Jazmin Li
Many airport codes are named after the airport itself, the location, or a historical figure. However, the three-character code is used by a maximum of 17,576 airports worldwide, leading to scarcity. The use of 'X' as a filler letter is a practice to create three-letter identifiers when more straightforward options were unavailable. For example, LA became LAX, and Portland's PD became PDX. Some airports in the United States retained their NWS (National Weather Service) codes and simply appended an X at the end, like PHX for Phoenix.
| Characteristics | Values |
|---|---|
| Airports with two-letter weather station codes | Added an X to the end to create a three-letter code |
| Examples | LA became LAX, Portland's PD became PDX, Birmingham International Airport in the UK is BHX |
| Reason for X | X is a filler or replacement letter |
| Reason for three-letter codes | Too many airports with two-letter codes |
| X represents | Nothing, specifically |
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What You'll Learn
- The letter 'X' is a filler or replacement letter
- Airports changed from two-letter to three-letter codes in the 1930s and 1940s
- The letter 'X' is uncommon in place names, making it a good placeholder
- Some cities use 'X' as shorthand for their airport codes
- The letter 'X' can represent a cross point where people change planes
The letter 'X' is a filler or replacement letter
The letter 'X' in airport codes is often used as a filler or replacement letter. Airport coding first began in the 1930s, and airlines typically chose their own two-letter codes. However, by the late 1940s, there were too many airports, and the system shifted to the three-letter code we know today. This change meant that the letter 'X' was added to the end of many airport codes to complete the new three-letter system. For example, Los Angeles International Airport was originally "LA", but this changed to "LAX" in 1947.
The letter 'X' is also used as a placeholder in some airport codes. For instance, Dubai International Airport in the United Arab Emirates uses the code "DXB" because "DUB" was already taken by Dublin International Airport. In this case, the letter 'X' is used as a filler to differentiate between the two airports. Similarly, Birmingham International Airport in the UK is coded as "BHX" because "BHM" was already assigned to Birmingham Airport in Alabama, USA.
The letter 'X' can also be found in airport codes where it doesn't seem to have a specific meaning. For example, the code for Portland International Airport is "PDX", and the X does not stand for anything. In this case, the X is simply a part of the airport's code name.
The use of 'X' in airport codes is not universal, however. The ICAO Airport Codes in the US, for example, start with the letter 'K', followed by three letters or numbers corresponding to the IATA designation. Despite this, the letter 'X' remains a common feature in many airport codes around the world, often serving as a filler or replacement letter to accommodate the shift to three-letter codes.
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Airports changed from two-letter to three-letter codes in the 1930s and 1940s
Airport codes were first established in the 1930s, and airlines could choose their two-letter designations. However, as air travel expanded rapidly, more airports were established, and within a decade, a two-letter code was no longer sufficient. There are only 676 possible combinations of two letters, but there are over 1,200 international airports today.
The expansion of air travel in the 1930s and 1940s led to the adoption of three-letter airport codes to ensure uniqueness and avoid confusion. The International Air Transport Association (IATA) stepped in during the 1960s to standardize the process. The change to three-letter codes meant that some airports added an "X" as a filler or replacement letter to complete the new three-letter format, for example, Los Angeles International Airport changed from "LA" to "LAX" in 1947.
The three-letter codes are usually derived from the first three letters of the city name, like Atlanta (ATL), Boston (BOS), or New York's John F. Kennedy Airport (JFK). However, some codes are named after the airport itself, like Charles De Gaulle Airport in Paris (CDG). Other codes may be based on the airport's location, like Harrisburg International Airport in Middletown, Pennsylvania (MDT), or they may honour a historical figure, like Knoxville Airport in Tennessee (TYS).
It's worth noting that while airports can change their names, IATA codes are typically permanent and cannot be easily changed without a strong justification. These codes are essential for air traffic control, airline logistics, and navigation systems, ensuring consistent identification of airports worldwide.
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The letter 'X' is uncommon in place names, making it a good placeholder
The letter "X" appearing in airport codes has sparked curiosity among many. Airport codes were originally two-letter codes chosen by airlines themselves. However, as the number of airports increased, a shift to a three-letter system was implemented in the 1930s to 1940s. This transition led to the addition of "X" as a placeholder for cities that previously had a two-letter abbreviation, ensuring the new code remained recognizable. For example, Los Angeles International Airport changed from "LA" to "LAX." The "X" serves as a filler, assuming that it is unlikely to be demanded by another city due to the rarity of "X" in place names.
The use of "X" as a placeholder is further illustrated by Dubai's airport code, "DXB." The desired code, "DUB," was already assigned to Dublin. Hence, the letter "X" was used as a substitute, forming "DXB." Similarly, Birmingham International Airport in the UK is coded as "BHX" because "BHM" was already taken by Birmingham Airport in Alabama. In some instances, the "X" is not merely a placeholder but part of the city's name, such as "MEX" for Mexico City.
The letter "X" has also been speculated to represent a cross point where travellers change planes or transfer to another city. This hypothesis adds a layer of functionality to the letter's inclusion in airport codes. While the exact reasoning behind the choice of "X" as a placeholder remains uncertain, its uncommon nature in place names makes it a convenient and memorable filler in airport coding systems.
The rarity of "X" in place names is a significant factor in its selection as a placeholder. It ensures that new three-letter airport codes are distinct and easily identifiable, avoiding confusion with existing codes. This characteristic of the letter "X" has proven valuable in the aviation industry, contributing to the efficient management of a growing number of airports worldwide.
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Some cities use 'X' as shorthand for their airport codes
Airport codes are three-letter designations given to airports by the International Air Transport Association (IATA). These codes are visible on everything from booking platforms to baggage tags and boarding passes.
When airport coding first began in the 1930s, airlines typically chose their own two-letter codes. However, as the number of airports increased, the system shifted to the three-letter code we know today. Airports with two-letter codes received an X at the end (LA became LAX and Portland's PD became PDX), and every subsequent airport was given three letters.
The letter 'X' in airport codes is often used as a placeholder or filler letter. For example, Dubai is DXB because DUB was already taken by Dublin International Airport. The X has no specific meaning and is used as a replacement when the desired two-letter code is already in use.
In some cases, the letter 'X' makes sense because the city name contains an 'X', such as MEX for Mexico City. However, more often than not, the 'X' is simply a filler or replacement letter.
The use of 'X' in airport codes is just one of the many quirks of airport coding. While some codes are immediately obvious, others are harder to decipher and may require knowledge of the airport's history or previous names.
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The letter 'X' can represent a cross point where people change planes
Airport codes are three-letter designations given to airports by the International Air Transport Association (IATA). These codes are visible on everything from booking platforms to baggage tags and boarding passes.
The letter 'X' is very common in IATA airport codes. Sometimes it makes sense because the city name contains the letter 'X'—for example, MEX for Mexico City. However, more often than not, the letter 'X' is a filler or replacement letter.
The use of 'X' in airport codes can be traced back to the 1930s when airports shifted from using two-letter National Weather System (NWS) city codes to the three-letter IATA system. Airports with two-letter weather station codes simply added an 'X' to the end to create a new three-letter code. For instance, Los Angeles International Airport changed from 'LA' to 'LAX', and Portland's 'PD' became 'PDX'.
The letter 'X' can be interpreted as representing a cross point where people change planes or travel to another city. This interpretation aligns with the idea of an interchange or transfer point in a transportation network.
In some cases, the 'X' is used as a placeholder or filler letter when the desired code is already taken by another airport. For example, Dubai International Airport uses the code 'DXB' because 'DUB' was already assigned to Dublin International Airport. Similarly, Marion Downs Airport in Australia is designated as 'MXD' instead of 'MAD', which is the code for Madrid Barajas International Airport.
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Frequently asked questions
Airport codes that end in X do so because they originally had a two-letter code or abbreviation and added the X when they changed to a three-letter system.
As the aviation industry expanded in the 1930s and 1940s, there were too many airports for the two-letter system to accommodate.
Not always. Sometimes the X is used as a filler or replacement letter, as in the case of Dubai's DXB code, which was chosen because DUB was already taken by Dublin.
Both. People often use airport codes as shorthand for the city itself, but the codes are designated for the airports.
No. Airport codes typically have three letters, but some have two or four.
