View Full Version : sidestick - different inputs
hi! .... something i always wanted to know: what happens if in an airbus-cockpit both pilots give different inputs to their sidesticks. e.g. due to avoid a collision one is pulling and simultanously the other is pushing the stick.
do the computers give priority to capt.īs or pfīs stick or does the plane execute a mixture of both inputs (as someone explained to me -but he was actually flying b737- and i canīt really believe it)?
TopBunk
6th Nov 2006, 11:02
SF25
The logic sums the inputs and acts on the resultant summation.
Put simply, if P1 says full left rate of roll and P2 full right, the aircraft goes striaght on. Quite amusing to demonstrate in the sim!
.... but isnīt that totally stupid? resulting summation in case one rolls left the other rolls right in order to avoid an obstacle can only mean u definitely hit it ....
and how about the 777? as far as i know its also fly-by-wire. does the right steering-horn move the same if the left is turned?
TheKabaka
6th Nov 2006, 12:13
dont know about the triple, but on the bus both sticks have a priority button, whoever presses the button gets full control.
L Peacock
6th Nov 2006, 18:37
SF25
The logic sums the inputs and acts on the resultant summation.
Put simply, if P1 says full left rate of roll and P2 full right, the aircraft goes striaght on. Quite amusing to demonstrate in the sim!
That is barking......isn't it?
WhiskeyDelta
6th Nov 2006, 21:52
dont know about the triple, but on the bus both sticks have a priority button, whoever presses the button gets full control.
So... stretching the imagination a little further; if the P1 stick is commanding full left roll, the P2 full right AND both priority buttons pressed, what happens then? Is it a case of quickest on the buzzer? Or is there a also a priority-priority button...? :ok:
Wizofoz
7th Nov 2006, 03:23
This logic almost led to a major accident. An Ansett A320 on approach went around because another aircraft entered the runway. The Captain took control to fly the go-around, but the FO still had his hand on the stick. The sumation logic gave them a half-rate pitch up and they missed the other aircraft by meters.
Chrome
7th Nov 2006, 03:50
When the Captain announced go-around flaps and took over control (or maybe he was PF all the time), the PNF shouldn't have had his hands on his sidestick. The logic didn't nearly lead them to an accident, the FO did.
John Holmes
7th Nov 2006, 04:56
When taking control from either seat depress the Take-Over Push-Button immediately. Imputs from the other side-stick are ignored.
The LAST pilot to press his Push-Button has priority.
If depressed for 40 seconds the other sidestick is deactivated until it's own Push-button is depressed.
The system is seamless if SOP are followed
FlapsOne
7th Nov 2006, 06:46
That is barking......isn't it?
So what do you think should happen............................a fight?
So what do you think should happen............................a fight?
...not a fight...
but i believe in "conventional" cockpits where both steering-horns are moving the same the pnf always gets an idea about what the other is doing ... which me thinks gives a higher amount of awarness (and security) compared to flybywire-cockpits
DozyWannabe
7th Nov 2006, 07:48
...not a fight...
but i believe in "conventional" cockpits where both steering-horns are moving the same the pnf always gets an idea about what the other is doing ... which me thinks gives a higher amount of awarness (and security) compared to flybywire-cockpits
Worth pointing out that the triple 7's cockpit looks conventional, but is actually FBW with all the force-feedback provided by software.
My handle will tell you that I don't know for certain, but I'm fairly sure that training on type will cover the methodology for different aircraft. As for the Ansett incident, back in my ATC days the second you heard the words "I have control" coming from the instructor, you let the controls go* toute suite! I'm fairly sure the same applies if you hear it from the skipper. The 'Priority' button should really be just a backup if you follow your training correctly.
* - Well, relaxed your grip and felt what the instructor was doing, but the gist is there...
Is the "dual input" automatic callout now implemented in all fbw airbus? I once read a very interesting incident report about an in flight incident with a lufthansa A340 in US airspace where dual input lead to a very fast pitch oscilation generating -1.2 and plus 2g in less than a second leading to some injured cabin crew. It was noted in that report that there was no dual input callout since that wasn't implemented in the A340 at that time so both pilots were unaware that they had added up inputs.
Another incident where the priority button probably saved the day was the lufty a320 wich had the left stick roll channel crosswired so that the PICs inputs worsened the effect of a gust after lift off instead of lessen it, a very fast FO (who was pnf) switched priority and took over (wing to ground clearance was as low as 30cm).
Preppy
7th Nov 2006, 10:31
No. :)
I understand that this feature is a "pin selectable" option.
Chrome
7th Nov 2006, 12:06
...not a fight...
but i believe in "conventional" cockpits where both steering-horns are moving the same the pnf always gets an idea about what the other is doing ... which me thinks gives a higher amount of awarness (and security) compared to flybywire-cockpits
On the Airbus, the PNF is trained to scan the PFD rather that the 'steering horns' in the other aircrafts to detect any abnormalities or departure from safe flight. I find that safer actually.
Gary Lager
7th Nov 2006, 12:18
BAe Systems is currently undergoing development of 'active-stick' technology where sticks are driven/cross-coupled but still retain the features of the FBW sidestick system.
Enhancements such as a 'break-out' detent which permit extension of the flight envelope for emergency manouevres (GPWS etc) can also be added.
As discussed above, with proper cockpit discipline, there ought never be two pilots trying to operate the controls at the same time, whatever aircraft you fly. What happens on a Boeing? The strongest pilot wins? That sounds just as barking to me.
... as i said before. itīs not a question of being the "stronger" one. itīs more a matter of being aware of what the other does. .... just by seeing how the steering moves ....
Chrome
7th Nov 2006, 14:48
What does it matter. The supporting pilot should be watching the aircraft performance and runway. Not the control columns.
Airbus38
7th Nov 2006, 14:56
So if both pilots pull hard back at the same time do you get double the pitch rate according to the fact that its a 'summation'?
Btw, I know little about the bus despite the pseudonym!
glhcarl
7th Nov 2006, 22:01
On the L-1011 if you pulled and locked the roll disconnect handle, then turned the Pilots wheel full left and the co-pilots wheel full right, with the hydraulics on all four ailerons will be standing proud.
Don't suggets doing this in flight but it looks cool on the ground.
ICT_SLB
8th Nov 2006, 01:27
BAe Systems is currently undergoing development of 'active-stick' technology where sticks are driven/cross-coupled but still retain the features of the FBW sidestick system.
Bombardier originally used a Sterling active sidestick (as recommended by NASA) in their ACT (Active Control Technology) demonstrator but had another version from Lear Siegler for the full flight testing. The software allowed all the required cues such as stick shaker, other stick etc to be programmed in. The demonstrator (Challenger A/C 3991 - ex A/C 1003) was retired to the Canada Aviation Museum in Rockcliffe, Ont. earlier this year.
http://www.aviation.technomuses.ca/collections/artifacts/aircraft/BombardierChallenger604.shtml
If you're wondering where the sidestick is, it was mounted on the Pilot's side console (just out of frame in the cockpit view). The lefthand yoke was made demountable for the trials.
FlightDetent
8th Nov 2006, 09:21
So if both pilots pull hard back at the same time do you get double the pitch rate according to the fact that its a 'summation'?
No, because to total sum is still limited to the magnitude equivalent to single full stick deflection.
Aircraft are not flown by watching steering column deflection, nor by watching control surfaces deflection. Aircraft are flown by setting their attitude which is availible on the attitude indicator. Fact is that on a FBW Airbus there is no other option.
In the LH incident described, the PNF had the benefit of a doubt and took over just in time having no other indication than his PFD. It is a stupid speculation, but imagine if he saw the PF apply correct (in a conventional sense) displacement of controls, 30 (or as I hear 15) centimetres worth of confusion could have been the difference between life and death.
About a month later Turkish AF had a fatal accident with medim size transport turboprop, which left maintenance with crossed controls.
FD.
(the un-real)
dartagnan
9th Nov 2006, 19:19
remember your first flying lesson, if the capt says "I have control", answer "you have control",... and that 's all.
no need of stick computers and green or red flashing lights!