Airbus Control Sticks Asynchronous?

[StrongEagle]

I came upon this article about what happened to AF 447 (Air France 447 Flight-Data Recorder Transcript - What Really Happened Aboard Air France 447 - Popular Mechanics (http://www.popularmechanics.com/technology/aviation/crashes/what-really-happened-aboard-air-france-447-6611877)) and on page 2 of the article it states:

Unlike the control yokes of a Boeing jetliner, the side sticks on an Airbus are "asynchronous"—that is, they move independently. "If the person in the right seat is pulling back on the joystick, the person in the left seat doesn't feel it," says Dr. David Esser, a professor of aeronautical science at Embry-Riddle Aeronautical University. "Their stick doesn't move just because the other one does, unlike the old-fashioned mechanical systems like you find in small planes, where if you turn one, the [other] one turns the same way."

I would assume that PM did some fact checking, but if this statement is true, then how would the aircraft determine which stick to use for input? The allegation in the article is that the copilot continued to raise the nose while the pilot in the left seat had no idea such inputs were being provided.

This seems problematical to me for at least two reasons. If asynchronous, how does the aircraft know which input to use if different? And, isn't this a dangerous situation?

TIA

[Diverskii]

It is a somewhat dangerous situation IMO, and has been criticised by many in the industry.

Regarding how they work, IIRC when both sticks are used at the same time, the algebraic sum of the movements is used. So if one pilot pulls it fully back, and one pushes it fully forward, they cancel out and nothing happens. There is obviously some complex maths used to determine where the plane goes when receiving two different inputs.

There is also a priority button, which when pressed gives that pilot priority and stops the other stick from working... unless the other pilot also presses for priority in which case the last person to press has priority (I think). There is some kind of warning alarm which sounds saying "Priority Right/Left" when someone presses for priority.

EDIT: A lot of people blamed the crash of AF447 on the asynchronous side sticks, but it was just a small contributing factor. Like I said Airbus designed it with alarms to make it clear who actually has priority - the pilots on AF447 failed to notice they both pressed for priority.

Still, that's no excuse to not have the sidesticks synchronised. To this day I still cannot figure out why Airbus would design them like that.

[Mad (Flt) Scientist]

To this day I still cannot figure out why Airbus would design them like that.

Having the two sidesticks linked would require either a direct mechanical connection OR a motor on each stick to drive it to the offside position.

Direct mechanical linkage would be difficult to engineer, given the positions of the sidesticks on opposite sides of the cockpit, and would create a risk of a jam in one stick (or anywhere along the linkage path, which would be complex in nature) jamming both sticks. So you'd need to be able to disconnect them anyway - JUST LIKE IN A BOEING.

A motorized backdrive would create the same jam one, jam both scenario, and it would also introduce failure cases of the more complex motor drive system.

The unlinked controls are perhaps different to what was once the conventional approach, but that alone doesn't make it wrong.

[halfofrho]

Active side sticks are currently in development by both BAE systems and Safran/Sagem.

Info here: NBAA: Safran reveals active sidestick development project - 10/22/2014 - Flight Global (http://www.flightglobal.com/news/articles/nbaa-safran-reveals-active-sidestick-development-project-405051/)

[Diverskii]

IIRC the Gulfstream 500 and 600 have active sidesticks that are electronically linked. No need for a heavy mechanical connection.

I find it hard to believe it was a technological reason for airbus not including it. The electronic technology surely existed when they were building the A320. I imagine they just didn't think it was needed.

Now the industry says it's needed, so hopefully the next Airbus jet will have it.

[StrongEagle]

You don't even need it to be high tech electronic technology to link the sticks. Millions of cars and motorcycles use cables... to run the clutch, the brake, and the throttle. Most car and bike throttles are doubles in case of failure... can't see why this wouldn't be a simple option to run across the cabin, side to side.