Ah, but with Mode S we (controllers) know what IAS the aircraft are flying...
Obviously in ATC we apply speed control using IAS...but even with same IAS for 2 aircraft there are differences in ground speed. I just wondered how significant these differences are?
Perhaps they are so negligible that it doesn't really matter right now but, with an ever increasing demand for increasing airspace/airport capacity, I foresee time based separation becoming more and more common at airport approaches worldwide.
I was just looking to quantify how big/small the difference in time was...
(Perhaps I should get out more...)