asynchronous sidestick

[vinayak]

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?

[gums]

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.

[LouthGirl]

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

[con-pilot]

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

Good point and excellent question.

[Denti]

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.

[NigelOnDraft]

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

[gums]

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.

[CliveL]

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

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

[Capn Bloggs]

I know you're on "our" side, Gums, but those scenarios are easily covered off:Imagine a failure that only allows one control stick to have the input to HAL.

Imagine a mechanical failure between the two controls that does not reflect what the other troop is doing.
Same as happens with conventional joined controls: you work out which one's working and use that.

Imagine a mechanical failure that locks both sticks!!!!
Breakout, like current designs.
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.

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:

[nitpicker330]

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??

[vinayak]

@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...

[gums]

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.

[CONF iture]

I think the side sticks ( actually not side but between the legs joy sticks? ) on the C17 Globemaster 3 have feedback between the sticks??
http://www.pprune.org/6790327-post2.html

So we saw what the jet was doing and made appropriate inputs.
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 ...

[A33Zab]

Quote: Originally Posted by gums
So we saw what the jet was doing and made
appropriate inputs.



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


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 ...

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

[CONF iture]

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.

[roulishollandais]

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... 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.

[Clandestino]

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

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.

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

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 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.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.

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.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.

Same as happens with conventional joined controls: you work out which one's working and use that.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.

Asynchronous sticks are merely an engineer's preference.So what if they are. They are certified and in widespread use. No unsubstantiated anonymous opinion can change that.

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. 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.

[CONF iture]

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.
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' ?

[Clandestino]

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.

[CONF iture]

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

[zondaracer]

C17 is FBW but both sticks are mechanically linked.

[Clandestino]

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

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

[mm43]

Those sidesticks are not the best tool for CRM. Wouldn't an "Iron Cross" flashing red on the largely blue FD have rung a bell or two?:}

[vinayak]

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 :)

[CONF iture]

Care to provide reference?
AAIB Bulletin: 12/2008 G-DHJZ (http://www.aaib.gov.uk/cms_resources.cfm?file=/Airbus%20A320,%20G-DHJZ%2012-08.pdf)

The AAIB investigator carried out an assessment exercise in a full flight A320 simulator taking the role of a ‘trainee’ pilot, together with an experienced A320 Type Rating Examiner (Aircraft) (TRE(A)). The TRE(A) was current in both line and base training of pilots of all levels of experience.
Having briefed the TRE(A) that he should act as he would during normal operations, the ‘trainee’ flew normal approaches and landings, interspersed with approaches and landings during which deliberate handling errors were made. No prior warning was given to the TRE (A) of these errors.
In the first of these ‘unusual’ approaches, a manual approach was flown with autothrust, but the ‘trainee’ ceased to make sidestick inputs at 50 ft RA. The TRE(A) was unable to intervene in time and the aircraft struck the runway without a flare. In other ‘unusual’ approaches, the TRE(A) was again unable to intervene, or intervened too late, to prevent a hard landing.

[DozyWannabe]

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.

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.


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

What, you mean the French BEA who stated:

It is worth noting that the inputs applied to a sidestick by one
pilot cannot be observed easily by the other one

in the final report on AF447?

AAIB Bulletin: 12/2008 G-DHJZ (http://www.aaib.gov.uk/cms_resources.cfm?file=/Airbus%20A320,%20G-DHJZ%2012-08.pdf)

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:

Therefore, the aircraft demands a relatively high level of ‘assured’ skill from the trainee; their ability to land the aircraft correctly, consistently, should not be in doubt before base training commences, and certainly not in doubt during line training where passengers are carried.

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.

[joema]

"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 "

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.

[CONF iture]

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.
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 :

During the landing phase of flight, an instructor pilot monitors the approach by assessing the aircraft's performance, ie, by visually scanning both the flight instruments and the ‘picture' through the flight deck windows. In addition, in a ‘traditional' aircraft, where the flight controls are fully interlinked, the instructor might also be able to monitor the direction and magnitude of any, albeit relatively small, control inputs made by the student by sensing their movements in a tactile manner. By doing so, they may be able to prime themselves for the flare motion on the control column and, if the motion is late or absent, make an appropriate input in sufficient time to attempt to avert a heavy landing.

In a fly-by-wire aircraft fitted with sidesticks, the instructor also monitors the approach by assessing the aircraft's performance, but does not have an option of sensing control inputs made by the trainee. By the time it is apparent that no flare, or an incorrect flare, has been made, it may be too late for the instructor to intervene and the aircraft to respond before a possible heavy touchdown occurs.

[DozyWannabe]

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":
the instructor might also be able to monitor the direction and magnitude of any, albeit relatively small, control inputs made by the student by sensing their movements in a tactile manner. By doing so, they may be able to prime themselves for the flare motion on the control column...

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:
I know you're on "our" side, Gums

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.

[jcjeant]

In addition, in a ‘traditional' aircraft, where the flight controls are fully interlinked, the instructor might also be able to monitor the direction and magnitude of any, albeit relatively small, control inputs made by the student by sensing their movements in a tactile manner

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

[DozyWannabe]

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.

[FullWings]

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...)

[Capn Bloggs]

They will if the other pilot is doing his or her job
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.

[RunSick]

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

[DozyWannabe]

When somebody that ACTUALLY FLIES THE PLANE says something like "it is hard to see what the PF is doing on an Airbus" ... consider that this person has been there for real and is telling you his real life experience.

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.

[joema]

"When somebody that ACTUALLY FLIES THE PLANE says..."it is hard to see what the PF is doing on an Airbus"...consider that this person has been there for real and is telling you his real life experience."

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 (http://criticaluncertainties.com/2011/09/16/pilots-in-the-loop-airbus-and-the-fbw-side-stick/)

[CONF iture]

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.

[CONF iture]

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

[gums]

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.?

[DozyWannabe]

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.

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

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.

[CONF iture]

Through control feedback no, but the instruments and the view out of the window should work just as well.
That's the point, one way to evaluate has been withdrawn.

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.
AAIB did not have to prove anything, they just mention that what is possible with a more conventional cockpit layout is not with an A320 concept.

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 point the report is making is that what would be unwise to do in a conventional cockpit layout is especially unwise in an A320.

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.
If dozy knows better than the AAIB ...

In normal operations, only one pilot should have their hands on the PFC in a control sense if going by the book.
Because "following through" means just that "following through"
Who said "controlling" ?

Anyway, are you really in the best position to comment on what's happening or should be done or not on a flight deck ... ?
Some guys around have Experience you know ... they can make such statements if they wish.

[Checkboard]

based on his own research the Airbus FBW concept was designed to *help* pilots, not hinder them,
It was designed because it is cheaper than conventional controls, and because they wanted a unique selling point. All of the "protections" are there as a simple requirement to overcome the drawbacks in the no-feedback concept - not included to help pilots.

[aerobat77]

you have just to accept that your stick and the stick of your buddy may perform differently.

[DozyWannabe]

If dozy knows better than the AAIB ...

I didn't say that... But on the other hand I think we're reading different things in the report. I can see the brief mention of conventional controls, but I can't see the AAIB mentioning anywhere that conventional controls are better - you're reading your own position into it.

Anyway, are you really in the best position to comment on what's happening or should be done or not on a flight deck ... ?
Some guys around have Experience you know ... they can make such statements if they wish.

Of course they can, and I'd never presume to tell them not to. However, they must also accept that their position is not universally held, and the number of pilots who are happy with the Airbus layout is not just confined to the younger generation, but also top-drawer ex-mil veterans of the kind they refer to as "real" pilots.

It was designed because it is cheaper than conventional controls, and because they wanted a unique selling point. All of the "protections" are there as a simple requirement to overcome the drawbacks in the no-feedback concept - not included to help pilots.

That's a bit cynical. In fact, the R&D costs of developing the control system were pretty massive and had been ongoing since the '70s. They're easier to maintain and provide weight savings, certainly - but the main reason (as I've said before) was the potential for unprecedented flight deck commonality between types - in the sense that conversion across the range from the A320 series through the widebodies up to the A380 is massively simpler (and thus more straightforward and less expensive) than for any of their competitors.

The protections do far more than overcome the drawbacks, particularly in terms of offering safe manoeuvering authority across the full range of control inputs, useful in avoidance of terrain and mid-air obstacles.

you have just to accept that your stick and the stick of your buddy may perform differently.

Indeed - it's not about size, it's what you do with it that counts (or so my wife reassures me... :E)!

[gums]

One mo' time

We have returned to many discussions from the AF447 thread.

Once the decision is made to move from a control stick/wheel that provides mechanical connections to the jet's control surfaces, we must consider the implementation of the controls.

We went thru this in the 50's when hydraulic valves at the base of the stick/wheel controlled pressure to actuators out on the wings or tail. Many commercial jets maintained actual mechanical linkages to the control surfaces, and maybe a few still do. By 1960, only a few military trainers and older designs did that. All we had were valves at the base of the stick/wheel to control pressure to the control surface actuators. Control feedback was extremely artificial, as using springs!!!! No aero force feedback whatsoever. One jet used a bellows to help with backstick pressures in order not to over-gee the plane. But that went away by the 70's.

Then we came to FBW.

Do we mechanically connect dual-control jet sticks/wheels? Do we implement some kinda feedback as to how much we pilots are commanding of the control surfaces? Do we use a stick that moves or simply use stick pressure? and the beat goes on.

And then we had the "protections" and the autopilot and autothrottle connections to our flight control systems. GASP!!! To this day I am amazed at all the modes and control laws of the systems in operation today. Even a techno-geek pilot such as myself gets confused. And make no mistake, I would appreciate a simple control law that closely resembled what we had in the "old days", like late 60's. Heh heh. This would still require electronic analogs to the old hydraulic valves and feedback springs and such that we had. Hence, we have "gains" that limit control surface rates and total movement depending upon dynamic pressure the jet is experiencing. So only a so-called "direct" control law would resemble the "old days", and even then such an implementation could have problems with over controlling.

From my point of view, mechanically connected flight controls in family models seem like a good idea most of the time. But we still have to engineer the electronic connections to the jet's flight control system. Failure modes and "who has control" issues come to mind. I can tellya that I "helped" many a nugget land during severe turbulence/crosswind landings in one of the "old" systems. Then did same in a FBW system with zero control feedback from the jet or the nugget in the other seat. Know what? No difference. The AF447 situtation was different, and I believe that control position feedback might have made a difference in the PNF reactions ( although he mentioned a few times "we're climbing", etc).

As with Asiana, et al, it's up to the "pilot in command" to harp on the nugget and/or take control himself when things aren't going right. Regardless of the control implementation, it's up the aircraft commander to do as much as possible to ensure a safe recovery from an unusual situation or a sloppy approach or...... This requires knowing what the jet is doing versus what it's supposed to be doing, no matter what the "other guy" is doing. There should be a clear chain of command, and if the aircraft commander decides to take action, then it is mandatory to do so regardless of the rank or experience of the other guy. Any objections to that point of view?

[DozyWannabe]

We have returned to many discussions from the AF447 thread.

Oh gums, if only that were true. This particular back-and-forth has been going on since long before I joined this forum. I suspect, sadly, that it will continue for some time to come - as the subject acquired a political dimension very early on.

This requires knowing what the jet is doing versus what it's supposed to be doing, no matter what the "other guy" is doing. Any objections to that point of view?

Absolutely none, and I couldn't have put it better myself.

There should be a clear chain of command, and if the aircraft commander decides to take action, then it is mandatory to do so regardless of the rank or experience of the other guy.

History tells us that being too rigid here can bite us badly - I'm thinking of examples such as Tenerife in 1977, Birgenair 301, Palm 90... to name a few off the top of my head. I'd agree that the aircraft commander carries ultimate responsibility, and as such makes the final call - but only in split-second life-or-death scenarios should that call be unilateral, because your colleague may have spotted something you haven't. The book on QF32 shows Aussie-style CRM at its finest, and Capt. de Crespigny is not ashamed to admit that his first ideas were not always the best.

EDIT:

You do bring up some interesting points though, so let's have a look-see.

To the best of my knowledge the only airliner types still being used in significant numbers to retain a cable-to-surface connection (albeit for backup/manual reversion only) are the various B737 models, and the DC9/MDx0 derivatives. The design trend since the '70s seems to have been more in favour of engineering greater failsafes into the hydraulic system than cable-based reversion. This was unavoidable for widebodies, as the forces required to move flight surfaces of the required size are way beyond human muscle power. As to why this translated to narrowbodies, I can only speculate - but I do remember reading an interview with the Aloha 737 Captain who stated that flying the 737 in manual reversion almost completely exhausted him physically.

So it would seem that one benefit of beefing up the hydraulics means that the controls would behave in a manner to which the pilot is more accustomed. This is also the reason for the existence of Alternate Law. On the AF447 thread, people seemed to get bogged down in the minutae and making things seem more complicated than they are. There are three control laws in the Airbus system - Normal (which very few Airbus pilots will ever leave outside of a sim check), Alternate and Direct. There is only one Alternate Law, but it has various submodes depending on the type of failure that caused the degradation - the specific submode is largely academic, because the purpose of Alternate Law is ultimately very simple - and that is to work around the failures to provide as close to Normal Law behaviour as possible. Direct Law only engages in the air in the event of multiple serious systems failures - going back to the example of QF32, they were down to 50% of their electrical systems and 25% of the hydraulics with significant damage to the fuel system and holes in the starboard wing - even with all that, the control law they degraded to was still Alternate.

[Checkboard]

That's a bit cynical.
Not cynical in the slightest. It was stated as fact in a nice airbus animated presentation at the beginning of the endorsement.

... and if you think about it - building aeroplanes is a business, and that's all it is. The airbus system is cheaper and saves operating costs. That's why they did it, and that's how they sell it to buyers.

... the problems start when someone starts "selling" the concept to pilots with rubbish about how safe it is and how you can't stall an airbus.

[CONF iture]

This requires knowing what the jet is doing versus what it's supposed to be doing, no matter what the "other guy" is doing.
The jet is supposed to be doing what is commanded by the PF but when the PNF is not aware of the PF inputs ... something is missing, something nice is lost.

I can see the brief mention of conventional controls, but I can't see the AAIB mentioning anywhere that conventional controls are better
Because the mention is not such. The mention is linked flight control commands allow things that unlinked FCC don't. That's something you don't have the experience to appreciate and you don't accept it to be mentioned.

[gums]

I have to agree with Conf.

If you are forced to fly a "crew" jet with dual controls, then having the visual and mechanical duplication of control stick/wheel is one addition to "awareness".

The implementation of such systems will be more complex than what the 'bus has, or the Shuttle or the Viper that I flew. Nevertheless, I can appreciate the added awareness factor.

All that being said, I still have a problem with several accidents where basic airmanship played a larger role than mechanically connected controls.

[DozyWannabe]

Hey gums,

If you are forced to fly a "crew" jet with dual controls, then having the visual and mechanical duplication of control stick/wheel is one addition to "awareness".

Agreed. However, looking dispassionately at recent civil aviation history it can be argued that said addition is of limited benefit in a two-crew airliner scenario.

CONF is right when he says that the non-linked controls do not allow for "follow-through" in the training scenario, and he's also right when he says this makes the FBW Airbus require a very strict interpretation of when a pilot transfers to line training in that he or she must be consistently competent in terms of handling the aircraft before being signed off for the line. However, if I understand modern airline ops, then that prerequisite is mandatory even with conventionally-controlled types. I suspect that if, say, a landing was performed in which a follow-through became necessary, then both the training Captain and trainee would be summoned for tea and biscuits, with the former being required to explain why they let the trainee proceed to that point.

As we're both painfully aware, a recurring theme in the AF447 discussion was the argument that if the controls were connected, the PNF would have been able to see the errors made by the PF and taken control. This is countered by the fact that the same scenario has cropped up several times on types with conventional controls - and the PNF either did not see what the yoke was doing or ignored it, resulting in a crash.

The implementation of such systems will be more complex than what the 'bus has, or the Shuttle or the Viper that I flew. Nevertheless, I can appreciate the added awareness factor.

Well, the T7 and 787 have FBW implementations with software-driven force-feedback, and yes - both systems are way more complex than that of the Airbus FBW types. But there are already differences in how the systems in the two aircraft operate vis. commanding rate vs. deflection - such differences would be anathema to Airbus's original goal of having the whole family of aircraft behave as close to identically handling-wise as possible.

I suspect that all of this would have been a non-issue had the subject not acquired a political dimension early on. The idea that the transition to sidesticks was a physical embodiment of the reduced role of the human pilot and increase in automation seems to be as widespread as it is inaccurate. The sidestick concept was being tested on a Concorde airframe years before the launch of the B757/767, which was when digital FMS became truly mainstream. We might have even seen sidesticks as an option on the T7 had United, the launch customer, not vetoed it.

All that being said, I still have a problem with several accidents where basic airmanship played a larger role than mechanically connected controls

Indeed - and truth be told there has not as yet been a single accident in which connected controls could definitively and provably made a difference.

[jcjeant]

Paraphrasing Gums I can say ..
All that being said, I still have a problem with several accidents where basic airmanship played a larger role than mechanically or not mechanically connected controls
And paraphrasing Dozy I can say ..
Indeed - and truth be told there has not as yet been a single accident in which connected or not connected controls could definitively and provably made a difference.
So that being said and accepted as irrefutable facts ! .. it is obvious that there is one who handles these commands that will be able to make the difference between a flight that ends normally or crash
Conclusion .. the problem is more than often the pilot(s) :}

[DozyWannabe]

Conclusion .. the problem is more than often the pilot(s) :}

No, jcj - not at all. It could be any number of things from insufficient or improper training to poor application of procedures, fatigue... the list is very long!

[jcjeant]

improper training to poor application of procedures, fatigueFatigue = pilot problem .. not aircraft problem
Poor application of procedures = pilot problem .. not aircraft problem
Improper training = pilot problem (pilots are trained by pilots) .. not aircraft problem
Exactly what I said ... the pilot(s) :}

Or if you want ...
Fatigue .. you don't drive a car with fatigue as you will fell asleep and have accident
Procedures ...You must respect the traffic laws or you will have accident
Training .. You must go to driving school and have a driving license .. or you will have problems
So ... the driver is the problem .. not the car ...

[DozyWannabe]

Exactly what I said ... the pilot(s)

Not at all - if the pilots have not been trained or briefed properly - or if they have been put in a position where safety is compromised and have been coerced into flying anyway, then at least some of the responsibility lies with the airline.

So ... the driver is the problem .. not the car ...

A car is usually a personal mode of transport - most drivers are not employed to do so.

[Cool Guys]

There are 2 aspects of this argument going on at once:

1. Asyncronous side sticks verses conected yokes based on crash statistics/reorts.

2. Asyncronous side sticks verses conected yokes based on pilot's evaluation/preference.

User feed back (pilots in this case) is very valuble when evaluating a concept.

[jcjeant]

Not at all - if the pilots have not been trained or briefed properly - or if they have been put in a position where safety is compromised and have been coerced into flying anyway, then at least some of the responsibility lies with the airlineIf you are a person who considers himself a responsible professional and intellectually honest .. you never accept or do what you explain above
However, if you agree ... you do not need excuses or loopholes and must agree to be designated as responsible if anything happens because of you

In my professional life I have been sometime (exceptional) forced to do things contrary to or not in keeping with the rules .. and always by verbal way (as always happens)
I always said I wanted it to be postponed by a written order signed by a senior or responsible person ...
It has always been told that they were going to study another way to do the job and so what they had asked was canceled ...
I've never had to suffer because of this trouble

[Jwscud]

Doze, have you had the opportunity to jumpseat at all?

I think if you were to jumpseat on a few line training flights for example or a base training session (simulator even) it would really help you understand what a lot of people are trying to get at.

(Sadly, I'm not in a position to offer such a thing or I would)

[FANS]

The snag with side sticks is training.

With the explosion in new 200 hours cadets straight onto an A320, it would make things a huge amount easier if there were moving side sticks so you could feel what forces were being put on at the earliest possible stage.

When you have more experienced crews, I think it is much less of an issue and the additional complexity and more to go wrong argument probably wins. The problem has been that our training is 200 hours then in the RHS, and for the first few hundred hours it's much more difficult for the RHS and LHS.

[gums]

Guess we have to have a few here that have flown the mechanically-connected sticks/yokes as well as the system implemented in the 'bus and the last jet I flew, where there was no visual or force feedback as to what the nugget in the other seat was trying to do.

I fully appreciate the views of those who make the point that "feedback" between the dual controls can make a difference. OTOH, with many, many circuits flying close chase in single-seaters, and then in the family model of the Viper, I can tellya that seeing and feeling what the jet is doing compared to what it is supposed to be doing counts a lot more than the connected flight controls.

The engineers will say that everything was working as designed, so why the crash?

I maintain that basic airmanship counts more than all the "protections" and AP modes and auto-whatever. The recent SFO crash showed how a seemingly perfect system, operating as designed, cannot protect a careless or whatever crew. I also see a trend in the AP/FMS/FLCS connections that do not help the credw when various sensors or malfunctions come into play.

We must have some common core flight control logic and autopilot logic and such to depend upon when things go wrong. Made my case on the AF447 threads, so 'nuff said. Asiana sems to confirm my beliefs.

If the law would allow ( too old to do it legally now, heh heh), and we had two planes with good comm between us, I would take any pilot up and fly chase, do patterns, and land successfully.

[Clandestino]

I've said it many times before but I'll guess it's not the last time I will repeat: if you are not familiar with basic flying, electronics and airline ops, your chances of correctly understanding the Airbus FBW are close to nil. If despite unfamiliarity with aforementioned you still have the urge "to know" about the uncoupled sticks it is very easy to satisfy it by believing folks claiming to be experts while airing theories that only show they either have never got into transport cockpit or enjoy misleading others.

Uncoupling the sticks is not an issue because when it comes to transports only one pilot can be in control at any time, be it left, right or auto. Grabbing the wheel from your cockpit significant other or "helping" him/her is not an usual, approved procedure (there is good reason for it) and can be used only in extremis and for very limited period of time. Also algebraic sum of sticks nicely replaces the rigid coupling; as simple spring makes displacement proportional to force the effect is the same as if two pilots were fighting over coupled controls.

Both AAIB and BEA noted it is not possible for assisting pilot to know what inputs the handling pilot makes with coupled sticks. Neither made any conclusion or recommendation regarding it; most of the interpretations of their position you could read on this thread are pure conjecture. It might come as news to some but while you are flying stable and not particularly maneuverable aeroplane with relatively large weight and C.G. range, it's not just amplitude of your colleague's across the cockpit inputs of concern to you, neither is your own when you are PF. How much pull? Just as much as it is needed and feedback is not through wheel/stick, it is from aeroplane's attitude as observed on AH or through windshield.

Artificial feel is not there to help you feel speed error, it is designed to a) prevent you from ripping your aeroplane apart through overload or killing passengers (http://aviation-safety.net/database/record.php?id=19990914-2) at high speed b) have reasonable forces and maneuverability at low speed maneuvering e.g. landing. If aeroplane gets mistrimmed, pilot trying to get the aeroplane to proper flying speed will have to fight the stick forces while retrimming. No need for a lot of imagination to understand what happens to pilot firmly believing he can feel speed deviation through wheel. Thomsonfly at Bournemouth might provide some clue.

That Airbus is unstallable is early marketing hype turned into libel. No such claim can be found in FCOMs or derived from them, at least by the reasonable and knowledgeable pilot. Airbus FBW has very clear architecture, modes of operations, operating procedures and limitations. Those unable to cope with it are welcome to air their inability to understand it on PPRuNe but shouldn't be type rated. In ideal world, that is.

200 hours wonders made their way into multi engine heavies' cockpits since at least WW2. Except the hype, there is nothing out there to suggest that they were inadequate in their role or that those who couldn't cope with basic items, such as flaring to land at 10 hours could somehow be magically taught at 200, in heavy. Type rating course just shows you the difference between flaring 172 and 777. In the days of yore, it was done in 6 circuits. I don't see folks who made their first landing in type on line after ZFT bending airframes a lot, can anyone?

As there are a few folks who managed to keep the bus within protection limits and still wreck it and LoC accidents are fortunately rare even on unprotected aeroplanes, protected FBW was not made mandatory on passenger transports. As what you read about it on PPRuNe is mostly untrue, it is not banned or Airbus was asked to redesign it either.

[Capn Bloggs]

Grabbing the wheel from your cockpit significant other or "helping" him/her is not an usual, approved procedure (there is good reason for it) and can be used only in extremis and for very limited period of time. Also algebraic sum of sticks nicely replaces the rigid coupling; as simple spring makes displacement proportional to force the effect is the same as if two pilots were fighting over coupled controls.
"I say again, AF447 was not an "in extremis" accident." It was a "usual, approved" procedure so there was absolutely no need for the PNF to either see, "grab the wheel" or "help" the PF, who was in the normal process of crashing the aircraft. :cool:

What's all this Dozy and Clandestino codswallop about the horrors of grabbing the (real) stick off the FO if he can't cope?? So what if I take over? If I was flying with 200hr FOs, I would expect to occasionally.

[rudderrudderrat]

Hi Clandestino,
No need for a lot of imagination to understand what happens to pilot firmly believing he can feel speed deviation through wheel. Thomsonfly at Bournemouth might provide some clue.
Since the autopilot was engaged during that approach, why do you think the crew could "feel" the speed deviation through the wheel with the AP trimming the stab?

From AAIB http://www.aaib.gov.uk/cms_resources.cfm?file=/3-2009%20G-THOF.pdf" Within 1.5 seconds the stick-shaker (stall warning) activated and in the following two seconds the thrust levers were advanced to the full forward position. The autopilot mode changed from localiser and glideslope to Control Wheel Steer (CWS) pitch and CWS roll."

Both AAIB and BEA noted it is not possible for assisting pilot to know what inputs the handling pilot makes with coupled sticks.
Do you mean "uncoupled sticks"?

Why do Airbus still fit coupled rudder pedals? Why not save weight and complexity with uncoupled rudder bars?

[CONF iture]

Also algebraic sum of sticks nicely replaces the rigid coupling
Absolutely un recommended procedure.
Should never take place.
Anything but nice.
Where have you been ?

[DozyWannabe]

What's all this Dozy and Clandestino codswallop about the horrors of grabbing the (real) stick off the FO if he can't cope?? So what if I take over? If I was flying with 200hr FOs, I would expect to occasionally.

Er - neither Dozy nor Clandestino argued against taking control from an FO out of their depth, or anyone else for that matter. The point is that whether in a conventional or Airbus FBW layout, such a transfer of control must be done correctly - with "I have control/My aircraft" etc., in conjunction with a "Go Around" call if necessary. Simply yanking on the primary flight control without warning is a very risky thing to do with any type of control layout - as I'm sure you well know - because it runs the risk of startling the pilot in the opposite seat which in turn risks an unpredictable outcome.

Why do Airbus still fit coupled rudder pedals? Why not save weight and complexity with uncoupled rudder bars?

I suspect you know why - because the absolute worst-case scenario in terms of control reversion in a FBW Airbus is manual trim only in pitch and rudder. Tying the THS and rudder control into the digital flight control system exclusively would remove that last fail-safe.

As with conventional types, the coupling of the rudder and trim controls is a side-effect of the electro-mechanical implementation - and it's the one aspect of control in which combined muscle power might still have an effect in terms of expediting the required control input.

Absolutely un recommended procedure.
Should never take place.

True, but it's also true in conventional-layout ops. Unannounced manipulation of the controls from the opposite side is risky, as I said above - and you must know that when going by the book, "follow-through" has no place in line ops, even line training. It should not be necessary in anything other than trainers and the simulator.

[Capn Bloggs]

Er - neither Dozy nor Clandestino argued against taking control from an FO out of their depth, or anyone else for that matter.

I never even implied that you did. Let me remind you what you said:

I suspect that if, say, a landing was performed in which a follow-through became necessary, then both the training Captain and trainee would be summoned for tea and biscuits, with the former being required to explain why they let the trainee proceed to that point.
The "horrors" of it all! Tea and bikkies, explanations required! The reality is nothing like what you hypothesise.

with "I have control/My aircraft" etc., in conjunction with a "Go Around" call if necessary. Simply yanking on the primary flight control without warning is a very risky thing to do with any type of control layout - as I'm sure you well know - because it runs the risk of startling the pilot in the opposite seat which in turn risks an unpredictable outcome.
It's a shame you don't fly RPT two-crew, Dozy. You'd realise it normally doesn't work like that in the scenario the discussion is alluding to.

and you must know that when going by the book, "follow-through" has no place in line ops, even line training.
And where did you drag that gem up from??

[CONF iture]

True, but it's also true in conventional-layout ops. Unannounced manipulation of the controls from the opposite side is risky, as I said above - and you must know that when going by the book, "follow-through" has no place in line ops, even line training.
Why you keep making such statements on things you absolutely have no experience on is a mystery to me ...

Tying the THS and rudder control into the digital flight control system exclusively would remove that last fail-safe.
Then hurry up to give a call to Airbus, rudders have now moved to the fully digital era ...

[Clandestino]

Since the autopilot was engaged during that approach, why do you think the crew could "feel" the speed deviation through the wheel with the AP trimming the stab?I don't. I took it just as an illustration of out of trim forces (which are usually but not necessarily introduced by autopilot), also significant was inability of the crew to immediately use manual trim to prevent nose from rising, which would not be issue with autotrim.

Do you mean "uncoupled sticks"?Yup, sorry, my mistake.

Why do Airbus still fit coupled rudder pedals? Why not save weight and complexity with uncoupled rudder bars? No savings there. Airbus was into preventing the pilots from going aerobatic since A300 - it is called flight augmentation. It is easier and cheaper to introduce limits into FBW than classic controls, that's why we have FBW since 320. Whether mechanical or electronic, rudder is just rudder, it's used for decrab and engine failures so no need to have sideslip protections as long as the pilot has some idea what he should be doing. If he keeps being clueless for prolonged period of time, even protections will be unable to save him.

I suspect that if, say, a landing was performed in which a follow-through became necessary, then both the training Captain and trainee would be summoned for tea and biscuits, with the former being required to explain why they let the trainee proceed to that point.Not necessarily. Depending on location (i.e. culture) it might end with note in the training log, air safety report or confidential report, a quiet word to chief pilot / head of training or training captain being reinforced in his opinion that all F/O trainees are indeed useless and should be administered beating until they improve.

It is worth noting that fight over controls does not leave a trace on QAR until it gets so extreme breakout mechanism gives up (if aeroplane is so equipped) and yokes go their separate ways while "Dual input" gets recorded and might get capt into trouble if it is discovered he made no attempt to elaborate the circumstances of it through ASR/CR. Darned Airbus. Darned. :E

You'd realise it normally doesn't work like that in the scenario the discussion is alluding to.Normally and overwhelmingly usually it does, resulting in major non-event. It is perfectly normal for PPRuNers to assume that the most extreme events are industrial norm, after all they are the only ones picked up by media.

Why you keep making such statements on things you absolutely have no experience on is a mystery to me ...I can only speculate whether his intention was to demonstrate that a) experience is helpful but not prerequisite for understanding b) personal remarks that can be reduced to "I know, you don't and I'm not telling more than that" are not particularly helpful in developing meaningful discussion but if it were, he made it.

[rudderrudderrat]

Hi Clandestino,

Whether mechanical or electronic, rudder is just rudder, it's used for decrab and engine failures so no need to have sideslip protections as long as the pilot has some idea what he should be doing
It's a bit more complicated than that as DozyWannabe pointed out.
In the event of a total loss of electrical power to the flight control computers, the only way to keep the aircraft level will be by using slip. When was the last time anyone practiced that on Airbus?

Boeing 777 has cable connection to spoilers 4 and 11 to maintain wings level. 11.5.2
http://www.davi.ws/avionics/TheAvionicsHandbook_Cap_11.pdf

[roulishollandais]

Any time I am reading the Tech-log threads list, I am asking me if "asynchronous" is a false-friend from "asynchrone" in French..:} My dictionary says no.:{

In FBW, both controls use the same clock and the same timer ! They are everything but asynchronous, and specially during dual inputs when they do an addition using the same processor!

The words "coupled" or "uncoupled" [sticks] is not much clearer in the deep of our discussion, and Clandestino himself tied his feet in that carpet:O

Thanks to Rudderuderrrat and gums who maintain the heading along the thread toward the only goal of pilot piloting : put the plane on the wanted path:), and so never land before the threeshold :ok: (They don't fly Asiana" ,they both are automation addict, and, like Bubbers44 and all the old-timers and younger hand-flying, don't put their eyes in their pockets :ok:)

[Clandestino]

When was the last time anyone practiced that on Airbus? November 12, 2001.

[gums]

I guess we have to define terms.

The digital FBW systems have a basic time frame/sample rate. So dual controls that feed the inputs to HAL are sampled at "x" rate, then used by the system.

The pioneer system I flew back in 1979 was analog. The force inputs on our controls was used by four computers, and the most benign output was used to command actual surface movement/rate/etc.

In our family models, the control signals were "summed", so I could equal the force that the nugget in the front seat was exerting. The FBW used the resulting electrical signal to command control surfaces.

So I would prefer the term "mechanically-coupled" to discuss those planes with dual controls, regardless of whether they are FBW or the "conventional" implentation many of us grew up with. out,

[A33Zab]

Boeing 777 has cable connection to spoilers 4 and 11 to maintain wings
level.


Did they forgot to install that one on 787?

or is a total power failure to the flight control computers - up to HOT BAT BUSSES (Airbii)- such a remote event it will probably never happen?