Which code is used for Washington DC's Reagan National Airport?

The code for Washington DC's Reagan National Airport is DCA. This is designated by the International Air Transport Association (IATA) and is officially recognized in airport and airline codes worldwide. DCA derives from the name of the airport, with the "D" representing "District" for Washington D.C., and "CA" standing for "National Airport." Reagan National Airport serves as a major hub for both domestic and international flights, and its IATA code is well-known among travelers and airline personnel.

The other options, while they may refer to different airports, do not correspond to Reagan National Airport. DAY represents Dayton International Airport in Ohio, DEN is the code for Denver International Airport, and DSM refers to Des Moines International Airport in Iowa. Each of these codes uniquely identifies a different location, underscoring the importance of knowing the correct airport codes when planning travel.