Airport Codes Explained: What Those 3 Letters Really Mean
Quick answer
The three-letter tag on your ticket is an IATA code, a unique worldwide identifier for a single airport — LHR for London Heathrow, JFK for New York Kennedy. Pilots and air traffic control use a separate four-letter ICAO code. Most codes come from the airport or city name, but historical quirks explain the odd ones. Always match the code to the full airport name before paying, especially in cities with more than one airport.
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Two code systems, two audiences
Aviation actually uses two parallel systems, and knowing which is which clears up most of the confusion.
| System | Length | Who uses it | Example (Heathrow) |
|---|---|---|---|
| IATA | 3 letters | Passengers, booking sites, bag tags | LHR |
| ICAO | 4 letters | Pilots, air traffic control, flight plans | EGLL |
As a traveller you will almost only ever see the IATA code. It appears on your boarding pass, your luggage tag and every search result. The ICAO code matters to the people flying and routing the aircraft, and its first letters group airports by region.
How IATA codes are assigned
The International Air Transport Association manages the three-letter codes and guarantees each one is unique. When a new airport opens, it applies for a code that isn't already taken. Because there are only so many three-letter combinations, newer airports sometimes end up with codes that look nothing like their city.
Codes usually come from one of a few sources: the city name (MAD for Madrid), the airport's own name, a former name of the site, or a nearby landmark. A handful of letters are effectively reserved — for instance many codes starting with N or W are avoided for civil airports in some regions because of other uses — which nudges airports toward less obvious choices.
The famously confusing ones
- ORD — Chicago O'Hare. The airport was built on a site called Orchard Field, so the code preserves the old name.
- MCO — Orlando. It reflects the former McCoy Air Force Base on the same land.
- YYZ — Toronto Pearson. Many Canadian airports start with Y for historical radio-station reasons.
- CDG — Paris Charles de Gaulle. Named after the airport itself, not the city, so it isn't PAR.
- PAR, NYC, LON. These aren't airports at all — they're metropolitan codes covering every airport in Paris, New York and London.
City codes vs airport codes
Big cities with several airports often have a shared metropolitan code plus individual codes for each airport. London is the classic example.
| Code | Covers |
|---|---|
| LON | All London airports (metropolitan code) |
| LHR | Heathrow only |
| LGW | Gatwick only |
| STN | Stansted only |
| LTN | Luton only |
Searching the metropolitan code is a handy trick: it lets a metasearch compare every airport in the city at once, so you can spot when flying into a secondary airport is meaningfully cheaper.
Why this matters when you book
A wrong-airport booking is one of the most expensive avoidable mistakes in travel. Two airports can serve the "same" city while sitting an hour or more apart, and a tempting fare into the far one can cost more once you add the transfer. Before you pay, read the full airport name next to the code, and check how you'll get from there to where you actually need to be.
You can browse popular routes by airport and compare the city's options side by side rather than guessing from the code alone.
Frequently asked questions
What is the difference between IATA and ICAO codes?
IATA is the three-letter code you see on tickets and bag tags; ICAO is the four-letter code used by pilots and air traffic control for the same airport.
Why doesn't the code match the city?
Codes often come from the airport's name, a former name of the site, or a nearby landmark, and some letters are avoided, which produces unusual combinations.
Can two airports share a code?
No — every IATA code is unique worldwide. Cities with several airports have separate codes plus sometimes a shared metropolitan code.
How do I avoid booking the wrong airport?
Match the code to the full airport name before paying and check the transfer time and cost to your final destination.
The bottom line
Airport codes look cryptic but follow a simple logic: three letters for you, four for the flight deck, each one unique so nothing gets confused in transit. Learn the codes for the cities you fly to, watch out for metropolitan codes hiding several airports, and always confirm the full name before you buy. Start a live search on ScanFlyGo or track a flight live once you're booked.
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