How to Read a Flight Number and Route Codes

A flight number like BA123 and a route like LHR to JFK carry a surprising amount of information once you know how to read them. This guide explains how to read a flight number and airport route codes, so the labels on departure boards and flight trackers start to make sense.

Anatomy of a flight number

A flight number has two parts:

1. A two-letter airline code (the IATA code).
2. A number identifying the specific service.

So BA123 is BA (British Airways) plus 123 (the flight). The two-letter code is the one you see on tickets and departure boards. Note that this differs from the three-letter callsign code used in operations and tracking, which we cover in what aircraft callsigns mean.

Airport codes: IATA and ICAO

Airports have two kinds of code, and it helps to know both:

The IATA code is the familiar one: LHR for Heathrow, JFK for New York Kennedy, CDG for Paris Charles de Gaulle. The ICAO code is used behind the scenes and follows a regional pattern, for example UK airports start with EG.

So a route shown as LHR to JFK simply means London Heathrow to New York Kennedy.

Do flight numbers mean anything?

Often, yes, though conventions vary by airline:

• Low numbers are frequently reserved for prestige or long-haul routes. An airline's flagship route might be flight 1 or 2.
• Even and odd numbers often indicate direction. Many airlines use even numbers for one direction (say, eastbound or northbound) and odd for the return.
• Number ranges can be grouped by region or type of service.

These are conventions rather than strict rules, so treat them as helpful hints rather than guarantees.

Codeshares: one flight, many numbers

You may notice the same physical aircraft carrying several flight numbers. This is a codeshare, where partner airlines sell seats on the same flight under their own codes. So one departure might be both BA123 and a partner airline's number. The callsign on a tracker reflects the operating airline, which is the one actually flying the aircraft.

Reading a route on a tracker

When you watch a flight tracker, route codes are translated for you. Instead of decoding LHR and JFK yourself, the tracker shows the origin and destination directly. This instantly tells you whether the aircraft overhead is at the start of a long journey, near the end of one, or simply passing through.

PlaneTicker Desktop shows the route alongside the callsign, altitude, and speed, so the story of each flight is clear at a glance. You can see this in the free demo by setting it to your location and watching the routes appear.

Putting it together

With flight numbers and route codes decoded, you can read a departure board or a tracker fluently: the airline, the service, and where it is going. Combine this with how to identify aircraft by callsign and you will be able to interpret almost everything about the flight passing over your head. To put it into practice, see what plane is flying over your house.