Quote: "Closing them down to open up airspace seems an odd proposition when there are other options that would free up airspace and (existing) airfield capacity - doing away with alternation at LHR and allowing flex departure tracks would solve the short term capacity constraints.
The political quotient will always get in the way though because the Westminster Crew seek election/re-election but if the UK is to prosper, it needs strong political leadership with the long-term vision to lay out the roadmap to growth."
Mixed mode will not address congestion at LHR. Not only will departing planes have queue to take off as at present but will also have to wait for planes to land. Arriving aircraft will be circling for longer as they queue to land and this will be lengthend by the need to wait for planes taking off, but it will increase airfield capacity, by about 12%(?).
However, it will end the daily half-day of quiet for residents under the flightpath and, politically, that may be fraught with difficulty. On the other hand, threatening mixed mode could be a way of neutralising opposition to LHR expansion.
Frankly this is not too far from the truth, for if there is no LHR expansion, and soon, it will become increasingly difficult to resist pressure for mixed mode operations (irrespective of the increase in congestion).