well-written "rationale" @hangten.
And as far as I know, 2.5nm is not just NATS-style but an ICAO approved (prescribed - with several conditions) separation as well.
However the question of Medium behind Heavy is still to be clarified;
According to standard (time) wake turbulence sep. - 2 min are needed.
Radar (distance) sep. - 5nm.
At least that is what the ICAO has produced in their books...
So, is the 4.5nm separation a "local" standard, prescribed by the appropriate ATS authority?
Last edited by UpperATC; 17th Dec 2012 at 18:56.