To find a particular aircraft again, start with its registration, also called its tail number. The callsign identifies its current flight or operation and may change on the next flight. The flight number on your ticket can be different from the callsign shown in a flight radar app.
You may also see an ICAO hex address, a technical address used in flight data. Each of these identifiers answers a different question. Knowing which one you have makes it easier to search for an aircraft in MODE1090.
The four identifiers at a glance
| Identifier | What it refers to | When to use it |
|---|---|---|
| Callsign | The current flight or operation | You want to find a flight on the radar. |
| Flight number | The service shown on a ticket or departure board | You are looking for a particular passenger flight. |
| Registration | An individual registered aircraft | You want to recognise the same aircraft on another day. |
| ICAO hex address | A technical 24-bit aircraft address | You already know the address and want to find the aircraft using it. |
What is a callsign?
A callsign is used to identify an aircraft in radio communications. A flight radar app usually shows the written identifier. Its spoken form on the radio may sound different.
For private aircraft, the callsign often matches the registration. Airlines often use a separate identifier. The FAA explains the difference in its callsign guidance.
A callsign is useful when you are looking for a flight that is happening now. It is less useful for following one particular aircraft over several weeks. After landing, that aircraft may depart on another flight with a different callsign. Tomorrow, a different aircraft may operate the service you watched today.
Why can a flight number differ from the callsign?
The flight number helps passengers find their service. It appears on the ticket, in the booking and on the departure board. The transmitted callsign identifies the flight in aircraft operations. The two can look similar without being identical.
If you start with a flight number, check the date and route too. A similar number on the radar is not enough to confirm that you have found the right flight. Compare the other available flight details.
MODE1090 searches the available flight data by callsign, registration and ICAO identifier. If a flight number produces no result, try the aircraft's known callsign or registration.
How do you recognise the same aircraft again?
The registration belongs to the individual aircraft. For spotting, it is usually the most useful detail when you want to know whether you have seen that particular aircraft before. A type such as “A320” is not enough: many aircraft share the same type.
The MODE1090 list shown below puts three details side by side. C510 is the type code, DFC3PZ is the callsign and OK-OBR is the registration. To look for this aircraft again, start with “OK-OBR”. “C510” describes its type and also applies to other aircraft.
The details in the image come from the time of capture. They show how to read the identifiers, not where this aircraft is now.
A registration is not a serial number that stays unchanged throughout an aircraft's life. Registrations can change. If you are comparing very old sightings, or the type and registration do not seem to match, take a closer look at the saved details.
What is an ICAO hex address?
An ICAO aircraft address contains 24 bits. Flight radar apps normally display it as six characters using the digits 0–9 and letters A–F. “Hex” is short for hexadecimal, the numbering system used to write it.
The address helps distinguish aircraft in the data. It is neither a flight number nor an airport code. If you already know an aircraft's address, you can use it as a search term. You do not need to memorise these addresses to get started with spotting.
As with a registration, do not assume that a technical address provides an unchanging match for the aircraft's entire life. EUROCONTROL explains how the addresses are assigned and the possible exceptions.
How to search for an aircraft in MODE1090
- Open a nearby aircraft. Select one on the radar or in the nearby list and read the available details.
- Choose what you want to find. Use the callsign for the current flight, or the registration to find the same aircraft again. You can also enter a known ICAO address.
- Check the displayed data. Compare the type, registration and position age. Position age tells you how old the displayed location is.
- Search worldwide if needed. Worldwide aircraft search is part of MODE1090 Pro. Local search, the radar and aircraft details are free.
- Check your collection. Look for the registration in your saved sightings to see whether you have recorded this aircraft before.
A search can only find aircraft for which the app currently has data. If nothing appears, you cannot conclude that the aircraft is on the ground or that it is not flying.
The guide to aircraft details, photos and position age explains the individual fields. For an overview of the app, visit the MODE1090 features page.