Say you have an eastbound flight at FL210 that wants to climb and a westbound flight on a converging track at FL220 that wants to descend. There's the minimum required 1000 ft vertical separation. Once the planes have passed each other can ATC clear them to climb/descend right away or do they have to wait until they are 5nm apart before they can break the vertical separation? And what about TCAS? Would it consider that a conflict?
Yes, this is allowed, subject to certain conditions. See FAA Order 7110.65 (the ATC "bible"), section 5-5-7, for the full details.
...all other approved separation may be discontinued and passing or diverging separation applied when ... Aircraft are on opposite/reciprocal courses and you have observed that they have passed each other; or aircraft are on same or crossing courses/assigned radar vectors and one aircraft has crossed the projected course of the other, and the angular difference between their courses/assigned radar vectors is at least 15 degrees.
That's in the terminal environment; it's still possible in the enroute environment but a bit more restrictive due to the greater aircraft speeds and poorer radar accuracy.
It depends wether you get procedural or radar service. In case of procedural service if both pilots report clear of traffic (beeing previously informed of the traffic) the longitudinal sepparation criteria is met. In case of radar service longitudinal sepparation minimas can vary from 5 to 10 NM or more.
In my experience it's moot. Usually when you observe that the tracks have crossed, by the time you issue the clearance to climb/descend the acft are 5 miles apart anyway due to speeds at those altitudes.
Cavver - Interesting that I've never heard it referred to as "procedural" separation before! Is that a non-us reference? We always called it manual separation or non-radar. It was always a challenge to try and set off the immediate alert buzzer at the desk and have a manual rule to invoke. Made management grumble :-D
You will have to comply with the minimum horizontal separation required by the regulations before crossing their levels.
TCAS might consider them clear of conflict before they have the minimum horizontal separation required (3, 5, 8Nm, whatever that may be), but remember TCAS is not a way of providing ATC separation.