Always allow small airport
From OpenTTD
This patch allows you to build small airports at anytime in the game.
[edit] Description
Under normal circumstances, as the game progresses, small airports become grayed out and can no longer be built. This can be a pain if you wish to build an airport but don't have the space for a city airport. If this patch is enabled, you will always be able to build small airports.
[edit] Use
This feature is disabled by default. You can enable this patch through the configure patches -> construction window or use the following syntax in openttd.cfg:
[patches] always_small_airport = true
