IATA vs ICAO Airport Codes: What's the Difference, Why IST and LTFM Mean the Same Place

When you buy a ticket, it shows a three-letter airport code – LHR, CDG, JFK. When that same plane lands, the navigation screen in the cockpit shows a four-letter code – EGLL, LFPG, KJFK. These aren’t separate systems for different airports. They’re two parallel codes for the same place.

One is for passengers and booking systems (IATA). The other is for pilots, air traffic controllers, and weather reports (ICAO).

Here’s what separates them and why both exist.

Two codes for one airport – and that’s intentional

Istanbul Airport has IATA code IST and ICAO code LTFM. Both refer to the same terminal building – they just get used in different contexts. IST is what you see on your ticket and the departures board. LTFM is what pilots, controllers, and meteorologists work with.

The confusion usually hits when a regular passenger stumbles across a four-letter code in a weather report or a flight tracking service and can’t figure out what airport it refers to. It’s still the same IST – just written to a different standard.

IATA – the three letters passengers see

The codes came out of practical necessity. Before standardization, each airline used its own abbreviations – some two letters, some three, some the full city name. Booking a ticket with two connections across three different airlines was a headache even for travel agents.

In the 1930s, US weather stations used two-letter airport codes – telegraph transmission was expensive, and every character cost money. As commercial aviation grew, there were more airports than two-letter combinations could cover. Two letters gave 676 options; three letters gave 17,576. The switch was straightforward.

Most IATA codes are readable at a glance – HAV is Havana, BKK is Bangkok, MAD is Madrid. Some cities got codes from the first letters of their name. Others inherited old weather station codes with a third letter added for uniqueness. That’s how Los Angeles became LAX (LA + a filler letter to make it three characters), Portland became PDX, and Phoenix became PHX. The X in these codes means nothing – it’s just a placeholder.

ICAO – four letters for the people flying the plane

ICAO built its system on a different logic. Four letters instead of three, with strict geography built in – the first letter identifies the world region, the second the country, and the remaining two the specific airport.

Turkey makes this clear immediately. The prefix is LT, and every Turkish airport starts with it – LTFM (new Istanbul), LTBA (Atatürk, now closed), LTAI (Antalya), LTAC (Ankara). The UK prefix is EG – hence EGLL (Heathrow), EGKK (Gatwick), EGCC (Manchester). France is LF, so LFPG is Charles de Gaulle and LFPO is Orly.

The US uses a simplified approach. A K prefix is added to the existing IATA code (KJFK, KLAX, KORD, KSFO). This was deliberate – American pilots don’t have to memorize a completely different set of letters for every airport they fly into.

Europe takes a geographic approach. The first letter marks the regional zone, the second the country within it, and the last two the specific airport. Continental Europe is split mainly between two zones – E (UK, Northern Europe, Germany, Poland) and L (France, Italy, Spain, Czech Republic, Austria, the Balkans, Turkey). This is why ICAO and IATA codes rarely match in Europe. Czech Republic is LK, so Prague is LKPR. Austria is LO, Vienna is LOWW. Poland is EP, Warsaw is EPWA. The first two letters tell you the country immediately, which is genuinely useful for pilots working international routes every day.

In the cockpit, I work entirely with ICAO. Flight plans, weather reports, NOTAMs – everything uses four-letter codes. IATA only comes up when I need to know where the passengers are actually going. When I tell a controller “proceeding to LTFM” – everyone knows exactly what that means. If I said IST, there might be a pause, because three years ago that code referred to a completely different airport.

Niko
· Boeing 777 pilot, explores cities on layovers

Where each code is used

The short version: as a passenger, you only need IATA codes.

ICAO codes come up in two situations. First – you’re a pilot. Second – you’re digging into specific flight details through specialist tools or looking for technical information about a particular flight or airline.

When the codes match – and when they don’t

The US is almost the only place where the system is transparent. JFK in IATA, KJFK in ICAO. Just add K at the front. That holds for virtually every American airport with an established code.

The UK follows a different logic. Heathrow is IATA code LHR, ICAO code EGLL. EG is the UK, LL is Heathrow specifically. No connection to the letters LHR at all. The same pattern plays out at Gatwick (LGW becomes EGKK) and every other airport in the country.

Frankfurt makes the contrast even sharper. IATA code FRA, ICAO code EDDF. EDDF breaks down as Germany (ED) plus Frankfurt am Main (DF). The logic is there, but it’s not obvious from the outside.

Military bases and small private airfields often have only an ICAO code and no IATA code at all. IATA only assigns codes where commercial passenger services operate. RAF Lakenheath in England is EGUL – no IATA code. Biggin Hill Airport outside London is EGKB; it technically has IATA code BQH, but most booking systems don’t recognize it.

Cities with multiple airports

London is served by six airports. Each has its own IATA code – LHR (Heathrow), LGW (Gatwick), STN (Stansted), LTN (Luton), LCY (City), SEN (Southend). There’s also an umbrella code, LON, which search engines use when you search for flights “to London” without specifying an airport.

Paris works the same way – the city code PAR covers CDG (Charles de Gaulle), ORY (Orly), and BVA (Beauvais-Tillé). New York is NYC for JFK, LGA, and EWR. Istanbul has IST (the new airport) and SAW (Sabiha Gökçen on the Asian side), but no city-wide umbrella code – which occasionally causes confusion when booking.

Metropolitan area codes are an IATA invention. ICAO has no equivalent. ICAO deals with specific airfields, not cities. Which makes sense – a pilot can’t land at “London in general.” They need a specific runway.

Practical examples

You’re booking a flight and see “IST – LHR”

That’s IATA. IST is the new Istanbul Airport, opened in 2018, about 35 km northwest of the city center. LHR is Heathrow. No further decoding needed – everything a passenger needs is right there.

You’re reading a METAR weather report for an airport

METARs always start with the ICAO code. “METAR LTFM 121150Z…” is the weather at Istanbul Airport. Many sites that display airport weather only accept ICAO codes – entering IST will return an error.

You’re tracking a flight online

When you follow a flight in real time, the flight card shows both codes – the IATA code for the airline and flight number (e.g. TK1980), and ICAO codes for the departure and arrival airports. Airports are shown in both formats.

You’re looking up a small-city airport

If an airport has no commercial flights, it has no IATA code. RAF Lakenheath in Suffolk has ICAO code EGUL and nothing else. If a flight search returns nothing for a location, the airport probably doesn’t have an IATA code – or you’re searching the wrong city.

When knowing ICAO is useless for a traveler

Honestly – 99% of travelers will never encounter an ICAO code in practice. If you fly as a passenger, don’t follow aviation beyond your boarding pass, and don’t track flights – there’s no reason to memorize four-letter codes. Every app, departures board, and booking system runs on IATA, and that will cover you for life. IATA codes are always printed on your ticket or booking confirmation.

ICAO becomes useful in three situations:

• First – you like watching live flights on a tracker (the flight card shows the ICAO code).
• Second – you’re planning a flight on general aviation in Europe (four-letter codes are used in all filings there).
• Third – you just want to understand how aviation works at a slightly deeper level than most passengers.

If none of that applies to you, you can safely forget ICAO exists after reading this.

The IATA code on your ticket is all you need for any trip.

Quick reference: codes for major airports

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