YYG is the "airport code" for Charlottetown, Prince Edward Island, Canada.

If you book an airline ticket from, say, Montreal to Charlottetown, look at your boarding pass and you'll likely see YUL as the origin -- the airport code for Trudeau Airport in Montreal -- and YYG as the destination .

But why is Charlottetown YYG while Boston gets the much more sensible BOS, San Francisco is SFO and Bangkok is BKK?

It turns out that the world of airport codes is multi-layered and somewhat arbitrary.

Three-letter airport codes are assigned by an airline trade group called the International Air Transport Association, based in Montreal. The IATA has several roles, including travel agent accreditation and regulating -- or some would say "fixing" -- international airline fares.

Interestingly, not all airports have an IATA code, and there is duplication in their system, with different airports sharing the same code.

And, confusingly, there's a parallel system of FOUR-letter airport codes, assigned by the International Civil Aviation Organization, a UN body, also baed in Montreal. Some of these ICAO codes are similar to the IATA designations and some are not.

Charlottetown, for example, has a three-letter code of YYG and a four-letter code of CYYG and indeed in Canada you can get the 4-letter code by prepend a "C" to the 3-letter one; the same thing for the USA, where prepend a letter "K".

But why is Charlottetown YYG?

It turns out that a definitive answer to this is hard to come by.

Most, but not all, Canadian airports have a three-letter code that starts with 'Y'. An query to the IATA about why this is elicited the following response from the "Administration Coordinator, Interline and Airline Codes" --

"The urban legend I have been told about how this came up, was that when the codes were first being distributed to airports around the world that the Canadian Representative failed to show up (or Canada failed to send one... the stories will vary from who you speak to). So the Canadian airports were just assigned different Y codes, because a list was not submitted as to what codes to have assigned to those airports. From that point on I guess it just stuck that any other major airport in Canada decided to continue the trend by being identified by a code that started with Y."

As to the "YG," answers are equally vague. Some on the web suggest that Canadian airport codes were originally based on weather reporting station codes, and these codes began with 'Y' for "Yes" if the station was also an airport, and "W" if it wasn't. Whether this true appears lost to history.

My man at the IATA did say, however, "any new applying airport in Canada can suggest to be assigned any available code, they are not forced or even recommended to select a code with the letter Y."

So perhaps we should mount an effort to ditch our odd YYG entirely and take up airport code PEI. It's already in use. But remember that the IATA does allow duplicates. And imagine the wonderful stories of tourists ready for an Island vacation mistakenly buying tickets for a city in Western Colombia.

Given the general fogginess of all this, I welcome comments with additional elaboration.