In subsequent communications, which component can be omitted?

In subsequent communications between the controller and the pilot, it is common practice to omit the ATC Facility ID. The initial transmission typically includes the facility ID to establish the communication link, but once that link is established, it is unnecessary to repeat the ATC Facility ID in every communication.

This omission helps maintain clarity and efficiency in communications, allowing the focus to stay on the critical instructions and information being exchanged without unnecessary repetition. It is understood that the communication is still occurring with the same facility, thus enabling smoother and more concise exchanges.

The aircraft ID must be maintained to ensure effective identification of the aircraft, and any instructions are vital for safe operations. While the word "over" is often omitted in modern communications as well, its inclusion or exclusion can vary based on communication etiquette and practices within different regions or among different pilots and controllers.