Spitoon,
2nm is where the separation monitoring function will trigger, if it triggers a fair way out on final approach then something has obviously gone fairly awry and needs to be investigated. If it's less than 2.5nm but more than 2nm then I guess it's up to the individual controller to report themselves because it won't be picked up automatically.
Otherwise, it is accepted that closer to the airfield as traffic starts to reduce to final approach speed the separation behind will reduce below 2.5nm.
That is why there are strict weather criteria for using the procedure such that at the point it normally reduces below 2.5nm the a/c will be visible to and talking to the tower controller and reduced separation in the vicinity of an aerodrome applies.
Last edited by Roffa; 10th Jun 2007 at 19:29.