What is a squawk code and who uses it?

• A. A three-digit altitude code used by air traffic control to identify altitude.
• B. A four-digit transponder code used by air traffic control to identify and track an aircraft.
• C. A two-digit speed code used by controllers.
• D. A five-digit flight number used by airline operations.

Answer: (B)

A squawk code is a four-digit transponder code used by air traffic control to identify and track an aircraft on radar. The controller assigns this code to a specific flight, and the aircraft’s transponder broadcasts that code in reply to radar interrogations. This lets ATC quickly distinguish one aircraft from another, maintain proper separation, and issue precise instructions. The digits are from 0 to 7 in each position (octal), and pilots enter the assigned code into the transponder. It’s not about altitude, speed, or flight number—those are separate pieces of data.