Many years ago, in a previous life, I was invloved in a multi-disciplinary investigation for expanding the capacity of the London airports. As with most things, it is never one factor alone which limits the overall capaciry. Yes - the runway is usually the limiting factor, but so also are the ways they are used, and the many other bottlenecks too - the terminals, the stands, the taxiways and the surrounding airspace management - the routes, the sectorisation, and the technologies used in the air and on the ground. Thus, a redefinition of the routes and airspace will help to advance the overall capacity - even though it will produce a backlash over noise.