When must controllers identify their ATC unit?

Controllers must identify their ATC unit at initial contact to establish clear communication and ensure that pilots are directed to the correct air traffic control facility as soon as they initiate their radio transmissions. This is a critical procedure in air traffic management as it provides the pilot with essential information about who they are speaking to, which is necessary for effective coordination and safety during flight operations. This practice also helps to prevent confusion, especially in busy airspace where multiple ATC units may be operating simultaneously.

While there are established procedures for communication during descent, filing a flight plan, or before takeoff, these moments may not always involve direct identification of the ATC unit, especially since pilots may be communicating with different entities throughout different phases of flight.