The old airport code for the old New York International Airport (Idlewild) used to be IDL. After President Kennedy's assassination in 1963 the airport and identifier were named after him.
IDL still soldiers on... it's now the airport identifier for Indianola, Mississippi.
When Washington Dulles was being built, it was planned that the identifier was to be DIA; as you can see it would have caused massive confusion with National Airport, whose code is DCA, That's why it's now IAD.
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AlphaSigOU
Causa latet vis est notissima - the cause is hidden, the results are well-known.
[This message has been edited by AlphaSigOU (edited 04-20-99).]