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 (http://www.smartcockpit.com/aircraft-ressources/A319-320-321-Flight_Controls.html) 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 :eek:


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) ... :O

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]

http://i58.tinypic.com/v2uv5i.jpg
http://i60.tinypic.com/2u9kb9k.jpg

[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. :rolleyes: )

The new Gulfstream and Bae sidestick system (http://aviationweek.com/technology/active-sidestick-controls-make-commercial-debut) 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.

[peekay4]

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.
Having the sidestick move with the autopilot provides additional visual and tactile feedback to the pilots.

This does not detract from aircraft monitoring -- in fact autopilot backdrive enhances monitoring and situational awareness, by giving extra (and natural) cues to the pilots.

[ShotOne]

That is a very arguable point. It does give additional cues. But they might be misleading ones. Airbus philosophy rightly lays stress on monitoring the actual state/attitude of the AIRCRAFT, not the stick or switch position. Ditto for earlier comment re. Thrust lvrs.

[Denti]

Having the sidestick move with the autopilot provides additional visual and tactile feedback to the pilots.

On an airbus that would only show the control input, but not the control surface deflection as those are not the same. Mainly due to the flightpath stable architecture.

Reduce speed with without changing altitude, the feedback would show exactly nothing. Although the pitch attitude will change considerably. What use is the feedback in that situation?

[peekay4]

Hi Denti, that's not quite correct.

With speed reduction, the autopilot will command pitch changes to maintain altitude. These pitch changes (up/down) will be seen on the active sidestick.

In fact, you will naturally expect to see these pitch changes, because if you were to fly the plane manually you will make those same pitch adjustments.

Over time, you start to develop an intuition of how active the sidestick should behave in different flight conditions when on autopilot.

E.g., in good weather straight-and-level flight, you would naturally expect the sidestick to only show continuous small movements corresponding to small autopilot corrections.

So if you happen to notice the autopilot commanding large and unexpected sidestick movements, then that might be an additional cue to you that there's something which might need your attention.

Today you might not have any indication of trouble until the autopilot gives up and disconnects.

This is not to suggest that you monitor the sidestick. However, as mentioned, having an active sidestick can provide additional visual and tactile feedback that's natural to the pilot -- almost at the intuition or sub-conscious level.

[Denti]

With speed reduction, the autopilot will command pitch changes to maintain altitude. These pitch changes (up/down) will be seen on the active sidestick.

In fact, you will naturally expect to see these pitch changes, because if you were to fly the plane manually you will make those same pitch adjustments.

In a conventional aircraft that would be correct. In an Airbus it isn't. Remember, the airbus is flight path stable, not speed stable. It will maintain the flight path without pilot input within the normal envelope.
´
The same thought experiment in manual flight, manual thrust. Pull back thrust and maintain the stick centered (just don't touch it). The aircraft will slow down and maintain (roughly) the same altitude with the same pitch change to do that.

The FBW system, not the autopilot, not the human pilot, will command the necessary control surface deflections. And if you have seen the "dance of the ailerons" (https://www.youtube.com/watch?v=YqLyKwx8KNE) after take off on an A380 for example you would know that any feedback of those control surface deflections would be very counter productive.

[Goldenrivett]

Hi Denti,
And if you have seen the "dance of the ailerons" after take off on an A380 for example you would know that any feedback of those control surface deflections would be very counter productive.
The feed back position of the master aileron (the internal aileron) is all that would be needed to be felt.
see: Page 12 of http://www.ukfsc.co.uk/files/Safety%20Briefings%20_%20Presentations/Airbus%20Safety%20First%20Mag%20-%20July%202012.pdf

"A similar differential deflection was also implemented on the two rudders and was called “VDR” or “Valse Des Rudders” (rudders waltz), a typical Airbus “British – French” acronym, as rudder is not a French word!"

I'm sure the crews don't find the feed back position of the rudders through their pedals counter productive.

[Denti]

Flight control surface deflection however serves no purpose as pilots do not control the flight controls surfaces themselves, except in direct law. The pilot controls the flight path (g-load and roll rate demand) and the FBW does what it needs to follow those demands.

Control surface feedback would be counter productive therefore, except if the bus would be reconfigured to fly in direct law all the time, by which time it is absolutely useless to have the FBW in the first place.

Now, a feedback of the stick position of the other pilot would serve a purpose.

[speed freek]

Now, a feedback of the stick position of the other pilot would serve a purpose.

But isn't that what people are saying with backdriven controls?

If you treat the autopilot as a third pilot in the flight deck, then surely you'd like to see what it's commanding alongside what the instruments are saying. I agree, it's pointless having the FBW feedback through the sidestick.

On an airbus that would only show the control input, but not the control surface deflection as those are not the same

Many conventional aircraft over the years have had low and high speed ailerons, with the change-over happening automatically and no indication in the flight deck. The control wheel still moves as normal though :ok:


And surely what you say is exactly what the set up is on the 777/787.

[ShotOne]

What happens in a contention situation to this new side stick?


An earlier poster (peekay?) wrote on some boeings "each sIdestick controls half the control surfaces". So if one pilot commanded left and the other right, it would command up aileron/spoiler on both wings(!!)? Please someone tell me that's nonsense?

[FlyingStone]

An earlier poster (peekay?) wrote on some boeings "each sIdestick controls half the control surfaces". So if one pilot commanded left and the other right, it would command up aileron/spoiler on both wings(!!)? Please someone tell me that's nonsense?

I know nothing of Boeing FBW, but...

1. Boeing does not have sidesticks.

2. Control columns on all Boeings are mechanically inter-connected, so even on FBW aircraft they are most likely to give the same commands to FBW system from either left or right control culmn.

[Denti]

Control columns on all Boeings are mechanically inter-connected, so even on FBW aircraft they are most likely to give the same commands to FBW system from either left or right control culmn.

There is usually a breakout mechanism, with enough force you can disconnect the columns and then you have indeed the case that different control surfaces get their commands from their column, or better said each side controls only a portion of them.

On Airbii of course you have either arithmetic summation of both control inputs or you can disconnect the other stick with the priority button.

[stilton]

Why on earth would you want 'arithmetic summation' of both sidesticks ?


The Airbus control philosophy seems counterintuitive, byzantine and needlessly complex with no consideration to human factors or simply
'whats it doing ?'


And for all its vaunted precision I read many accounts of its lag and the difficulties this causes in gusty crosswinds.


I don't believe it was outside the state of the art for the sidesticks to be linked and backdriven when the A320 was introduced and I know it wasn't an issue for the autothrottles to have had the same arrangement.

[friend007]

Why on earth would you want 'arithmetic summation' of both sidesticks ?

Because both sidesticks are not connected and this makes it intuitive for the other pilot to make/add corrections. Eg trainee does not pull enough in the flare. LTC's sidestick is neutral. He just wants to add a bit of nose up so he just pulls his stick a bit and his input is added to that of the trainee.

If you want to take control regardless of what the other guy is doing, just push the disconnect button to override him...

[peekay4]

The need for summation is simply a legacy of sidestick technology that was available 30 years ago. With non-linked passive sidesticks, summation was (and is) the only logical arrangement.

Denti: you may want to check out how the autopilot and auto-throttle back-drives are integrated into the F-35 FBW. (And soon on the G500 & G600).

[fizz57]

Don't the coupled yokes on a conventional system provide "arithmetic summation" of the force applied by each pilot?

[Goldenrivett]

Hi fizz57,
Don't the coupled yokes on a conventional system provide "arithmetic summation" of the force applied by each pilot?
Correct. But the advantage of having displacement feed back is that you will have a much better idea of how much input was required.

Active Sidesticks: A New Way to Fly (http://airwaysnews.com/blog/2015/03/23/active-sidesticks-a-new-way-to-fly/)

[peekay4]

Don't the coupled yokes on a conventional system provide "arithmetic summation" of the force applied by each pilot?
Not exactly the same.

Scenario: FO applies 10 lbs back pressure causing the plane to start pitching up. At 3 degrees nose up, the Captain applies same magnitude forward pressure.

Airbus. Sum == 0, no commanded change, so the nose stops pitching up at 3 degrees ANU.

Conventional. Equal forces, so the yoke stops moving rear-of-center. Plane continues to pitch up past 3 degrees nose up.

Also note:

Airbus. FO's sidestick is now rear-of-center while the Captain's sidestick is front-of-center. But the plane continues "straight" -- contrary to both pilots' natural expectation! See AF447 to see why this is bad.

Conventional. Both pilots' yokes are at the same rear-of-center position, and the plane behaves exactly as both would expect.

Active sidesticks will basically restore what's already natural to pilots / human beings.

[safelife]

peekay4, that is exactly the reason why it is taught on the airbus not to make use of dual input, but rather take over control (via tha button) and gain exclusive control.

[FCeng84]

As stated above, the Boeing columns are mechanically linked through a breakout that allows relative motion if the force applied to the link exceeds the breakout level.

Separate sensors measure the positions of the left and right columns. For the non-FBW models and the FBW models operating in Direct Mode, left column position commands the left elevator and right column position commands the right elevator. On the non-FBW models the command path from column to elevator actuator is via mechanical cables (plus the manual reversion path on the 737). On FBW models this command path is via electrical signaling.

For Boeing FBW models operating in either Normal or Secondary mode the flight control computer receives data from both the left and right column position sensors. The average of the left and right column positions is used to drive the longitudinal control laws. In Normal and Secondary modes both elevator surfaces are commanded to the same position.

[FCeng84]

The objective behind pilot controller backdrive on the Boeing airplanes is to move the controllers as they would need to be moved by the pilot to achieve the same response as is being delivered by the autopilot were the autopilot disconnected and the pilot flying manually. On non-FBW models this indicates the position of the associated surfaces. That is not the case on FBW models where surface position is defined by maneuver demand, stability augmentation control laws.

One outcome of this approach is that only minimal airplane transient will result if at any time the crew grabs the controllers and disconnects the autopilot while maintaining controller position.

[Bkdoss]

"One outcome of this approach is that only minimal airplane transient will result if at any time the crew grabs the controllers and disconnects the autopilot while maintaining controller position"

Regardless of whether the aircraft is fbw or non-fbw ideally this should be the motive behind any aircraft design. Even in fbw aircraft like the a320, which doesn't boast of control surface feedback on the yoke, the moment Autopilot is disconnected the aircraft continues in its established stable flight path under normal circumstances, when the aircraft doesn't suffer from any serious system degradation.

One critical instance I can think of where an active control column or yoke would come in handy is at the time of landing. There have been cases when as a copilot I get to land the aircraft and despite me being confident to pull off a safe landing, the skipper impulsively plays around with the controls. God forbid if we both pitch it up at the most inopportune moment there are plenty of chances of going home with a tail strike(more so on a 321). Some captains, working with the same operator I work for, are reluctant to trust the copilot with landings simply because of the fact that they are not confident with their abilities to react to the copilot's inputs by just judging the changes in the flight path alone.

[Winnerhofer]

Active sidestick controllers to be used on MC-21
Active sidestick controllers will be used on a large commercial aircraft for the first time, with the Irkut MC-21 to use a system that has been in development for more than two decades by UTC Aerospace Systems’s (UTAS) French-based subsidiary Ratier-Figeac.
The deal offers a potential breakthrough in commercial cockpit situational awareness, by using a FBW actuation system with new controllers.
“Active sidesticks significantly improve the level of safety, mak- ing evident control inputs of pilots to one another and allowing prompt recovery actions,” says Roman Taskaev, chief test pilot for the MC-21 programme.
UTAS’ actuation and propeller business unit began experimenting with the sidestick controllers in the early 1990s, and Irkut selected the system for its MC-21 family in 2010, says Ratier-Figeac international business development manager Marc Gouault.
Cockpits equipped with decoupled sidestick controllers that do not provide active feedback to pilots have been highlighted in several aviation incidents, including the loss of AF447.

[T28B]

Mr Winnerhoffer, is this your summary or is the above a cut and paste from a news article? :confused:
I looked into the MC-21 information (thank you) and find that it may be a competitor with the B737 and AB320, when it comes out.
This discussion seems to have drifted from a question about the A320 side stick priority into another discussion.
Might there be a thread on pros and cons of sidestick design, which is a different topic than how a particular design works? :confused:

[DozyWannabe]

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

What are the advantages, when the link between the command method and the response are entirely electronic?

Airbus had to fight hard to get digital FBW accepted by civil aviation authorities
...
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.
Rubbish.

Look, we've been through this before. The reason two/three crew airliners which had direct cable control had those controls duplicated and replicated was so that in the event of an external control problem, the muscle power of both pilots could be used to rectify the issue. Having one side feel what the other side was doing through the tactile channel was a side-effect only. Once hydraulic-assist (and eventually all-hydraulic) controls became the norm, there was no fundamental need for one side to mimic the other, as the flight surface deflection was entirely down to the hydraulic systems.

In fact, in modern airliners with an all-hydraulic linked yoke system, abnormal configurations may not result in the outcome that many would expect (e.g. EgyptAir 990, where one yoke forward and the other back resulted in a split-elevator condition).

The Airbus FBW passive sidestick design grew out of the Concorde "minimanche" experiments in the late '70s. The decision to go with a passive design was as much a result of the potential safety benefits (e.g. in an incapacitation scenario) as it was anything else. Yes, avoiding technological complexity was an issue - but it was far from the only issue. Remember that one of the primary people behind the development and evaluation of the design was Gordon Corps - Dai Davies' successor at the ARB/CAA. It follows that the design decision was absolutely not based on economic considerations alone.

The presence of force-feedback on the B777's PFCs is in fact the reason that design requires a bypass mode (the oft-discussed "Big Red Button") for safety reasons while the Airbus design does not. The bypass mode exists purely to counter the scenario in which the computer controlling the force-feedback may fail.

There have been cases when as a copilot I get to land the aircraft and despite me being confident to pull off a safe landing, the skipper impulsively plays around with the controls.
A skipper doing that in a FBW Airbus can expect tea and biscuits with the chief pilot at best, and the heave-ho at worst. The design absolutely requires the handling pilot to be the only one manipulating the controls at any given time. To be fair, that should really be the case on any type. If the Captain feels the landing may be beyond the capabilities of the FO, they've got to follow the book and brief accordingly.

[vapilot2004]

The reason two/three crew airliners which had direct cable control had those controls duplicated and replicated was so that in the event of an external control problem, the muscle power of both pilots could be used to rectify the issue. Having one side feel what the other side was doing through the tactile channel was a side-effect only. Once hydraulic-assist (and eventually all-hydraulic) controls became the norm, there was no fundamental need for one side to mimic the other, as the flight surface deflection was entirely down to the hydraulic systems.

To your first sentence, it was also just how things were done due to mechanical necessity in a two pilot cockpit. As to the last sentence (my bold), ...yet the interlinking remained, surely for some reason.

The presence of force-feedback on the B777's PFCs is in fact the reason that design requires a bypass mode (the oft-discussed "Big Red Button") for safety reasons while the Airbus design does not. The bypass mode exists purely to counter the scenario in which the computer controlling the force-feedback may fail.


That's not quite right, my friend!

The design absolutely requires the handling pilot to be the only one manipulating the controls at any given time.

I will give you, DW, that with the priority switch arrangement, and SOP around it, sure, the overall idea is that of one guy flying the aircraft at a time, but dual input summing makes me agree only if you remove the offending words in bold and replacing with something along the lines of 'encourages.' :ok:

[peekay4]

A lot of self-contridictions in your post there Dozy.

Btw you may want to read about Bernard Ziegler. He was the guy who pushed very hard for Airbus to adopt digital FBW sidesticks and for the industry to accept the new system. This was an entirely different than what was on the Concorde. (Concorde had analogue controls).

Bernard was the son of Henri Ziegler, Airbus founder and CEO.

Both Zieglers were intimately aware with limitations of the Concorde's control design... many consider Henri to be "the father of Concorde".

There's nothing wrong to revisit the design choices Bernard made 30 years ago for Airbus. The world has changed since then. Had reliable active sidestick technology existed back in 1980, there's little doubt Airbus would have adopted it.

[Winnerhofer]

Well Ziegler stole Klopfstein's HUD and which is a cut-down version on Airbus.
IT's A320s came with HUDs (LH-side only) and AoA display but no EGPWS.
When IT merged with AF, the latter began dismounting all of IT's HUDs and disabling AoA displays.

[DozyWannabe]

Btw you may want to read about Bernard Ziegler. .
I know who BZ was - if you look at my earlier posts we covered a lot of this stuff - repeatedly. He was the nominal head of the A320 project, but the grunt work of development and testing was done by Gordon Corps and his team. The sidestick design was developed from the "minimanche" experiments on Concorde, which BZ had nothing whatsoever to do with (and neither did Henri - this was an experimental development involving the engineers only). It was absolutely *not* "[BZ]'s design" or his "decision".

In fact, I have a strong suspicion that if Capt. Corps had not died tragically and prematurely (of altitude sickness visiting a crash site in the Himalayas), a lot of the hearsay doing the rounds regarding A320 development would have been nipped in the bud.

(If you go and Google Flight's archives on A320 development, you'll note that BZ is briefing the mainstream press, but when it comes to technically explaining the system, it's GC that is providing the information.)

That's not quite right, my friend!
It is if you read what I said. ;) It may not be the only reason it is there, but that is the only reason it *has* to be there in a computer-controlled backdriven design.

dual input summing makes me agree only if you remove the offending words in bold and replacing with something along the lines of 'encourages.' :ok:
The system goes out of its way to discourage dual input with visual and aural warnings, so it follows that the only way it should be happening is with the full consent and intention of both flight crew.

[EDIT : @Winnerhofer - I strongly doubt that BZ "stole" anything. As I've just discovered, Air Inter had been using HUD for years on their Caravelles long before the A320 project even began:
http://www.headupflight.net/Images%20diverses/Cockpit_NetB.jpg
(this is not a Caravelle, but this article (in French) - http://www.headupflight.net/lami/historique.htm - uses it to illustrate the point...)

[roulishollandais]

BZ had no shame with that acronym : Zyclon B, (in his book "Les cow boys d'Airbus) used by those who killed young Jews like Klopfstein. That lobby stoled possible royalties and Klopfstein's fame. Sorry to have to deserve memory.:{

[vapilot2004]

It is if you read what I said. ;) It may not be the only reason it is there, but that is the only reason it *has* to be there in a computer-controlled backdriven design.

I read what was written, and I still say it was disingenuous. As it relates to backdriven controls, the PFC off switch is there because Boeing required it - not the FAA nor EASA.

The presence of force-feedback on the B777's PFCs is in fact the reason that design requires a bypass mode (the oft-discussed "Big Red Button") for safety reasons while the Airbus design does not. The bypass mode exists purely to counter the scenario in which the computer controlling the force-feedback may fail.

The FAR 25/EASA type certificate limitations of what you refer to as "force-feedback" on the 777 are satisfied through the use of slip clutches in the case of AFDS back drive actuators going 'rogue' due to computer/electronic malfunction. (no relation to the FBW PFCs).

The elevator feel units are mostly mechanical devices that get their input from the ACE and not the PFC directly. During a fallback to DIRECT MODE (your "big red button") the feel units are still in operation, but the airspeed-commanded variable resistance is replaced by a flap position based command.

EDIT: Additional info: Even with a "full" command from the PFC via the ACE, the effect on the controls from the feel unit is limited by mechanical design. The mechanism, by design is unable to place the full feel load (upwards of 100lbs) at small deflection positions. All of the feel units and backdrives on the 777 can be overridden by control inputs, albeit, at slightly higher than normal command pressures. Should one set of backdrives or a feel unit jams, there is the breakout mechanism allowing one guy to fly the aircraft unimpeded.


The system goes out of its way to discourage dual input with visual and aural warnings, so it follows that the only way it should be happening is with the full consent and intention of both flight crew.

I like this explanation much better. Thanks!

I appreciate your expert knowledge of critical computing systems and otherwise find your posts informative. :ok:

[vapilot2004]

Btw you may want to read about Bernard Ziegler. He was the guy who pushed very hard for Airbus to adopt digital FBW sidesticks and for the industry to accept the new system.

I understand M. Ziegler was a key figure in the development of the Airbus FBW system. In an ironic twist, I also understand in 2006 the French courts placed Ziegler under a manslaughter charge stemming from the the Colmar crash in 1992. I am guessing he was not found to be guilty here.

In talking with a friend yesterday (prompting this post) I was surprised to learn of M. Ziegler's cowboy stunt in an F-84 in the early 1960's led to the deaths of six people traveling on aerial trams. Were there no charges made against him back then? Ziegler's father, Henri, was highly influential in the upper echelons of French government. Perhaps he 'saved' his son the 'trouble' of facing criminal charges?

[DozyWannabe]

I read what was written, and I still say it was disingenuous. As it relates to backdriven controls, the PFC off switch is there because Boeing required it - not the FAA nor EASA.
Sure - and I don't think I said or implied otherwise. What I was getting at was that the reason Boeing required it was as a result of the force-feedback based design.

The FAR 25/EASA type certificate limitations of what you refer to as "force-feedback" on the 777 are satisfied through the use of slip clutches in the case of AFDS back drive actuators going 'rogue' due to computer/electronic malfunction. (no relation to the FBW PFCs).
As I've admitted to in the past, I'm not as au fait with the T7 architecture as I am with the Airbus system. However....

During a fallback to DIRECT MODE (your "big red button") the feel units are still in operation, but the airspeed-commanded variable resistance is replaced by a flap position based command.
Right - in essence it's bypassing the more complex computerised system in favour of a simpler setup.

All of the feel units and backdrives on the 777 can be overridden by control inputs, albeit, at slightly higher than normal command pressures. Should one set of backdrives or a feel unit jams, there is the breakout mechanism allowing one guy to fly the aircraft unimpeded.
Sure, and I appreciate the information - much of which I didn't have before.

I still think that we're talking at cross-purposes though. I wasn't saying anything about regulatory requirements versus Boeing's inputs, I was simply saying that by introducing a digital computer into the feel system it was a necessity to provide a bypass at the time purely on the basis of sensible engineering principles, and that by making their feel system passive, Airbus didn't have that requirement.

I understand M. Ziegler was a key figure in the development of the Airbus FBW system.
Your understanding is a little off-base. Bernard Ziegler was the nominal engineering head of the A320 project, but he did not have a significant degree of technical input. The passive sidestick system originated from the French/British Concorde "minimanche" project, and I am very reliably informed that M. Ziegler had nothing whatsoever to do with it.

[peekay4]

I don't know what the vendetta against the late Bernard Ziegler is all about.

More on him here:

Lifetime Achievement Award (http://www.flightglobal.com/page/achievement-awards/2012/lifetime-achievement/)

@vapilot2004

Obviously the accident was huge news in both France and Italy back then. Under public scrutiny, Bernard Ziegler was cleared by the courts:

- The gondola / aerial lift was apparently built without the proper permits and its construction was contrary to the decision of the local planning authority

- The gondola was also unmarked in aeronautical charts, and was located in an area considered a "safe route"

[vilas]

Passive side stick has a problem during initial training on landing the plane. You cannot demonstrate from the other side how much side stick input is required to flare or you cannot ask the trainee to follow on controls. Similarly if any assistance was rendered during landing by the instructor the trainee cannot appreciate from his side stick. Other than that the system is doing fine. Considering the popularity oh A320 this doesn't seem to be much of an issue.

[vapilot2004]

My friend from whom I was given the story of Ziegler's F-84 tram crash may have harbored bad intentions - he is certainly a strong "All American" type and NIH is another of the guy's beliefs!

What I didn't know was the final 'adjudicated' outcome - numerous searches on the internet yielded little into outside of some yellow journalism. I think we can agree the well-connected are more often than not given the benefit of the doubt that lesser souls fail to receive in government courts claiming 'justice for all' around the civilized world, but judging by your tone and the facts you offer, he was not to blame via the valid excuse of a lack of advisory info on published aero maps. So thank you kindly for clearing that up, PK4.

Regarding acknowledgements of BZ's contributions to aviation safety, I know M. Ziegler was also the recipient of some of France's highest honors and received a FSF award for his role in developing the Airbus FBW system. I did not know until the other day of his father's role in developing Concorde's analogue FBW - which is what started the conversation on the Ziegler clan.

In other areas related more to the thread, I agree with your statement earlier regarding linked sidesticks and the technology limits being the primary reason it was not attempted at the time. Makes perfect sense.:ok:

[DozyWannabe]

I did not know until the other day of his father's role in developing Concorde's analogue FBW - which is what started the conversation on the Ziegler clan.
Henri Ziegler (BZ's father) was, like his son in the case of the A320, the nominal head of the French end of the project, but I've seen no evidence whatsoever that he had any direct involvement in the systems design (which was very much a collaborative effort).

I agree with your statement earlier regarding linked sidesticks and the technology limits being the primary reason it was not attempted at the time. Makes perfect sense.:ok:
That's not the only reason though. The "clean room" thinking was that with an all-hydraulic control setup and with only one flight crew member being PF at any given time, there was no real need to backdrive or connect the flight controls in the manner of earlier designs.

The head of the A320's pilot engineering team was the late Gordon Corps, who had previously been the successor to D.P. Davies (of "Handling The Big Jets" fame) at the ARB.

[vapilot2004]

Henri Ziegler (BZ's father) was, like his son in the case of the A320, the nominal head of the French end of the project, but I've seen no evidence whatsoever that he had any direct involvement in the systems design (which was very much a collaborative effort).


Really? The Ziegler family must have been incredibly powerful promoters of themselves. Ziegler senior is mentioned a few times in Concorde historical accounts. On the other hand, much of the media coverage has Bernard acknowledged as a key figure in the Airbus FBW design. The FSF award text seems to be fairly clear on BZ's influence:

Bernard Ziegler was the most influential figure in developing the cockpit design and fly-by-wire control system for the Airbus airliners. He was the guiding force in the creation of the flight-envelope protection incorporated in the Airbus flight-control software.

Not that it matters that much, but who am I (and others) to believe? Was the redoubtable Flight Safety Foundation (and Flight Global and the French government) so out of touch with reality that they too were taken in by some sort of subterfuge?

I would like to know more about Mr. Corps. Any references DW or recommended reading? Thank you! If Gordon Corps was the true "father" of FBW as opposed to M. Ziegler, then a terrible injustice and misinformation campaign bordering on fraud seems to be happening here.

That's not the only reason though. The "clean room" thinking was that with an all-hydraulic control setup and with only one flight crew member being PF at any given time, there was no real need to backdrive or connect the flight controls in the manner of earlier designs.

I follow this line of thinking if we are discussing a fighter where there is only one control stick, but on a transport aircraft it seems odd to me. Could you recommend some books on the history of the Airbus FBW development? Aside from the Cowboys book by Ziegler himself, there seems to be very little published on Airbus history (as opposed to voluminous materials published on the players aerospace, both large and small in the US) and I am not sure why that is, although several theories have been offered in attempts account for this.

[DozyWannabe]

Really? The Ziegler family must have been incredibly powerful promoters of themselves.
I don't know about Henri, but Bernard Ziegler was known to be something of an inveterate self-publicist. In fact that has a lot to do with the reason Airbus made him VP of Engineering during the advent of the A320. I should point out to peekay4 that as far as I know BZ is in fact still with us, but last I heard he wasn't in the best of health.

...much of the media coverage has Bernard acknowledged as a key figure in the Airbus FBW design. The FSF award text seems to be fairly clear on BZ's influence:
Right - he was the VP of Engineering and thus the person with whom the buck stopped in terms of high-level specification, but he was not a nuts-and-bolts engineer. Furthermore as I said, the sidestick design grew out of the Concorde "minimanche" experiments which BZ had no involvement with to the best of my knowledge. BZ may have championed the notion of using the fruits of that work in the A320, but he did not come up with the idea and he did not have a direct hand in the implementation.

Was the redoubtable Flight Safety Foundation (and Flight Global and the French government) so out of touch with reality that they too were taken in by some sort of subterfuge?
No, but the media do tend to like a simple narrative when the truth of the matter is rather more prosaic. So in much the same way as, for example, Bill Gates is credited with inventing MS-DOS (he didn't) and Steve Jobs is credited with inventing the Apple Macintosh (he actively avoided the project in favour of his pet project "Lisa", which flopped) - articles tend to associate BZ with Airbus FBW when in fact he was more of an enabler and figurehead than someone actively involved day-to-day in the project. Of course he would chair the development meetings with the aero, software and pilot engineering groups and he probably had final say in arbitration, but that's about it as I understand it.

I would like to know more about Mr. Corps. Any references DW or recommended reading? Thank you! If Gordon Corps was the true "father" of FBW as opposed to M. Ziegler, then a terrible injustice and misinformation campaign bordering on fraud seems to be happening here.
Heh - I'd argue that's a bit melodramatic! As I said above, the truth is somewhat prosaic. The Concorde "minimanche" experiments and the development of the A320's flight deck and systems from that work were a long-term evolutionary and collaborative effort involving large teams led by the best people Airbus could hire - there is no individual "father" of Airbus FBW. Captain Corps was, as I said, D.P. Davies' successor at the ARB, and according to CliveL (resident Concorde engineer), he became the ARB's Chief Test Pilot for Concorde - hence his involvement with the "minimanche" project and his subsequent poaching by Airbus, presumably for that very reason (after all, who better to lead development of the technology for production than the person who had more experience of it - both theoretical and practical - than any other person on Earth?).

If you've read "Handling The Big Jets", then you'll know that the ARB role required a polymath who was not only well-versed in physics and engineering, but was also a "pilot's pilot" who could explain the technical ins-and-outs in understandable terms and had an innate feel for aircraft and their behaviour. In short, at Airbus it fell to Capt. Corps to mediate between the ground-based engineers and his pilot engineering team, as well as being the lead test pilot who would take the aircraft up and be able to give feedback to the other teams.

Here's a FlightGlobal article from 1987 - you'll note that while Bernard Ziegler is the one giving the high-level overview, when it comes to actual technical information and flight characteristics, it's Gordon Corps they're talking to : airbus industrie | 1987 | 0873 | Flight Archive (http://www.flightglobal.com/pdfarchive/view/1987/1987%20-%200873.html)

And here's the man himself giving a tour of the A320's FBW systems during a test flight:
9fqy8uPzW90

You may be wondering why he's not better-known, and here's where the story gets sad. After the A320 went into service, Capt. Corps transferred to head up the flight safety department at Airbus. In 1992 a Thai Airways A310 crashed in the Himalayas, and true to form from what I've been told, he insisted on heading the team and visiting the site personally. While on-site he developed altitude sickness and passed away - he was only 62.

Not only was this a tragic and premature loss in itself, but it was a massive loss to aviation - he never did get to write his own book, and without his innate ability to bridge the gap between the piloting and engineering worlds there arose a lot of misunderstandings in the piloting arena regarding the Airbus FBW systems he helped develop. This was not helped by the ongoing vendetta that the French SNPL pilots' union have been waging in the press against Airbus since the '70s - in fact I'd argue that it's largely down to their efforts that Bernard Ziegler and his foibles have come to be more associated with Airbus FBW than the (from what I've been told) down-to-earth and meticulous character that Capt. Corps was.


I follow this line of thinking if we are discussing a fighter where there is only one control stick, but on a transport aircraft it seems odd to me.
Could you elaborate as to why you think it's odd? Sure, it was a departure from the de facto standard but from an engineering standpoint it makes sense. As far as Airbus were concerned it made commercial sense too, because it meant that their entire fleet could share an unprecedented level of flight deck commonality and handling characteristics whether you were flying a short-haul narrowbody or a long-haul widebody - something that Boeing and MD would be unable to match.

Could you recommend some books on the history of the Airbus FBW development? ... there seems to be very little published on Airbus history (as opposed to voluminous materials published on the players aerospace, both large and small in the US) and I am not sure why that is, although several theories have been offered in attempts account for this.
Well, one of the reasons there aren't many books on the subject is that the person best qualified to write one died before he had the chance. It's a tragic shame.

[Winnerhofer]

Sorry but wasn't Gordon Corps the real brain behind the A320?

[DozyWannabe]

No, he was the (effectively) "Chief" Test Pilot and lead pilot engineer on the project. There was no single "brain" behind the A320 - it was a long-running collaborative project, as I said above.

[EDIT : Corrected re: peekay4's reply. While GC was not officially the Chief Test Pilot by title, he was the test pilot who oversaw the majority of the practical work, as well as the lead pilot engineer who provided the feedback on the systems. ]

[peekay4]

No, he was the Chief Test Pilot and lead pilot engineer on the project. There was no single "brain" behind the A320 - it was a long-running collaborative project, as I said above.

Chief Test Pilot for A320 development was Pierre Baud.

Chief of Engineering was Bernard Ziegler.

Gordon Corps was a Flight Test Engineer.

Pierre Baud became Airbus Chief Test Pilot in 1978, succeeding Bernard Ziegler (A300 Chief Test Pilot) who moved over to Engineering. After the A320, Mr. Baud remained as Chief Test Pilot on several programs until 1994.

The A320 first flight was piloted by Pierre Baud, and co-piloted by Bernard Ziegler. Gordon Corps was the observer.

[DozyWannabe]

Chief Test Pilot for A320 development was Pierre Baud.

Chief of Engineering was Bernard Ziegler.
That's for the company in general. I'm talking about the roles on the project itself, not the time period.

Baud and Ziegler were both "Veeps" (i.e. senior company vice presidents of flight division and engineering). They'd chair meetings and take the thing up on marquee flights, such as...

The A320 first flight ... piloted by Pierre Baud, and co-piloted by Bernard Ziegler. Gordon Corps was the observer.

...but they wouldn't be the people doing the actual day-to-day work of engineering the systems and ironing out the bugs, as I said. Gordon Corps was the one with the real in-depth knowledge and understanding of the systems.

[vapilot2004]

So our friend M. Ziegler seems to be a bit of a Gallic Mr. Sutter - also head of engineering on another well known aircraft, although from what I have heard and read, Sutter was very hands on (nuts, bolts, and slide rules), often down on the floor solving engineering problems - although the story of the Sutter Twist, (the work-around that precluded a complete and very expensive redesign of the 747 wing) is admitted by Joe himself as being a group realization and effort.

In the video you linked, Mr. Corps covered the thing that most impressed me about the A320 FBW system - the autotrim function (nicely done in normal flight) extending out to an engine out scenario. Being a key engineering test pilot, I would imagine GP had not only extensive knowledge but indispensable feedback to offer on the system. I agree that it would have been nice to hear more from this gent, particularly (for me) the Anglo point of view on the history of the programme.

I will delve into our other discussion when the sun is over the yardarm and am mainly responding to thank you for your links and information good sir! :ok:

[DozyWannabe]

So our friend M. Ziegler seems to be a bit of a Gallic Mr. Sutter...
Hmm - kinda-sorta... As you say, Joe Sutter could and did act as a hands-on engineer for much of the 747 project, whereas M. Ziegler was more of a project manager/high-level concept man.

Being a key engineering test pilot, I would imagine GP had not only extensive knowledge but indispensable feedback to offer on the system. I agree that it would have been nice to hear more from this gent, particularly (for me) the Anglo point of view on the history of the programme.
Well, as you can tell from the video, GC was very adept at showing how the technology was there to assist pilots when manually controlling the aircraft, as opposed to the somewhat mangled press narrative popular at the time - which many people took to mean that the A320 was designed to be almost entirely flown under automation (an assertion which was utterly incorrect - the autoflight system on the A320 was no more intrusive than that of the B757/767).

One of the anecdotes I read regarding GC and the A320 was that when he encountered pilots who were somewhat sceptical of the technology, he'd invite them for a simulator ride in which he'd demonstrate the protections, explain why the technology was there to assist rather than hinder or replace and give the pilots a chance to pit their reactions against the EFCS. Which would invariably if not always end up with the systems demonstrating a significantly improved safety margin and the pilots walking away at least somewhat more convinced that the technology was sound. With 20/20 hindsight I think this was not only an apt example of understanding how pilots could best be won over, but also a very necessary counterpoint to the misguided reference to concierges which BZ became infamous for.

[EDIT : Managed to dig up the reference on here - first-hand, no less - http://www.pprune.org/rumours-news/433616-airbus-prepares-safety-warnings-following-a321-incident-7.html#post6117850
Partial quote:
I thought so too. Back in the late 80s, I got into a lengthy argument with Gordon Corps, an Airbus test pilot. I suggested a contest. We would each dive at the ridge, and when I said "Now" we would each pull, me at slightly under the 3.75 g ultimate and he at 2.5 g. Whichever one missed the ridge would win.

What I didn't realize (and Airbus didn't explain well) was that he could snap the stick back to the stop and get to 2.5 g's right now. I would have to ease the yoke back and would ultimately take a few seconds. Later ALPA promoted an evaluation and found that snapping the stick right back smartly actually had the airplane bottom out somewhat higher.
]

My time on this forum has been an invaluable learning experience in many ways, not just technical - one thing it has confirmed is that pilots do tend to be very protective of their professional pride and tend to react badly if that sense of pride is undermined. BZ seemed disinclined to take that into account, and the SNPL and press made hay with it.

[Winnerhofer]

Now here's what cars and planes have in common in France: WW
WW means unregistered / delivery.
Recent changes to French plates now have only one W.

[Winnerhofer]

[18 ÇÈÑíá 1988] 20 ÓäÉ Úáì ØíÑÇä Ãæá ÑÍáÉ ÃíÑÈÇÕ A320 (http://www.flyingway.com/vb/showthread.php?t=24882)