Why some airport codes are actually city codes, and why LAX isn't "LA" anymore

Does a city's airport code always mean one specific airport?

Not necessarily. IATA's own rule is explicit: if only one airport serves a metropolitan area, a single code covers both the city and the airport — Geneva Airport and the city of Geneva are both GVA. But if a metropolitan area has more than one airport, each airport keeps its own distinct code, and the metro area gets a separate code of its own to avoid confusion. Washington, D.C.

is the textbook case: it's served by three airports — DCA, BWI and IAD — and the metropolitan area code is WAS, distinct from all three.

Who actually decides what three letters an airport gets?

A formal, documented process: IATA Resolution 763, whose main objective is ensuring every three-letter code stays unique. The first choice is the location's own name; the second choice is another unassigned combination, preferably starting with the same letter.

Codes aren't issued speculatively — they're only assigned at a commercial airline's request, and it's usually the first airline flying to that location that requests it.

Why three letters, and why did LAX used to be called something else?

Because the two-letter system airlines started with in the 1930s simply ran out of room. By the late 1940s there were too many airports for the number of two-letter combinations available, and the industry shifted to the three-letter system still in use today. Los Angeles International Airport is the clearest example: it was originally just "LA," and became LAX in 1947 as part of that transition.

IATA formally took over standardizing the whole process in the 1960s.

The single-airport rule, and the multi-airport exception

Most cities you fly to make this simple: one airport, one code, done. Geneva is the clean example IATA itself uses — GVA names the airport and the city interchangeably, because there's only one airport to name.

Multi-airport cities work differently on purpose. Each airport keeps a distinct code of its own, and the metropolitan area is assigned a separate code specifically to avoid confusion between the two. Washington, D.C. shows exactly how this plays out: Reagan National is DCA, Baltimore/Washington is BWI, Dulles is IAD — and the metro-area code that can represent all three at once is WAS.

Deciding whether a city gets its own metro-area code, or which airports fall under it, isn't automatic; it's settled by an industry poll among the airlines involved.

The formal process behind the three letters

This isn't ad hoc. IATA Resolution 763 governs how location identifiers are assigned, with uniqueness as the core requirement — no two locations get the same three letters.

The process prioritizes the location's actual name: first choice is an unassigned code built from the location's first three letters, and only if that's taken does the process move to another available combination, still preferably starting with the same first letter.

Nothing gets a code just because it exists. Codes are assigned strictly at a commercial airline's request — typically whichever airline is first to actually fly there — which is also why some small or newly connected locations simply don't have one yet.

From two letters to three: a system that had to grow

Airport coding is older than most travellers assume. It began in the 1930s, when individual airlines picked their own two-letter codes with no central coordination. That worked until it didn't: by the late 1940s, the number of airports had outgrown the number of possible two-letter combinations, and the industry moved to the three-letter system that's still standard today.

Los Angeles is the example IATA itself points to: the airport was simply "LA" before 1947, when it became LAX as part of the broader shift. IATA didn't take formal ownership of standardizing the process until the 1960s, once airlines collectively decided they needed one coordinated system rather than each carrier choosing its own.

Why some airports seem to have two different codes

If you've ever noticed an airport referred to by a completely different four-letter code somewhere else, that's not an error — it's a second, separate coding system with a different purpose. IATA's three-letter codes exist strictly for commercial airline purposes, issued at an airline's request, and can also cover non-airport intermodal locations like train and ferry stations with an airline connection.

ICAO's four-letter codes serve flight-operations purposes instead, and are issued to commercial and non-commercial airports alike — which is why a small regional or private airfield can have an ICAO code without ever having an IATA one. The two systems answer different questions, which is exactly why the same airport commonly carries both.

Can a code ever change, and what should you check before booking?

Codes are built to last, but not to be immovable forever:

• Assigned three-letter codes are treated as permanent, and IATA states they're almost never changed — only with strong justification, primarily around air safety.
• One documented case: Washington Dulles was originally coded DIA, changed to IAD specifically to avoid confusion with the nearby Reagan National (DCA) — a safety-motivated exception, not a routine relabeling.
• Of roughly 17,000 possible three-letter combinations, about 11,300 are currently in use, with 40 to 50 new codes assigned in a typical year — so the system still has plenty of room left to grow.
• Before booking against an unfamiliar code, check whether it names a single specific airport or a metropolitan area that could span several — the practical consequence is which terminal, and possibly which city outskirt, you actually depart from or land at.
• If a code and an itinerary don't match your expectations, don't assume an error — check whether you're looking at a metro-area code, then confirm the specific airport your actual flight uses.

FAQ

Sources

• IATA: Location Codes fact sheet — Resolution 763 assignment rules, city vs airport codes, coding history, IATA vs ICAO codes, code permanence (checked 2026-08-20)