A320 over controlling/PIO fix.
 

I’m looking at trying to find reasons reasons for A320 pilots over controlling resulting in PIO.

There’s the obvious factor of not fully understanding the airbus FBW concept but I’m more looking at effects of seat and armrest positions causing over controlling the sidestick.

I think there’s an airbus article saying armrest position can negatively effect physical control of the sidestick but I’m wondering what the extremes could mean? For example would too high armrest position does this result in not enough control? Too low an armrest position too much?

Likewise with pedal positions. I’ve seen 6ft tall pilots have pedal positions at 2 or 3. Surely this could result in strange arm settings and thus increase chance of over controlling?

I’m interested in finding a correlation between over controlling and physical seat/armrest position so hopefully can help with over controlling in not just inexperienced but also experienced crew.

Would be interested to hear other viewpoints or advice on fixing this. Thanks

https://cimg2.ibsrv.net/gimg/pprune....29d16c19fc.jpg
Don't know why but this resurfaced back to consciousness...

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I’m looking at trying to find reasons reasons for A320 pilots over controlling resulting in PIO

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If this is happening in the simulator, then turn the motion off for a while. Sometimes the lag between input and expected motion clue can affect some pilots more than others.

If this is happening in real life - then let go of the stick between each “nudge of attitude change”.

Thanks for the reply. Very much looking on the line not the sim. Yes I think this method certainly helps let’s say down to a 100ft but below that and into the flare I’m not so sure ( just trying to think what I do).

What sometimes surprises me is on turnarounds is the vastly different pedal and arm rest positions for pilots of roughly the same proportions. I also see different ways pilots handle the aircraft and wondered wether there’s a link as the airbus magazine suggested.

Getting back to basics if you have a brand new pilot to the A320 how are they taught to find the right pedal and armrest positions?

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Yes I think this method certainly helps let’s say down to a 100ft but below that and into the flare I’m not so sure.

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This picture from DSC-27-20-10 Normal Law shows that Lateral Control control is still in Normal Law until touchdown (then blends into Ground Mode over 0.5 sec). Most PIO I've witnessed below 100 feet was in Roll because of continued roll input whilst applying back pressure during the flare. Roll control must still be "nudged" rather than held.

Whilst on the ground, I suggest you ask your student to show that that they can hold a bit of constant back pressure whilst they "nudge" a roll input left then right. If they can't - then get them to change their arm rest position until they can.

On SIM day 1 of any airbus fbw type rating in the history trainees are told how to “consider” the side stick to avoid PIO. The abundance nowadays of politically correct makes it difficult to use the same comparison though.

Another thing to teach the trainees that will help them is that, to make a pitch input, the sidestick has to be handled slightly to left hand side (for an FO sitting on the RHS). The ergonomy of the side stick dictates it to be slightly tilted to the left hand side to accomodate to the natural position of the right hand when it is resting. On ground, and with the engines running, ask them to make a pitch-only input on the side stick, and observe the cross on the PFD, Vast majority of them will pull or push the side stick following a perfect vertical motion, making the cross go up (or down), while turning slightly to the right. Let them find their own way with the side stick until they are able to make a pure pitch input, so when they flare they don't inadvertently command a roll as well.

Sounds complicated (even more so when English is not my mother tongue), but once they see it they understand what it is all about.

And, about arm rest position, they should be able to make a round circle on the side stick without having to move or elevate the wrist, to avoid having some positions of the side stick in which they'll be using the full weight of their arm, which may cause them to overcontrol. As for the legs, same old thing: full pressure on either pedal should be achieved with the leg slightly bent, not perfectly straight, to make sure they can hold the pressure without shaking during an engine failure.

About the height, I teach them to find the height where the top frame of the PFD touches the bottom side of the FCU panel, and do to it with the seat in an upright position. Much easier for them to get their visual references right for landing.

No trainee of mine has crashed so far during landing, so I guess these tips helped them...

During the first sessions I ask the trainees to open the hand if they are not making any input. As soon as they get adapted to normal law they forget about it and leave the hand on the side stick, where it should be.

I started telling them this when I realized that many times they were making random inputs on the side stick without being aware of it, most probably out of pure stress.

In the airplane this also helps them, when I see that they don't stop "stirring the coffee" I tell them to open the hand for one second or so, let the airplane stabilize, and then correct the trajectory, if needed.

Often happens in Cessnas, Pipers and B737s
 

I had the “mistake” yelled out of me by my first, and best Flight Instructor. He flew Hueys in Vietnam and demanded a soft touch and would not tolerate any over controlling.

The SIM phase of my Airbus FBW type rating was badly taught.

The instructor told us nothing about how to set the seat or the rudder pedals or how to control the aircraft, despite my saying more than once that I had never used a side-stick so would need some instruction.

It was day 2 or 3 when I was struggling and making PM and TRE feel sick when he leaned over and said "no wonder you are having difficulty, you're not using the arm rest" I said "what arm rest?". Every day when we got in it had been left vertical, and in the dark cockpit I had never noticed it, and the TRE never said anything about it or how to use it :mad:

Also nobody ever gave me any sensible advice about how to use the side-stick and FBW combination, so I was over-controlling and getting into PIOs.

I eventually taught myself how to use it after happening to see a film of a Tornado bomber, which I believe has a similar joystick and FBW system. The Tornado pilot was making inputs to adjust the attitude and returning the 'stick to neutral after every input. And each input was a nudge. So nudge, neutral. nudge neutral etc. Works like a dream. You can hold the 'stick properly in a full pistol grip, as long as you nudge and return to neutral. As soon as the aircraft starts responding to your input; return to neutral. On very turbulent approaches you might need to hold full travel until the aircraft responds - to pick up a wing for example - but as soon as it does, release to neutral.

And of course, if you realise that the FBW will help you by holding the attitude you set, (within reason), your controlling will become an order of magnitude better :ok:

Interesting to note that the force required to move the stick in roll is different for the outboard and inboard movement, your arm has more strength moving in the inboard direction than the other so to make the stick feel consistent in both directions they used different spring rates.

The purpose of setting arm rest is to remove the forearm involvement in moving the stick. With the forearm involved it is difficult to make precise inputs to side stick. With forearm resting it is easier to make the small inputs that are needed for flight path change with only the wrist. Second, any time the stick is out of neutral it's ordering the computers to change something. So after achieving the intended change to the flight path the stick must neutralized. stick free the Airbus maintains 1g path with whatever bank or wings level. It's intermittent contact handling. Pilot handles controls(side stick) only to change the flight path but not to maintain it. That's done by the aircraft automatically. That's the way it is designed. This needs to be emphasized often initially because it differs from non FBW aircraft. Any undesired aircraft movement is pilot induced and answer to that is to leave the stick alone and start again.

I've never flown an Airbus, but from reading stuff over the years I thought it maintained level flights with no pitch input in turns?

In a turn it maintains the AoA and bank if within 33°. If in a level, climb or descent stick free it maintains 1g. To elucidate, in a stick free level flight if thrust levers are brought to idle the nose doesn't drop but keeps pitching up trying to maintain 1g path and speed drops.

Is there any document which says so? Because it only the spring which brings back the stick to neutral and when moved out the rate of roll or g demanded is linear. How a spring could have differential force inboard and outboard is not understood. May be you feel so.

FWIW, I have seen PIO routinely, in any heavy aircraft I have flown: A320/330/350, but also B737/777. The problem lies not so much in the flight control laws, but rather in the fact that some pilots will give an order, and then the opposite order without waiting for the aircraft to complete the first order. Any heavy aircraft has inertia and will take some time before executing what you request from it. Be patient…

I guess it is probably hydraulic valving rather than springs that creates the different stick force but either way its quite obvious if you hold the stick from above with your other arm and move it side to side, you can clearly feel the different resistance. The fact that nobody notices (as intended) in normal operation shows how well judged the mechanism is.

Here is a scan from "The Airbus Fly-by-wire".


https://cimg3.ibsrv.net/gimg/pprune....79af09729a.jpg

I was told to treat the sidestick like it's your mates dick. Touch it as little as possible! Good advice at it worked for the ten thousand hours I flew on the Airbus FBW types.

And we have a winner!

It’s a feedback loop and the general answer is to reduce the gain and increase the time constant if you find yourself in the PIO zone. Some pilots make measured, controlled inputs between periods of inactivity and some seem to flail away with the stick/yoke constantly. It’s like the two different kinds of drivers: one saws at the wheel all the time and the other just makes corrections when needed using a relatively soft grip. There must be some kind of primacy here, so it’s really down to their first flight instructor for not teaching them properly and/or sorting it out before it becomes habitual...

The manual says "In normal turns (up to 33° of bank), the pilot does not have to make any pitch corrections once the turn is established."

Assuming that they mean maintaining altitude through the turn is the task that the pitch corrections (don't) have to be made for, then... it will maintain altitude. Does it actually do that? If so, then then it's increasing AOA and G, and not maintaining them.

Vessbot, you are scientifically correct on this one.

Mainitaining strict 1g would never achieve what Airbus FBW advertises to be doing and it actually does!

It is a short-hand written in the pilot's manual for 'flies itself steady where you point it to thanks to complex proprietary magic whose creators are sadly no longer with us'.

Have mercy not to hijack the thread. The FCOM/FCTM says 1g and has a little picture of transition and a steady climb (not a 1g segment opposing the explanation itself) thus sometimes when not relevant we just say 1g. It does not hurt that much because nobody knows how large 1 g is or needs to be for level flight anyways.



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Hi Vessbot

FCOM explains it better. “With the sidestick at neutral, wings level, the system maintains 1 g in pitch (corrected for pitch attitude), and there is no need for the pilot to trim by changing speed or configuration. Therefore pilots only need to perform minor corrections on the sidestick, if the aircraft deviates from its intended flight path. [bold]If the pilot senses an overcontrol, the sidestick should be released.[/bold]

Pitch trim is automatic both in manual mode and when the autopilot is engaged. In normal turns (up to 33 ° of bank) the pilot does not have to make any pitch corrections once the turn is established.”


So stick free and with wings level the system maintains 1g.
With up to 33° of bank, the system will maintain 1g in the vertical direction but the wings will be pulling >1g due to the centripetal acceleration in the horizontal plane.

Several people told me similar things, but it was very unhelpful to me because it did not explain what I was doing wrong, (which was not centring the stick after every input: I was holding each input too long, and the attitude went beyond what I wanted so I had to correct in the other direction, hence a PIO). Vilas's reply in #12 explains the system and use of the arm rest very well and would have helped a lot.

After teaching myself how to correctly use the side-stick and FBW combination, I became quite proficient in handling the aircraft, (he says modestly :)).

A very early Airbus publication A320 Flight Deck and Systems Briefing for Pilots had this to say:
"control inputs are made to alter the flight path, not to hold it."

Thankyou everyone for your replies and insights. Genuinely very helpful.

Uplinker did try and find that video on YouTube o the Tornado sidestick but sadly couldn’t find it.

With pedal positioning I was reminded recently to set your shoe size (UK).

Remembering my airbus type I remember lots of colourful ways to describe what to think the sidestick is in order not to touch it much but I think it’s the point that Vilas just made on the previous post which maybe should have the more emphasis.

With spring rates in the sidestick does anyone know if it’s different for the NEO. I find it definitely feels different.

Hi Mooneyboy,

I’m assuming that you are new to Airbus and are asking for yourself, not to help others with this problem.
There has been some great information here but talking from personal experience, the big issue that you’re struggling with is trying to convert all that technical stuff into something practical that you can use.

Knowing the technical is required. Knowing how to convert that into “the performance” is also required.
Seating position, as discussed, is very important. Keep in mind that you need to start with the correct eye height. Some aircraft have systems for getting this step correct. Some Airbus types have balls set on small posts set to align when eye-height is correct. Then set armrest and then set rudder pedals so you can achieve full travel AND brake input. Please don’t set shoe size.
Also keep in mind that you need to check that this position still is correct when you are hands on side stick and thrust levers. Seat back position needs to be the same, as this will change your armrest and position. You will also potentially be a little shorter by the end of a long day, changing eye height. Think how you get into your car to drive home and need to adjust your rear view mirror.

Some have mentioned to watch your PFD during the control check. I like to also check the Flight Control SD page. You’ll see exactly the moment that any pitch input invokes lateral output and vice versa. Practice this so that you can “disconnect” the two axis.
Our job is all about “output” when it comes to hand flying. Telling you what inputs to make is pointless but understanding that the Flight Control Computers are flying the aircraft in parallel with you is important to always remember. It’s a bit like having another pilot maintaining the attitude that you demand through stick position and that pilot is still under training! As Vilas said, the aircraft maintains flight path but only in a “book” sense. For example, a disturbance on short final such as a wing drop will have you now aiming at a new aim point after the “aircraft” makes inputs to return to the demanded attitude. YOU now have to make an input to reacquire the aim point. If you react to the turbulence by flying via the “seat of your pants”, you will be effectively making a “dual input” and will have demanded a roll that now makes you opposite wing down. PIO, here we come! Factor in that, as you progress down the funnel of your approach path, you can’t really sit back and wait for the aircraft to make it’s input, so you’ll have to anticipate both your inputs and what the aircraft inputs will be.
The unfortunate gulf between how the simulator presents it’s reality and how the real world is, doesn’t always set you up to succeed. In the sim, you can fly a very good approach off an IP almost without making any inputs until the flare. Try this on the line and you will most likely have the PM take over as you lose the aim point. If the sim was set up to have varying layers of W/V as one descended to the runway, the vagaries of the wind on a real life approach would be more realistically represented.
Approaching the flare, having made sure that you held the aim point, now consider how flare law changes pitch and therefore trim and how lateral is the same, ie lateral disturbance will induce an input from the aircraft. You’ll probably have to make one too but DON’T do the dual input thing, anticipate your input. In crosswind, if you “rush” the rudder input, the aircraft will roll and your input to counteract this will be demanding an opposite roll. Once you touchdown and Ground Law takes over, understand these changes too.
If you are making corrections to aim point or the Autothrust is reacting to speed changes as you pass through 100’, you may now have an out of trim aircraft, so flare as required not from memory.
Finally, treat this aircraft like a conventional aircraft whilst considering the above and don’t forget to keep your sky pointer in your scan and you’ll get your head around her.

Sorry for the lengthy post and good luck.

The environment keeps displacing any aircraft from it's present State. The question is how to restore the status quo in Airbus. Correct that's not in order like any other aircraft but after that leave it alone. As posted previously input to change but not to maintain flight path. It's definitely different but easier not difficult.

Sorry, I cannot offer an address for it - I just happened to see it somewhere down a youtube rabbit hole one day.

The Tornado was flying up a valley in Wales or Scotland I think, and you saw a view over the pilot's shoulder of his cockpit. You heard him say to his navigator through his oxygen mask, "I am coming left 10°". You could see his hand on the joystick, and he just went: nudge nudge, In other words; nudge - centre - nudge - centre, in very quick succession of less than a second - more of a digital input than an analogue one, almost like clicking a switch. You could see the aircraft bank and then stay in the new attitude he had put it in, without any further inputs from him.

Suddenly, everything about the Airbus Side-stick and FBW made sense for me, and the next time I flew the A320, I operated it in a similar way and it was a revelation to me.

As well as centring the side-stick between inputs, the thing to realise is how the FBW will assist you; (it never "fights" you, despite what some might say).

In a turbulent approach with say a wing drop, you will sometimes need to hold full opposite side-stick for a couple of moments to pick it up. Meanwhile the FBW will be doing the same. You have 25°, the FBW has 15°, so between you and the FBW, you have the 40° roll demand*.

The crucial thing to do is: As soon as the wing starts picking up, bring the side-stick back to neutral - to reach side-stick centre neutral at the same moment the aircraft reaches zero bank. If you hold the side-stick over until you have zero bank, you will bank too far the opposite way and get into a PIO.

*Please note the figures I give here are from memory - no time to check, but it is the principle that is important.

Hi Uplinker, This is where we differ in our understanding of the system.
From FCOM Normal Law Roll Control:
"When the aircraft is in the “in flight” mode, normal law combines control of the ailerons, spoilers (except N° 1 spoilers), and rudder (for turn coordination). ….. it also limits the roll rate and bank angle, coordinates the turns, and damps the dutch roll.
The roll rate requested by the flight crew during flight is proportional to the sidestick deflection, with a maximum rate of 15 °/s when the sidestick is at the stop."

The instinctive reaction to a wing drop is to do as you say and use full side stick - but it is only necessary to hold a small side stick deflection to request say 5 °/s roll rate. The FBW system will now command up to full aileron / spoiler deflection to achieve that requested roll rate.

I have found myself reverting to previous Boeing type handling in roll during turbulence and had to remind myself to only give small roll requests on the side stick in order to avoid PIO.

OK maybe it is the other way round: 15° and 25° instead of what my dodgy memory tells me.

I am not sure which of us is correct about the FBW - I just know that I have had times on turbulent approach while holding full side-stick deflection to pick up a wing when I have thought: if this doesn't respond in the next 2 seconds; I am going around. :eek:

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Asking for a friend
 

So is the armrest use mandatory or is it upto the pilot? Fcom says “adjust”. Does this mean I can lift up the arm rest all the way back and not use it at all?

It's mandatory with suitable adjustment.

so why is it not a “no - go” item then?

Our MEL spells differently.
25-11-08 through -10.


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Our MEL says not required provided it is acceptable to the affected crew member.

Dare I ask: The whole armrest itself or its adjustable mechanism? (provided the stuck position is acceptable to the crewmember)

For info only - the “nudge” technique makes passengers motion sick and it’s very obvious from the back. Smooth small corrections are the way forward.

EASA MMEL rev FEB 2022
multiple single-aisle variants of the airframe/engine, sub-2k MSN.


https://cimg6.ibsrv.net/gimg/pprune....f249158ba8.jpg

Exactly! Imagine it being stuck in the upright position.Basically this means that arm rest use is not mandatory but only a convenience.