Thanks for that..I do understand a bit better now, but it also leads to another question.
If the inner stacks are full and there are holding areas outside of this, would these areas, in the case of Bovingdon etc.. affect say.. Luton stacking area and/or any other airport by overlapping?
I suppose what I am asking here is, how does an airport (Heathrow in this case) accommodate heavy traffic? I assume they must have 'free slots' of some sort to clear a backlog!
Best wishes
Shaz