PA
Controller notices two aircraft close together at the same level, acts by issuing a climb clearance to pilot A... but the airborne systems in both aircraft have "co-ordinated" their own avoiding action, giving pilot A a descent instruction, whilst Pilot B is told to climb.
Pilot A is compelled to take the descent.
No. I don't think you misread me at all. That is exactly my point, except. I issue my climb instruction to aircraft A who, because he's yet to know any difference, initiates a climb. The scenario i'm dreading is, what happens during the next couple of seconds when, say, he's applied the power - just pulling back - when - Aircraft B gets's a TCAS climb instruction. A is told to descend even though he's started a climb!
It's complicated and probably the timing could never happen. But what I'm trying to get at is;
A) If ACAS gives an instruction the best ATC can do is give TI
B) If the aircraft aren't close enough yet for ACAS to give an RA then ATC give avoiding action.
Question;
At what point does B) happen, and, what happens during that little gap between A) & B)?
Okay it's been a long day! Perhaps what I've just written will make sense in the morning!