It’s one of those things that you’ve perhaps never explicitly thought about, but it may have tickled the back of your mind a few times as you make airplane reservations or stare at a departure screen. Where do the three letter codes used to delineate between airports actually come from? What’s the deal with the “X” in LAX? Why EWR for Newark?
Called International Air Transport Association (IATA) codes, the clean, visually appealing site lets you click on a number of different codes (laid over an image of the airport’s location), which delivers provides a simple, concise explanation of its origin.
The mysterious X is finally understood: it’s simply the letter that’s plugged in if the necessary letter is already taken by another airport. The site also points out that up until the 1930s, airports only used two letter codes. That’s how you get LAX for Los Angeles International Airport, which was previously just LA. The strange Newark code EWR is also revealed. After switching the three letter codes, the Navy reserved all codes beginning with N. Thus, Newark was forced to begin with their second letter.
Many more fun tidbits like these can be found in this very informational little site. Have fun.