A320 Dual input and side-stick priority
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"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.
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.
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Active S/S
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.
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.
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Mr Winnerhoffer, is this your summary or is the above a cut and paste from a news article? 
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?
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?
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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.
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.
Last edited by DozyWannabe; 1st May 2015 at 03:41.
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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.
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 design absolutely requires the handling pilot to be the only one manipulating the controls at any given time.
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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.
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.
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Klopfstein
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.
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.
Last edited by Winnerhofer; 1st May 2015 at 21:32.
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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.)
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.
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:
(this is not a Caravelle, but this article (in French) - http://www.headupflight.net/lami/historique.htm - uses it to illustrate the point...)
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.)
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.'
[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:
(this is not a Caravelle, but this article (in French) - http://www.headupflight.net/lami/historique.htm - uses it to illustrate the point...)
Last edited by DozyWannabe; 2nd May 2015 at 00:30.
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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.
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Originally Posted by DozyWannabe
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 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 appreciate your expert knowledge of critical computing systems and otherwise find your posts informative.
Last edited by vapilot2004; 5th May 2015 at 04:12. Reason: Felt the need to add to the feel unit discussion
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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.
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?
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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).
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.
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.
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.
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.
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I don't know what the vendetta against the late Bernard Ziegler is all about.
More on him here:
Lifetime Achievement Award
@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"
More on him here:
Lifetime Achievement Award
@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"
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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.
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PK4
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.
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.
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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.
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.
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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).
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.
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.
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...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:
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.
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
And here's the man himself giving a tour of the A320's FBW systems during a test flight:
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 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.
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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. ]
[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. ]
Last edited by DozyWannabe; 29th May 2015 at 22:46.