2nd q: At LHR, is there an order in which the four stacks are emptied? It seems to go very quiet on the r/t at times when you're at BNN or LAM, so I wondered whether that's when the south holds have their turn?
Essentially first come first served but may be manipulated otherwise to ensure best overall landing order taking into account the wake vortex categories of the traffic in the stacks.
Also the Traffic Manager may request a particular stack be given priority if the traffic into it is particularly heavy.
Given the way the system works it's quite possible to hold for 10 mins at BIG and be the only a/c on the INT S frequency whilst waiting for a bunch of traffic that arrived ahead of you at BNN and LAM and working INT N to land first.
WF.