asynchronous sidestick

[Capn Bloggs]

Originally Posted by Clandestino

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.

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...9%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]

Originally Posted by Clandestino

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]

Originally Posted by Capn Bloggs

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.

Originally Posted by rudderrudderrat

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.

Originally Posted by CONF iture

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]

Originally Posted by Dozy

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:

Originally Posted by Dozy

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.

Originally Posted by Dozy

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]

Originally Posted by dozy

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]

Originally Posted by rudderrudderrat

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.

Originally Posted by Dozy Wannabe

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.

Originally Posted by Capn Bloggs

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.

Originally Posted by CONF iture

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/TheAvion...ook_Cap_11.pdf

[roulishollandais]

"asynchronous"

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

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 (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 )

[Clandestino]

Originally Posted by rudderrudderrat

When was the last time anyone practiced that on Airbus?

November 12, 2001.

[gums]

Connected?

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]

@RRR:

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?