The new Game World #3 features a completely revised set of rules for the base airports feature. The changes in a nutshell are: Each airline can now base at 10 different airports (HQ + 9 bases). Airline must be at least 12 months old and operate (own/lease) at least 10 planes before bases are "unlocked". There are no aircraft limits other than a companywide limit on aircraft scheduled outside your HQ (in bases). So no more limits on minimum number of planes in HQ or in bases. The total number of aircraft allowed outside your HQ is related to the game year and is always visible on the Base Airports page. You can choose a base level for all the additional base airports. This determines the operation size and cost level of the base. There are 4 base levels corresponding to the aircraft size classes (small, medium, large, very large); 4 levels of bases. The base size equals the largest allowed aircraft size class for your operation in that base (= medium class base can support small/medium planes, and very large base can support all planes etc). The base levels can be up/downgraded after opening (with certain restrictions). The costs of opening and maintaining a base are now mostly related to the base level. This means that you can run a small base in a major international airport with rather limited costs if you wish. So good news for regional / small carriers... The Office -> Base airports page has been renewed completely. There are also other minor interface changes. The aim for this update is to remove unnecessary limitations and allow small airlines to expand more easily (more bases, smaller costs). But the update should benefit also large airlines as well as the total number of aircraft allowed to be based is increased in the modern era. The changes also help in some other new features planned for the future. You can read more from the Manual, and more technical details are available from the Changelog (links below). This feature is currently exclusive to the Game World #3, but may be later expanded to other running games.