Denver International Airport is "DEN" or "KDEN" depending on which system you're using.
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Just because the story is from Denver, it doesn’t necessarily mean they were talking about DEN. Maybe Southwest has started flying to Doha. DIA is Doha International Airport.
At least they weren’t heading to Antsiranana. The airport there apparently uses DIE. (Northern tip of Madagascar).
Local Denver Fox station, and we all call it “DIA” here. I worked for the airport for many years, and while “DEN” and “KDEN” are the proper identifiers, using “DEN” as the common reference only arose as part of a branding effort the airport began several years ago. DEN works fine as a brand on printed materials, or as a logo, but sounds odd and awkward when spoken because it’s an actual word. Identifiers like “DFW”, or “PDX”, etc. work fine because they don’t form a word, DEN doesn’t.
It is called DIA.