Examples: ATR departing straight ahead, A320 on final, ATR must commence roll before the A320 crosses a 7 mile final. Becomes 5 miles if the ATR is on a side SID.
Wow, what do you guys do when your busy? seven miles? thats a massive spacing!
The whole thing is a bit of a blunt tool, and there is, at times, a lot of wasted airspace. For example, no allowance is made for the fact that a lower performance departure might climb like a rocket. Nor for the fact that, although the speed of approach tested on the sim is 175, most a/c will be 10-30kt slower than that for the last 4 miles of the approach.
So why is this used? isn't it a bit like boxing with one arm tied behind your back?
Surely SSR radar has the required accuracy to provide proper separation inside the terminal area and on approach to make this process look a bit antiquated?
Using Wellington as the example....how often do you get anything bigger than a 767-300 operating on a regular basis? Even at Max landing weight your approach Vref is still only about 140ish knots..which is well below the 175 you quote....
Whats wrong with 180kts till 8 miles...reducing to 160kts till 4 miles etc...? It works bloody well in Europe, and appears to be gaining traction in the USA as well.
No attempt from me to be crtitcal, I'm just trying to understand the thinking behind what appears to be an ill thought-out procedure.