Originally Posted by KathyWdrf
Thanks for the examples.
In the case of DEN/DIA, at least, I know a new Denver airport was built a number of years ago. Could that explain why there is more than one code?
Thanks for the link.
The alternative scenario I was envisioning was one code represented an old airport in that city that was now shut down, and the other represented the city's new airport. IIRC DEN and DIA are examples of this (?), also I think Singapore or Hong Kong (?) changed the airport code when they built a replacement airport for the city and shut the old one down. In such situations it's conceivable that people used both the old and new code to refer to the city's airport for a while during the transition.