Why Do Airport Codes Always Have 3 Letters?

Airport codes are three-letter acronyms that are used to quickly reference a particular airport. They are vital in the world of air travel and are used on various travel documents, such as boarding passes and luggage tags, as well as for radio communication. The three-letter code is determined by ensuring that it is unique and not in use by any other entity. The code might be based on the name of the airport, the name of the city, or some other meaningful and relevant identifier if those letters are already taken.

Why airport codes are useful

Airport codes are useful because they provide a standardised way of identifying airports across the world. The three-letter codes are unique to each airport and are easier to remember and quicker to process than full airport names.

The International Air Transport Association (IATA) introduced the three-letter code system in the 1930s to replace the two-letter codes that were previously used by pilots in the US. The two-letter system was becoming unmanageable as it did not work for cities without a National Weather Service (NWS) identifier, and there were only a few hundred combinations available. The three-letter system allows for 17,576 permutations, assuming all letters can be used in conjunction with each other.

The three-letter codes are particularly useful when a city has multiple airports, as is the case in most major cities. For example, instead of having to specify that you are flying to "New York City – LaGuardia", you can simply refer to the airport code, LGA. They are also useful when cities around the world share the same name. For instance, "Portland" in the US could refer to Oregon's largest city or Maine's largest city.

The three-letter codes are also used on baggage tags, boarding passes, and inflight trackers, and have even become synonymous with certain cities.

How airport codes are assigned

Airport codes are assigned by two official entities: the International Civil Aviation Organization (ICAO) and the International Air Transport Association (IATA).

The ICAO assigns four-letter codes, the first of which indicates the country and the remaining three indicate the specific airport. For example, Florida's Fort Lauderdale-Hollywood International Airport is assigned the code KFLL, with the "K" denoting the airport is in the US.

The IATA assigns the three-letter codes that are most familiar to passengers, such as "LAX" for Los Angeles International Airport. These codes are determined by first ensuring they are unique and not in use by any other entity. The code might be based on the name of the airport, the name of the city, or some other meaningful and relevant identifier if the desired letters are already taken.

The practice of assigning airport codes began in the 1930s, when airlines typically chose their own two-letter codes. As the number of airports increased, the system became impractical and, by the late 1940s, the three-letter code system we know today was introduced. IATA stepped in during the 1960s to standardise the process and prevent confusion.

The three-letter code system allows for 17,576 permutations, assuming all letters can be used in conjunction with each other. This has presented a challenge as, since the 1960s, over 10,000 airport codes have been registered.

• City name directly: AMS for Amsterdam, SYD for Sydney, and MEX for Mexico City.
• City name abbreviation: HKG for Hong Kong, JNB for Johannesburg, or SFO for San Francisco.
• Airport name: JFK for New York's John F. Kennedy Airport, and LGA for LaGuardia Airport.
• Airport location: LHR for London-Heathrow Airport, HND and NRT for Tokyo's Haneda and Narita airports, respectively.
• Historical city or airport name: BOM for Mumbai (formerly Bombay), CAN for Guangzhou (formerly Canton), and LED for Saint Petersburg (formerly Leningrad).
• Filler letters: LAX for Los Angeles (originally "LA", with "X" added when the three-letter system was introduced).

ICAO vs IATA codes

Airport codes are a common source of confusion, and there are three main types: IATA, ICAO, and LID codes. IATA (International Air Transport Association) codes are 3-letter codes that are the most widely understood and used for airline travel. ICAO (International Civil Aviation Organization) codes are 4-letter codes that are the next most widely recognised and are used more broadly for international flight operations. LID codes are the least understood and are mostly used in the US, Canada, Mexico, and Russia.

IATA codes are used for airline travel purposes such as schedules, bookings/ticketing, boarding passes, flight status, and baggage tags. They are also used for city and metropolitan area codes, which in many cases duplicate a related airport code.

ICAO codes are used for interoperability between air navigation service providers, so pilots, dispatchers, and air traffic controllers work primarily in the ICAO code scheme. They are also used to identify other aviation facilities such as weather stations, international flight service stations, or area control centres, whether or not they are located at airports. The first one or two letters of the ICAO code indicate the country, and the remaining letters identify the airport.

LID codes are "local identifiers", local to the country in which they are assigned. They are used to uniquely identify airports for operational reasons by air traffic control.

ICAO and IATA codes are assigned for different purposes. ICAO, as a UN body, focusses on the international harmonisation of civil aviation regulations. Its codes are used for official purposes such as Air Traffic Control and flight plans. IATA, as a trade association, focusses on making air traffic businesses profitable, safe, secure, reliable, and efficient. Its codes are mainly used for ticketing.

History of airport codes

The use of airport codes began in the 1930s, when airports in the US would use two-letter city codes from the National Weather Service (NWS). As air travel became more popular, there was an increasing number of airports, including in cities with no NWS code, so three-letter codes were introduced.

The three-letter code is determined by first ensuring that it's unique and not in use by any other entity. The code might be assigned based on the name of the airport, the name of the city, or some other meaningful and relevant identifier if those letters are already taken. No two airports share the same IATA code.

• City name directly: AMS for Amsterdam, SYD for Sydney, and MEX for Mexico City.
• City name abbreviation: HKG for Hong Kong, JNB for Johannesburg, or SFO for San Francisco.
• Airport name: JFK for New York's John F. Kennedy Airport and LGA for LaGuardia Airport.
• Historical city names: BOM for Mumbai (formerly Bombay), CAN for Guangzhou, China (formerly Canton), and LED for St. Petersburg, Russia (formerly Leningrad).
• Historical airport names: ORD for Chicago O'Hare (formerly Orchard Field), MCO for Orlando International Airport (formerly McCoy Air Force Base), and MSY for Louis Armstrong New Orleans International Airport (formerly Moisant Stock Yards).
• Airport location names: HND for Tokyo Haneda Airport and NRT for Tokyo Narita Airport.
• Filler letters: LAX for Los Angeles (formerly LA) and DXB for Dubai (with "X" as a filler letter).

Unusual airport codes

Airport codes are typically three-letter combinations, commonly called IATA codes, that are used to easily identify a specific airport. While some airport codes are easy to understand, like MIA for Miami International Airport, others are harder to decipher. Here is a list of unusual airport codes and the stories behind them:

• MSY for Louis Armstrong New Orleans International Airport: The code comes from the airport's previous name, Moisant Stock Yards, named after the pioneering pilot John Moisant, who died in a plane crash on the site in 1910.
• ORD for Chicago O'Hare International Airport: The code comes from the airport's former name, Orchard Field Airport, named after a nearby farming town.
• YUL for Montreal-Trudeau International Airport: The "Y" at the beginning of the code indicates that there was a weather reporting station nearby. "UL" was the radio station code for Montreal.
• LAX, PHX, and PDX: The "X" at the end of these codes for Los Angeles, Phoenix, and Portland is an arbitrary placeholder added when airport codes expanded from two to three letters in the 1940s.
• BNA for Nashville International Airport: The code comes from the airport's former name, Berry Field Nashville, established in 1937.
• CVG for Cincinnati/Northern Kentucky International Airport: The code is derived from Covington, Kentucky, the closest city to the airport at the time of construction.
• ECP for Northwest Florida Beaches International Airport: The code is rumoured to stand for "Everyone Can Party," referring to the area's popularity among Spring Break revellers.
• FAT for Fresno Yosemite International Airport: The code comes from the airport's former name, Fresno Air Terminal.
• GEG for Spokane International Airport: The code honours Army aviator Major Harold Geiger, after whom the airport was renamed in 1946.
• MCO for Orlando International Airport: The code comes from the airport's former occupant, McCoy Air Force Base, which closed in 1975.
• OGG for Kahului Airport, Maui: The code honours Captain Bertram "Jimmy" Hogg, a Hawaiian Airlines pilot and aviation pioneer.
• GRR for Grand Rapids, Michigan: A playful warning about grrizzly bears.
• YUM for Yuma, Arizona: A playful reference to dining options in the area.
• IOU for Île Ouen, New Caledonia: A playful reference to owing someone money.
• PEE for Perm, Russia: A playful reference to passengers who prefer the aisle seat.
• WOW for Willow, Alaska: A playful expression of amazement.
• GAG for Gage, Oklahoma: A playful reaction to a passenger's unpleasant-smelling food.
• FUN for Funafuti, Tuvalu: A playful invitation to relax in the sun.
• AWK for Wake Island Airfield: A playful reference to awkwardness.
• BUM for Butler Airport, Missouri: A playful reference to a less elegant backside.
• DAD for Da Nang, Vietnam: A playful reference to a parent.
• COW for Coquimbo, Chile: A playful reference to cows blocking the landing strip.
• BRR for Barra, Scotland: A playful reference to cold temperatures.
• IDK for Indulkana, Australia: A playful response when unsure about travel plans.
• SAD for Safford, Arizona: A playful reference to feeling sad.
• EEK for Eek, Alaska: A playful reference to an exclamation of fear.
• BOO for Bodø, Norway: A playful Halloween reference.
• DOH for Doha, Qatar: A playful reference to a well-known cartoon character.
• ODD for Oodnadatta, Australia: A playful reference to something strange.

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