I read over this probably in the rules...
How do you choose your start location on the bottom part of the board?
Upon an airship’s first move in the game, it has no Starting Location, so it can take its first step in any Location.
2-player special rule: in an airship’s first move in the game, every Location it enters must contain 2 Citizen Cubes.
(*you can also find these lines in the bottom right corner of page 12.)