The base airports feature has been upgraded to the latest version in Game World #4. This update enables the new features pioneered in the Game World #3. The players can now open more bases than before with a lot more freedom in choosing the size of the base. They are able to control the base costs better with the new 'base level' setting too. The whole interface has been fully updated too. This change does not require any actions from the players: All your existing bases will be automatically at the highest level ("base level 4"), but you may downgrade them if needed (from Office -> Base Airports page). The changes to your airline's financials should be minimal, but you can expect some variation in your fixed costs (staff, maintenance, offices etc). If you are on manual staff settings we'll automatically set your staff to 100% levels if it's lower at the time of the upgrade (but won't fire anyone; most likely you will be slightly overstaffed after the upgrade - in other words your cost base will then remain the same as before, but you may wish to gradually fire some of the extra staff to cut costs). It's also advisable to read the manual page about this feature. This update will be rolled also to Game World #1 shortly (but not to GW#2 as it will end in three weeks).