Definition
The four-digit numbers assigned to ATC transponders that, when set by the pilot, generate a discrete signal allowing radar facilities to identify and track the aircraft on their displays.
Plain English
Four-digit numbers a pilot dials into the transponder so air traffic control can see and identify the aircraft on radar.
Context Anchor
You encounter codes when ATC assigns a number to enter in the transponder, often during departure, flight following, or arrival.
Derivation
From Latin codex, meaning a system of signs or symbols used to represent something else. Here, each four-digit number is a 'code' that stands for a specific aircraft on the controller's screen.
Why Pilots Care
Proper use of assigned codes ensures ATC can provide traffic advisories, vectors, and separation; using the wrong code can cause loss of radar identification or safety conflicts.
Intuition Check
Do not read “codes” here as secret messages or computer programming. In this context, codes are the numbered transponder settings used by ATC to identify aircraft or conditions.
Example Sentence 1
ATC instructed the pilot to squawk code 4271 before entering the Class B airspace.
Example Sentence 2
We verified the assigned code was set before entering Class B airspace.