Airport Expansion

An airport can be expanded if both these criteria are met:

1. It's currently a small or medium sized airport.
2. All of the gates of the airport are owned. They don't have to be used in routes, just owned.

When expanding an airport, you have the option of taking one of the newly created gates in exchange for expanding the airport.

Expanding an airport:

1. Adds additional gates
2. Increases the size of the airport, which increases the maintenace cost of gates, and increases the size factor of all routes at the airport.
3. Increase the minimum bid for gates at the airport.