Codes/Transponder Codes

Codes, or transponder codes, are four-digit octal numbers (using digits 0–7) set by the pilot on the transponder to allow ATC to identify a specific aircraft on radar. Each four-digit code is called a squawk code.

Special Codes

• 7500: Unlawful interference (hijacking) — never squawk accidentally
• 7600: Radio failure (NORDO)
• 7700: Emergency
• 1200: VFR flight in uncontrolled airspace (North America)
• 2000: Aircraft entering controlled airspace without an assigned code

Assigned Codes

In IFR operations, ATC assigns a discrete four-digit squawk code that uniquely identifies the flight. This code travels with the flight as it is handed between sectors. Mode S transponders also transmit the aircraft’s unique 24-bit ICAO address, enabling direct aircraft identification without a manually assigned code.

On the TC Written Exam

Know the three emergency codes (7500, 7600, 7700) and the VFR code (1200). Accidentally squawking 7500 will trigger an immediate security response — always announce squawk changes to ATC before changing codes.

Related Terms

See also: Transponder, Squawk, SSR.