Originally posted by Vunder31:
It seems like 'X' stands for rail service, at least in Sweden, Denmark, and Canada (if you look up airport codes staering with 'X' on ITN, you'll find lots of Canadian cities with rail service)
There's at least one airport that starts with X: XNA, for Northwest Arkansas.
Ever notice no U.S. airports start with K, N or W? I think this is done so there's no confusion with broadcast stations (K and W) or tail numbers (N)
If anyone has a Bloomberg workstation, check out its list of Z-codes sometimes. It looks like a lot of codes beginning with Z have already been assigned as overflows.