Some thoughts on Real and Game World things.
I mention Manchester in my posts above because UK plans more runways near London ignoring Manchester, which runs at 60pc capacity with just a single main runway. That's not what the game shows by the way. The proposed game 'City Model' is only going to work when excess Pax at one airport migrate to more than the local airport with Fares reducing by distance perhaps. I'll be know the new City Model is working when half the aircraft going into Heathrow are B737 size, which is what I see in the cheaper hours now. Also in real world more landing slots are made available by operating both runways for landing at busy times with the aircraft staggered to land alternately to just maintain minimum distances. That puts pressure on departures too so departure slots need to be balanced [or controlled] by demand each hour for landing slots.
Airport PAX numbers are also a big issue in the real world so maybe, after Cargo is sorted, the City Pax model needs to control the available Take-off v Landing slots by demand in each hour (It could be manually changed, say each game month, as traffic levels grow). Where the City Demand isn't being met then additional Runways or Airports can be 'created' (or Expand Luton/Stanstead?). My personal favourite for the new Southern UK Airport is the old USAF base north of Oxford where existing rail and Motorway links are within a couple of miles and within 70 miles to London, Birmingham etc. It could have been active in a few years with a single (existing) runway.
Incidentally I was involved in the creation of T5 at a lowly level. The opportunity then was to put building outside the runways and put a new runway between the current runways to operate for smaller aircraft departures only. T1 is now being demolished. T3 has already been rebuilt, but the lack of forward thinking, or political interference, means Heathrow can only increase capacity by demolishing homes needed to support the City.
Jan2016 and London City Airport is currently operating at a loss, and is up for sale. Current offers suggest the site is more valuable than the Airport operation.
The London Shambles has let neighbouring countries start robbing the London airports, Shannon by Operating US Immigration Clearance at the airport but those sort of Marketing things are some way down the line for the Game, but Pax migration has to be more than per City.