The Mystery Behind Airport Three-Letter Codes Revealed

Airport codes are a quick way to reference an airport on various travel documents and for radio communication. The three-letter codes, also known as IATA codes, are mostly based on the first three letters of the airport's city and can be found on boarding passes and luggage tags. The four-letter codes, also known as ICAO codes, are used by pilots and air traffic controllers and follow a different structure, with the start of the code denoting the country or region.

The three-letter codes are established by the International Air Transport Association (IATA). The four-letter codes are defined by the International Civil Aviation Organization (ICAO).

Why three letters?

The use of three-letter codes to identify airports arose from the convenience it brought to pilots for location identification in the 1930s. Initially, pilots in the United States used a two-letter code from the National Weather Service (NWS) to identify cities. However, this system had its limitations, as it did not account for cities and towns without an NWS identifier, and it only allowed for a few hundred combinations.

The three-letter system, on the other hand, offered 17,576 permutations, assuming all letters could be used in conjunction with each other. This provided a much larger pool of unique codes and helped to avoid confusion, especially in the case of cities with similar names.

The three-letter code is also easier to use and remember than a longer code would be, for pilots, controllers, travel agents, frequent flyers, and all other stakeholders involved. It is simpler to say and write "LAX" than "Los Angeles International Airport", for example. These codes are also prominent on baggage tags, making it easier for baggage handlers to sort and distribute luggage efficiently.

In addition, the three-letter code system allowed for flexibility and creativity in certain cases. For instance, some airport codes are based on the pronunciation of the location's name rather than the spelling, such as "NAN" for Nadi, Fiji, where the "d" is pronounced as a prenasalized stop ([ⁿd]). Other codes may be derived from a combination of letters in the location's name, such as "JNB" for Johannesburg or "SLC" for Salt Lake City.

While most large airports in Canada have codes that begin with the letter "Y", indicating that the station shared its location with an airport, there are exceptions to this rule, such as "ZBF" for Bathurst, New Brunswick. This highlights the adaptability of the three-letter system to accommodate unique situations and ensure efficient identification of airports worldwide.

How are the codes assigned?

The three-letter airport codes, also known as IATA location identifiers, are assigned by the International Air Transport Association (IATA) and governed by IATA Resolution 763. They are published semi-annually in the IATA Airline Coding Directory.

The codes are often derived from the first three letters of the city in which the airport is located, for example:

• IND for Indianapolis
• JFK for New York's John F. Kennedy
• LHR for London's Heathrow Airport

The code may also be a combination of the letters in the airport's name, such as:

• JNB for Johannesburg
• SLC for Salt Lake City
• SGN for Ho Chi Minh City (formerly known as Saigon)

Sometimes, the airport code reflects the pronunciation of the location, rather than the spelling. For instance, NAN reflects the Fijian pronunciation of "Nadi" as [ˈnandi], where "d" is realised as the prenasalized stop [ⁿd].

In some cases, the code comes from the airport's former or unofficial name. For example, Chicago's O'Hare International Airport is coded ORD for its original name, Orchard Field. Orlando International Airport's code, MCO, comes from McCoy Air Force Base.

For airports that serve cities with multiple airports, the code is often derived from the name of the airport itself, rather than the city it serves. For instance:

• BDL for Bradley International Airport in Hartford, Connecticut
• BWI for Baltimore/Washington International Airport
• LGW for Gatwick Airport in London

Some airports are named for an administrative division or nearby city, rather than the one they are located in. For example, Juan Santamaría International Airport in Alajuela, Costa Rica, uses the code SJO as it is close to the capital, San José, and serves the whole Central Valley.

In the United States, certain letters were reserved or avoided in airport codes. As the U.S. Navy reserved "N" codes, and to prevent confusion with Federal Communications Commission broadcast call signs, which begin with "W" or "K", some airports had to adopt "irregular" codes. For example:

• EWR for Newark, New Jersey
• ORF for Norfolk, Virginia
• BNA for Nashville, Tennessee (originally Berry Field)

Additionally, since three-letter codes starting with "Q" are widely used in radio communication, cities whose names begin with "Q" had to find alternate codes, such as:

• YUL in Montréal, Canada
• YYZ in Toronto, Canada

Canada's unusual codes, which bear little to no similarity to conventional abbreviations of city names, often originated from the two-letter codes used to identify weather reporting stations in the 1930s. The letter preceding the two-letter code would indicate whether the station shared its location with an airport or not. For example:

• "Y" indicated "yes" and was used when the station was located at an airport.
• "W" hinted at "without" and was used when the station was not located at an airport.

Many Canadian airport codes start with "Y", although this is not always the case, and not all airports starting with "Y" are in Canada.

In New Zealand, many airport codes contain the letter "Z" to distinguish them from similar airport names in other countries. For example:

• HLZ for Hamilton
• ZQN for Queenstown
• WSZ for Westport

How are the codes used?

The three-letter airport codes, also known as IATA location identifiers, are used to designate many airports and metropolitan areas worldwide. They are defined by the International Air Transport Association (IATA) and are published semi-annually in the IATA Airline Coding Directory. The codes are used in aviation and logistics, and they are particularly useful for pilots, controllers, travel agents, frequent flyers, computers, and baggage handlers. For example, JFK is the code for New York's John F. Kennedy International Airport, and LHR is the code for London's Heathrow Airport. These codes are often more convenient and easier to use than the full airport names.

The three-letter codes are prominently displayed on baggage tags attached at airport check-in desks, making it easier for baggage handlers to sort luggage by destination airport. The codes are also used in reservations and baggage handling, as well as in flight planning and airline operations.

In some cases, the three-letter codes are derived from the first three letters of the city in which the airport is located. For example, IND is the code for Indianapolis. Sometimes, the code is a combination of the letters in the airport's name, such as JNB for Johannesburg or SLC for Salt Lake City. In other cases, the code may reflect the pronunciation of the location, rather than the spelling. For instance, NAN reflects the Fijian pronunciation of "Nadi" as ["nandi"].

Some airports have codes that do not follow the standard schemes mentioned above. This may be due to the airport serving multiple regions, having a name change, or being named after an administrative division or nearby city. For example, DFW is the code for Dallas/Fort Worth International Airport, which serves two regions. Orlando International Airport's code is MCO, which comes from its former name, McCoy Air Force Base. San Ignacio Town Airstrip in Belize uses the code CYD because it is located in the Cayo District, rather than the town's name.

In addition, some airports have multiple codes, especially those that serve multiple countries. For instance, EuroAirport Basel Mulhouse Freiburg, which serves France, Switzerland, and Germany, has three codes: BSL, MLH, and EAP. The French part of the airport uses MLH for Mulhouse, while the Swiss part uses BSL for Basel. The airport as a whole also has a neutral code, EAP, which stands for EuroAirport.

Why are some codes irregular?

The three-letter airport codes, also known as IATA codes, are used for passenger-facing operations. These are the codes used on tickets, boarding passes, and signage. The codes are determined by how the airport wants to identify itself and the availability of the letter combination.

However, some airport codes are "irregular" and do not follow the usual pattern. This is due to a few reasons:

• Preventing confusion: The U.S. Navy reserved "N" codes, and the Federal Communications Commission reserved broadcast call signs that begin with "W" or "K". Therefore, airports in cities whose names start with these letters had to adopt irregular airport codes. For example, EWR for Newark, New Jersey, and ORF for Norfolk, Virginia.
• Radio communication: Three-letter codes starting with "Q" are widely used in radio communication. Hence, cities whose names begin with "Q" had to find alternative codes, such as SPN for Saipan.
• Historical reasons: Some airport codes are based on former names of the cities or airports. For example, Mumbai was named Bombay during British rule in India, and its airport code BOM is from that era.
• Country-specific practices: In Canada, airport codes usually bear little to no similarity to the city's name. Most large airports in Canada have codes that begin with the letter "Y". This dates back to the 1930s when the Canadian government established airports using the existing two-letter railway codes and added a "Y" to indicate the presence of a weather station.

What are the rules for US airport codes?

Airport codes are three-letter geocodes that are used to designate airports and metropolitan areas around the world. The use of these codes is governed by the International Air Transport Association (IATA) and its headquarters in Montreal, Canada.

In the US, airport codes are assigned by the Federal Aviation Administration (FAA). These codes are three or four letters long and are only used for domestic flight operations. The FAA's Location Identifiers (LIDs) are alphanumeric and can include numbers as well as letters.

When creating airport codes for US cities, there are a few rules that must be followed:

• The US Navy reserves "N" codes, so cities whose names begin with "N" must adopt "irregular" airport codes.
• To prevent confusion with Federal Communications Commission broadcast call signs, which begin with "W" or "K", cities whose names start with one of these letters must also adopt "irregular" codes.
• Since three-letter codes starting with "Q" are widely used in radio communication, cities whose names begin with "Q" must find alternate codes.
• The letters K, N, Q, W, Y, and Z are not supposed to be used at the start of LIDs. K and W are reserved for public radio stations, Q is used in Morse radio codes, N is for Naval Air Bases, and Z designates Air Route Traffic Control Centers.
• EWR for Newark, New Jersey
• HVN for New Haven, Connecticut
• ORF for Norfolk, Virginia
• EYW for Key West, Florida
• BNA for Nashville, Tennessee
• APC for Napa, California
• ILM for Wilmington, North Carolina

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