dhkendall wrote:X was added for a reason, though, as all previous 2-letter airport codes had to be 3 letter, and was done by tacking an X on. (Same way PDX came into being if I'm not mistaken.)
Basically, yeah. Used to be, airports simply used a designator for the nearest weather station. When they went to the 3-letter designator, they just decided to tack on the X.
Or Canada. (I still haven't the vaguest idea why Canada, of all countries, has a special exception to airport naming codes. If an aviation geek could explain that to me, I'll be forever grateful.)
[To TPH: Canadian codes all start with Y: YVR (Vancouver), YWG (Winnipeg), YYC (Calgary), YYZ (Person International, Toronto - which, for some reason I've heard pronounced more often as wye-wye-zee than the assumed wye-wye-zed). Y do they do that? Damned if I know!]
They aren't special ... sorta. Each airport on the planet has 2 (or 3 in the US, as the FAA has its own) codes assigned to it. There's the 3-letter IATA code, which is used for things like baggage and reservations. Then, there's the 4-letter ICAO code. This is used in formal communications, air charts, etc. In most cases in North America, the IATA codes becomes the ICAO code simply by tacking on a C (Canada), K (the US), or M (Mexico). So, ATL (Atlanta) becomes KATL. YYC (Calgary) becomes CYYC (this doesn't usually work overseas, as Heathrow's LHR becomes EGLL and Paris Charles de Gaulle's CDG becomes LFPG).
From what I understand, although it may not be true, is that the C was used by the ITU as the radio designator for Canada and CY and CZ were used specifically for air transport communications, so it stuck that way.
Also, notice that many of the Canadian cities simply use two letters from the name as the two 'other' letters in the code (Vancouver - VR, Winnipeg - WG, Calgary - YC)