X means international I think

LAA and LAI are currently taken by two other airports. Here's what I could find:

You may wonder where the "X" comes from in the codes for Los Angeles International Airport (LAX), Phoenix Sky Harbor International Airport (PHX) and Portland International Airport (PDX). The Phoenix code finishing with an "X" seems logical, but the other airport codes seem pretty random.

In fact, the "X" for LAX and PDX is merely an arbitrary placeholder, created by IATA in the 1940s when airport codes in the U.S. expanded from two to three letters.

At the time, airports used the National Weather Service codes for cities — in this case, with the logical "LA" and "PD" designations. As the number of airports rapidly increased in the 1940s, IATA had to add an extra letter to existing airport codes to make room for new codes.

For the sake of simplicity and not to confuse pilots or passengers with new letter combinations, IATA added an "X" to the end of the existing codes for Los Angeles, Phoenix, Portland and a number of smaller airports. And that's the way it remains today.

Disappointed the Midway code is MDW so you can't call Chicago MID.

It was ORD because the original was Orchard Place