duelling controls
Under FAA check criteria it would be a simple fail. 2 crew on controls at same time = fail. Thats what a control handover is about.
I checked a crew once on a B744 and after a horrible landing by the FO duly chastised by the Captain, the PIC finally asked if I had any comments... to which I just asked who had logged the landing... the PIC promptly attributed it to the FO, so then I wondered openly why the PIC was trimming the aircraft from 200' through to the middle of the flare. This is bad at so many levels it's hard to work out where to begin.
There is precious little that needs split second response, in fact a substantial number of the pilot induced scrapes I have investigated have resulted from incorrect but instantaneous responses (where the pilots have been aware of anything going on... which is a subset of the total events...). Of those events that need split second responses, most cannot be saved once the wrong input has been applied, and a failure of a handover/takeover just exacerbates a large proportion of these.
Interesting comment by one of the posters, that they put their hands/feet on the controls when PNF/PM but resents it when the other pilot does the same when they are PF...
Control check is another matter, the books (Boeing) require the rudder check to have both pilots touching the pedals to ensure their control throw is adequate