National Airport in DC (technically in Arlington, VA, across the river) has always been DCA, DC Airport. When they built Dulles International Airport about 25 miles away, they called it DIA ( Dulles International Airport). However, this was back in the '60's and early 70's, when baggage tags were hand written. If a clerk was in a hurry in writing the codes, DIA can look a lot like DCA, and vice versa. And when baggage handlers are in a hurry reading the codes, again, DCA can look a lot like DIA. Why happened was hundreds of bags were sent to the wrong DC airport, DAILY. It got so bad, the airlines petitioned to get the name of Dulles changed. They eventually changed it to IAD, which is the French way of saying Dulles International Airport (something like International Airport Dulles). So now, DC had DCA and IAD.
An additional issue is that there's a rule (I forget the specifics of it) that two airports within a physical proximity of each other can't be just one letter apart. it's why Washington's Dulles is IAD -- if it were DIA, that'd be very close to DCA, which is an airport 25 miles away.
National Airport in DC (technically in Arlington, VA, across the river) has always been DCA, DC Airport.
When they built Dulles International Airport about 25 miles away, they called it DIA ( Dulles International Airport).
However, this was back in the '60's and early 70's, when baggage tags were hand written. If a clerk was in a hurry in writing the codes, DIA can look a lot like DCA, and vice versa. And when baggage handlers are in a hurry reading the codes, again, DCA can look a lot like DIA.
Why happened was hundreds of bags were sent to the wrong DC airport, DAILY. It got so bad, the airlines petitioned to get the name of Dulles changed. They eventually changed it to IAD, which is the French way of saying Dulles International Airport (something like International Airport Dulles). So now, DC had DCA and IAD.
An additional issue is that there's a rule (I forget the specifics of it) that two airports within a physical proximity of each other can't be just one letter apart. it's why Washington's Dulles is IAD -- if it were DIA, that'd be very close to DCA, which is an airport 25 miles away.
They don't opt not to change them. They're required to keep the existing code.