This what I completely love about SDMB.
No matter how obscure the question… 
Sorry about the DWI. I got the D and W right, though.
Any idea why all Canadian airports start with the useless W. Only place in the world like that.
maybe its a brainfart or something but i just dont get the humor in DWI, whats so funny about that?
The airport code is a three letter designator for a commercial airport, or other travel point – e.g. a large bus station. These are the codes that airlines and pilots use to identify airports and are used in timetables, baggage tags, tickets, advertisements, Airline and Global Reservation Systems. There are approximately 9,000 of them in use of a total of 17,576 available. IATA in Geneva is responsible for the designation of these codes.
“DWI” can also stand for “Driving While Intoxicated” It would be funnier ( :rolleyes: ) if it was “FWI”
Same reason all airports in the Continental United States start with a useless K. Yes, they really do - ORD is really KORD, JFK is really KJFK, LAX is really KLAX… It’s an international naming convention. So if the code starts with a K you know it’s in the lower 48 of the US. If it starts with a W it’s in Canada. And so forth.
Because every airport in the lower 48 has the K, it’s commonly dropped when traveling about in that area. However, many GPS units do require you to dial all four letters of the code in (their database being interantional in scope) and there’s an occassional need for it other places.
I think (but don’t quote me on that) they originally were just three characters (numbers are used as well as letters) but at some point the fourth was added due to increased cross-oceanic travel and growing numbers of official landing spots - you need a comfortable number of codes, and also I think there had been some duplication of codes back in the days when all these things were much less regulated.
Other handy 4-letter code facts:
If I recall correctly, both Alaska and Hawaii use a P instead of a K or W
Many Carribean islands (Antigua, Barbados, British Virgin Islands) have airports starting with T
Bahamas, Belize, the Caymans and Cuba (among others) use M
And, of course, Europe, Asia, Africa, South America and Australia have their own codes. For all I know, Antartica might even have a designated “starting code” for it’s airports.
[nitpick]The codes are used for ALL airports, commercial or private. There is no airport without a code. If it has no code, it is not legally an airport/heliport/sea(airplane)port (although it might be a landing strip)[/nitpick]