Atc Separation

[SPEEDBIRD5FP]

COULD SOMEONE REMIND ME THE DIFFERENCE BETWEEN ATC PROCEDURAL SEPARATION
I CAN REMEMBER SOMETHING ABOUT 15MIN 10MIN 5MIN 3MIN BUT CANT REMEMBER WHAT DETERMINES WHAT SEPARATION YOU CAN USE?
IF SOMEONE COULD RESPOND I WOULD APPRECIATE IT
CHEERS

[Spitoon]

Depends on so many things. All the standard seps are in Manual of Air Traffic Services Part 1 (http://www.caa.co.uk/publications/docs/CAP493__Part1.pdf) Section 1 Chapter 3.

Now and then there will be diifferences (usually known as deemers) that can be used by a particular ATC unit but these are not normally published. Deemers are usually to speed things uo when the aircraft will be the same distance apart as the standard seps would achieve but the beacons or whatever are in the wrong places.

[WX Man]

If you are talking longitudinal, which it seem like you are then:

15 mins for a/c on same or crossing tracks where there are very few navaids
10 mins for a/c on same or crossing tracks where there is navaid-navaid navigation
5 mins for a/c on same track (not crossing tracks) where you are absolutely dead certain about the position of a/c 1 and a/c 2, and a/c 1 is 20 kts faster
3 mins in the above scenario if a/c 1 is 40 kts faster.

Note that to be sure of the exact position of the a/c, they both need to have departed the same airport, reported over the same point. And in the case of the 3 and 5 min separation, it needs to be increasing.

WX... procedural wannabe.