Machinbird

It appears that there are two types (at least) of control inputs being made on the stick by Airbus pilots.
One group applies pressure on the stick to create the desired aircraft response.
The other group makes short pulsing movements of the stick to make quick successive adjustments to the aircraft's flight path. (Sometimes called mayonnaise stirring.)

From my observations of the control motions following the autopilot drop out, Bonin was probably in this latter category.

Does anyone have an idea of how to get the control motions data immediately after AF447's takeoff when Bonin was also flying manually? This would help characterize his style of piloting.

Since I have never flown Airbus FBW, I'd appreciate comments from those that have regarding control techniques they prefer when flying the Airbus and if and when they switch techniques.

The control technique used seems to be relatively unimportant in Normal Law but has critical implications in Laws that involve direct motions of control surfaces such as Alt2b.

G0ULI

DozyWannabe
I deliberately picked an example of a car which is available to purchase today rather than a self driving car, which I agree would have been a more accurate comparison.

The point being that automation covers many deficiencies in technique to the point where a less experienced pilot can be unaware of, or forgets to check trim settings and fails to use secondary instruments to infer missing information when the primary systems fail.

In the interests of fuel economy and cost saving, aircraft are being flown automatically at and beyond the ability of the best human pilots. When that automation fails, seeking to maintain extreme altitude for a given aircraft weight is not a wise course of action. It is however contrary to a pilot's instincts to deliberately fly to a lower altitude at night, in bad weather, over the middle of an ocean.

Machinbird
I suspect that pulsing, twitching the controls, or mayonnaise stirring is symptomatic of the PlayStation generation of pilots. It certainly is a popular technique among computer games players to speed up reaction times and maintain finer control. The technique works well so long as you have a computer to interpret and modify the inputs, less so when everything is hooked up directly to the controls.

jcjeant

We can automate most .. improve existing systems .. invent others .. make extensive training pilots ... all this is possible .. this is often done ... everything evolves
But one thing is certain .. the man is always the same .. with its strengths and weaknesses .. and that no automation or system will not be able to change this
There will always be people who have a particular momment do the opposite of what is required and action will succeed even with all the barriers placed to prevent them of such actions

PJ2

Hi Dozy, thanks for your replies. Points made and understood. It's complex, no?!

Machinbird, interesting thoughts. I wonder about the notion that the stick was there in one's hand and so one had to 'do something' with it. It is an extremely powerful extension of the hand as you know. It takes time, a bit of experimentation, discussion and particularly paying attention in class to learn what the stick actually does and as a result, how to use the stick well.

Stirring the stick was a well-known action. I recall many years ago, (early 90's), examining some data of an Airbus aircraft on approach in gusting conditions. The autopilot was on and the aileron parameters showed small, sometimes slightly larger deflections as the bank angle was held as commanded, (level, on an ILS approach, not turning). The autoflight system has roll information more accurately and quicker than pilots are able to perceive through the PFD and their human sensory equipment; the autoflight anticipates more quickly and makes smaller adjustments. ....(Even when disconnected, the Airbus remains in what Boeing drivers today would call CWS, control-wheel-steering; within certain limits, the airplane stays in its last-commanded pitch-and-bank attitudes. This is because lateral movement of the stick is a roll-rate request and longitudinal movement is a 'g' request - many here will know this from the extensive discussions on the autoflight system's design to maintain 1g flight, but what may not be appreciated is the implications for manual flight.)

When the autopilot was disconnected just prior to touchdown, one could see the difference immediately, (different, not bad, not good, just different) - the aileron deflections using stick control were notably greater in amplitude. I did not note any PIO by the way but it seems to me that that would have been an ideal circumstance in which PIO was "in-forming" the airplane-pilot combination.

The important understanding in use of the stick here is of course, neither bank nor pitch change unless commanded, ergo, in gusting conditions, leave the airplane alone and it will return to it's last-known-and-commanded attitude.

Very difficult though for a pilot to "leave the stick alone" when in hand, and watching the rocking-and-rolling in turbulent conditions; one must by virtue of being a pilot "do something" to make the machine do as one wants. The notion that it will if one just leaves it alone has not been "exorcised" either in training or in the industry; stirring the pot is endemic because, (the subtle thought or 'the psychology' goes), "when one has one's hand on the stick, one does things, for why is the hand there if not to move the stick?"

I know the notion seems simplistic; the vast majority of pilots are keenly purpose-driven and will quite legitimately state that unless one "controlled the airplane" it wouldn't do as one wanted in manual flight. I think that is largely true, but not exclusively - I tried "leaving the stick alone", (holding, not moving) and it is a challenge.

One could leave the stick alone in a gusting approach to wait to see what the autoflight (not the autopilot) system was going to do when a wing dropped momentarily on short final..., or one can do what comes naturally to any pilot and use the available control (column or stick) to pick the wing up and settle the airplane.

FWIW, I think the stick arrangement is more condusive to PIO than the wheel/column arrangement which is why it is important to learn how to fly the stick. When one makes inputs, one must make small movements, (move the hand nearer to the base of the stick, use only thumb-and-forefinger and move from the wrist...those kinds of things).

In doing so, one must learn when to leave it alone, even while it is in-hand. It is old, old hat for Airbus pilots now, but one can rotate the airplane on takeoff to 15deg and just let go of the stick until the next requirment for attitude change arrives. The airplane maintains the attitudes, despite gusts.

In practise one doesn't do this because one is "in command" of the airplane; the subtlety is that one must move things to "be in control", but knowing when to "do nothing", (different than the AF447 "do nothing - that entreaty would apply to all airplanes, not just the Airbus), is as important an understanding with such a system.

Of course in Alternate Law, it is just an airplane, and (essentially, though not wholly) WYSIWYG, and the discussions on AltB and gain have been had.

In the vast debates regarding stick-or-column one wonders how a stick-as-column, (like a fighter) would fare in the "visibility-of-the-other-pilot's-input" discussion. I'm sure Airbus considered it. To me it is a non-sequitur because the PFD certainly says sufficient to know what needs doing to correct whatever the other pilot may be doing incorrectly, and there is always the take-over button which one can either take over momentarily using the Priority button or take over permanently by holding the button in for, (IIRC), 15 seconds.

I hope this little input is helpful. I'm sure you know most of this but there are some subtleties from an Airbus guy's p.o.v.

jcjeant

We have also had seen how this can be used .. in the AF447 case !

_Phoenix_

Only the roll was in direct law. Pitch was never direct.
"When the airplane's nose was pointed up, it stayed pointed up - to maintain the same g-load and pitch rate.."
Bonin's "heavy hand" fully controlled the roll, he kept the wing at horizontal during 38000ft stalled descent, this might say something about his piloting skills, apart of imaginary PIO
Bonin held the sidestick back in that initial pull up, just long enough to pitch the airplane to 12°, we still don't know why... however it happened relatively fast and similar to AF471, see post #524.

Consider this analogy, if you want: the driver sees the traffic light turning from green to yellow, initially he brakes (pulls up), but it is not good (stall alarm goes off). The driver decides to go through the intersection, he bottom the acceleration pedal but for some reason the car's computer continue to apply brake and service brake all together (THS max NU and elevator half way NU), the engine's torque simply cannot overcome the brake applied to disks, the driver is confused "I lost all control of the car I don’t understand anything, I've tried everything"... he brakes again, the car stops in the middle of intersection, independent of any other action of the driver.

jcjeant

Hi,

Anyways .. those test flights are useless
1- Not performed in the same environment of the one of the AF447 encoutered
2- The pilots knows in advance what will happend .. what alarm will sounds .. etc ...
We know already by BEA report that the aircraft performed "as per design"

Only interesting if those test flights were performed by the AF447 pilots (same as a reconstitution on a crime scene)
Unfortunately the pilots are no more there ...

DozyWannabe

Nope. The "pulsing" method of control is the one recommended by Airbus, and it has nothing to do with video games, it's simply that it provides a method for observing the effect of the input and thus moderating the next input (or indeed figuring out whether further input is necessary or not).

I'm pretty sure that the term "mayonnaise stirring" as applied to Bonin's input patterns related not to the "pulses", but to the abnormally large degrees of deflection and the unusual number of reversals.

The nadir of this was his extreme and sustained pitch-up input between 02:11:40 and 02:12:15:


Right, but the point I was making was that traction control and Normal Law roll and pitch rate techniques are not automation.

If he hadn't pulled up so aggressively, the trim setting would have been a moot point.

I wouldn't say that about ability, though it is true that even the most basic gyro-driven wing leveller will be able to react to and damp out turbulence-driven bumps and rolls better than human pilots just because of the inherent lag in human reaction time.

The aircraft was not flying at an extreme altitude at the start of the sequence. Bonin discussed going higher with the Captain prior to the latter taking his rest break, and the latter said it was inadvisable for safety reasons.

He didn't need to go to a lower (or higher) altitude, just maintain the altitude he had.

I've uploaded a grab of Fig. 64, as I was describing before:


Again, note in particular the brief and significant drop in the right crosswind at 02:10:07, which would go some way to explain the initial overcontrol to the left, and also note the pink plot in the "Roll Attitude" graph, indicating that the turbulence would not have rolled the aircraft over.

@PJ2 - Cheers. Depends what you mean by "complex"! Certainly the final paragraph of the VF article would indicate that the author did not do their research when it comes to the combined Airbus/Boeing overhaul of stall training and Airbus's move to increase manual handling training as part of the A350 programme.

@_Phoenix_ - Again, the "intersection" analogy is muddled. The THS movement happened as a *consequence* of the pilot's input, not in opposition. He never applied enough nose-down input to have a significant effect. The aircraft was complying with the commands given the whole time, not acting against them!

_Phoenix_

If you wish, zoom again (200%) in segment 2:12:30 to 2:12:45. The average input value sent to computer was clear ND. But the elevator doesn't rotate more than half NU and THS doesn't bother from max NU.
Doesn't matter the law, if PF demand ND rotation A/C should start rotate that direction not opposite, especially under stall warning. By the way, maybe you noticed that stall "wakes up" with each ND input 2:12:35 and 2:12:40.

See the video below at 25:08, how much time was required in this case?
https://www.youtube.com/watch?v=WAiA6ep95Sc#t=1508

Machinbird

Dozy, where did you find that information? I haven't seen that in print before.

RetiredF4

Just a reminder, with a nose down side stick input a ND rotation is intended by the PF, but a reduction of a former g-demand is executed by the fbw system. The aircraft was already falling with less than 1g, not having been able to execute the former demand of 1g (if stick neutral) or positive g (if stick aft). That overall small demand change moved the elevators a bit from the full nose up position, but was not enough to move the THS.

@ Dozy
How would those small intervals between the SS inputs give any feedback how the aircraft is responding to the input? Only the effect of the sum of multiple inputs would show in a reaction of the airframe, but not the single input itself.

If that pulsing is recommended by airbus (which i doubt until proof is shown) there should be an explanation available to this steering method we all would sure be interested in.

rudderrudderrat

FCTM OP-020 Flight Controls
Normal Law.

"OPERATIONAL RECOMMENDATION:
From the moment the aircraft is stable and auto-trimmed, the PF needs to perform minor corrections on the sidestick, if the aircraft deviates from its intended flight path.
The PF should not force the sidestick, or overcontrol it. If the PF suspects an overcontrol, they should release the sidestick.
AT TAKEOFF AND LANDING
The above-mentioned pitch law is not the most appropriate for takeoff and flare, because the stable flight path is not what the PF naturally expects.
Therefore, the computers automatically adapt the control laws to the flight phases:
GROUND LAW: The control law is direct law
FLARE LAW: The control law is a pitch demand law.
OPERATIONAL RECOMMENDATION:
Takeoff and landing maneuvers are naturally achieved. For example, a flare requires the PF to apply permanent aft pressure on the sidestick, in order to achieve a progressive flare. Whereas, derotation consists of smoothly flying the nose gear down, by applying slight aft pressure on the sidestick."

Alternate Law.
"Alternate law characteristics (usually triggered in case of a dual failure):
In pitch: same as in normal law with FLARE in DIRECT
In roll: Roll DIRECT
Most protections are lost, except Load factor protection.
At the flight envelope limit, the aircraft is not protected, i.e.:
In high speed, natural aircraft static stability is restored with an overspeed warning
In low speed (at a speed threshold that is below VLS), the automatic pitch trim stops and natural longitudinal static stability is restored, with a stall warning at 1.03 VS1G.
In certain failure cases, such as the loss of VS1G computation or the loss of two ADRs, the longitudinal static stability cannot be restored at low speed. In the case of a loss of three ADRs, it cannot be restored at high speed.
In alternate law, VMO setting is reduced to 320 kt, and α FLOOR is inhibited."

In Normal Law, most pilots use the "pulsing" method i.e. they release the side stick between attitude changes.

In ALT Law, FCTM says roll is DIRECT but makes no recommendation on how to handle it.
Bonin seems to have found the difference in handling qualities to be significant.

PJ2

A "pulsing" characterization of stick movement makes sense when one does it...the notion is "small movement, neutralize-wait...small movement, neutralize-wait...", rather than ordering pitch and roll almost randomly or at least in a series of opposing orders.

When there is stick movement, there are roll-rate and 'g' orders being sent. No movement, no orders - the airplane remains at its last "set" attitude. When change of either is desired, move the stick, neutralize it, - wait.

In a sense the ideal motion with the stick is what we do with the control column & wheel. We don't see a lot of push-pull on the column, nor left-right on the wheel, we don't "stir the column", (nor would we tolerate it!); - the movements are "squeezed" on the column and so should they be on the stick.

I wouldn't have used the term "pulsing" as that could imply a jabbing motion and it's not - it's a "squeeze", just like moving the thrust levers/throttles.

Sidestick movement:
Example of roll angles & rates, autoflight engaged then disengaged at about 300ft, or where the yellow line is no longer flat.

Touchdown is where the black line is more or less flat. Crosswind was 25kts+ from the left.

CONF iture

That's how Airbus wants to justify to the world its technical choice, but AF447 again tells a different story.
Having a direct knowledge of the PF control inputs is a GOLDEN mine for a PM in his capacity to thoroughly analyze a situation, to be deprived of it is a waste of precious data.

jcjeant

Indeed .. when Robert ask Bonin to go down .. and bonin answer "I go down ..." but instead pull the stick .. we do not hear Robert say .. " if you go down why are you pulling on the stick ? "
And he don't ask because he see nothing of the stick

vilas

jcjeant
This is very interesting thread which keeps running but the question is did the pilots know that the aeroplane had stalled? If so how do you recover without looking at the PFD? conventional dual yoke has an advantage for the other pilot being able to follow on controls but that is not the cause of this accident. Lack of recent training for the failure leading to inappropriate control response and virtually zero scan by all including the captain on his return to cockpit is the cause. Even a blind folded pilot on hearing stall warning would push the stick forward here he keeps pulling back. It is more of shock and awe rather than any planned action. All things being equal this crew may have done the same thing even in B777. There is an incident in Airbus where pilot started both engines with fuel pumps off, ECAM warning was twice cancelled without noting the failure, take off and climb to FL 380 was made with pumps off. Dual engine flame out and successful restart and landing was done without noticing the pumps. So propensity to ignore indications direct or indirect is unlimited.

PJ2

CONF iture, jcjeant;

I have read and understand your arguments regarding the sidestick.

The sidestick solution is successful as millions of flight hours, thousands of crews quietly going about their work and the incident-accident rates all can attest. It is neither reasonable nor possible to point to one control solution over the other by citing the record in support of a personal opinion; the record is not there. Nor is it reasonable to cite one accident in support of a general theory. Even so, that door swings both ways.

What is reasonable is personal preferences, even using the same reasons; but a preference isn't an argument.

Regards.

Cool Guys

It has been clarified previously that statistically there is no evidence to prove whether the unconnected side sticks or connected yokes are better. Where the differences become apparent is under high workload situations where it is advantageous to know what the other pilot is doing. The sample base of these events is pretty small so we cannot make a judgement.

However there have been numerous pros here that have provided good reasoning why one is better than the other. Some have even provided a bit of scientific evidence to back up their beliefs. Granted, Airbus cannot take this information and change their cockpit layout based on a few peoples’ beliefs on an anonymous forum but on the other hand it can’t be discounted completely because there is no statistical evidence to prove otherwise.

Cool Guys

Regarding the above discussion about the 2 types of control inputs made on the stick by airbus pilots (1. Applying the appropriate pressure for the appropriate aircraft response 2. short pulsing movements). My interpretation of this is if a pilot has been using the “pulse” method in normal law and the system degrades to alt law he has to change his input method. This pilot may have been pulsing the side stick for thousands of hours and one dark stormy night he gets into alt law and along with handling all the issues that caused the law reversion he also has to change the way he controls the plane.

I really think the designers of this system could of been a bit kinder to the pilots.

roulishollandais

It i a design issue, but it is not a designer's issue,It is a regulators' issue. The regulators must do sure that training programs and airlines's operations comply with design . Designers are inventors, they must be free to design.