What does a transponder code consist of?

A transponder code, commonly referred to as a squawk code, is a four-digit number that is assigned to an aircraft by air traffic control for identification purposes. Each digit in the code can range from 0 to 7, allowing for a total of 4,096 unique combinations. This set-up enables air traffic control to differentiate between multiple aircraft operating in the same airspace, enhancing safety and management.

The choice indicating four letters from A to D or three numbers from 1 to 5 are not applicable because transponder codes are strictly numerical and do not involve letters or use a different range of numbers. The configuration of four numbers 0 to 9 also does not align with the transponder system, as only specific digits (0-7) are utilized to create those combinations. Thus, the correct understanding of transponder code structure supports effective communication and tracking in air traffic control operations.