance is that the trim moved to that position under STALL WRN, it is true to state that the inputs were more UP than DN :

http://i45.servimg.com/u/f45/11/75/17/84/wiz_pi12.gif

... but is it unreasonable to think that the PF would not have manually trimmed or at least to that extent ... ?
And if he had, then I would not show up here to reply to your post.

As I said earlier, leave to the pilot that responsability to trim if that's really what he was looking for.

mm43, thanks for that trace. It painted a very sad picture for me. At around 2 and 13, you had two pilots making control inputs, and given the way the SS inputs are summed, PNF's inputs (though this was a very late in the game state, maybe not recoverable by that point, somewhere around 10000 feet) of nose down were nulled out by PF.

Horror of horrors, to me, is that even after the control change to LHS the RHS was still making SS inputs.

:(

takata has told the THS is inop for trimming up with accelerations above 1.25 g. It will not Auto trim when 'manouerving with this load or more. Elevators only.

Looking at the track of g just after pilot 'Ihave controls.' The Ths has not moving during all g above 1.25, so we should be thankful it has courteously not cause even a faster crash. This THS did as was told. Too bad the pilot isn't counting these chickens.

The Ths became the factor mafter excess g load was lost in the climb. It is inhibited above 1.25 g for trimming. So up til the time of Ths starting to trim up (plenty of time to Sa and calm down and do as pj2 says.)

At this much g in the first climb, it wants a new display to tell the pilot "nose down, please?"

Human factors? Fancy words for manhandling the Poodle?

Climb and "Go down"
 

Quote:

---

Originally posted by spagolia:

---

Consider this bit of conversation on page 90 of the report:

Watch your speed
Watch your speed
Okay, okay okay I’m
going back down
Stabilise
Yeah
Go back down

What does "Go back down" refer to? I think it refers to KIAS not altitude. If so, aft stick fits in with the conversation.

Again on page 95:

The speed?

One second later:

You’re climbing
SV : “Stall, stall”
You’re going down
down down
Am I going down now?
Go down
No you climb there
I'm climbing okay so
we're going down

I think "climb" refers to altitude and "going down" again refers to KIAS. Otherwise, the conversation doesn't make sense.

On page 96:

Amazingly this is the first mention of the word altitude.

What do we have in
alti?

And both the Captain and PNF react with total surprise.

(...) it’s impossible
On alti what do we
have?
What do you mean on
altitude?

On page 98:

Nine thousand feet
Climb climb climb climb
No no no don’t climb

Why would the Captain ask not to climb after PF calls out nine one thousand?

Because it is at this point he sees PF climbing (wrong) as PNF is trying to descend. He sees they are both inputting, and hears it on the SV prompt.

It is this PF overcontrol he demands be stopped.

Climb and "Go down"
 

@ CogSim

Climb and Go down are from the French Monte et Descend. There is no ambiguity in French. "Descend" can't be any else. IMHO.
I pasted the French (pages 98 ans 99) beside the English page 95:

http://i44.servimg.com/u/f44/14/14/01/64/95en_f10.jpg

If you want to try some "electronic" translation from French, you can have a "à" with Alt+133 and "ç" with Alt+135 :)

But its the PNF who has asked for the climb. I think the Captain is overruling the PNF here.

Looking at the BEA plots or better at mm43’s re-arranged plots (#1770) pitch response to the few consistent nose-down sidestick inputs appears very weak. Except the last one, pitch curve minima seem more related to high roll angle than stick down input. During these nose-down sick periods the elevator angle never increases above -15 deg. Why would the THS start moving up?
A possible reason could be that in the stall domain decreasing AoA increases a little Nz in an almost unchanged trajectory. Remembering that the pitch control is still C* it is easy to see that an Nz increase will decrement the actuating signal in the control loop. Moreover, the default gains used when CAS is invalid likely play against a fast response.

I think I am correct from nine thousand. Both piloits are at cross purposes. I am so sad to say, that Though I may be wrong, or right, it does not matter/ none of the three knew either, and they were There./

Thanks for the clarification Shadoko. Why not just use descend in the translation then?

@ CogSim
"Why not just use descend in the translation then?"

For an old man like me, the PF speaks a very poor French. I think to make this understandable in English, they use what they think the simplest words. I am not enough fluent in English to tell if they achieve that.

Sorry, I'm a little bit lazzy (or too busy), as I didn't quoted the reference. It is from my notes about AMM 27-90-00, but I suppose it was from an A320 document as the g-load limits for an A330 THS is rather 1.3 / 0.5 g (instead of 1.25 / 0.5 g quoted). But both THS are basically the same thing, as far as the operating system is concerned.

Lyman, (#1804)
I suspect that BEA’s examination of ‘Human Factors’ will consider the many aspects within the scientific discipline. This should avoid the often bigoted dismissal of human factors, human error, etc, as a coverall for many complicated and interacting issues in such accidents.
Such an investigation might only be comprehendible with some speculation; this requires activity beyond the scope of ICAO guidance for accident investigation (factual reporting), but this work could provide a valuable resource for learning about the crew in AF447 or similar humans/situations.

The major threats in accident scenarios are in the extremities of the ‘SHEL’ human factors model. The risks are in the interface with the central ‘L’ – the human interaction with the situational environment.
The contributing causes to an accident can be found in all aspects of the model – threats, risks, situation, and management – human activity; the difficulty is deciding which had the greater contribution, or which might be more effective for improving safety.
A human factors view might only be another view, but in such a complicated accident another view might be valuable.
With hindsight, perhaps the crew of AF 447 would have benefited from another view.

One thing that stands out is at circa FL350 the Captain should have taken his seat. Why would he not do that?
Why would a Captain decide to be only a back seat observer and commentator?
With my limited experience I have found that all the pro pilots (civy and military) are of the assertive/like to have control personality more than passive observer personality. (sorry I'm not a psychologist so I lack the fancy words).
Equally the PNF should have given his left seat back to his boss and insist he take it. Especially after the insane teenage nagging conversations he had with PF.
What am I missing here - is there an AF policy in an emergency for CAPT to stand back and oversee/bark orders?
I don't think trading seats would take that long given the adreniline.

Hi,

I think that at that time the rule in AF should be absent .. or if it existed .. it was not considered by some pilots
According to the Colin report .. it seems that a certain indiscipline prevailed (and perhaps still exists) in AF
Colin report (2006) available here (PDF french)
rapport_colin__juin_2006_.pdf

Extract

Raw google translation

Trial and Error
 

It seems to me that what everybody is forgetting, is that the co-pilots have never had the opportunity to hand fly the aircraft at altitude nor in different modes/laws. And therefore all of the inputs were merely trial and error. At altitude and during turbulence and under stress.
How this could have been overlooked is literally unbelievable to me.

Hi wallybird7,

I agree. According to: http://www.pprune.org/tech-log/376433-af447-132.html post 2632, the author points out the handling of the aircraft with UAS was different to the simulator.
I think the sims. will need better data to imitate the handling more truthfully.

Trim
 

No different as any conventional aircraft.
You did trim already in the sim when the aircraft was in direct law, didn't you ?
How was is any different ... ?

Trim
 

O come on, you are kidding?

In a conventional aircraft you set desired attitude with stick input and relief the resulting stick pressure (either natural or artificial one) with trim.

would not work in an aircraft without feedback?

OK Franz, how is it different from direct law on the bus ?

1. Have you ever flown the bus ?
2. Have you ever flown the bus in direct law ?

No, i´ve flown conventional aircraft with natural and artificial feedback,therefore i know that forcefeedback to the stick is an elementary necessity for trimming.

And i know also, that there is no feedback to the SS in airbus.

That is all i need to know, that trimming must be different.

I dont say, that it is not possible or more difficult, but it is not like trimming a conventional aircraft with feedback.

I would be very interested though in a detailled description, how it is done when autotrim is not available. I.e. concerning the pitch, do you steer pitch only with the trim like turning the trim wheel and look what it gives? Then readjust and finetune?

Same procedure is used with the FBW in direct law - As long as stick deflection is needed in order to maintain the choosen attitude, it means the aircraft is not properly trimmed.

To trim the Airbus feels as natural as trimming any other type.

Is it another urban legend?

http://takata1940.free.fr/sidestick0.jpg

Thank you for mentioning that.

Artificial feel - with a spring rod.

Aha.....

So it feels the same in a stall as with 340 kts.

Artificial feel from springs is not the same as feedback. ...but yes, it should be sufficient to tell the pilot what forces he's having to maintain, and therefor, how to trim.

Force versus movement for trim
 

Interesting about trim feel, and it could have played a role in Viper stick implementation.

The thing uses stick force per gee or roll rate, so it was real easy to trim off the control pressure to get a gee (gear up) or AoA (gear down). Max force was about 24 pounds in pitch and 16 or 17 pounds in roll. Neat thing about roll was the jet would command up to 180 deg per sec calculated aileron deflection at ZERO stick input to maintain zero deg/sec actual rate. This saved a jet and pl' Gums when one leading edge flap folded up on me after raising the gear one day ( see the pic in my profile bio).

So maybe force per aircraft movement could be emphasized for the 'bus.

Trim
 

@takata and @ CONfiture

Please note again, that i didn´t comment at all on the subject, that the trimming feels like trimming an conventional aircraft or that it is worse or better or not possible.

I said (at least that was and is my intention), that it is not like concerning the process of doing it.

The SS has an artificial feel, i did not deny that. It tells you stick deflected NU, than trim NU to equalize, or vice versa. It´s not comparable to a tactile feedback (be it natural or artificial), where the amount of mistrim and therefore the amount of necessary correction can be felt in the hand on the stick due to stick deflection from neutral and force required to keep it deflected. It is therefore airload related feedback.

That is IMHO one of the main reasons, why there is autotrim present and necessary in normal and alternate law, as in those laws SS deflection in pitch results in a change of loadfactor, which is kept stable when SS is back to neutral (as long as protections do not intervene). If i understand the system, the elevator is positioned by the flight control computer upon ss input, feedback from the response of the aircraft is fed back to the flightcontrol computer (not the SS) and elevator position is again adjusted by the flight control computer. With some delay the THS trim will zero out the elevator deflection. During this process (except the initial SS input) the SS is in neutral position. How should a pilot zero the elevator demand with manual trim without tactile feedback? Look on a gauge with elevator position? On behalf of the aircraft reaction? Therefore the need of autotrim.

That also poses problems to disable the trim in special flight conditions in normal or alternate law, where to start and where to end the input of autotrim? It would solve one problem and cause some others.

In direct Law there is a direct relationship between SS deflection and elevator deflection (some other factors like CG and configuration and ??? play a roll though), but neither tactile feedback to SS nor to the flightcomputers. Only the feedback from the behaviour of the aircraft is present. But this feedback is dependent on how fast the aircraft reacts to the inputs (as in this stall very slow to react to ND inputs), therefore trimming process (trim, check, trim again, check, trim some more, uups that was too much..) would be slower and a process needing more attention.

Unfortunately (in my oppinion) AF447 didn´t go into direct law, otherwise the aircraft behavior and the trim behavior could have changed the outcome of this accident.

Hope that clarifies my statement somewhat, no intention to post urban legends or to dsicredit airbus or to join any anti airbus comunities. I´m a german tax payer and lot of german tax money is working with EADS.

I´m just trying to understand the system in its detail like i was used in the aircraft i´ve flown, but in looking on many posts with different understandings on two threads and reading nearly every available documentation from AB over a period of 2 years still keeps me mainly in the dark concerning lots of subjects.

And i´ve the impression that the crew of AF447 found themselves in a worse situation, because all the time they´ve got where a few minutes.

Is it possible then that the autopilot was not sufficiently rapid to keep control? (447) What happens when 330 Auto can't be so quick as your Viper?

What happens if roll rate for gums is too slow by half when one slat fouls?

What happens to 447 when auto is too lazy? airplane is an airplane?

F4 For two years, no progress has been made on either side. You and smilin have nailed the problem each time, and each time it is ignored by "The a/c did what was directed."

It also did what was directed, apparently, by NOT trimming whilst the a/c was in an aspect commanding certain g. So if the Autotrim is disabled when the airframe is under maneuvering load, whty does it return "automatucally" (at the top of the gd climb, of all places), to seal the fate of the pilot who probably couldn';t have recovered anyway, even knowing the Auto trim was active?

Don't be sly, messrs. AB. Whether the pilot knew or did not know the Autotrim was active may well have been irrelevant. "Red Herring"? A "helpful" Gremlin in the tail cone, with a prod to mystify the crew? Changing the handling of this airframe in ways not EVER practiced by the humans?

My point about force versus deflection is that the stick felt more like what we were used to. We trimmed off pressure not stick deflection. the thing only moved about 1/8 th inch.

Unless the 'bus springs are weird, it should take more "force" to move it further, so manually trimming off "pressure" should not be a big deal.

In my case, the jet commanded a left roll to counter the loss of right wing lifties and roll due to yaw. That sucker had lottsa drag. So I had to add more control surface deflection, and post-flight analysis indicated I had about a pound or two force to play with. In short, I basically held full left stick for about 10 or 15 minutes.

As other pilots point out, the ideal stick would require increased pressure/movement according to dynamic pressure. Just like old days when you could feel the forces on the control surfaces due to those air molecules. Go fast and stiff stick, slow down and stick gets mushy, as does the plane, duh.....

If the force feedback system fails, then you have the basic spring/torsion tube/whatever built into the thing. No big deal.

The problem with the 'bus is that a small continuous input from neutral eventually causes the HS to move ( ours didn't do this - it always wanted to get back to the manually set trim gee or trimmed AoA). The autotrim is neat when maintaining level flight or a climb/descent, as you can gradually relax pressure.movement to get the desired attitude or AoA.

However, in this case it helped the plane to achieve an ever-increasing AoA due to speed decay and the "one gee" default trimmed gee condition. Had the pilot used only roll and a neutral back stick, the THS would not have continued to command nose up.

Once zooming thru all the AoA protections with back stick, the plane entered uncharted territory and only a few folks would have understood the exact aerodynamic condition and need for manual down trim and forward pressure. Despite some folks' thots here, I don't think pure elevator can overcome the pitch moment that the HS can exert when fully deflected one way or the other when flying slow. Mach effects could have been a player initially, but once slow enough, they probably were not a significant factor.

"I basically held full left stick for about fifteen minutes" That sounds eerily familiar to 447. Drag? Right wing drop (Chronic and/or acute?)

Don't forget though, that PF could not "forget about aft stick", he had a bobbing nose to lift and drop to maintain "level" and avoid a SPIN. He heard the initial Warning, and if he was a pilot, he knew instinctively if he hears the horn, he gaddam better keep the wings level.

He "started" his "climb" WITHOUT AUTOTRIM, for once he exceeded 1.25 g, the slab inhibits (g prot). After his load (g) diminished, the Autotrim started up, at the top of his "climb", did he know? Could he have compensated if he did know?

The entry to manual reversion is not addressed at all well. Someone take a breath and discuss what may have happened if roll rate demand was beyond AutoPilot, and did the "Upset" (at handover) corrupt the Speedata?

Honest question. Was Pf "playing the g prot" his inputs were not held initially, he appears to have been "bumping" the elevators. How does he lockout Auto Trim? His full back and held inputs come later, AFTER the THS has planted on its Stops? Is mayonnaise a technique to lockout the slab by pilot device, and not in the FCOM?