The airport capacity is a precentage that shows how full the airport is. You can see this on the routes page at the end of each line for each city. If a city is too full you will not be able to land your planes if they were in route to that city.
The current limit for capacity is 20% before the airport will be too full to land.
Itzamna 03:43, 17 April 2008 (UTC)