Why Newark is EWR, and other codes that dodged a clash

Some codes look strange because the obvious choice was already taken, or not allowed.

Newark: EWR

In the US, codes starting with N are reserved for the US Navy. So Newark couldn't be NEW. It took the next letters of its name instead: nEWaRk.

Washington Dulles: IAD

Dulles first used the code DIA. On handwritten tags that looked too much like DCA, Washington's other airport, so the letters were rearranged to IAD.

Osaka Kansai: KIX

When Kansai International opened, Osaka already had an airport, ITM (Itami). The new one became KIX, and Osaka's city code OSA covers both.

Houston: IAH

IAH stands for Intercontinental Airport of Houston, the airport's original name. Houston's older airport, Hobby, is HOU.