Originally Posted by
LuCst
It is the standard used by my ANSP for national P/R/D areas as per our MATS pt1.
We have some international D-Areas that border us and to those we have a blanket 2.5NM radar reparation in the LOAs regardless of what goes on within the areas. One of our neighbours has different vertical separation minima however their areas are presented to us with an added buffer which allows us to use "our own" minima and still be safe.
That 2.5 nm separation is down to ICAO Doc 4444 which requires aircraft to be vectored no closer than 2.5 NM to the edge of contiguous volumes of controlled airspace. The theory being that if that is followed on both sides of the "line", then you will have 5 NM lateral separation between flights.