OY
In the London area we tend not to say "cleared pproach" because it has implications as far a descent is concerned. We would more usually say descend on the glide path and I always then add maintain 180kts or 160kts to 4D as I require. I would suggest that most other ATCOs would be the same.
Dick
Yes, I think the problem tends to be people slowing up before 4D, presumably in order to stablise. If you slow earlier the gaps will shrink outside 4 D which is the point at which we are no longer responsible for vortex. We would therefore have to increase the spacing.
Also, as has been said the problem these days is the different requirements of the various types. If ATC have to allow for each of the types then the final director's brain will soon overload. B757, B737 and B773 already desire significantly different appraoch speeds to work at their optmum. We have had some KLM B739s say they can do 160to 4D but want to increase inside! It is something that perhaps would be best left to a computer talking to the FMS systems and then giving us the "slow down" at the appropriate moment to get the optimum gap/ speed profile.
Point 4
