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How Are Airport Codes Determined?

Quick, you’re taking a flight from EWR to NRT — where are you, and where are you going? (Answer: You’re traveling from Newark Liberty International Airport in Newark, New Jersey to Narita International Airport in Tokyo, Japan.) Airport codes are a series of shorthand letters used to identify each airport in the world. However, with more than 40,000 airports around the world, it is very easy to confuse which code belongs to which airport, regardless if you’re a light traveler or frequent flier. Here’s all you need to know to know about airport codes.

The Beginning of Airport Codes

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In the early days of commercial flights, there were only a handful of airports around the world, so codes weren’t necessary. But as flying gained popularity in the 1920s, a system was needed to keep the growing number of airports organized.

Airport codes made their debut during the 1930s. In the beginning, airports would use the same two-letter codes given to their cities by the National Weather Service. However, in the 1960s, airports began using a unified three-letter system. Airports that already had a two-letter identifier simply added an “X” to their name. For example, LAX (Los Angeles International Airport) and PHX (Phoenix Sky Harbor International Airport) used to be LA and PH, respectively.

How Airport Codes Are Assigned

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Officially, two governing bodies determine airport codes for all airports around the world. The familiar three-letter code is created by the International Air Transport Association (IATA), a trade association that focuses on the airline industry. These three-letter codes are used by airlines to coordinate flight plans and are the ones you see on tickets.

The other group that determines airport codes is the International Civil Aviation Organization (ICAO). The ICAO is a United Nations subgroup that focuses on maintaining a unified set of aviation standards, and ICAO codes are exclusively used by air traffic control. What separates ICAO codes from IATA codes — besides that amount of letters — is that ICAO codes include a unique country identifier. For example, EWR is KEWR with the “K” identifying that EWR is located in the contiguous United States.

For the most part, airport codes are named either after their location, like BOS for Boston Logan International Airport in Boston, Massachusetts, or after the airport name, like CDG for Charles De Gaulle International Airport in Paris, France.

But there are some instances in the U.S. where intuitive codes aren’t always the case. For instance, Orlando International Airport in Florida is MCO, and O’Hare International Airport in Chicago, Illinois is ORD — neither code resembles the name of the city or airport. In both cases, these airports were once military installations. MCO stands for the now-defunct McCoy Air Force Base, and O’Hare was the former site of Orchard Field.

Airport Code Rules

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There are certain rules that the IATA and ICAO must adhere to. Most of these rules center around U.S. airports, but a few apply to international audiences as well.

“N” cannot be used for domestic airports: For the most part, the U.S. Navy has claimed airport codes that begin with “N” for their bases. This is why Newark International Airport is EWR instead of NEW.

No “K” or “W” airports: In the U.S., only radio stations can have call signs that begin with “K” or “W.” “W” designates all radio stations east of the Mississippi River, like WHTZ (New York’s Z100), while “K” represents all stations west of the river, like Los Angeles’ KIIS-FM.

“Q” cannot be used as the first letter: “Q” is reserved exclusively for international telecommunications, so no matter where you are in the world, you won’t find an airport code that begins with “Q.”

“Y” is only used in Canada: Canadian airport codes used to only have two letters, so in the same way “X” was added to LAX and PHX, “Y” was appended to the front of Canadian airport codes.

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