How to read a flight number
A flight number is the airline's two-character IATA code followed by one to four digits, like UA100. The letters tell you the airline; the digits tell you which of its flights. Here is how to read the whole thing.
The two parts of a flight number
Every flight number splits into a code and a number. The code is the airline's two-character IATA code, and the number is one to four digits identifying the flight. So UA100 is United Airlines flight 100, and BA117 is British Airways flight 117. Read on the radio, the number uses the airline's callsign instead of the code: BA117 becomes "Speedbird 117".
| Airline | Code | Example flight number |
|---|---|---|
| United Airlines | UA | UA100 |
| American Airlines | AA | AA100 |
| Southwest Airlines | WN | WN100 |
| British Airways | BA | BA100 |
| Ryanair | FR | FR100 |
What the digits mean
The digits identify the route and the departure, not the aircraft (the same plane flies many numbered flights in a day). Airlines follow loose conventions rather than a strict system:
- Lower numbers often go to flagship, long-haul or historically important routes. Single and double-digit flights tend to be an airline's marquee services.
- Even vs odd usually splits direction: even for flights heading broadly north or east, odd for the return leg, so a round trip reads as a pair like 100 and 101.
- Number blocks are often grouped by region or hub, so a range of numbers all serve one part of the network.
None of this is guaranteed, so treat the digits as a label the airline assigned, not a code you can fully decode from the outside.
Codeshares: one flight, several numbers
A single physical flight can carry several flight numbers when airlines sell each other's seats. One carrier operates the aircraft, but each partner markets it under its own airline code, so the departure board may list the same departure twice under different numbers. The "operated by" line on your ticket tells you whose plane it actually is.
Retired flight numbers
Flight numbers are reused every day a route operates, and reassigned when routes change. The exception is after a major accident: airlines routinely retire that flight number out of respect, so it is never flown again.
Frequently asked questions
What is a flight number?
A flight number identifies a scheduled flight. It is the airline's two-character IATA code followed by one to four digits, for example UA100 or BA117. The letters say which airline, the digits say which of its flights.
What do the digits in a flight number mean?
The digits identify the specific route and departure, not the aircraft. Many airlines follow loose conventions: lower numbers for flagship or long-haul routes, even numbers for one direction of travel and odd for the other, and blocks of numbers grouped by region. The conventions are not universal, so the digits are best treated as a label rather than a code you can decode.
Why do eastbound flights often have even numbers?
Many carriers assign even flight numbers to flights heading broadly north or east and odd numbers to the return leg heading south or west, so a round trip reads as a pair like 100 and 101. It is a convention, not a rule, and plenty of airlines do it differently.
What is the difference between a flight number and an airline code?
The airline code is just the two-character prefix (UA is United). The flight number is that code plus the digits (UA100). One airline code appears on thousands of different flight numbers.
Can the same flight number be used twice?
Yes. A flight number is reused every day the flight operates, and after a route changes an airline can reassign the number. Numbers are also retired after a major accident out of respect, so that exact flight number is never flown again.
What is a codeshare flight number?
One physical flight can be sold under several flight numbers by partner airlines. The aircraft is operated by one carrier, but each partner markets seats under its own code, so the same departure might be both UA100 and a partner's own numbered flight.
Look up an airline
The prefix is the airline. Find any carrier's code, ICAO code and callsign in the airline codes directory, or read how the codes themselves work in IATA vs ICAO.