At about 30-40 miles out if you are less than 10 miles behind and the same speed
I'm sorry but every international airport that I have flown to/from outside good OL Aus (and there has been a few) requires a 5 mile separation between landing aircraft and the runway is always bloody well clear every time. Yet we require 10?
Read his lips. AT 30-40nm. After the second airframe has continued on at 250kt whilst the first decelerates, that distance will close up to much less. Depending on how the decelerations are flown by each aircraft, the distances can be close.
Be nice if someone had the balls to make all pilots fly a standard decel profile... Now that would be an ACE idea...