What is a squawk code?

A squawk code is a 4-digit octal number (each digit 0–7) that a pilot sets on the aircraft transponder. ATC radar displays this code alongside the radar return to identify each aircraft. The full range is 0000–7777, giving 4,096 possible codes.

What does squawking 7700 mean?

Squawk 7700 is the universal emergency code. A pilot sets it to alert ATC of a general emergency — engine failure, medical emergency, or any life-threatening situation. Radar systems highlight it immediately for controllers.

What is the difference between 7500, 7600, and 7700?

7500 means unlawful interference (hijack). 7600 means loss of radio communication (NORDO). 7700 means general emergency. Collectively these are called the "Big Three" emergency squawks and are never assigned by ATC for normal flights.

Why are squawk codes octal?

Transponder hardware historically encoded the code in octal because each of the four rotary dials ran from 0 to 7. The underlying Mode A transmission sends 12 bits (4 groups of 3 bits), mapping directly to four octal digits.

What is squawk 1200 used for?

In the US, squawk 1200 is the standard VFR code. Pilots flying visual flight rules without ATC communication set this code so controllers can see general VFR traffic on radar. Other countries use different VFR defaults (e.g., 7000 in Europe).

Can ATC assign any code?

ATC assigns codes from the non-reserved blocks. Certain codes are permanently reserved (7500/7600/7700, 7777 for military interception, 0000, 1200 VFR, and others). The assignable pool varies by region and ARTCC facility.

Aviation Transponder Code Reference

Name: Aviation Transponder Code Reference
Availability: InStock
Author: Nham Vu

Look up any squawk code or search the full reference table of standard ICAO and ATC transponder codes.

Squawk Code Lookup

Enter any 4-digit octal code (0000–7777).

Type a squawk code above to decode it.

Emergency Codes — Quick Ref

7500 Hijack — unlawful interference. Set discreetly if safe.

7600 NORDO — radio failure. Follow lost-comm procedures.

7700 Emergency — general emergency. Alerts ATC immediately.

Full Squawk Code Reference

Code	Type	Name / Description	Region

Summary

Look up any squawk code or search the full reference table of standard ICAO and ATC transponder codes.

How it works

Type any 4-digit octal squawk code (0000–7777) in the search box.
The tool instantly shows if the code is a reserved or special code.
Browse the full reference table below to see all standard ICAO and ATC squawk codes.
Filter the table by typing a code number or keyword in the search field.
Reserved emergency codes are highlighted in red; informational codes in amber.

Use cases

Quickly verify what a squawk code means during flight planning or briefing.
Student pilots memorizing standard ATC transponder assignments.
Flight instructors explaining emergency squawk procedures.
Sim enthusiasts configuring transponders accurately in X-Plane or MSFS.
Aviation enthusiasts monitoring ADS-B feeds and decoding squawk codes.
Dispatchers cross-checking assigned codes against reserved ranges.

Frequently Asked Questions

Last updated: 2026-07-22 · Reviewed by Nham Vu