>So, basically this was a reprise of the AF 447 crash at sea, where lack of clear command authority combined with a maddeningly poorly-thought-out UI resulted in a serious accident with loss of life.
I don't want to take this off on a tangent, but this theory of the AF 447 crash keeps getting repeated online despite the fact that the accident report did not conclude that the UI was a factor.
If it's got to the point where the pilots have lost track of who's flying the plane, are ignoring the (audible) "dual control" warning, and are making conflicting control inputs, the plane is probably going to crash anyway. Linking the sticks physically has potential safety downsides in addition to safety upsides (e.g. in the case where one stick gets stuck, or a incapacitated pilot holds it in a particular position).
See e.g. here for further info on sidesticks and safety:
With linked controls, the sane pilot at the controls would have immediately realized that the crazy one was fighting him, and it would have been brought to a swift end.
I know a lot of pilots and I don’t recall ever hearing one express the opinion that non-linked dual controls were anything other than idiotic. I’d personally be quite wary of ever flying such a machine. (Although of course the stuff I fly uses purely mechanical controls so there’s no choice in the matter.)
Once Bonin told them he had been holding the stick back the entire time, they immediately began a proper recovery, it was just far too late. This might have happened much, much earlier if the other pilot at the controls had been able to feel this.
What is your source for this? It does not seem consistent with sections 2.1.3.4-5 of the report.
In any case, the captain was not holding a stick when he returned to the cockpit, as both pilots were in their seats. So the captain could not have gotten any tactile feedback regardless of the stick design.
I’m not talking about the captain, I’m talking about the other pilot at the controls, Robert. He also held the stick back for some time, but he appears to have done this in the mistaken belief that the correct recovery procedure had been tried and failed.
That is an article in popular mechanics that contains a few excerpts from the transcript selected in order to make a particular point. The accident report gives a detailed description of the behavior of both pilots before the copilot entered (2.1.2.3).
One possible misconception here is that the copilot would have had his hands on the stick. It isn't normal for both pilots to have their hands on the stick. Only the pilot flying does -- for obvious reasons. At the stage where the problem developed, the copilot's attention, as the report explains, was mostly concerned with trying to interpret the ECAM warnings, and later with calling the captain. The idea that the copilot would have closely observed his own (hypothetically linked) stick and detected the problem, despite being fundamentally confused about what was going on, and having many more things on his plate, is little more than wishful thinking. The possibility cannot be conclusively ruled out, but there is no evidence that this would have happened.
I see that the first link I posted doesn't contain everything, but I don't see any major omissions either.
At 2:11:37.5, Robert takes control of the plane. According to the report, he pushed the stick to the left twice. Bonin then took back control. Figure 69 on page 96 of the report you linked shows Bonin's pitch inputs during this period. He applies near maximum nose-up pitch right as Robert takes control, and keeps it there. Robert would have felt this had the controls been connected, since he was attempting to control the plane at that time. The report says that Bonin quickly took back control, but the transcript indicates no communication regarding this, which makes it likely they were both attempting to control it for at least a brief period. That figure also indicates that at no time was Bonin's stick ever neutral, so it seems that he never stopped trying to fly the plane even when Robert was nominally in control. Without physical feedback, neither one seems to have realized this. No wonder they were confused about what was going on!
Figure 69 shows Bonin's stick inputs before Robert took control (and a few seconds after). As explained on p. 182 of the report, Robert pressed the override switch at this point and took control, so Bonin's stick inputs would have been ignored. Bonin then took back control by himself pressing the override switch. In effect, then, at this late stage, the pilots were fighting over the stick. If it had been a physical fight via linked control columns, the outcome would most likely have been the same. What can you do if the pilot and co-pilot just don't agree on the correct input, and neither is willing to yield to the other?
For context, all of this is happening at a relatively late stage. Recovery may still have been possible, but the problem developed when the PF was unambiguously in control and the PNF would not have been holding the stick.
There's a big difference between unknowingly fighting over the controls and knowingly fighting over the controls. If Robert had realized that Bonin was making the completely wrong control input then maybe he would have put a stop to it somehow. "Stop that, you'll get us all killed" is likely to be effective. He could have told the captain about it as soon as the captain arrived, rather than just before impact. Note that when the incorrect input was finally identified by someone other than Bonin, it was corrected immediately, it was just far too late.
According to the report, ~20 seconds after the events I described above, the plane was still above 30,000ft and recovery was still possible. Yes, the problem developed before this, but it sure looks to me that the bad control design was a major factor in the failure to correct the problem.
Whether or not they knew they were fighting is not quite the relevant bit. What's relevant is knowing what the other guy's inputs are. Given that the other two pilots were quite surprised once Bonin finally said that he had been holding the stick back the entire time, they clearly were not aware of this.
You say it's not so clear that this ever really happened, but it's pretty clear to me from the official transcript:
Robert: remonte remonte remonte remonte
Bonin: mais je suis à fond à cabrer depuis tout à l’heure
Captain: non non non ne remonte plus là
Robert: alors descends
Robert: alors donne moi les commandes à moi les commandes
My quick and dirty translation:
Robert: climb, climb, climb, climb
Bonin: but I've had the stick back all the way this whole time
Captain: no, no, no, don't climb anymore
Robert: then descend
Robert: then give me the controls, I have the controls
But look at what Robert says before the captain enters: "climb climb climb". He still didn't have a clue that the plane was stalled, even though this could easily have been figured out from the absolutely crazy combination of attitude, throttle setting, and rate of descent. It's the captain who's surprised by the stick being held back, not Robert. In fact, earlier portions of the trascript suggest that Robert was keeping track, more or less, of what the pilot was doing.
The captain entered when, according to the report, the plane was at about ~30,000 feet with a 40 degree angle of attack. The report states that "up until the end of the flight, no valid angle of attack value was less than 35°". It seems, then, that even once everyone was aware of what the PF was doing, a correct stall recovery procedure was still not initiated. Or perhaps the stall was already unrecoverable -- I don't know if airliners are designed to recover from such extreme configurations.
So, could linked sticks conceivably have helped before the captain entered? Probably not, because there is no evidence that Robert would have recognized that the stick inputs were inapporpriate, given that he was focusing on the ECAM warnings and appeared unable to grasp the implications of the readings from his primary flight instruments. Could linked sticks have helped after the captain entered? At that point, it was just a question of whether either pilot would take control and push the nose down. There's no way of designing the stick system to make sure that most sensible pilot ends up getting control.
What do you mean, it seems that once everyone was aware of what the PF was doing, a correct recovery procedure was still not initiated? Once they realized what was happening, in the bit of the transcript I quoted, they immediately initiated the correct recovery procedure. It was just much too late by then.
Before that, yes, Robert didn't realize the plane was stalled. But I would bet that this is partially due to having no idea what Bonin's control inputs were. One of the signs of a stall is stick back. If he didn't think the stick was back, he wouldn't think the plane was stalled.
In an earlier reply you wrote "Neither of the pilots in the cockpit ever figured it out" where "it" appears to be that they were fighting over control of the airplane.
I realize that this is somewhat unfair, in that your earlier statements are not part of the official report, but what indication would you expect to see that they were fighting unknowingly? There will not necessarily be evidence for it on the voice recorder, and especially in the "unknowingly" phase. The evidence would be in the pilots simultaneously making conflicting control inputs while the airplane was in the dual-control state, and IIRC, the data recorder did show that. Also, according to Langewiesche [1], 'Bonin, using his own priority button, and without saying a word, took control back. This left Robert with a sense that his side-stick had failed. He said, “Fuck, what’s going on?"' - i.e. the nature of the controls introduced additional doubt over what was happening, rather than that it was all a consequence of Bonin's actions (OK, so maybe there is evidence on the CVR.)
A similar situation (sustained, pilot-commanded stall) occurred in the AirAsia flight 8501 crash into the Java Sea.
While I agree that the nature of the side-stick control was far from being the primary cause of either accident, I am not convinced that it has been ruled out as something of a contributory factor.
There is also an entirely different user interface issue here: the stall warnings stopped when Bonin raised the angle of attack beyond a certain point (as the system no longer treated the data as 'plausible') and resumed when he lowered it.
To me it still sounds like physically linked sticks would have been helpful here, if the fundamental problem was that the pilots did not understand the situation. At 11:38, when this first "fighting over the stick" episode happened, Bonin held his stick fully back to the nose-up limit stop, and Robert was not aware of that fact. If the sticks had been linked, he would presumably have noticed it, which might have helped him make sense of the stall warning etc.
I guess it's still a bit of random luck that he actually took the controls for a moment here. Like you say, this was already at a late stage.
With physically linked controls, direct physical feedback will tell you if the person in the other seat is fighting your inputs. Without them, that doesn't happen, so any explanation for the aircraft not responding to your inputs is potentially valid.
Read the report. There is no simple answer to that question. It was a complicated and confusing situation, and the pilots in the cockpit made a number of mistakes.
It's the job of the UI/UX designers to make that less likely.
Like most air crashes, it took at least two things going wrong to make this one happen. Three in this case. Factor #1, a couple of morons were flying the aircraft. Factor #2, pitot tube icing. Factor #3, the aircraft was designed with certain unintuitive control features that depart from longstanding industry practices. The sticks that everybody's talking about were only one of those elements.
An arguable (if perhaps not politically-acceptable) conclusion is that if the pilots aren't sure who's doing what, the control system engineers and the pilots need to go back to school.
The report examined UX issues but didn't identify the side sticks as a significant factor. You can keep insisting that they were a factor if you like, but you haven't actually provided any evidence in support of that contention.
> I don't want to take this off on a tangent, but this theory of the AF 447 crash keeps getting repeated online despite the fact that the accident report did not conclude that the UI was a factor.
This is incorrect. The BEA report explicitly blames the lack of an AoA display and recommends that an AoA indicator be directly visible to the pilots. The aircraft already has sensors to measure AoA to feed the flight computers; asking for a direct readout of AoA is nothing beyond a UI change recommendation (and not fundamental aircraft re-engineering):
> It is essential in order to ensure flight safety to reduce the angle of attack when a stall is imminent. Only a direct readout of the angle of attack could enable crews to rapidly identify the aerodynamic situation of the aeroplane and take the actions that may be required.
The AoA invalidation logic ("mark AoA measurements as invalid if airspeed is less than 60kt") made the stall warning turn off as the stall became even deeper, making diagnosis of the stall more complicated. Worse, the BEA report states that the appropriate (nose down) control input led to the stall warning reactivating (since such an input would increase airspeed above the 60kt threshold -- inherent to a proper stall recovery), leading the pilot flying to reverse their control inputs and return the aircraft into a worse stall:
> A few seconds after the transition to alternate law, the stall warning sounded briefly, even though the PF’s inputs should have made this warning sound for several seconds. The reason for this is the drop in the measured airspeeds, some of which fell temporarily to below 60 kt, while the angle of attack reached 40°. Furthermore, the drop in measured airspeeds to values of less than 60 kt during the stall caused the repeated activation and deactivation of the warning which may have made it considerably more difficult for the Captain to effectively analyse the situation on his return to the cockpit.
> Several nose-down inputs caused a drop in the pitch attitude and the angle of attack, whose values then became valid, such that a clear nose-down input resulted in the triggering of the stall warning. It appears that the PF reacted, on at least two occasions, with a nose-up input, whose consequences were an increase in angle of attack, a drop in measured speed and consequently stopping the stall warning.
Lacking an AoA readout, the pilots would have had to reverse-engineer AoA from their extant instrument displays, the warnings they were presented, the "feel" of the airplane (is it buffeting? how is it responding to various control inputs?, etc), and past control inputs. Every one of those sources were degraded per the BEA report: they didn't trust (to the point of changing the selected inertial data source even if there was no indicated issue with inertial data) their instruments because of the airspeed inconsistency, the stall warning would reactivate every time they made the correct control input (the exact opposite behaviour of a stall warning simply based on an AoA threshold), and buffet might have been interpreted as overspeed buffet.
Expecting pilots to reverse-engineer the aircraft's warnings to guesstimate AoA -- a value that the machinery simultaneously measures and hides from the pilots -- is fatally bad UI (BEA uses the fancier term "ergonomics"), especially in cases when the flight computers deal with air data inconsistencies by forking over more authority to the pilots.
> The AoA invalidation logic ("mark AoA measurements as invalid if airspeed is less than 60kt") made the stall warning turn off as the stall became even deeper, making diagnosis of the stall more complicated. Worse, the BEA report states that the appropriate (nose down) control input led to the stall warning reactivating (since such an input would increase airspeed above the 60kt threshold -- inherent to a proper stall recovery), leading the pilot flying to reverse their control inputs and return the aircraft into a worse stall
This sounds extremely confusing indeed. Having this kind of inconsistencies under high pressure is something that would need a really experienced and steel-nerve person to handle.
> This sounds extremely confusing indeed. Having this kind of inconsistencies under high pressure is something that would need a really experienced and steel-nerve person to handle.
It's made even more confusing by the fact that the usual/sensical pilot approach to guesstimating AoA in an aircraft with a stall warning that is boolean (can only be sounding or quiet, nothing else) is to see where its threshold is. When you're right on the threshold (modulo some hysteresis) where the horn turns on and off, that's your stall angle, and pulling the stick back makes it stall more, pushing it forwards recovers from the stall.
Flipping the sense/polarity of the stall horn's semantics -- the effect of the 60kt invalidation threshold -- certainly contributed to making the upset recovery harder and more confusing.
In an aircraft that has multiple AoA sensors, I (and the BEA concurs) maintain that it is pointlessly cruel and baroque to make the humans try to guess what the AoA value is. AoA is no obscure technical parameter of interest only to avionics engineers, it's amongst the most crucial instrument readings, and it should be presented to pilots right next to their airspeed and attitude indicators.
If you're going to go against the conclusions of the accident report, which is very thorough, you'll have to do more than just assert that the side sticks were responsible.
First, I did not say the side-sticks are the fully responsible factor for the accident, but a contributing factor.
Second (and as noted in the parallel subthread), the BEA report does not include cockpit transcripts in section 2, 2.1, and relevant subsections, in describing the cockpit situation. It mentions specific utterances of the crew, but not in the specific context and sequence they occurred. Other reports do include these transcripts and from them it's highly probable that multiple inputs were being supplied, or that even if that was not the case it could not be ruled out readily.
There are multiple references in the BEA report of the level of confusion and complexity of the situation. The merits of scheduling the Captain's relief in the ITCZ crossing, the flight path itself relative to other aircraft which had diverted around the region, the loss of instrument readings, autopilot disconnects, multiple audio alerts, the disabling of a master alarm that wasn't clearly deliberate, the stated confusion of both co-pilots, the switching to and from "alternate law" of aircraft controls, and more.
Adding ambiguity of flight controls, feedback, and possible multiple inputs in the context of all of this again strikes me as, well, a disaster that actually happened.
In a description based on the full transcript:
02:11:21 (Robert) On a pourtant les moteurs! Qu'est-ce qui se passe bordel? Je ne comprends pas ce que se passe.
We still have the engines! What the hell is happening? I don't understand what's happening.
Unlike the control yokes of a Boeing jetliner, the side sticks on an Airbus are "asynchronous"—that is, they move independently. "If the person in the right seat is pulling back on the joystick, the person in the left seat doesn't feel it," says Dr. David Esser, a professor of aeronautical science at Embry-Riddle Aeronautical University. "Their stick doesn't move just because the other one does, unlike the old-fashioned mechanical systems like you find in small planes, where if you turn one, the [other] one turns the same way." Robert has no idea that, despite their conversation about descending, Bonin has continued to pull back on the side stick.
I've addressed the popular mechanics article in other comments. It's difficult to square some of its key claims with the description of events in the accident report. In particular, the report gives no indication that any of the three pilots successfully identified that the plane was stalled.
The fundamental issue here is that if only one pilot has his hand on the stick (which should always be true) then linked sticks won't help much, and if both have their hands on the stick (which triggers both audio and visual warnings on the airbus) then they are already fighting over the sticks, indicating a total breakdown of cockpit discipline. The author of the popular mechanics article appears to think that it's normal for both pilots to be holding their sticks at the same time.
It's also worth noting that a half-competent PNF could have looked at (i) the pitch attitude, (ii) the throttle setting and (iii) the rate of descent and concluded that the plane was stalled. The fact that the PNF never managed to integrate these three very basic pieces of information makes it seem rather unlikely that he would have paid close attention to the position of his (hypothetically linked) control stick.
Note that when the PNF took over the controls briefly, he made a lateral input rather than pushing the stick forward! (p. 183)
Finally, sidesticks don't really have "a position". The airbus is usually flown using short movements away from center with the stick then returning to the center.
Pilot error based on the actions of a single pilot, or even, in extreme cases, two pilots, might reasonably be attributed.
To have three pilots fail to grasp a situation central to principles of flight, and to have similar situations arise in other aircraft, suggests exogenous factors at play.
You've repeatedly made the case that multiple pilots fighting for control indicates a breakdown of cockpit discipline. You've failed to note that the pilots showed no awareness of such a conflict, or, further, that the stick-back position couldn't be readily identified by anyone other than the pilot applying that input.
You're insinuating that AF had three other-than-half-competent pilots in the cockpit, which raises numerous other concerns.
You're litigating use of the term "position" rather than the general understanding of "force feedback" which applies whether controls have a significant range of motion (traditional mechanical yoke) or a very short throw (sidestick).
In general, you're showing very little charitability to points of view differing from your own, which raises concerns.
It's clear from the available transcripts that there were only brief moments when both pilots were making stick inputs, as otherwise the "dual input" alarm would have sounded repeatedly. So it seems likely that for the most part, the pilots knew which of them was in control. That would makes sense, as there are clear audio and visual indications of this.
I have not been able to find any source other than the popular mechanics article (and its descendants) suggesting that there were extended periods of time where both pilots had their hands on their sticks and were making conflicting inputs.
Accidents almost by definition involve rare confluences of factors. This one seems to have involved two incompetent pilots in the cockpit, and a captain who came in too late to resolve the situation. Pilot error does happen. There have previously been accidents caused by pilot error when three or more people were present in the cockpit.
I'm not "litigating" the use of position. My point is that if you looked at the position of the pilot's stick, it would usually be in the center position, even if the control surfaces were significantly deflected. For example, if you push the stick forward and then let it return to the center, the plane will pitch down, and remain in that attitude until the stick is pushed again. To know the deflection of the control surfaces, you'd have to mentally track "number * length of forward movements - number * length of backward movements".
Great, the pages and sections are numbered, so it's easy to refer to the parts of it that support your theory. Or alternatively, you can direct us to whatever conflicting sources of information you believe are more reliable than the official accident report.
This theory isn't citing the report itself, but independent analysis that's been done on the same data. The Wikipedia article on the topic has a whole section for these [1], and a section about this theory in particular [2].
Furthermore. The official accident report for crashes is not always considered the authoritative source for what happened. One good example is EgyptAir Flight 990 which the official report claims is a mechanical failure [3], but which is widely considered to have been pilot suicide. In that case the Egyptian investigative body was thought to be politically motivated.
Similarly, it's not at all implausible that the French BEA would be reluctant to make conclusions that could result in the grounding of the entire worldwide Airbus fleet while they're retrofitted with Boeing-style controls while France is the main Airbus manufacturing partner country.
The theory is generally sourced from a popular mechanics article. There's nothing particularly authoritative about that "independent analysis". Goodness knows what you mean by the "same data". No third party has access to all the data recovered from the flight recorders and the wreckage.
>conclusions that could result in the grounding of the entire worldwide Airbus fleet
Concluding that the sidesticks were a contributing factor would not have resulted in the grounding of the fleet. That only happens in the case of extremely severe and extremely immediate threats to safety. UX tweaks would more likely just be included as recommendations. And in fact the report does make some UX recommendations, IIRC.
I think PM brought wide attention to it, but it's not like it's just some fringe theory of theirs, see e.g. this CBS report [1] from 2012 (after the PM article was published) with Captain Chesley Sullenberger (of the 2009 Hudson crash fame). Many aviation experts have weighed in on this.
Yes they don't have all the data, but they have enough to draw this sort of conclusion, including flight path, status of the plane at any given point, and the cockpit transcripts.
And true. Suggesting the fleet would be grounded was hyperbolic on my part. But I stand by my general point. Aside from happened in this accident, you're assuming that anything worthwhile to be learned from a given incident must be covered in the final report, or it must not be worth considering at all.
This expects too much of accident investigators, and doesn't account for the sort of institutional blindness that happens when everyone is used to things being done a certain way. Of course that was pilot error, two disconnected joysticks are just how planes are flown!
This wasn't the first case of an incident being attributed to Airbus's overdesigned flight controls, QF72 [2]. comes to mind.
Every Airbus crash gives rise to lots of FUD in the media. Initially, everyone was blaming AF447 on the vertical stabilizer breaking off (http://www.businessinsider.com/henry-blodget-air-france-447-...). I guess they thought they had "enough" data then, and of course plenty of "experts" were on hand to lend credence to this particular speculation. But anyway, the accident report says what it says. I see no reason to put more trust in random newspaper/magazine articles that just riff on a standard template for covering Airbus accidents (it was the scary computers what dunnit).
Equating initial media speculation not even 3 weeks from the crash when the black box was still at the bottom of the ocean with analysis done after all the data was in by industry experts in flight safety is absurd.
My point regarding the Business Insider article is that lots of pilots and other 'experts' were willing to give quotes to journalists back then, even though they knew nothing really about what had happened. Captain Sullenberger was hired by CBS as an aviation safety expert in 2011. He's expressing an opinion about the sidesticks that many other professional pilots disagree with (see e.g. the endless forum discussions on pprune). You can find pilots who support all kinds of wacky theories of various accidents. Sullenberger has a high profile (deservedly), and can get on TV.
The fundamental issues with Sullenberger's claim that the accident would be much less likely in an aircraft with conventional controls are (i) that there have been multiple crashes in such aircraft caused by unrecovered recoverable stalls (e.g. Colgan 3407, Turkish 1951) and (ii) that there is pretty good evidence from the transcript that the PNF was aware of the PFs inputs in any case. This forum post has a good summary:
I think it's wrong. If you think I am some kind of shill (?), then I guess it makes sense that you would be some kind of conspiracy theorist, given your unwarranted skepticism about the conclusions of the official report.
There is considerable informed and expert opinion voiced that the conflicting inputs were a potential issue. A fair bit of that discussed here. There are other instances of conflicted inputs. And despite considering numerous elements of confusion, uncertainty, and information overload, the BEA report doesn't even consider the matter.
This calls into question the report itself, the investigation, and the investigators. Such processes are not perfect and may be subject to political pressures (say:
EgyptAir Flight 990).
I've given the basis on which my skepticism is warrented. You've chosen not to accept it.
You insinuated that I had some kind of ulterior motive, in the same way that you are now insinuating that the accident report was a cover up.
As for expert opinion, could you give references? All I can find are articles in the popular press where a journalist emailed someone in the know to confirm that yes, indeed, Airbus control columns are not linked -- which is not a point in dispute.
There's a really simple explanation for why the accident report doesn't consider the issue of the control sticks not being linked. It just wasn't a significant factor in the accident, as far as anyone can tell.
If you have evidence of a cover up, you should provide it. The fact that the report did not draw the same conclusions that you would have drawn is not evidence of a cover up.
If you're willing to put your real name up here, then we can start speculating on who's being paid by whom to shill for what. Until then, I'll assume that you're on the Boeing payroll...
(I don't in general intend this account to be associated with my real identity, so I may remove the link above in a day or two.)
Fair enough. I'm a space alien cat, and choose not to disclose my identity online. Though I can assure you if I'm on Boeing's payroll, they've been severely delinquent in remittances.
That said, there might be a more productive discussion, perhaps in future, on linguistics rather than French aviation mishaps.
I'd call it an interpretation, not a theory. But clearly the conflicting inputs was a UI problem, and while there may be tradeoffs, a better UI could have prevented the AF 447 crash.
This really won't die. It's clear if you read the accident report (linked in another comment) that the plane was already doomed by the time that conflicting inputs were potentially a factor.
You normally can't stall an Airbus aircraft, except in cases where the flight mode changes as it did in this situation. This was a huge part of the problem, an emergency occurred and the pilots were effectively flying an aircraft they hadn't flown before.
Fully pulling back the stick is what you'd normally do in an Airbus to gain altitude. It's guaranteed not to stall the plane.
UI issues contribute to situational complexity, stress, ambiguity, and failures to respond appropriately to circumstances.
And whilst the BEA report ... rather inexplicably, frankly ... fails to mention the inputs issues, it does address all the other factors I've described here.
I don't want to take this off on a tangent, but this theory of the AF 447 crash keeps getting repeated online despite the fact that the accident report did not conclude that the UI was a factor.
If it's got to the point where the pilots have lost track of who's flying the plane, are ignoring the (audible) "dual control" warning, and are making conflicting control inputs, the plane is probably going to crash anyway. Linking the sticks physically has potential safety downsides in addition to safety upsides (e.g. in the case where one stick gets stuck, or a incapacitated pilot holds it in a particular position).
See e.g. here for further info on sidesticks and safety:
https://aviation.stackexchange.com/questions/14027/sidestick...