We use Stands instead of hangars in Airport City. A Stand is a maintenance zone for planes. Here a plane waits for its flight; meanwhile the plane is refueled, takes passengers on board, and returns when the flight is over. A Stand can provide services for any type of plane, from Swallow to Condor, including both your own and your guests’ planes.
Note that you’ll also need an open Stand to receive a guest plane. You can therefore reserve one Stand for guest planes or receive them on whichever Stands are free because your planes are on flights.
The number of Stands available to you depends on your level. However, note that if the Control Tower level does not allow you to purchase one more plane, you won’t be able to build another Stand either.