A Beginner's Guide to Airport Codes: IATA vs ICAO

You have seen them on baggage tags, boarding passes, and booking websites: short sequences of letters that stand in for the full names of airports around the world. But have you ever stopped to wonder why London Heathrow is LHR to your airline's booking system yet EGLL on aviation charts? The answer lies in two parallel coding systems that serve different masters — and understanding both makes you a more informed traveler and a better aviation enthusiast.

What Is an IATA Code?

The International Air Transport Association (IATA) is the trade body that represents most of the world's airlines. Its three-letter Location Identifier system, introduced in the 1930s and formalized in the 1960s, was designed primarily to support ticketing, reservations, and baggage handling in commercial aviation.

IATA codes are the ones passengers encounter every day:

• JFK — John F. Kennedy International, New York
• CDG — Paris Charles de Gaulle, France
• NRT — Tokyo Narita, Japan
• SYD — Sydney Kingsford Smith, Australia
• GRU — São Paulo Guarulhos, Brazil

The three-letter format allows for a manageable namespace: with 26 letters and three positions, there are 17,576 possible combinations, more than enough to cover the roughly 10,000 airports that handle scheduled commercial service worldwide. IATA assigns codes on application from airport operators and maintains the master list. When airports are renamed or relocated, their code may change — though in practice, codes tend to persist because the administrative cost of updating all downstream systems is enormous.

Why Some Codes Seem Strange

The history behind unusual IATA codes is often illuminating. Chicago O'Hare's ORD code derives from "Orchard Field," the airport's original name before it was renamed in 1949 to honor World War II ace Edward "Butch" O'Hare. Changing the code at that point would have been operationally disruptive, so ORD remained.

Los Angeles International (LAX) acquired its X because two-letter codes were the standard in the 1930s — LA was the original designation — and a padding letter was added when the industry moved to three-letter codes. The X carries no particular meaning.

Some cities have multiple airports, each with its own IATA code. London is served by LHR (Heathrow), LGW (Gatwick), STN (Stansted), LTN (Luton), and LCY (City). IATA also assigns the metropolitan code LON to refer to all London airports collectively, which is why some broad searches return results from any of these facilities.

What Is an ICAO Code?

The International Civil Aviation Organization (ICAO) is a United Nations specialized agency that sets global standards for aviation safety, security, and efficiency. Its four-character Location Indicator system serves a different audience: pilots, air traffic controllers, weather services, and flight planning systems.

ICAO codes are structured hierarchically. The first letter (or two letters for some regions) designates a geographic area:

• E — Northern Europe (EG = United Kingdom, EF = Finland, ES = Sweden)
• K — Contiguous United States
• Z — China
• Y — Australia
• R — Korea and Japan region

The remaining characters further narrow the location. London Heathrow becomes EGLL: E for Northern Europe, G for United Kingdom, LL as the local identifier for the Heathrow facility. New York JFK becomes KJFK: K for the contiguous US, JFK matching the IATA code. This last point — that many US airports have ICAO codes formed simply by prepending K to the IATA code — is a notable convenience, though it does not hold universally.

When You Encounter Each Code

As a traveler, IATA codes are what you will see on every passenger-facing system: boarding passes, baggage tags, itinerary emails, booking apps, and airport display boards. If you want to look up an airport on AirportFYI, the IATA code is what you should use — try SIN for Singapore Changi or HKG for Hong Kong International.

ICAO codes appear in contexts that passengers rarely encounter directly. They are used in:

• METAR and TAF weather reports (meteorological data for pilots)
• NOTAMs (Notices to Airmen — official advisories about runway closures, etc.)
• Flight plans filed with air traffic control
• Aeronautical charts and approach plates
• Airline scheduling and operations software

If you ever find yourself reading a pilot's weather briefing or examining a flight tracking website that shows full flight plan routes, you will encounter ICAO codes in their natural habitat.

Airports Without IATA Codes

Of the roughly 55,000 airports and airfields in the world, only a fraction — perhaps 10,000 — have IATA codes. The rest exist exclusively in the ICAO system, or in national aeronautical databases. These are typically general aviation airfields, military facilities, or remote strips that serve no scheduled commercial service.

This distinction matters if you are using AirportFYI's database. Our airport pages are anchored by IATA codes where they exist, because that is the identifier most travelers will encounter. For airports without scheduled service, data is included where available, but the code on display may follow a different convention.

A Simple Way to Remember the Difference

If you take away one thing from this guide, make it this: IATA codes are for passengers, ICAO codes are for operations. The three-letter codes on your boarding pass exist to route your bag and your ticket. The four-character codes in the cockpit exist to ensure safe and standardized communication with controllers and weather systems worldwide.

Both systems have served aviation reliably for decades, and despite occasional calls to harmonize them into a single global standard, the industry's investment in both is so deep that any transition would be generational in scope. For now, travelers and pilots alike navigate a world of parallel identifiers — and understanding both adds a layer of depth to the experience of flying.