IATA vs ICAO codes
 

Some IATA airline codes are easily recognisable, while some are cryptic.

No one would hesitate to guess what AA, DL, KL, AF etc are. Who would have guessed what IT is, not to mention 9W, B6, WN. ICAO codes, as three letters makes it possible to assign recognisable codes to more airlines.

The same is for city codes also. Who would guess what YOW is, while ATL, PHL, DEL, AMS, HKG, BOM are recognised right away? The flexibility afforded by 4 letters makes it easier to assign recognisable codes to more cities than is possible with 3 letters. But I like three letter codes.
If airports have three letter codes, airline codes will have to be two letter codes other wise it would be impossible to tell whether a code is referring to an airport, or an airline.
So I am screwed. Do you prefer IATA codes or ICAO codes for airports? What about Airlines? Those who claim ICAO for airlines and IATA for airports will be sentenced to undetermined number of years to terminal confinement with TSA.

P.S. It tuirns out that Ottwa (YOW) and Toronto (YYZ) are just as cryptic in ICAO regime as IATA regime. Leave it to Canadians.

IATA codes are used by airlines to send baggage etc to the right destination, ICAO codes are used by pilots to plan flights etc. ICAO is the UN organization so it is generally wider use. Many small airports do not have IATA codes.

Thank you. I do know what IATA and ICAO are. I did not know which codes were used for which function in functions not uaually tranparent to travellers. It's the IATA codes most visible to travellers. Fare rules that we see also use IATA codes. The two sets of IATA codes,two letter codes for airlines and three letter codes for airports, are also used here on FT, although some people do use ICAO codes for airports.

The max number of distinct two letter codes is 26*26=676 and the max number of distinct three letter is 26*26*26=17576. Some simple codes such as XX (except a few like AA, LV though), II, and XXX, XXI XVI, that have other interpretations are probably not meant to be used.

My frustration is having to look up codes that are not easily recognisable.

Both IATA and ICAO have their headquaters based in Montreal, Canada. As an international distributor of airport codes, they chose their own country to be the last country in order for getting recognizable airport codes.
In fact only the last remaining letters were given to big airports in Canada.

That is why TOR is Torrington, Wyoming and YYZ Toronto.

As has been discussed in various previous threads...:

The reason most Canadian airports have IATA codes starting in Y is that Canada has chosen to base its IATA codes on its ICAO codes, and that the ICAO country codes for Canada are CW, CY and CZ (with CW only used for weather stations).

If you ignore the initial CY then some of the Canadian codes do make sense - OW is Ottawa, VR is Vancouver. (I don't know why Toronto is YZ or why Montreal is UL, though!)

The USA is pretty unique in having the whole of the K series to itself - meaning there are three letters to play with for ICAO airport codes rather than just two. All other countries have two-letter ICAO country codes - EG for the UK, EH for the Netherlands, LF for France and so on.

Oh, and just as an aside... airlines have both two and three letter codes. The three-letter ones are used in flight plans (and often bear no relationship whatsoever to the two-letter ones)

There's an app for that...

"IATA/ICAO Dictionary" in the Android market.

Most likely, there are legacy reasons for the YZ code (e.g. there was originally a weather/railway station with such a code at that location).

Also, TO is, in fact, used for the Toronto IATA City Code (YTO).

But the ICAO 4-letter codes aren't based on pronunciation (or city name) like the IATA codes are. They're based entirely on location, as a previous poster explained. EGLL is much less recognizable than LHR, if you're not familiar with the codes.

Toronto, Ontario YTO (YYZ YTZ)

Edmonton, Alberta YEA (YEG YXD?)

Montreal, Quebec YMQ (YUL YMX)

A history on airport codes for anyone who is interested:
http://www.skygod.com/asstd/abc.html

I'm pretty sure the FAA controls the P series as well. It's used in the Pacific for Alaska, Hawaii, US Territories, and Compact of Free Association Nations (Palau, Micronesia, Marshall Islands) only.