The International Air Transport Association (IATA), an airline trade association, assigns the airport codes you're most familiar with—the three-letters you'll see when you're booking your flight or on your ticket.
Unfortunately it is true that two airlines can have the same IATA code. The airlines are generally in different regions. But it does happen since there are only a limited number of two-letter codes available.
ICAO codes have 4 letters because there are so many airports in the world. Usually, the last 3 letters identify the airport domestically, but when searching worldwide you have to use all 4.
(C) YYZ – Toronto Pearson International AirportAs for the 'YZ' part, that dates all the way back to the Morse Code railway stations along the Canadian National Railway, which had two-letter identifiers. The code for the station in Malton, Ontario, was YZ, which is where Pearson sits today—hence YYZ.
The International Air Transport Association's (IATA) Location Identifier is a unique 3-letter code (also commonly known as IATA code) used in aviation and also in logistics to identify an airport.
With the rapid growth in the aviation industry, in 1947, the identifiers expanded to three letters and LA received an extra letter to become LAX. The letter X does not otherwise have any specific meaning in this identifier.
Pilots, as well as air controllers, use the ICAO code in their day to day as there are never two identical ICAO codes. Additionally, once you know how the code is made up, you can find out, without a doubt, which airport youre flying to.
Lack of codesThere are several airports with scheduled service that have not been assigned ICAO codes that do have IATA codes. For example, several airports in Alaska have scheduled commercial service, such as Stebbins and Nanwalek, which use FAA codes instead.
As IATA airlines are somewhat stricter in their requirements than the ICAO Technical Instructions, the DGR specifies more precisely how to prepare a shipment.