Jabird:
Because the amount of space is constrained, the airport will be too - although I had assumed airports like HKG & KIX would have been built for parallel ops. So ATL too - can only do so on the two outers - correct? Surely, tht is what Foster is thinking of?
I don't think even the outers are far apart enough, with the original Foster proposal. But even if they were, you could not use them for quick parallel approaches, because you would have to hold all outbounds until the inbounds had landed (because of the potential conflict for go-arounds) - which defeats the whole idea of an efficient high capacity airport.
If the landings are on the inners, then the outers can take off with a 15 degree turn away from the centerline, because the inbound on the inner now has enough clearance for any go-arounds.
But if you are in Foster's Isle of Grain site, you would have to check when the left runway can make that initial left turn, because there is some higher ground to the SE of the climb-out. The right runway is not so constrained in its right turn, and can operate simultaneous on the inner with no problem.
This means the inner runways need to be at least 1.5km apart. And if we are to prevent the taxiway/terminal overcrowding that we see at LHR, then they need to be at least 2km apart. And to really prevent overcrowding and improve flow, we need a domestic/short-haul runway another 2km to the NW (with its own terminal, and a really fast rapid-transit).
.