CONF iture

That's where Control Columns have the advantage to tell the PM what the PF is trying to achieve.

What happens on PFD is not necessarily the consequence of a control input.

wiggy

Machinbird

I was an interested "bystander/bysitter" ....but not for long

Can't say much...but

FWIW, me PM, PF is handflying. On final the aircraft starts abruptly oscillating in roll...Your's truely thinks "WTF" ? Wake vortex/Flight Control problem? Are we controlling the aircraft or not? ... I then see, out of the corner of my eye, the magnitude and phase of the control wheel inputs being applied....Seeing the control wheel fully over with the aircraft already rolling back through wings level and heading towards the control input is a heck of a stimulus/big clue, even I can pick that one up... Roll inputs terminated.. Aircraft stops oscillating and subsequently lands OK.

FDR trace examined by various interested parties. PIO most definitely diagnosed.

Now I'll admit to being an ex "basic" QFI which kind of also colours my POV but there's no doubt in my simple mind that being able to see your colleagues control inputs and see/feel the aircraft's response to the same might sometimes be of just a little use....., but having never flown an "A" I'm not really able to objectively enter the A vs. B debate...

Qantas_A380

Why does sidesticks keep getting brought up in the debate about AF-447?

Panic Pull is a syndrome that affects all types of flight control interfaces. I'm just a small time private pilot and it was drummed into us during training to trust the aircraft and don't fall back on your instincts.

I have an idea - what about a stall warning system that gets progressively louder & louder the longer pilots fail to heed it? It might just be enough to get a pilot to "snap out of it" when they've gone into instinctive mode and push the nose down when in a stall.

Also, in Colgan 3407 the stick shaking caused the pilot flying to instinctively pull up and stall. So in some situations a yoke may help the other pilot identify a stall there are other situations where it may actually cause a reflex panic pull. Both systems are completely safe and are equally as prone to "panic pull" type stall situations as we've seen on both types in the past.

CONF iture

Except that there is no panic pull in AF447, all the time the right seater has been verbalising his concerns, trying to understand the situation.
The time all on board have been fully pulling the sidesticks is at the GPWS warning ... and this is part of the Airbus procedure.

Machinbird

Wiggy, your description of that PIO incident is fairly typical. It usually takes a second person freezing the yoke to stop a PIO because the the flying pilot is too immersed in the problem to realize what is going on.
Afterwards, your PF was probably very confused about what had just happened, right?
How big were the roll oscillations?

About all a PNF on an A type aircraft can do is take control. PF will probably be so highly stressed that his/her ears may not work.

FWIW, you are only the third person I've encountered who has seen a PIO up close and personal. Thank you for taking the time to respond.

wiggy

Yep, just a bit...

That, in hindsight, was the interesting bit ...The trace showed a max on the final excursion of merely a tad over 10 degrees, but given the circumstances (night, somewhere on finals) and above all the abruptness of the control reversals it felt like a heck of a lot more....I would hate to experience a roll PIO that really got going...

Lonewolf_50

Clandestino: Wing Commander Spry's point is of course agreed. In other news, fish swim.

As to your bit about manuals, you can't have it both ways.
Either is it "too complicated to explain" or it isn't. Make up your mind.

Thanks you for the usual Clandestino style in playing the internet argument game.
As to your last point: it could happen to anyone.
Indeed.
In other news, fish swim.

roulishollandais

As already said in a AF447 thread, I'm interested by degenerating dutch roll since 1979, and was creating only in 1992 a method to stop it with greater efficiency than just put hand off the stick and feet on the floor. I recovered with bank never more than 30°, lost less than 1000 Ft, in less than 30 seconds (MD83 Sim in Helsinki).
Before that, the other crew -6000 hours on type- lost 11000 Ft, understood nothing, flying right and left on the back, with overspeed, alarms and tutti quanti. The instructor -in flight instructor too- was not able to comment, and rejected the idea to ask me how I had done, himself had many thousands hours flying Learjet....
I never found an editor to publish my method.

1. As Machinbird said it, in AF447 the roll oscillation started immediately, and we know it was after the law change, where the roll rate has been modified (increased with facto 4 if I remember well) and get different from pitch rate.

2. In that situation no need of panic or starttle factor to think " I will immediately get level again pulling the stick right or left to stop the roll" and attention is immediately captured forgetting to watch the pitch. In that bank correction the good pilot is the quickest to counteract the bank change... Imagine your body being suddenly at 10° from vertical ! You think only to get vertical again and don't fall (I liked Machinbird's snake comparison!)
Since that first moment, if never trained to that situation in the Sim and theory of systems, you are on the bad way...

The crash of the KC-135 in Kyrgistan in a dutch roll shows that roll PIO was not enough taught..… when taught - in airlines it is never taught.

Machinbird

I would like to point out to the casual observers here, that the PIO here that Wiggy described was less in amplitude than the AF447 initial roll excursions (if I correctly understand the meaning of the 10 degree roll readout of Wiggy's example.)

One way a problem can occur is when the flying pilot tries to zero the roll rate rather than just bring the wings back to level. When the roll rate is high enough, the eye is drawn to the motion and it is easy then with a large, inherently slow rolling aircraft to predict the roll rate and provide a synchronous opposite phase aileron input. When you start responding to rate signals though, you advance the timing of your control inputs by 90 degrees of phase angle and this has the effect of driving an oscillation. You can see this effect in the chart I posted here: http://www.pprune.org/tech-log/53975...ml#post8868131

There have been tests run on the threshold roll rate needed to trigger a roll rate cancelling response from a pilot. From memory, it is in the 10-11 degrees per second rate which AF447 achieved in its initial roll oscillations.

I would like to echo that comment. Until you have experienced a PIO/APC event, you cannot imagine the impact it can have on your ability to control the aircraft.

seagull967

Machinbird,

Excellent post. Do you happen to have a pointer to the research on role rate threshold to gain that pilot response? Anything you might recall would be helpful.

roulishollandais

Hi Machinbird,
In your figure the roll rate is maximum/minimum when the roll angle is zero (wings passing the level position).
The important is to train roll oscilations in simulator.as well as law of flight transitions .

Jimmy Hoffa Rocks

Interesting to note that the FAA places more emphasis on jet upset recovery than in the EASA and in Europe.

Airbus does little training on recovery from unusual attitudes, re PIO, etc, in their Type Rating as well.

This should be improved on in Europe. no ?

gums

Not sure if we all understand the "feel" of the roll/pitch commands in most FBW implementations, and what you see and get when stirring the stick.

The best I can find is the majority of FBW jets command roll rate with yokes or sticks or sidesticks. Not bank angle, but roll rate. Anybody else here with a different experience?

The Viper roll rate could be trimmed, as could the gee command for pitch. Airbus appears to be pure roll rate for lateral stick and the gee command is corrected for pitch with fore/aft stick( and you can't trim for roll rate or gee). The 'bus also stops you at certain bank angles if in the various laws above "direct".

So if you let go of the stick you are gonna get a zero roll rate command for the 'bus and trimmed rate command for the Viper. You may not maintain your bank angle, but the system is giving her all it can. With my leading edge flap failure configuration I could not trim out for roll. But could trim yaw. I had to hold 16 - 17 pounds of left stick until I landed.

So to help roll problems or roll rocking you relax pressure/degrees of stick displacement and then go from there. The computer will try to keep you at the trimmed roll rate - zero for the 'bus. If the bank angle keeps increasing or decreasing, then you have problems with the control surfaces or a truly screwed HAL. The exercise is even easier than with the old conventional controls whether direct from cables or hydraulics.

You only get into trouble trying to deal with unusual roll rates ( and maybe some yaw back and forth). We saw that with the 'bus outta JFK when the tail came off and the KC-135 in one of the 'stans.

I can understand the inertia effects for a big jet like the 'bus or 777 or .... Even if HAL is doing its best, roll may take a second or two or three to stop. I bet it also took a second or two to establish a high roll rate, huh?

enuf of flight control laws and implementations from this old fart...

Machinbird

As one old fart to another , roll direct is not a roll rate law. I know you know this, but it somehow got omitted in your story.

That is one of those step changes that can happen when control laws change and that the pilot flying had better be aware of.

Problem is, the law changes are not enunciated verbally by the aircraft system, and if the aircraft suddenly rolls sharply in response to a now excessive pilot roll input, the pilot may not see the annunciation on his PFD for a long time which can allow other significant problems to develop.

Instead the aircraft seems to prefer to play C chords and shout loud Stall-Stall warnings that are rapidly tuned out by a crew that needs a quieter environment to figure out WTF just happened.
Anyone else think there might be room for improvement in the annunciation of Control Law changes?

roulishollandais

Wonderful Viper's systems ! And, of course, pilots were trained to use these trims Airbus may Copy better and learn from our dear old farts

Clandestino

I don"t and have never intended to. If technology in 2010s can render force feedback sidesticks as useful and reliable as artificial feel systems of 1960ies or no-feel sidesticks of 1980ies - good for everybody. That they will provide better SA is marketing hype as much as "My concierge can fly it" or "Our aeroplanes feel natural to pilots" were.

I am not subject of this thread. Do you have any relevant question?

I made it pretty clear who originally posted it so I object your misattribution.

Ah, we are getting somewhere. So why would F-GZCP first follow the stick inputs, then abruptly stop following them?

Were interested parties interested enough to provide report?

There are couple of videos with stick positions around, if someone finds graph-reading too strenuous.

That's not the way things work in the real world. Whether message is understood largely depends on receiving side too. Manual explains it very adequately for someone who will later go on and try it in aeroplane. Whoever tries to malign Airbus FCS without ever experiencing it must indulge in proclaiming the manual incomprehensible because its content do not support the claim that FBW really is dangerous per se.

Sorry to disappoint you, you can get no patent on this one. DP Davies was here before.

And if you read about PIO in relevant publications, you can see that your interpretation of roll disturbances after AP threw the towel in as serious PIO are extreme exaggerations.

Because you say so or you have references?

Airbus does type ratings?!? Will I be asked again if I know something about airline ops?

I am sure you all don't. See examples:

Every aeroplane commands roll rate with lateral yoke/stick displacement. Difference on FBW Airbi is that it is constant with displacement and independent of speed/config/loading.

"Alternate", not "direct".

Gee command in Airbus is also corrected for roll up to 33 deg bank.

Could you please explain how can one manage to find unusual roll rates in the accidents of AA587 and Reach 806? Before airframe failures, that is.

G trim is useful as one can trim it to 1 for patrol and 0 to achieve instant unloading during ACM by letting go of stick. Roll trim is nice to have when your external stores get asymmetric. Lack of these features will surely prevent Airbus 330 from ever getting accepted as an air superiority fighter.

roulishollandais

Clandestino
No patent wanted for safety !
It seems Learjet did not consider Davies had the solution to divergent dutch roll when they taught rapid pedal sharing , the lethal method used in AA587 against wake turbulence oscillations.
And airlines did never teach Davies' method, AF nor others. The AF447 crew did not seem to know it.

Machinbird

Quote:
Originally Posted by Machinbird
I would like to echo that comment. Until you have experienced a PIO/APC event, you cannot imagine the impact it can have on your ability to control the aircraft.

Words of a gentleman who has obviously never experienced a PIO event.

vilas

Dutch roll on B707 has no similarity in Airbus. 707 was notorious for that and whatever little time I had on 707 I experienced it on a commercial flight, yaw damper failure kept causing vicious yaw and turn till I think the weight and altitude reduced to a certain level. I was trained for yaw damper failure in A310 simulator and it was nothing as compared to 707. Airbuses are not prone to this. So KC 135 comparison is futile.

Lonewolf_50

In your own words.
Suggest you learn what a training audience is. Your cavalier assertion, underlined, is at odds with good training methodology. Caveat: if your assertion behind that line is that one or two of the three in that AF crew were unworthy of certification and unable learn this oh so complicate thing, but became regular crew at AF, that is another matter. Is that your position?

Your point on the dubious percentage of retention of whatever training was indeed received by the flight deck crew in AF 447 is not entirely masked by your failure in argument. As you noted previously, a significant number of other crews had similar problems and sorted things out.
In training, you first learn it in the book and other ground based instruction, then these days you seem to try it out in a sim, and then later you may experience it in an aircraft. Or you may not be permitted to try it out in the aircraft. Reasons for that vary.

Quote:

So why did Airbus made the system that is so difficult to describe? To make it simple to operate!

Your logic failure is highlighted in bold. That cause and effect you assert is neither necessary nor sufficient. Making something simple to operate does not require it to be difficult to describe. Note: your assertion comes across that it is somehow necessary to make it too hard to understand. If that wasn't your intended meaning, then perhaps what you meant to say didn't come across.

Enough carping, thanks for the usual.