chuboy
Sometimes.
At any given time I can see your delay but the sequence doesn't become set until all the aircraft ahead of you become "stable". If you ask what your delay is before all the aircraft ahead of your are stable you are probably not going to get an inaccurate time because
a) the flow has not had a chance to optimise the sequence by closing up any gaps in the sequence by direct tracking/max speed/different runway assignments.
b) aircraft have yet to depart that will be ahead of you in the sequence.
Because of these effects it is common to see a given aircrafts delay vary by 10 min within the space of 20-30 min.
We all know that you want your delay as early as possible. We all know that you hate "slow down, no speed up, no slow down again" If you are given a slow down before the sequence is stable there is a high probability it is going to be wrong. You can have your delay early and inaccurate or later and more accurate. Now think of this from an ATC point of view:- do I give out a bunch of inaccurate times only having to revise them later adding to my workload or wait until they become stable and do it once. If a give you a slow down to early and a gap opens up, you may not be able to increase enough to get back into that gap and a slot is lost and everyone loses. You may not be given your slowdown until you have overtaken an aircraft that you are ahead of in the sequence because you will restricted on descent. Particularly if there is a track miles issue with instrument vs visual stars.
haughtney1
If you can't understand why you are thumped with a 10 min delay at 200nm after reading all this then I cant help you anymore. But I will try to help you with the "unrealistic expectation"
We know that you probably can't make that time. It is just our way of saying that this is the time you are going to cross. Like any instructions we give, it is always subject to pilots ability to comply.
For example "ABC 123 turn left heading 360...ABC123 Unable due thunderstorms, best we could do is heading 340,
"ABC123 climb F390.....ABC123 unable we're to heavy we can accept F380"
"ABC123 increase to maximum speed....ABC123 unable due turbulence"
Do you see where I'm going with this? We make the assumption that you will tell us what you can do and I personally think it is a waste of time to add "let me know if you need vectors or holding" to every feeder fix time I issue.