I know that I'm wrong and not a pilot and all that, but the image comes to mind of a car with two separate power-steering wheels and no feedback between the two.
Now put up a screen between the drivers so that both can see the road ahead, but not each other.
Set 'em off 'em on a motorway exit and wait for the bang. I doubt whether you'd have to wait more than ten minutes.
Mac (ignorant but not stupid)