The study I referred to in my previous post was undertaken jointly in the early 1990s by BAA, NATS and IATA. It was mainly aimed at Heathrow, but also took into account the effects on Gatwick, Stansted, Luton and London City. By a combination of using both LHR runways in mixed mode, together with modifications to the taxiways on the ground to reduce runway occupancy times, and in the air, new SIDs with modified minimum noise routes to spread the departing traffic, we are able to show a very substantial increase in airport capacity (I forget the actual figures).
Three impediments prevented any substantial changes from being realised. (1) To use both runways simultaneously in mixed mode required planning consent. (2) Equally, any change to minimum noise routes also required planning consent:-
https://www.london.gov.uk/sites/defa...ise-report.pdf (3) British Airways, when it found that a significant proportion of any increase in the slots made available would have to go to its competitors, threw could water on the results.
Extra parking stands would have also been needed, and BAA had plans to show how this could be done. All our new SIDs were proved to be practical by flying them out in aircraft simulators. And the improved runway occupancy times and throughput were all validated by BAA simulation models.
It was all interesting work which got no where. Nevertheless, many of the proposals we trialled are now in use many years later.