What does "SQ" signify in ATC communication?

In Air Traffic Control (ATC) communication, "SQ" signifies "squawk," which refers to the identification code transmitted by an aircraft's transponder. The transponder is an essential piece of equipment that helps ATC identify and track aircraft on radar. When ATC directs a pilot to "squawk" a certain number, the pilot adjusts the transponder to transmit that specific code, which allows ATC to see the aircraft's information on radar, including its location and altitude.

The term "squawk" originated from the sound of the transponder's replies to radar inquiries. When pilot and controller communicate, accurate squawk codes and their timely adjustment are crucial for ensuring safe separation and efficient management of air traffic. This communication is vital, especially in busy airspace, as it helps avoid misidentification of aircraft and ensures proper coordination with ATC.

Understanding squawk codes and their use is fundamental for pilots, as they play a significant role in navigation, safety, and compliance with ATC instructions.