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A location identifier is a symbolic representation for the name and the location of an airport, navigation aid, or weather station, and is used for staffed air traffic control facilities in air traffic control, telecommunications, computer programming, weather reports, and related services.

ICAO location indicator

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Main article: ICAO airport code

The International Civil Aviation Organization establishes sets of four-letter location indicators which are published in ICAO Publication 7910. These are used by air traffic control agencies to identify airports and by weather agencies to produce METAR weather reports. The first letter indicates the region; for example, K for the contiguous United States, C for Canada, E for northern Europe, R for the Asian Far East, and Y for Australia. Examples of ICAO location indicators are RPLL for Manila Ninoy Aquino Airport, KCEF for Westover Joint Air Reserve Base and EGLL for London Heathrow Airport.

IATA identifier

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Main article: IATA airport code

The International Air Transport Association uses sets of three-letter IATA identifiers which are used for airline operations, baggage routing, and ticketing. There is no specific organization scheme to IATA identifiers; typically they take on the abbreviation of the airport or city such as MNL for Manila Ninoy Aquino Airport.

In the United States, the IATA identifier usually equals the FAA identifier, but this is not always the case. A prominent example is Sawyer International Airport in Marquette, Michigan, which uses the FAA identifier SAW and the IATA identifier MQT.

FAA identifier

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The Federal Aviation Administration location identifier (FAA LID) is a three- to five-character alphanumeric code identifying aviation-related facilities inside the United States, though some codes are reserved for, and are managed by other entities.[1]: §1–2-1 

For nearly all major airports, the assigned identifiers are alphabetic three-letter codes, such as ORD for Chicago O’Hare International Airport. Minor airfields are typically assigned a mix of alphanumeric characters, such as 8N2 for Skydive Chicago Airport and 0B5 for Turners Falls Airport. Private airfields are assigned a four-character identifier, such as 1CA9 for Los Angeles County Fire Department Heliport. The location identifiers are coordinated with the Transport Canada Identifiers described below.

In general, the FAA has authority to assign all three-letter identifiers (except those beginning with the letters K, N, W, and Y), all three- and four-character alphanumeric identifiers, and five-letter identifiers for the United States and its jurisdictions. The Department of the Navy assigns three-letter identifiers beginning with the letter N for the exclusive use of that department. Transport Canada assigns three-character identifiers beginning with Y. The block beginning with letter Q is under international telecommunications jurisdiction, but is used internally by FAA Technical Operations to identify National Airspace equipment not covered by any other identifying code system. The block beginning with Z identifies United States Air Route Traffic Control Centers.[1]: §1–2-2 

In practice, the assigned identifiers are not always consistent with the current "encoding" rules adopted by the FAA, nor are all the assigned identifiers distinct between the United States and Canada. The coding system has evolved over time, and to ensure safety and reduce ambiguity, many "legacy" codes have remained intact,[1]: §1–2–4  even though they violate the currently ordered rules. For this reason, the FAA regularly publishes detailed listings of all codes it administers[1]: §6 

General assignment patterns

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In general, three-letter identifiers are assigned as radio call signs to aeronautical navigation aids; to airports with a staffed air traffic control facility or navigational aid within airport boundary; to airports that receive scheduled route air carrier or military airlift service, and to airports designated by the United States Customs Service as airports of entry. Some of these identifiers are assigned to certain aviation weather reporting stations.

Most one-digit, two-letter identifiers have been assigned to aviation weather reporting and observation stations and special-use locations. Some of these identifiers may be assigned to public-use landing facilities within the United States and its jurisdictions, which do not meet the requirements for identifiers in the three-letter series. In this identifier series, the digit is always in the first position of the three-character combination.

Most one-letter, two-digit identifiers are assigned to public-use landing facilities within the United States and its jurisdictions, which do not meet the requirements for identifiers in the three-letter series. Some of these identifiers are also assigned to aviation weather reporting stations.

  • One-letter, two-digit identifiers are keyed by the alphabetical letter. The letter may appear in the first, middle or last position in the combination of three characters. When the letter signifies an air traffic control center's area, the assignment will not change if the center's boundaries are realigned.
  • Identifiers in this series which could conflict with the Victor, Jet or colored airway numbers are not assigned.

Two-letter, two-digit identifiers are assigned to private-use landing facilities in the United States and its jurisdictions which do not meet the requirements for three-character assignments. They are keyed by the two-letter Post Office or supplemental abbreviation of the state with which they are associated. The two-letter code appears in the first two, middle, or last two positions of the four-character code.

The use of the FAA identifier system in meteorology ended in 1996 when airways reporting code was replaced by METAR code. The METAR code is dependent wholly on the ICAO identifier system.

National Civil Aviation Agency of Brazil

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Since January 2019, the National Civil Aviation Agency of Brazil (ANAC) issues a six-digit designator called Aerodrome Identification Code (Portuguese: Código de Identificação de Aeródromo, CIAD) for each aerodrome. The first two digits are the letters related to the State of the Federation where the aerodrome is located and the next four digits are numbers assigned by ANAC. In the case of military aerodromes, the first number is 9.[2]

Transport Canada identifier

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Transport Canada assigns two-, three-, and four-character identifiers, including three-letter identifiers beginning with letters Y and Z, for its areas of jurisdiction. These identifiers are designed to mesh with the FAA Identifier system described above, though a few conflicts exist.[citation needed]

Federal Civil Aviation Agency of Mexico

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The Federal Civil Aviation Agency of Mexico (Agencia Federal de Aviación Civil, AFAC) is a designator of airfield codes, each consisting of three letters, used to identify each civil airfield in Mexico. (These characters are chosen with the same methodology as for IATA codes, i.e. taking three letters of the airfield name, for example ZPU for Zacapu Airstrip.) These airfields can be airports, private airstrips, land heliports, boat heliports, and platform helipads. For more substantial airports the IATA designators are used, for example TLC for Toluca International Airport, although there are some exceptions, such IATA XAL and AFAC ALA for Alamos National Airport, Sonora.

Russian location identifier

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Within Russia (and before 1991 within the Soviet Union), there are airport identifiers (внутренний код - internal code) having three Cyrillic letters.[3] They are used for e.g. ticket sales. Some small airports with scheduled flights have no IATA code, only this code and perhaps an ICAO code. Unlike the IATA codes, they changed when renaming some cities of the former USSR in the 1990s, e.g. Saint Petersburg (formerly Leningrad), which was ЛЕД and became СПТ. As of 2009, about 3,000 code combinations of internal code are in use. List of three-letter internal cyrillic codes used in Russia can be found in the list of airports in Russia.

Many smaller aerodromes in Russia do not have an ICAO code. Instead, they are assigned an entry in the State and Experimental Aviation Point Location Index, or perhaps two: one civilian, normally beginning with Cyrillic "У" (=Latin "U"), the other for "state" or military operations, almost always the same except that the first character is now a Cyrillic "Ь" (=Latin "X"). These codes are given in the official document [4] which has separate columns for national codes (civilian), national codes (military & state), and some also have "international" codes; only the latter correspond to ICAO codes. For example, Magadan Sokol Airport is listed with the national civilian code УХММ, the national military code ЬХММ, and the "international" UHMM.

WMO station identifiers

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The World Meteorological Organization used a system of five-digit numeric station codes to represent synoptic weather stations. An example is 72295 for Los Angeles International Airport (LAX).

  • The first digit specifies the region: 0 to 1 for Europe, 2 to 3 for Russia, 4 for Asia, 5 for the Far East, 6 for Africa, 7 for North America, 8 for South America and Antarctica, and 9 for the Pacific.
  • The remainder of the digits are set at the regional and national level.

A modernization of WMO station identifiers was performed as part of the WMO Integrated Global Observing System (WIGOS).[5]

  • Previously, observing stations were registered using WMO Identifiers, which had the form of five-digit numbers for synoptic and climate stations. Many countries ran out of numbers within their allowable ranges and were unable to register additional stations.
  • The new WIGOS Station Identifiers (WSI) were created with a structure of four blocks, using digits and alphanumeric characters that allow essentially an unlimited number of stations to be registered.
  • The four parts of WSI are identifier series, issuer, issue number, and identifier. Existing WMO identifiers were migrated to the WSI format, e.g. "0-20000-0-72295" for LAX. "20000" is the issuer code for WMO itself, and countries use their three-digit ISO code as issuer code

A presentation at the WMO site[6] explains:

  • A critical component: WIGOS Station Identifiers Basic concept of the WIGOS Station Identifiers (WSIs):
    • Many countries have run out of numbers within their allowable ranges and are thus not able to register additional stations
    • Created to allow essentially an unlimited number of stations to be registered in WIGOS
    • Its implementation by Members is mandatory, as part of the WIGOS Technical Regulations, including the WIGOS Metadata Standard
    • WSIs should not have meaning in themselves: Users should not look for metadata in the patterns of a WSI, they should go to OSCAR/Surface for the metadata of the station associated with that WSI
  • Assigning of WSIs (A)
    • For "new stations" (those that started to operate or became affiliated with a WMO Program after 1 July 2016) to develop and document their WSI national schemas, meaning:
      • using the three-digit ISO Country code in the Issuer of Identifier (second block)
      • and defining the national rules for distributing the numbers in the third and fourth blocks (Issue Number and Local Identifier) for the stations in their territory
    • For stations registered in WMO No. 9 Volume A prior to July 2016:
      • They have been migrated into OSCAR/Surface with their traditional five-digit WMO identifiers being automatically converted into WSI:
      • range 20000–20010 in the second block, "0" in the third block and the traditional WMO ID in the fourth block.

United States weather agency identifiers

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The National Weather Service uses several schemes for identifying stations. It typically relies on the ICAO and WMO identifiers, although several weather forecast offices (WFOs) and weather radar sites that have moved away from airports have been given their own codes which do not conflict with existing codes. These typically end in X, such as where Birmingham, Alabama (BHM) had its radar site replaced by one south of the city (BMX), or where the Knoxville (TYS) office was moved to nearby Morristown, Tennessee (MRX). Others have changed such that Miami, Florida is now MFL instead of MIA, and Dallas/Fort Worth (formerly DFW) is now FWD. Climatological applications use the WBAN (Weather Bureau Army Navy) system, which is a five-digit numeric code for identifying weather stations under its jurisdiction.

Recently it began using four-letter-plus-one-digit identifiers for specialized weather requirements such as hydrometeorological stations. These are used by the USFS RAWS system, and by the stream gauges operated by the USGS, both of which report through GOES weather satellites operated by NOAA. These use three letters which are a mnemonic for the location, followed by the first letter of the U.S. state, followed by a numeral indicating the alphabetical order within that letter (for example, North Carolina stations end with N7). The mnemonic may be the nearest town, or the name of the stream, or a combination of the two; and the same names may be rearranged into different mnemonics for different nearby locations. For example, VING1 is the gauge at Vinings, Georgia, and is differentiated from other stations along the Chattahoochee River (such as CHAG1 in nearby Oakdale) which are also at the Atlanta city limit like Vinings is, and from other streams in Atlanta such as Peachtree Creek (AANG1).

The United States Air Force Weather Agency (AFWA), acting on behalf of all the American military services, assigns special use ICAO identifiers beginning with "KQ", for use by deployed units supporting real-world contingencies; deployed/in-garrison units providing support during exercises; classified operating locations; and units that have requested, but not yet received a permanent location identifier.

One system still used by both the Air Force and National Climatic Data Center is the Master Station Catalog or MASLIB code. This is a 6-digit numeric code that is essentially the same scheme as the WMO station identifier but adds an extra digit, allowing many more stations to be indexed. This extra digit is always "0" when referencing an actual WMO station using the five-digit identifier, but may be 1..9 to reference other stations that exist in the vicinity. The MASLIB identifiers are not generally recognized outside the United States.

Transplanted identifiers

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There have been rare instances where identifiers have been transplanted to new locations, mainly due to the closure of the original airport. Prominent examples are DEN/KDEN, which migrated from Stapleton International Airport to Denver International Airport in 1996, and AUS/KAUS, which migrated from Austin Mueller Municipal Airport to Austin–Bergstrom International Airport in 1999. Both of these cases occurred because the original locations were closed.

Occasionally a code will be discontinued entirely, with no successor. Sometimes this is a small airport that has closed, such as Stone Mountain Airport, whose identifier 00A is now used for an R/C heliport in Bensalem, Pennsylvania. In another case, the identifiers for Idlewild Airport in New York were changed to JFK and KJFK when it was renamed after John F. Kennedy, and its original IDL and KIDL were later reused for Indianola Municipal Airport in Indianola, Mississippi.

Transplanted identifiers tend to be poorly documented, and can cause problems in data systems and software which process historical records and in research and legal work. A similar problem also exists for broadcast callsigns.

See also

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  • UN/LOCODE: locations used in trade and transport with functions such as seaports, rail and road terminals, airports, Postal Exchange Office and border crossing points

References

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[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Location identifier

View on Grokipedia
from Grokipedia
A location identifier is an assigned alphanumeric code used to simplify the identification of facilities such as areas, navigational aids, stations, and locations. These codes serve as symbolic representations that enable efficient communication among pilots, air traffic controllers, and operational personnel worldwide. The most prominent types of location identifiers include the four-letter codes established by the (ICAO), which designate aerodromes, heliports, and other aviation entities globally for purposes like and international coordination. In parallel, the (IATA) assigns three-letter codes to airports and intermodal locations such as bus, ferry, or train stations, primarily supporting commercial operations including ticketing, baggage handling, and reservations. Within the United States, the (FAA) issues Location Identifiers (LIDs), typically three to five characters long, tailored for domestic use in charts, flight plans, and NOTAMs, with assignments managed to avoid conflicts and ensure uniqueness. These systems are governed by specific standards: ICAO's codes follow rules in Doc 7910, the Location Indicators Manual, which bases assignments on geographic locations; IATA's are cataloged in the Airline Coding Directory; and FAA LIDs are detailed in Order JO 7350.9, emphasizing permanence unless operational changes necessitate revisions. While distinct, these identifiers often align for major airports (e.g., ICAO KJFK corresponds to IATA JFK and FAA JFK), promoting across aviation domains.

International Aviation Identifiers

ICAO Location Indicators

ICAO Location Indicators are unique four-letter alphanumeric codes assigned to designate aerodromes, airports, heliports, and other aviation-related geographical locations worldwide. Established by the (ICAO), these indicators serve as standardized identifiers within the international aeronautical telecommunication service, facilitating precise communication and coordination among aviation stakeholders. They are compiled and published in ICAO Document 7910, Location Indicators, which also includes corresponding three-letter (IATA) codes where applicable, along with addresses for (FIR) and upper flight information region (UIR) centers. The structure of ICAO Location Indicators follows a systematic four-letter format designed for global organization. The first one or two letters indicate the country or geographical region, while the remaining letters identify the specific location. For example, codes for the typically begin with 'K' followed by a three-letter identifier, such as KJFK for in New York. This hierarchical design ensures no duplication and supports efficient international referencing. Assignment of these indicators is coordinated through ICAO's nine regional offices, which oversee the process to maintain uniqueness and alignment with global standards. National authorities typically propose codes for new or modified facilities, submitting requests that include details on the location's aeronautical significance, such as its role in air traffic services or meteorological reporting. The regional office reviews and approves the proposal, incorporating it into subsequent editions of Doc 7910, which is updated quarterly to reflect changes. This decentralized yet supervised approach allows for adaptability while upholding ICAO's standardization principles. In operations, ICAO Location Indicators are essential for seamless integration across key systems and procedures. They appear in Item 16 of ICAO forms to denote departure and destination aerodromes, enabling accurate routing and clearance issuance by (ATC). Similarly, they form the location identifier in Notices to Air Missions (NOTAMs), alerting pilots to temporary changes like runway closures or airspace restrictions, and are used in ATC for unambiguous communication. Beyond airports, the codes extend to other sites like meteorological offices and communication stations, supporting the (AFTN). Historically, their evolution traces to the post-World War II era, with standardization formalized under the 1944 Chicago Convention that birthed ICAO in 1947; this framework addressed the chaos of disparate national systems by promoting uniform codes for enhanced safety and efficiency in burgeoning international . Following ICAO amendments adopted in to Annexes 2 (Rules of the Air) and 10 () for integrating remotely piloted aircraft systems (RPAS) within unmanned aircraft systems (UAS), Doc 7910 has seen expansions to accommodate emerging facilities. These updates enable the assignment of location indicators to vertiports and UAS operational sites, supporting digital aviation ecosystems for beyond-visual-line-of-sight (BVLOS) operations and infrastructure.

IATA Airport Codes

IATA airport codes, formally known as location identifiers, are unique three-letter alphanumeric codes assigned by the (IATA) to airports, cities, and other transport hubs involved in and intermodal travel. These codes serve as concise identifiers essential for streamlining operations, including flight scheduling, passenger ticketing, baggage handling, and reservations processing. As outlined in the IATA Standard Schedules Information Manual (SSIM), they standardize the exchange of scheduling data among airlines, airports, and global distribution systems (GDS), enabling efficient coordination of commercial services worldwide. The structure of IATA codes consists of three uppercase letters, typically derived from the name of the airport or city for mnemonic ease, such as LAX for Los Angeles International Airport or SYD for Sydney Kingsford Smith Airport. This design prioritizes brevity and recognizability for passengers and airline staff, while ensuring no overlap with the four-letter ICAO location indicators used for and operational purposes. Assignments follow strict guidelines to maintain global uniqueness, with one code often serving single-airport cities and separate metropolitan codes for multi-airport regions, like WAS encompassing Washington, D.C. airports. The assignment process is governed by IATA Resolution 763, which requires requests from airlines or computer reservation systems (CRSs) to initiate allocation, incorporating input from relevant airports and carriers to reflect operational needs. IATA's headquarters in administers this, publishing updates in the Airline Coding Directory three times annually; codes are generally permanent, with changes only in cases of mergers, closures, or safety concerns, such as reallocations post-airport renaming. As of 2025, over 11,300 codes are active, with approximately 40 to 50 new ones issued each year to accommodate expanding commercial networks. Periodic reviews ensure codes remain relevant amid industry evolution. In practice, IATA codes are integral to aviation ecosystems, appearing on tickets, boarding passes, and baggage tags to facilitate seamless passenger journeys. They underpin GDS platforms like Sabre for real-time reservations and itinerary management, while supporting mobile travel apps for flight tracking and bookings. For instance, entering LAX or SYD in a booking system instantly retrieves relevant airport details, enhancing efficiency in global travel. Post-COVID-19 recovery has seen air travel demand reach 99% of 2019 levels by late 2023, reactivating services at numerous airports and boosting the operational use of dormant codes as routes resume.

National Aviation Identifiers

FAA Location Identifiers

The (FAA) assigns location identifiers, commonly known as FAA Location Identifiers or LIDs, to simplify the identification of facilities within the , including airports, heliports, bases, and other landing areas. These three-letter alphanumeric codes serve as standardized references for , aeronautical charting, , and regulatory purposes, as outlined in FAA Order JO 7350.9GG. Unlike international ICAO indicators, which use four letters, FAA LIDs are primarily domestic and prefixed with "K" (e.g., KORD) when aligned with ICAO for global flights. They are essential for ensuring clear communication in and are authorized under FAA policy to support safe and efficient operations in the (NAS). The structure of FAA Location Identifiers follows specific patterns to promote clarity and minimize confusion. Most are three-letter codes, selected for phonetic distinctiveness and ease of pronunciation, with provisions to avoid duplication within the same facility type—such as limiting one three-letter code per unless separated by at least 200 nautical miles. Assignment prioritizes facility names or geographic proximity, often incorporating initials or abbreviations that reflect , like "ORD" for Chicago O'Hare International Airport or "LAX" for , though the FAA does not mandate strict regional prefixes. For private-use airports or certain weather stations, four-character codes (e.g., two letters followed by two numbers) may be used, while five-letter pronounceable codes apply to airspace fixes. Temporary "Q-" prefixed identifiers can be assigned for construction sites, testing, or contingencies by the U.S. or FAA as needed. These patterns ensure compatibility with voice communications and reduce errors in high-traffic environments. The assignment process is managed by the FAA's Mission Support Services, Aeronautical Information Services (AIS) group, which evaluates requests to prevent conflicts and maintain consistency across the . Facility owners or operators must submit written requests at least 120 days in advance to AIS in , including details on the facility's location, type, and intended use; AIS then assigns a permanent identifier unless operational changes warrant revocation. Once approved, identifiers are published in official FAA resources, such as the National Flight Data Digest (NFDD) and the electronic Resources (eNASR) database, which serve as the authoritative lists for professionals. This centralized process supports ongoing updates to accommodate new facilities, with the most recent comprehensive revision to the assignment guidelines occurring in January 2024 via Order JO 7350.9GG. In practice, FAA Location Identifiers are integral to (VFR) and (IFR) operations, appearing on sectional aeronautical charts, en route charts, and in tools like the FAA's Chart Supplement. Pilots use them for filing flight plans, requesting clearances, and navigating via databases such as the Airport/Facility Directory; for instance, "JFK" designates in New York. Air traffic controllers employ these codes for radio communications and radar identification, enhancing . As part of the FAA's NextGen modernization efforts, location identifiers are increasingly integrated into digital systems for automated flight data processing and trajectory-based operations, improving efficiency in the evolving . Recent developments in 2024, including Engineering Brief 105A on vertiport design, extend this framework to support advanced air mobility (AAM) infrastructure like drone vertiports, which are assigned identifiers akin to heliports to enable safe integration of (eVTOL) operations.

Transport Canada Identifiers

Transport Canada identifiers are four-letter alphanumeric codes assigned to airports, aerodromes, and other aviation facilities across , serving as standardized symbols for , regulation, and operational coordination. These identifiers facilitate precise communication in , , and aeronautical information services while ensuring compatibility with international standards for North American integration. Managed under the oversight of 's branch, they support , incident reporting, and enhanced in diverse environments, including remote and northern regions. The structure of Transport Canada identifiers adheres to ICAO conventions outlined in Doc 7910, beginning with the national prefix "C" for followed by three additional characters that denote the specific location or facility. For instance, CYYZ designates , while CYVR identifies ; this format distinguishes Canadian sites globally and avoids overlap with other regions. Unlike purely domestic systems, the prefix ensures harmonization for international flights, with the trailing three letters often aligning with IATA codes for commercial use. Assignment of these identifiers is handled by Transport Canada's Aeronautical Information Management (AIM) group in collaboration with , the designated , following ICAO guidelines and national regulatory needs. Requests for new codes or modifications are evaluated based on facility certification, operational requirements, and geographic uniqueness, with final approvals ensuring no conflicts with existing assignments. Updates, including additions for emerging sites, are disseminated through the (CFS), a key aeronautical publication that lists approximately 2,000 certified and registered Canadian facilities, encompassing remote northern aerodromes critical for search-and-rescue and resource extraction. In practice, identifiers appear in official aeronautical charts, NOTAMs (Notices to Air Missions), and ATC clearances within , as well as on plans for cross-border operations. They enable efficient data exchange in systems like the Automated Flight Service Station (AFSS) and promote interoperability with adjacent U.S. , where FAA location identifiers coordinate with the trailing three letters of Canadian codes for seamless transboundary flights—such as YYZ aligning with CYYZ for approaches. Representative examples include CYYC for , underscoring their role in supporting both major hubs and isolated sites vital to Canada's vast geography.

ANAC Brazil Identifiers

The ANAC Identifiers refer to the ICAO location indicators assigned to Brazilian airports, aerodromes, and heliports by the National Civil Aviation Agency (ANAC), 's regulatory body for . These codes are essential for maintaining regulatory compliance with international standards, enabling precise flight operations, and facilitating coordination within South American airspace as governed by the (ICAO). By standardizing references, they support safe navigation, , and interoperability across regional borders. These identifiers adhere to the ICAO's four-letter alphanumeric format, beginning with the prefix "SB" to designate within the South American region, followed by two additional letters or numbers unique to the specific site. For instance, SBRJ identifies Rio de Janeiro/Santos Dumont Airport, while SBGR denotes . This structure ensures global uniqueness and aligns with ICAO Doc 7910 for reference codes. Assignment of ANAC Brazil Identifiers occurs as part of ANAC's rigorous process under the Brazilian Air Code (Law No. 7,565/1986) and RBAC 155 regulations, where operators submit applications for , including infrastructure assessments for safety and operational viability. ANAC coordinates with ICAO to secure the final code allocation, prioritizing coverage in underserved areas such as the Amazon region to bolster logistical connectivity amid environmental and geographical challenges. Once approved, the codes are officially published in Brazil's (AIP), issued by the Department of Air Space Control (DECEA), serving as the authoritative reference for aviation stakeholders. In practice, these identifiers are integral to via systems like the Integrated Aeronautical (SIAR), issuance of Notices to Air Missions (NOTAMs), conduct of safety audits, and collaboration in regional frameworks such as the Southern Common Market () for harmonized air services. For example, SBFI designates , aiding efficient border operations with and . Additionally, they underpin specialized applications, including transport to remote sites. Recent developments under ANAC include 2023 legislative advancements toward the National Sustainable Aviation Fuel Program (ProBioQAV, via Bill 4516/2023), which promotes production and distribution at designated hubs to reduce carbon emissions, potentially necessitating updated or new for enhanced sustainable infrastructure. Furthermore, ANAC has expanded coding to offshore heliports, assigning ICAO-compliant to support energy sector logistics on the Brazilian , such as those for facilities certified under RBAC 175 for helideck operations.

AFAC Mexico Identifiers

The AFAC Mexico Identifiers are the ICAO-compliant four-letter location indicators assigned to airports, heliports, and other aviation facilities across , under the oversight of the Agencia Federal de Aviación Civil (AFAC), 's civil aviation regulatory authority. These identifiers serve a critical role in by enabling precise , , and meteorological reporting within 's complex terrain and busy . They also underpin the expansion of tourism-driven , supporting over 50 major that handle millions of passengers annually to destinations like and Los Cabos, while promoting integration with North American partners through the United States--Canada Agreement (USMCA) by standardizing cross-border flight data exchange. Structurally, all AFAC-managed identifiers follow the ICAO format with the regional prefix "MM" for , followed by two additional letters denoting the specific location, such as MMMX for (). This prefix distinguishes Mexican facilities from those in the United States (K-) or (C-), ensuring unambiguous global identification in accordance with ICAO Doc 7910. The system accommodates diverse sites, including high-altitude airports like Mexico City's at over 2,200 meters elevation, which require specialized performance considerations for aircraft operations. AFAC assigns and maintains these identifiers through the national (AIP Mexico), published in collaboration with the Mexican Navigation Services (SENEAM), which lists codes for public-use airports, private airstrips, and specialized facilities. The process involves ICAO coordination for new assignments, with updates issued via AIRAC cycles to reflect changes, such as expansions near Gulf Coast oil fields exemplified by International Airport (MMCE), which supports offshore energy logistics. This ensures codes are integrated into NOTAMs and flight documentation for safe operations. In practice, AFAC identifiers are employed in regional flight corridors linking to the U.S. and , facilitating efficient routing for commercial and traffic. They are essential for and procedures at international entry points, where codes trigger automated border clearance systems under USMCA protocols. Additionally, the identifiers aid volcanic ash monitoring, particularly around active sites like , by pinpointing affected airports in SIGMETs and rerouting flights to mitigate engine damage risks. A representative example is MMUN for , a primary gateway for with over 25 million annual passengers, where the code coordinates high-volume international arrivals and environmental advisories. AFAC's identifiers harmonize with FAA systems to support seamless cross-border flights.

Russian Aviation Identifiers

Russian aviation identifiers consist of four-letter ICAO location indicators prefixed with "U" to designate facilities within the Russian Federation, serving civil, military, and joint-use airports across its expansive Eurasian territory. These codes facilitate , , and , while incorporating national security protocols managed by the Federal Air Transport Agency (Rosaviatsia), which oversees operations and ensures compliance with international standards. They extend to closed military bases, where identifiers may remain allocated for restricted or contingency purposes, reflecting Russia's dual civil-military framework. The structure follows ICAO guidelines, with the "U" prefix followed by three alphanumeric characters denoting regional or specific site details, such as major hubs in populated areas or remote outposts in and the . For instance, codes like those for Moscow's primary airports and Novosibirsk's Tolmachevo exemplify this system, enabling precise identification amid over 200 active sites. Rosaviatsia assigns these identifiers in coordination with ICAO, proposing codes based on operational needs and submitting them for global to avoid conflicts. The process involves evaluation for uniqueness and relevance, with final publication occurring in Russia's (AIP), maintained by the Information Center and updated via amendments to reflect infrastructure changes or status shifts. Recent AIP amendments, effective as of May 15, 2025, have incorporated procedural adjustments without major code alterations. These identifiers support critical applications, including trans-Siberian passenger and cargo routes, Eurasian international links, and for maritime operations and projects, despite operational disruptions from Western sanctions. In 2025, amid ongoing conflict effects, southern facilities like Airport (reopened after wartime closure) have resumed using their established codes to enhance regional access, while Siberian sites near the Power of Siberia 2 pipeline corridor—such as those in and regions—continue aiding infrastructure without new identifier assignments. Frequent geopolitical updates ensure adaptability, with Rosaviatsia prioritizing stability in flight scheduling post-restrictions.

Meteorological Identifiers

WMO Station Identifiers

The traditional WMO station identifiers are five-digit numerical codes assigned by the World Meteorological Organization (WMO) to uniquely identify global surface and upper-air observing stations for the collection and international exchange of synoptic meteorological observations and climate data. These identifiers facilitate standardized reporting in coded formats, such as SYNOP messages, as outlined in the WMO Manual on Codes (WMO-No. 306). They support the World Weather Watch (WWW) program by enabling consistent data sharing among 193 Member States and Territories. Since 2016, the WMO has transitioned to the WIGOS Station Identifier (WSI) as the global standard for all observing facilities. WSIs consist of a four-block alphanumeric structure—WIGOS ID series (e.g., 0-20000 for surface), issuing body number, issue number (for changes), and station type/designation—providing unique identification and supporting metadata in the OSCAR/Surface database. Legacy five-digit codes continue to be used in reporting and are mapped to WSIs for stations established before July 2016. The structure of these traditional identifiers divides the five digits into a two-digit block followed by a three-digit station number. The block (first two digits) denotes a geographic area, with ranges allocated as follows: 00–29 for , 30–59 for (including parts of the former ), 60–68 for , 69 for special applications, 70–79 for North and and the , 80–89 for (with 89 reserved for ), and 90–99 for the Southwest Pacific and oceanic islands. The final three digits provide a sequential identifier for the specific station within that block, often assigned to increase from west to east and north to south within sub-regions. For example, the identifier 72386 corresponds to in , , falling within the 72 block for the western . Marine stations use a modified format with three or four digits prefixed by a region code, while upper-air stations typically share the same identifier as co-located surface stations. Assignment of these identifiers is coordinated by the WMO Secretariat in collaboration with National Meteorological or Hydrological Services (NMHSs) of Member States, ensuring uniqueness and alignment with geographic and operational needs. Historically documented in WMO Publication No. 9, Volume A (Observing Stations), the process transitioned to the OSCAR/Surface database in , where NMHSs submit updates via national focal points or automated interfaces from systems like GAWSIS for upper-air stations. This includes provisions for marine platforms through JCOMMOPS. The system accommodates both fixed land stations and mobile or temporary sites, with blocks 89 and 90–99 supporting specialized observations in and remote islands. These identifiers are integral to the Global Telecommunication System (GTS), where they prefix observational data, numerical weather predictions, and forecasts disseminated in real-time for global analysis and disaster response coordination. They enable seamless integration across WMO's Integrated Global Observing System (WIGOS), supporting applications from aviation meteorological reports—where airport stations use the same codes in formats like METAR—to climate monitoring archives. In 2024, WMO launched the Polar Coupled Analysis and Prediction for Services (PCAPS) project to enhance weather, water, ice, and climate observing and prediction systems in polar and high-mountain regions, addressing gaps in observations for climate change monitoring.

United States Weather Identifiers

United States weather identifiers are alphanumeric codes employed by the and the to designate observation sites for meteorological data collection, including those issuing (Meteorological Aerodrome Report) observations from Automated Surface Observing Systems () and Automated Weather Observing Systems (AWOS). These identifiers enable standardized reporting of conditions such as temperature, wind, visibility, and precipitation, supporting , public warnings, and under NOAA operational guidelines. Primarily aligned with standards, they ensure interoperability for domestic and cross-border data sharing. The structure of these identifiers typically consists of four letters, prefixed with "K" for stations in the contiguous 48 states, as in KORD for the weather observations at Chicago O'Hare International Airport. Variations include "PA," "PF," "PO," or "PP" prefixes for , "PH" for and Pacific territories, "TJ" for , and "TIST/TISX" for the , maintaining the four-letter format for ICAO compatibility. For certain radar installations, such as the Next Generation Weather Radar () network, three-letter codes are used (e.g., ABR for ), often extended to four letters like KABR in contexts. These codes are distinct from purely numerical WMO identifiers but are cross-referenced for global reporting. Assignment of these identifiers is managed by the (FAA) in close coordination with NWS and NOAA, particularly for sites co-located with airports to align weather data with navigation facilities. Requests for new or modified identifiers are submitted through FAA's processes, with approvals based on operational needs like proximity to existing sites and avoidance of conflicts. Assignments are documented in FAA Order JO 7350.9 and published in the for transparency, as well as in periodic supplements and the National Flight Data Center digests. These identifiers play a critical role in weather briefs provided by the Aviation Weather Center, where data from sites like KJAX () informs pilot decision-making and . In hurricane tracking, the relies on them to integrate station observations with satellite and model data for real-time storm analysis and forecasts. For climate archives, NOAA's National Centers for Environmental Information (NCEI) uses these codes to catalog historical ASOS/AWOS records, enabling long-term trend analysis in and datasets. In 2025, NOAA expanded its observation networks to incorporate additional sensors for detection and monitoring, funded through post-2023 climate initiatives including the of 2022 and the Bipartisan Infrastructure Law, with new alphanumeric identifiers assigned to integrate these sites into the national system. This enhancement includes experimental tools like the Fire Weather Testbed for hourly hazard predictions and improved post- sensing using mobile radars, bolstering resilience against extreme events.

Special and Historical Cases

Transplanted Identifiers

Transplanted identifiers refer to the reassignment of location codes from defunct or closed aviation facilities to new or relocated sites, serving to maintain operational continuity and prevent confusion in systems. This practice is most commonly applied to IATA three-letter codes, which prioritize city or regional representation over precise site details, allowing codes to follow infrastructure changes without disrupting commercial ticketing and scheduling. The primary purpose is to preserve database integrity, limit the expansion of the limited pool of available codes, and ensure seamless transitions for airlines and passengers during airport closures or upgrades. Such reassignments are coordinated by the relevant issuing authorities—IATA for its location codes and ICAO for four-letter location indicators—with strict guidelines emphasizing rarity to uphold stability in and navigation aids. These changes typically occur in scenarios involving permanent closures, mergers of facilities, or significant relocations, requiring approval after thorough review to avoid conflicts with existing assignments. For ICAO codes, which are inherently tied to specific geographic coordinates, reassignments are even less frequent, as alterations demand updates to international charts and systems. Representative examples include the IATA code BKK, which was reassigned from the former to the newly opened in , , in 2006, following Don Mueang's shift to domestic operations only. Another case is the IATA code HKG, transferred from the closed to the replacement at in 1998, where the ICAO code VHHH was also reused to support uninterrupted . These instances demonstrate how transplants facilitate major infrastructural evolutions while minimizing systemic disruptions. The implications of transplanted identifiers encompass logistical challenges, such as migrating historical flight data from the original site to the new one, which can complicate accident investigations, weather records, and statistical analyses. Pilots and operators may require updated training materials to link the code to the revised , potentially affecting route planning and familiarity. ICAO provides documentation on these procedures through its operational safety guidelines to guide states and organizations in managing such transitions effectively. Recent global events have underscored the relevance of transplants in crisis contexts. The 2022 resulted in the prolonged closure of multiple airports, including International (LWO), prompting temporary relocations of operations to neighboring countries and discussions on code management for potential post-conflict reopenings or shifts. Similarly, sea-level rise poses risks to airports in Pacific island nations, including several in the , where adaptation options may include relocation of facilities, potentially involving reassignment of existing codes to sustain vital air links amid environmental changes. These developments highlight the adaptive role of identifier management in addressing conflict and climate-induced changes.

Deprecated or Replaced Systems

Deprecated location identifier systems refer to historical coding schemes predating the (ICAO) or national variants that were superseded to enable uniform global standards in and meteorological communications. These systems emerged in the early , primarily for telegraphic brevity in weather reporting and nascent , but proved inadequate for the post-World War II expansion of international . A prominent example is the pre-1947 U.S. two-letter telegraphic codes, assigned by the Department of Commerce and based on conventions, such as "LA" for or "PD" for Portland. These facilitated efficient transmissions but limited uniqueness as airport numbers grew. Similarly, early (IATA) phases utilized two-letter airport designations in the 1930s and early 1940s, like "PD" for Portland, before evolving to three letters to address scalability. In the , prior to formal ICAO adherence in 1970, aviation sites employed internal alphanumeric codes often starting with "U" for domestic operations, independent of Western standards and focused on centralized state control. The transition from these deprecated systems was driven by ICAO's international agreements, with the four-letter location indicator framework developed in 1946 and officially recommended for adoption on March 24, 1959, entering force on October 1, 1959, to ensure across borders. This process required mapping and conversion of legacy codes in national registries, affecting archival records, historical flight logs, and early digital simulations that replicate pre-ICAO operations. Although no longer in operational use after the widespread ICAO implementation by the late , these systems retain value in historiography, legacy tools for research databases, and flight simulation platforms that model historical routes and communications.

References

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