Other contributors have said "What airport is KLM and abbreviation for?" is the same question as "Which airport has the abbreviation CLT?" If you believe that these are not asking the same thing and should be answered differently, click here
The National Oceanic and Atmospheric Administration (NOAA, at www.noaa.gov) uses "AP" as the abbreviation for airport. This is the only place where I could find an actual abbreviation in use.
Unless...