A flight number and a call sign serve different purposes in aviation and follow different standards:

Flight Number

  • Managed by IATA (International Air Transport Association), which handles commercial aspects like ticketing and route management.

  • Format: Usually consists of the airline’s two-letter IATA code followed by a numeric identifier (e.g., DL123 for Delta Air Lines Flight 123).

  • Purpose: Primarily used in booking and ticketing, so passengers see the IATA code on their tickets and in airport displays (e.g., DL123 from London Heathrow (LHR) to New York JFK).

Call Sign

  • Managed by ICAO (International Civil Aviation Organization), focusing on operational and navigational safety standards.

  • Format: Typically a three-letter ICAO code representing the airline, followed by the flight number (e.g., DAL123 for Delta Air Lines Flight 123) or other alphanumeric identifier.

  • Purpose: Used by pilots and air traffic control for communication and flight tracking, providing a standardized way to refer to the aircraft during its journey (e.g., DAL123 from EGLL to KJFK).

Additional Notes:

  • Charter and Business Jet Operators: Often only have a three-letter ICAO code for call signs since they don’t sell tickets or need IATA flight numbers.

  • Small/Private Aircraft: Generally use the aircraft's registration number as the call sign.

  • Airports: Larger, passenger-handling airports have both a four-letter ICAO code (e.g., EGLL for Heathrow) and a three-letter IATA code (e.g., LHR for Heathrow). Smaller airports may only have an ICAO code.

For more on alphanumeric call signs, which are becoming common for improved clarity and safety, check out our blog.

Let us know if you have more questions about flight tracking or aviation terminology!