Squawk Codes
Last updated: April 20, 2026 · Maintained by Aviatr Editorial Team
What is Squawk Codes?
Squawk codes are four-digit octal transponder codes (each digit 0-7, giving 4,096 possible combinations) used to identify an aircraft on ATC radar. Pilots set codes assigned by controllers, and a small set of reserved codes — 7500 (hijack), 7600 (radio failure), 7700 (emergency), 7000 (European VFR default) — trigger specific ATC alert responses.
- 7500
- Hijacking
- 7600
- Lost communications (radio failure)
- 7700
- General emergency
- 7000
- VFR conspicuity (Europe default)
How is Squawk Codes used?
Every transponder-equipped flight squawks an assigned code. On departure the controller issues a discrete code that follows the aircraft throughout its route, allowing radar identification across multiple sectors. The three emergency codes trigger immediate ATC action: 7500 initiates a hijack protocol locking down the airport, 7600 causes ATC to provide navigation assistance without radio contact, 7700 dispatches emergency services. A Mode C transponder adds altitude readout; Mode S (mandatory on most new European aircraft since 2017) adds aircraft identification and data-link capability, forming the backbone of surveillance. Pilots must guard against accidentally dialling an emergency code — an inadvertent 7500 triggers a major security response. EASA theoretical knowledge and PPL skill tests include transponder operation as a standard item.