here's a few...
why do most flights get to LHR via Lambourne when most of the world is not to the north-east?
why are there days (with decent weather) when all the stacks are full for hours on end and other days when holding is the exception?
why do some US/Canada/Dublin flights arrive via Ockham?
why would two consecutive flights to Singapore turn right and left on leaving LHR?
how much disruption is caused by the 1500 runway swap, and how much when the runway changes from 09 to 27 or vv?
when LHR's capacity is stated as 498000 movements per year (I think), how is that calculated? Not on the basis of an arrival and a departure every minute from 06:00-23:00.
Why do aircraft fly Biggin-Epsom-almost back to Biggin before lining up with the runway? It makes for a lot of unnecessary noise and pollution over London and I've have thought the purpose could be served just as well by flying out east until it's time to turn onto the approach.
Why do some planes cross the centreline on their approach - e.g. Ockham to ~Edgware?
Do aircraft flying to say Farnborough or Biggin Hill have a sort of dedicated tunnel to fly through, or are they directed to avoid whatever other traffic is around at the time?
Most Detling departures fly past Biggin at < 8000', but a few are well clear at 10-12000'. Couldn't they all get that high to avoid inbound traffic?
The first time I took off on 09R at Heathrow we were warned we'd be making an extremely sharp right turn immediately after take-off for noise abatement reasons. That duly happened - but they don't do it now. Why not? (It was a MAS 747).