Airport problem (Golden Rainbow)

there are 216 airports
supply 2
18 in demand
the owned ones are fine
but the c3 ones don't buy their
cargo airplanes

and 6 billion shortage in construction
if you build an airport company can you buy your own airport?

The text about the cargo airplanes is unclear. but:

when you build an air transport company, it will automatically setup an airport.

the c3 airport companies are not buying cargo planes