A320 Dual input and side-stick priority

[BMATB]

Hi everyone,

I'm new to this forum so I do apologise if I have posted this in the wrong section. I have tried searching for an answer but to no avail.

I'm currently doing my FYP at University which is looking into the Airbus flight control systems. This also means that I need to include information regarding the dual input and side-stick priority system. I have a few questions in which any response from anyone with experience on the Airbus flight deck will be massively appreciated!!!

1. I understand that the dual input system is in place, however how does it work exactly in regards to the warning messages on the glareshield/PFD?

2. How does the autopilot/priority button on the side-stick work (in terms of how long it needs to be pressed for)?

3. If anyone has ever encountered a dual input situation, is the system in place effective enough and clear to gain an immediate understanding of who has control?

I am currently doing some training/work experience at a base maintenance facility so I have studied the Airbus flight deck in person on an A330, however I have never seen the system in action. Any input would be greatly appreciated.

Thanks again!

[Lonewolf_50]

If you go here(smartcockpit web site) A319 320 321 Flight Controls and select the Flight Controls choice, you should get a downloadable .pdf with descriptions of the flight controls. Please note the caveats. Starting about page/slide 58 the extended coverage of the priority choices begins. If that doesn't answer your questions, it may help you refine the questions you do have.

If you have already taken a look there, or have an up to date manual as reference, apologies.

Have you considered inquiring whether or not you could observe an A320 simulator session at a training facility through your university? Not sure how things like that work in the UK, but you may be able to get a look at how it works during a sim session if your university has contacts in the industry.
Best of luck to you.

[Denti]

1. I understand that the dual input system is in place, however how does it work exactly in regards to the warning messages on the glareshield/PFD?

In the event of a simultaneous input on both sidesticks (2° deflection off the neutral position in any direction) the two green SIDE STICK PRIORITY lights on the glareshield come on and "DUAL INPUT" voice message is activated.

2. How does the autopilot/priority button on the side-stick work (in terms of how long it needs to be pressed for)?

A pilot can deactivate the other stick and take full control by pressing and keeping pressed his priority takeover push button.
For latching the priority condition, it is recommended to press the takeover push button for more than 40s.
This allows the pilot to release his takeover push button without losing priority.
However, a pilot can at any time reactivate a deactivated stick by momentarily pressing the takeover push button on either stick.
If both pilots press their takeover push buttons, the pilot that presses last gets priority.
Note: If an autopilot is engaged, any action on a takeover push button disengages it.

In a priority Situation:

- A red light comes on in from of the pilot whose stick is deactivated.
- A green light comes on in front of the pilot who has taken control, if the other stick is not in the neutral position (to indicate a potential and unwanted control demand).

3. If anyone has ever encountered a dual input situation, is the system in place effective enough and clear to gain an immediate understanding of who has control?

In a pure dual input scenario both stick inputs will be algebraically added and the sum of both inputs will be used by the FBW system. Therefore they both are in command. That system is very unintuitive in my opinion but difficult to built otherwise without force feedback. A priority situation is pretty clear on the other hand, but takes some getting used to especially if coming from a conventional airplane.

[BMATB]

Thanks for the replies! It makes much more sense now.

One more question though. If a Pilot continues to press the priority button, the other side-stick can not be reactivated and take control?

[Dave Clarke Fife]

A330 flight controls - EFCS

Priority logic

• Normal operation : Captain and First Officer inputs are algebrically summed.

• Autopilot disconnect pushbutton is used at take-over button.

• Last pilot who depressed and holds take-over button has priority ; other pilot's inputs ignored.

• Priority annunciation : - in front of each pilot on glareshield - ECAM message - audio warning.

• Normal control restored when both buttons are released.

• Jammed sidestick : - priority automatically latched after 30 seconds - priority reset by depressing take-over button on previously jammed side stick.

[stilton]

Yes its all clear now


I'll take my Boeing thank you.

[Wirbelsturm]

Most common case of 'Dual Input' scenarios, IMVHO, is during the training of new convertees to the airbus.

As the aircraft has no sensory feedback from either the side stick or the throttle quadrant the instructor in the LHS must 'gauge', 'judge' or 'anticipate' what the trainee is going to do, especially in the flare.

It is an odd system that provides additive input as one of the most common requirements for assisted input is in the landing flare when you need to be extra careful that you are not feeding potential recovery input into the stick for a badly judged flare at the same time as the trainee 'hoicks' in a handful of stick to arrest the ROD.

You get used to it pretty quickly though.

[BMATB]

Another question (s) ...

I'm now slightly confused with pressing/holding the priority button haha.

So if a pilot presses the priority button, the autopilot is disconnected but BOTH side-sticks have control? (algebraically summed together)

If a pilot then presses on HOLDS the button, he/she has has full priority? If so, can the other side-stick take control whilst the opposing button is pressed?

If a pilot presses and HOLDS the button for more than 40 SECONDS, does this lock the other side-stick? If so, how long for and when does it return to normal mode?

Thanks!

[BMATB]

... and will the system ever IGNORE both inputs in a certain situation?

[MrSnuggles]

Follow-up to BMATB...

If pilot A presses the button for 40s (isn't that a REALLY long time in an emergency btw?) and takes priority, can pilot B overrule that by pressing his/her button for 40s? (Assuming now that the B sidestick will go back to NORMAL mode after a while.)

And, reading Dave Clarke Fife, is there one autopilot disconnect button and one sidestick priority button (total sum of two buttons) or are those one and the same? I have looked at Airbus sidesticks but never really thought about this before.

[sabenaboy]

So if a pilot presses the priority button, the autopilot is disconnected but BOTH side-sticks have control? (algebraically summed together)

No! When a pilot continues to press his priority button, the a/p is disconnected and his side stick and only his is in control. When no button is pushed but both sidesticks used at the same time, the inputs are summed together. In such case the pilots will gett a dual input warning.

If a pilot then presses on HOLDS the button, he/she has has full priority?

Correct!

If so, can the other side-stick take control whilst the opposing button is pressed?

Yes, he can, by pushing his priority button again. It has been said before: Last pilot who depressed and holds take-over button has priority

If a pilot presses and HOLDS the button for more than 40 SECONDS, does this lock the other side-stick?

Yes. The other sidestick is deactivated.

If so, how long for and when does it return to normal mode?

Indefintely, unless the priority button on this deactivated sidestick is pressed. Then it's active again.

... and will the system ever IGNORE both inputs in a certain situation?

No, dual sidestick faults are lethal

If a pilot presses and HOLDS the button for more than 40 SECONDS, does this lock the other side-stick? If so, how long for and when does it return to normal mode?

Why would you ever disconnect the other sidestick? When there's a sidestick fault (false internal contact with unwanted input or when a pilot drops dead on his sidestick. 40 seconds seems reasonable. It can be returned to "normal" mode by pressing the priority button on that sidestick. Something you wouldn't do if there was a fault, but might want to do if the fainted pilot is removed from the controls. ;-)

[sabenaboy]

Here it is

[BMATB]

Thank you very much Mr Sabena.

All clear now, gracias!

[stilton]

I think I understand it a little better now and I know i've asked this question before but I never got a reasonable answer.


Apart from weight savings what are the advantages of non linked sidesticks with no feedback and non back driven autothrottles ?


Trying not to be so biased against Airbus here but I just don't see the point of this design.

[peekay4]

There's no real advantage to "passive" sidestick systems except simplicity: less things to go wrong. And by now this design has been proven to be highly reliable and successful.

Yet despite its success, the A320 sidestick is literally 1980s technology. A bunch of springs and dampers -- it's ancient tech by today's standards. But there were no other options back then. Airbus had to fight hard to get digital FBW accepted by civil aviation authorities. They needed to demonstrate a fail-proof system. And a big reason Airbus pushed so hard for certification was because the chief proponent of the sidestick system was none other than the CEO's son, who had been a military pilot.

Only now in 2015 has technology advanced to the point that "active" sidestick systems with full force-feedback are becoming a commercial possibility.

Gulfstream will become the first civil aircraft manufacturer in history to use an active sidestick in the all-new G500 & G600, which will incorporate a new system designed by BAE.

It's just a matter of time until other commercial aircraft manufacturers will adopt this technology as the new standard.

[ShotOne]

Stilton, try asking your question the other way. What is the point of linked controls? In the event of incapacitation or a dispute over control they present a serious problem. There's no perfect answer of course, but the Airbus fbw approach is surely better than the straight trial of strength that would ensue in, say a 737?

[sabenaboy]

What is the point of linked controls? In the event of incapacitation or a dispute over control they present a serious problem.

I've been flying the A320-series for 10 years+ now. The current system does work, but I still believe it would be a major improvement if the PNF's side stick was somehow linked to and moving in the same way as the PF's one. Nobody can deny that would be a welcome feature. Obviously this should not necessarily be a mechanical linkage. An electronic feedback, combined with today's "dual input" warning and priority button would be optimal in my opinion. There's little doubt in my mind that that's what the future will bring. No problems in case of incapacitation in this way either.

(If you want to eliminate the risk of ONE rogue pilot wanting to do something wrong with the plane, I can't think of any other solution then introducing a 3 pilot cockpit each with their own sidestick or yoke where two inputs will have priority over the third pilot. But something tells me that's not going to happen. )

The new Gulfstream and Bae sidestick system looks very promising to me!

[BMATB]

The current system does work, but I still believe it would be a major improvement if the PNF's side stick was somehow linked to and moving in the same way as the PF's one. Nobody can deny that would be a welcome feature. Obviously this should not necessarily be a mechanical linkage. An electronic feedback, combined with today's "dual input" warning and priority button would be optimal in my opinion. There's little doubt in my mind that that's what the future will bring. No problems in case of incapacitation in this way either.

This is the sole aim of my University project. Summed it up nicely!

[peekay4]

That's exactly how the new Gulfstream active sidestick I mentioned above works!

The active sidesticks are not direct-linked mechanically, but rather uses a system of electronic servos via a computer to provide positioning and force-feedback. So an Airbus-style "priority button" can still be implemented if desired -- or alternatively a "split control" configuration can be applied, where in a contention situation each sidestick controls half of the control surfaces a la some Boeings.

The cool thing is that the position and force feedback gradient of each sidestick can be altered in real time. E.g., they can be made more sensitive or smooth during certain phases of flight, or alternatively the feedback can be made stronger when approaching aerodynamic or safety limits. Commands from the auto-pilot also move the sidesticks so they can be observed immediately, reducing "surprises" in cases where the A/P suddenly disconnects.

[ShotOne]

With 18 years on fbw airbuses I can see the point of a feedback system, if I understand you right, of the other pilots control inputs. (What happens in a dual input?) But what's the point of the stick moving with the autopilot? That's arguably worse than pointless since the pilots should be monitoring what the aircraft's doing not stick position.