What should prefacing a clearance or instruction include?

Prefacing a clearance or instruction with the aircraft ID is essential because it serves to identify the specific aircraft that will be receiving the clearance. This identification is crucial for maintaining clear and effective communication between air traffic control and pilots, as it helps to prevent any confusion, especially in busy airspace where multiple aircraft are operating. By mentioning the aircraft ID first, controllers ensure that the instruction is directed to the correct pilot, allowing for a more organized and safe handling of air traffic.

In contrast, while including the ATC Facility ID, the location of the aircraft, or a summary of the clearance may provide additional context, they do not directly fulfill the primary purpose of clearly identifying the aircraft involved in the communication. Therefore, emphasizing the aircraft ID as the prefacing element aligns with best practices in air traffic control communication protocols.