asynchronous sidestick
 

Hellos,

We have gone over this on the AF447 threads... I am trying to find out, is airbus the only manufacturer to have asynchronous sidesticks?

I understand that airbus is the only successful commercial jetplane maker to use side sticks.

What about other airplanes, i.e., fighters that use side sticks? Are they asynchronous as well?

As the resident FBW pioneer, here goes:

The F-16 stick inputs and manual trim inputs are summed. As the sticks are not mechanically connected, there is no feedback to the troop in the other seat ( family model). Besides, the sticks only move about an eigth of an inch to help with fine corrections flying formation. From the 447 thread, my understanding is the sticks move quite a bit, as they are not pure "force transducers" as in the Viper. But they, too, sum the two inputs.

No family models for the F-22 or F-35, so N/A.

Have to ask an F-18 troop how theirs work, as they have the basic control stick between the legs. They are also not 100% BFW as the USAF birds.

Same question for Concorde crews.

what's the whole point of them being asynchronous on the bus anyways? :*

Good point and excellent question.

As far as i know the Embraer Legacy 500/450 uses an asynchronous sidestick concept, however with haptic feedback in case of dual input. Which is quite different from the conventional controls on the E-Jet family.

Pretty obvious I'd say - it is far cheaper, less complex, and provides better redundancy than trying somehow to mechanically link them.

They are as noted electronically linked, albeit various modes to isolate one stick as required.

Some good questions here.

A lot of the functionality of the control input devices are part of the overall design philosophy for the FBW sytems.

Once the decision is made is to go pure FBW, then the human inputs implemented are a composite of the participating pilots in the design and the "dreams" of the engineers that think they can have a system that improves safety, reduces pilot/crew workload, accomplish the mission, etc. Sorry if I appear to have any criticism of the "engineers", but this opinion comes from a pilot that flew the first operational FBW system in USAF. Maybe Concrode prototypes were already flying, dunno. I only know that the jet should fly about as can be compared to what we were used to and what the average light plane pilot would expect. Basic flight laws that Wilbur and Orville figured out over a hundred years ago.

Several reasons not to have mechanical connections between the controls in the family models.

Imagine a failure that only allows one control stick to have the input to HAL.

Imagine a mechanical failure that locks both sticks!!!!

Imagine a situation where the troop who has a good awareness of what the jet is doing and the other troop is clueless. Think AF447.

Imagine a mechanical failure between the two controls that does not reflect what the other troop is doing.

And the beat goes on.


All I know for sure is that we never had a problem with the Viper implementation since 1973.

gums
If I have understood the system neither stick moved, so on the Viper also the PNF never knew what commands the PF was making, i.e. the Viper sticks are asynchronous in practice?

Concorde b.t.w. was electrically signalled but it was an analogue system with mechanical backup and conventional stick arrangements

I know you're on "our" side, Gums, but those scenarios are easily covered off:Same as happens with conventional joined controls: you work out which one's working and use that.

Breakout, like current designs.
Good! You don't have to tell him to do something "stuff the nose down you moron!" you just do it; he gets feedback thru his stick and might even snap him out of his clueless state, esp if it jams his finger against the panel! :ok:

Asynchronous sticks are merely an engineer's preference. Uh oh, here comes Dozy... :hmm:

I think the side sticks ( actually not side but between the legs joy sticks? ) on the C17 Globemaster 3 have feedback between the sticks??

Any C17 Pilots reading this??

@Capn Bloggs

Having said that it is an engineers preference... They have not just left the side sticks control to being just asynchronous.

They have taken the pain of having the 'Dual Input' call outs and the take over push button as well, wonder what is the school of thought that has gone in.

Also, I'm trying to find out if the other FBW airplanes with side stick have a similar take on it.

There's always a reason to madness as there's madness to every reasoning. Wonder why chose one over the other...

Capn Bloggs has cracked the code, heh heh. I was just offering the standard responses to those that wanted mechanically-linked controls.

And I 'spect Doze, et al, will chime in.

I discussed the stick implementation on the 447 thread because some folks thot that having 1) sticks mechanically linked and 2) being able to see what the other troop was doing could have helped the crew.

As I explained, we a) could not see what the other guy was doing, and b) it would not have made any difference because the sticks did not move! So we saw what the jet was doing and made appropriate inputs. As with the 'bus, we had a "take control" switch below the stick grip.

I always liked the force transducer implementation over a "position" design. Less to go wrong mechanically, 4 solid state transducers, and no doubt what the human command was if you relaxed pressure on the stick.

http://www.pprune.org/6790327-post2.html

For AF447 the nose came to its lowest when the the PF maintained full back stick, but none of the other guys could see the inputs ...

Think gums is referring while inside flight envelop and without 'STALLSTALL' in his ear.


Only after being high for about 90 sec, depleting airspeed (in view!) and 60 sec of 'STALLSTALL' without any appropriate input.

Except that the continuous STALLSTALL ceased when the CMD came back and that's also the time the PF applied full back stick for a 30 sec period.
Let me tell you that a fully visible control column fully aft deflected would have been the most shocking sight for that returning Captain.

Those sidesticks are not the best tool for CRM.

School of thought
 

I hope I will not be deleted once again on that subject?
The reason I see is the choice of using the C* law, piloting Nz and not speed. Not only A and B limit Nz (they called that "protection", and A managed a hard limitation when B managed a soft limitation), but A and B pilot their effective system to Nz=1. It attenuates low turbulence, and that is a commercial choice done with the engineer fantasm to reduce "noise" and to realize more than the pilots are able to do (competition between pilots and enginers).

The feedback in the closed loop in consequence modifies the result of pilot's stick input with the help of aerodynamic force of autotrim. In result nor A nor B can disconnect the autotrim.
And you put the Nz law equation in the feedback. Nz is not the speed but its derivative. The output Nz of the feedback goes bakwards to meet the pilot's stick want, both are compared in the sommator and difference is the "input" of the closed loop.
If you want to add the pilot's want (the stick position and tendances) the system must use use the same dimension than Nz that is acceleration L.T-² and no more speed. In the direct loop the first thing you have to do then is an integration of the input signal. You can watch that integration appears as the factor 1/s in the A333Zab old schematic, where "s" is the Lagrangian operator).

That integration logic operates and appears in the small movements of the stick described by PJ2 or Bubbers44 and gums and in the slow accumulated movement of elevator autotrim and in the fact that seeing the stick position (of both pilots) cannot be interpretated like classic position of sticks and control.

The Viper needs the Nz feedback to realize hard and high limitations needed by modern air combat uses, not to try to increase the crews comfort... with nz=1! They need other values of Nz that gums could modify with the thumb on the top of the stick, piloting himself Nz and not leaving Nz control to the effective system like A or B.;)

Could some of you (A, B, FBW fighter pilots, engineers, designers, salers) confirm? Thanks.

Airbus is the only successful producer of widebody and mid range commercial jet transports in the world that equips its planes with sidesticks.

"The only one" in this context actually represents 50% of world's successful commercial jetplane makers.

Airbus mechanically independent sidesticks enable people with scant knowledge and understanding of: a) flying in general b) way passenger aeroplanes are flown and operated c) Airbus FBW to provide some low quality entertainment by airing their unsubstantiated and wrong opinion on uncoupled sidesticks as if it were factual.

I suspected that replacement of wing warping with ailerons and body cradle with roll-articulated stick was first sign of decadence! :E

Seriously; there are folks who know quite a lot about how the jet transport should behave and their views are regarded most solemnly; we call them certification test pilots. They have taken a hard look at Airbus FBW and pronounced it airworthy. Lo and behold! A couple of decades and a couple of million flight hours later, their judgement has been vindicated by reality.

Except virtual one, prospering on anonymous internet fora.

Nope. Both troops were pretty clueless there. Rather think DLH incident where captain as PF was unaware his sidestick was reversed in roll polarity and unwittingly exacerbated the initial roll. Alert F/O did not know or had any reason to care what was capt doing to his stick; he has seen way too much roll way too low and taken the control as taught and trained. No damage, no injuries and it could have easily ended up with A320 cartwheeling through forest just off EDDF18. Think NOAR at Recife where conventional controls didn't make pilot aware what was wrong to stop pleas to clueless PF and take over so ended tragically just like Airblue at Islamabad.

Similar but far from same. Splitting the "conventional" control either through breakout mechanism or dedicated handle leaves you with half the control - the one that is not stuck. It gets interesting when uncoupling was unwarranted and you get each wheel driving its controls independently (Egyptair 990). OTOH, getting other stick out of equation through stick priority button leaves you with full control authority.

So what if they are. They are certified and in widespread use. No unsubstantiated anonymous opinion can change that.

Pretty reasonable and knowledgeable, I'd say. Please spare me going into long essay and just substantiate your opinions why you think "Dual input" and takeover button are unusual or unnecessary so I can deal with it shortly and precisely, provided you are taking TechLog seriously, which I estimate to be the case with about fifty PPRuNers.

The Airbus sidestisk philosophy suppresses valuable information to a PNF.
This is a reality documented also by the ... AAIB.
Are they also 'low quality entertainment' ?

Until such a time when reference is provided that unequivocally demonstrates BEA considers the Airbus sidestick philosophy is suppressing valuable information to a PNF, it might be.

Because Clandestino has decided the French BEA has to be the sole Reference ... ?

C17 is FBW but both sticks are mechanically linked.

Sorry, lapsus; should have wrote AAIB. Care to provide reference?

Wouldn't an "Iron Cross" flashing red on the largely blue FD have rung a bell or two?:}

Clandestino,

I urge you to please not think that I think I'm smarter than any of the airbus certification test pilots

Infact, I know it's the other way around :)

I merely want to understand why chose one over the other! The "Dual input" and takeover button are IMHO very good design, but they probably wouldn't have to incorporte them if they weren't asynchronous, right?


Just trying to understand this from people such as yourselves :)

AAIB Bulletin: 12/2008 G-DHJZ

Have a closer look at the relevant parts of the AF447 thread. The short version is that it was a "clean room" design. Believe it or not, airliner yokes weren't connected for the purpose of one pilot being able to follow through the other's inputs (strictly speaking that's only necessary on a trainer). They were connected in the days of direct cable control of flight surfaces, so that if something went awry, you'd have two sets of muscle force acting on the controls rather than just one. In today's airliners that are all-hydraulic, this feature is redundant. That's the main reason, but there are others.


What, you mean the French BEA who stated:

in the final report on AF447?

You're playing fast-and-loose with that ol' devil called context again. The AAIB performed that test on the A320 in isolation, which is reflected in the later statement:

What they explicitly do not do is compare the A320 setup with conventional controls in a similar test - I'd be prepared to bet that more often that not, the same scenarios in a B737 sim would have the same outcome.

Difficulty in determining what the other pilot is doing with the stick is a factor of the design, sure - but that's a known thing, and given the safety stats, it has not proven detrimental to safe operation of the aircraft compared with a more conventional layout. It'll always split opinion, but you can't argue with the numbers.

This is correct and was discussed in detail in the book "Understanding Air France 447", by Bill Palmer, who was an A330 Check Airman for nine years.

The moment both pilots give sidestick commands, a synthetic voice loudly and repeatedly announces "Dual Input", and a light in front of each pilot flashes. There is both audible and visual indication of conflicting commands.

I worked at an airport where a student pilot stalled a light plane and refused to release full back pressure, no matter how loudly the the instructor shouted. This was similar to AF447. Finally the instructor struck the student with such force it broke several ribs and he finally released the controls. The instructor recovered the aircraft so low the landing gear was broken, but they both survived.

When total mental confusion and panic takes over, it can make little difference whether the indication of control conflict is audible, visual or tactile.

Bill Palmer analyzes several cases where similar situations happened in Boeing aircraft, and the conventional control system did not prevent an accident. It's not a pro-Airbus book, but analytically and impartially studies all data related to AF447.

That's implicitly what they do by purposely setting the test on the A320 and not on an aircraft with linked flight control commands.
The Airbus sidestisk philosophy suppresses valuable information to a PNF.
That's explicitly what they mean by the following :

Again, context is key. I said they did not perform a similar *test* to the one they performed on the A320 sim with a conventional equivalent like a B737. The quotes are from completely different sections of the report.

Note the use of language - "might" and "may":
But the kicker is that this section is speculative - it would seem that if it were a BEA report you'd be admonishing the above section for lack of clarity. In this section they are talking about conversion training - not line flying, as the gist of the report highlights the fact that the PF was not, in their opinion, sufficiently well-trained to be on the line yet.

If you pay attention to the wording of the AAIB report, you'd note that when they refer to the actual *test* they did in the A320 sim, the TRE was explicitly instructed *not* to act as an instructor, but to behave as if he was a senior line pilot in the PNF role. They did not then perform a test in a conventional-layout sim for comparison and thus are not trying to definitively compare the two. Some would argue that the Turkish B737 accident at Schipol illustrates that conventional controls didn't make any difference, because neither of the training pilots noted yoke or thrust lever position despite both being of the articulated kind beloved by the anti-Airbus brigade.

Oh, and I noticed this earlier:
CB - this makes me very despondent, because there shouldn't be any "sides". For what it's worth, gums and I have had some very civil and enlightening chats away from the public boards and while our backgrounds differ, meaning that we approach the subject from different angles, there's no animosity there.

As far as I'm concerned, we're all in this to try to make flying safer. While I won't hesitate to call out positions that I know to be misunderstood or misinformed, I don't do so to get into a slanging match - in fact it upsets me when things deteriorate to that level.

Truth be told, if it were up to me I'd be all in favour of having you guys handfly as much as you want as long as it is safe to do so, and I'm all in favour of the industry compelling more sim training in the nuances of handflying - especially for those who have had less opportunity to do so on the line. More to the point, I have always held this position - take a random dip into my post history if you don't believe me!

Where my position differs from some is that I think it is counter-productive to get into the blame game, especially as far as automation is concerned. What I find especially saddening is the adoption of an "us and them" siege mentality, usually defined as a nefarious collusion of airline management, engineers and the dreaded "beancounters" versus pilots. At the very least it's not that cut-and-dried, and I for one don't think it's even true. As a techie and reasonably frequent SLF, I have no problem with the use of technology in terms of making your lives easier and civil aviation safer and more efficient. But I'm just as opposed as you are to misuse of that technology to drive down costs and deprive you of the ability to keep your basic piloting and airmanship skills well-honed.

Surely, by any reasonable measure that puts me on your "side", if it must be put that way.

The facts are:
In a "traditional" aircraft the relatively small control inputs will be sensed by the other pilot and he will react if necessary or will not react even if it's necessary and we will call this a human error
In the "non traditional" aircraft small control inputs will never be sensed by the other pilot and so he will not react even if it's necessary and we can not call this a human error

They will if the other pilot is doing his or her job - I've seen TREs do it in the sim with a combination of instrument scan and experience.

I'm a believer in force-feedback, coupled controls and so on but it does seem to be secondary to crew training/currency/experience. In the recent B777 Asiana crash at SFO, the PF must have had the control column well aft, against some fairly high trim forces for quite a while but no-one noticed.

That said, it appears you do have to be on your "A" game near the ground as a line trainer on the Airbus (going off others' anecdotes rather than personal experience...)

You're defending the indefensible.

As I was bumping down the (hand flown, "through" the FD:}) ILS last night I also thought of the incapacitation situation. If I was to become subtly incapacitated, it would become immediately obvious to my FO because the control column would stop moving or be not moving in accord with what was required, and well before any callable deviation occurred. On a "normal" approach, the control column is alway moving and is plainly visible to the other pilot. Not so a sidestick.

Dozy, I do respect you post a lot, mostly because they are well fundamented and I personally consider them a good source of info about the aircraft I fly, the Airbus. But please, stop thinking that because you read something it is like that. :ugh:

When somebody that ACTUALLY FLIES THE PLANE says something like "it is hard to see what the PF is doing on an Airbus" pause for a second and before coming back with what the Manual/Test/Simulator/Report says, consider that this person has been there for real and is telling you his real life experience.

You have already said that you are not a pilot, just an aficionado (and I must admit one of the better informed I have ever seen) and that´s OK but consider also that your situation has it´s limitations. You just don´t know what is REALLY happening up there. Real life is not the Simulator checkride, nor the manuals certification process, nor the nuances of a report wording...

I love the Airbus but I (as I´m sure many other pilots) can also vouch for the fact that it is EXTREMELY hard to know what the PF is doing on his sidestick, evenmore if we´re talking about small inputs. I´m not going to debate wheter it is right or wrong but I can tell you it IS so.

And please don´t reply with "I have seen an experienced instructor with excellent monitoring skills do so.." Just think about it for a while and maybe include it in your ideas about how Airbus and aviation could be safer in the future.

Cheers

Thanks for the heads-up. However, I have to take some pains to point out that what I'm saying isn't just coming from theoretical book learning, but also from long conversations I've had with pilots who fly the FBW Airbii. Many of them started out worrying about that aspect of the design, but quickly grew to realise it wasn't as much of an issue as they'd feared. Some never had an issue with it. Some still don't entirely feel at home in that flight deck - but acknowledge that it may be down to their own perceptions rather than the flight deck layout itself.

@CB - there's a flipside to the incapacitation scenario - namely that if your opposite number slumps over (or otherwise fouls movement of) the control column, then you have to shift their weight from it. In an upset scenario, that's going to be extra difficult, but in the FBW Airbus, you just push a button and it is no longer an issue.

As I mentioned above, Bill Palmer who has nine years experience as an A330 Check Airman discussed this in his recent book. He also flew the AF447 scenario in multiple commercial simulators, although dual control conflict was only one factor in that case.

He explained the issue isn't simply whether the async sidestick design makes it difficult to see what the other pilot is doing. Rather it's what material difference does that make, and in what situation. He said: "While it is difficult to see the other pilot's sidestick position, there is rarely a reason to."

Also, dual control input is enunciated by a voice warning, plus a warning light on the glare shield. In the AF447 case, both pilots were also pressing their "takeover priority" button trying to lock each other out. Each time they did this an additional red warning light notified the locked out pilot his stick was taken over, plus an additional "priority left/right" voice warning. They obviously knew the other pilot was interfering, else they wouldn't be fighting over the controls -- repetitively. In a mechanically linked system it would be a "force fight", or maybe it would degenerate to a fist fight. That would be better in some cases but how representative is that?

On the opposing viewpoint, see this critical history of the AirBus async control design and various steps taken to improve it: Pilots in the Loop? Airbus and the FBW Side Stick « Critical Uncertainties

Yes dozy, "might" and "may" are of circumstance to signify that the possibility does exit compare to to the unlinked sidesticks where such possibility simply does not.

... far from it according to the published data ... What are your sources ?

sides
 

Sides

I gotta tellya. Only "side" I am on is the one that emphasizes safety via airmanship. Of most incidents I have reviewed, most had more airmanship factors than design factors.

Except for my war experience, most fatalities I was close to were due to poor airmanship and not aircraft design.

Only "crew" jet I flew had a radar guy in the back seat and no dual controls. Only "override" he had was the ejection seat. And he didn't know what I was doing with the controls, only what the jet was doing.

I fully appreciate the inputs here from the "engineers" that have credibility from close contact with the pilots and also actual flying experience of their own. Nevertheless, I shall still maintain a position, or "side", that favors the pilot inputs to design of a jet.

I must admit that the roles and missions I flew necessarily flavor my bias, as my experience in the high performance jets is not akin to the commercial jets with a crew of two or more that are jointly responsible for the safe conduct of the mission assigned. Only exception was when I was the pilot-in-command in a family model.

My first 1,000 hours in a family model resembled the 1950's designs, about the time the jet was designed. Pure mechanical controls to the control surfaces and mechanically-connected sticks. The brakes were not "summed" and I had a tire blowout one day when the nugget in the other seat wasn't braking hard enough and my "extra" pressure locked up a tire and it blew! Caught a lotta flak for that one, heh heh.

My second 1,000 hours as an IP was in a single seater. I flew close chase ( figure 30 - 40 feet) and tried to figure what the nugget was doing with the controls. It was easy to see what his jet was doing with zero feel for his inputs. And I would make "suggestions". So my conversion to the Viper was no big deal.

The Viper was designed as a single seater, so not much thought as to connected sticks. When we got the family model, the engineers and pilots decided that we did not need to mechanically connect the sticks.. Further, that design would have been awkward, as the origianl design did not involve a stick that physically moved!!! Those things, and the first 40 or so models, had zero stick movement, including the family models.

I can fully appreciate the value of physical feedback as to what the other "crewmember" is trying to do. But I also question some of the actions of the "other" crewmember in accidents such as AF447 and the recent Asiana one. In both cases, I believe that just seeing what the jet was doing should have been enough to forcefully talk about or even take control. I can get a "feel" for the problems with crew coordination when things go to hell. But I cannot fully appreciate all the problems due to my background.

So my "side" is for super airmanship and to hell with the specific design of the jet, O.K.?

Through control feedback no, but the instruments and the view out of the window should work just as well. The use of "might" and "may" is also important in another sense, namely that they were unable to prove it one way or another - and based on the historical record it has made far less of a difference than some like to claim. The point the report was making is that taken in isolation, it is unwise to train a pilot on the line in an A320 if that pilot is not yet confident when it comes to approach and landing, and they should have that mastered in the simulator first. The report touches on the possibility of following through with conventional controls, but it does not directly compare the two - probably because even in a conventionally laid out flight deck, there should be no "follow through" necessary when training on the line. In normal operations, only one pilot should have their hands on the PFC in a control sense if going by the book.

As a general aside, I've just had a very entertaining read of Captain Richard de Crespigny's book on QF32. I won't link to it lest I incur the wrath of the moderators, but one of the aspects I found most interesting was this. Capt. de Crespigny is an ex-RAAF pilot who trained in Macchi fast jets, was posted to fly STOL Caribous, thence to Iroquois helicopters and back to Macchis as a training pilot, only missing out on F111s due to his age on transfer. He started his civil career flying 747 Classics, then the 747-400, got his command on the A330 and finally the A380.

Now with a CV like that I don't think it's possible to say anything other than he's a very experienced "pilot's pilot", and if such pilots are usually averse to the sidestick concept, he'd be at or near the head of the queue - especially given what happened over Singapore.

But he isn't. He admits to being a technophile (in fact he ran a software company with his wife in the late '80s and early '90s), but what he seems to be more than anything is a born nuts-and-bolts engineer (from his youth, putting old motorcycle engines back together). Rather than seeing the concept as antagonistic, he seems to have gone above and beyond in trying to understand the reasons behind it from the beginning - not just *how* it works, but *why*. He makes a point of stating that based on his own research the Airbus FBW concept was designed to *help* pilots, not hinder them, and he has nothing but positive things to say about his time on the A330 and A380.

The reason I'm summarising what I've just read is that it just goes to illustrate the dangers of generalisation. Ultimately your aircraft is a tool, and no matter what control setup it has, you'll get the best out of it by taking the time to understand it - and in doing so start (as best you can) with no preconceptions. By which I mean if you go into training or conversion to an Airbus FBW type with the belief that the FBW systems are there to hold you back, ignoring the fact that they're also there to assist you - then you're not going to get the best out of the aircraft you're flying.

EDIT:

Going back to the OP-
True enough, but as alluded to earlier they account for around 50% of the market at this point, because there are only two major civil airliner manufacturers in the West.

What needs to be understood is that even if you restrict your field of comparison to the US from the '60s to the early '80s, you used to have three airliner manufacturers (Boeing, McDonnell-Douglas and Lockheed), and even with all their products of the time having "conventional" control layouts, they all worked slightly differently, and a technique that worked in one type might have disastrous consequences in another.