What does squawk mean?

To squawk is to set a four-digit code on the aircraft transponder so it is sent with every radar reply. Controllers use the code to identify the flight on radar, and a few codes (7500, 7600, 7700) raise alerts on ATC displays.

What are the emergency squawk codes?

ICAO, the FAA and EU SERA.13005 all use 7500 for unlawful interference (hijacking), 7600 for radio communication failure and 7700 for an emergency. SERA lets a pilot under unlawful interference use 7700 instead of 7500 if circumstances warrant.

What does squawk 7000 mean?

In Europe, 7000 is the VFR conspicuity code. EU rule SERA.13005 says a pilot not receiving air traffic services selects 7000 unless the competent authority prescribes otherwise. The US equivalent is 1200; in the US, 7000 is just an ordinary code.

What does squawk 2000 mean?

Code 2000 is set when ATC has given no code instruction. SERA.13005 requires it in Europe in that case, and it is used when entering radar coverage from an area without secondary radar and as the default in North Atlantic airspace. In Canada it is used by uncontrolled IFR flights at or above 18,000 ft.

What is the difference between squawk 1200 and 7000?

Both mean a VFR flight without an assigned code. 1200 is used in the US and Canada; 7000 is used in Europe and the UK. Use the code required by the airspace you are flying in.

What is squawk 7400 used for?

FAA Order JO 7110.65 states that an unmanned aircraft system may transmit 7400 when the control link between the aircraft and pilot is lost. The UK added 7400 for UAS/RPA lost link in its code allocation plan in 2026.

Why should pilots avoid 7500, 7600 and 7700 when changing codes?

The FAA AIM tells pilots to avoid selecting 7500, 7600 or 7700 by accident during a routine code change, because even a moment on those codes can trigger alarms at ATC. On rotary-knob transponders, change the digits in an order that never passes through them; the code-change helper on this page finds that order.

What does squawk ident mean?

When ATC says "squawk ident", the pilot presses the IDENT button. The transponder then adds a special position identification pulse for a short time so the aircraft's target stands out on the controller's display.

Why do squawk codes only use digits 0 through 7?

A Mode A squawk is four octal digits. Each position has eight possible values, 0 through 7, so there are 8^4 = 4,096 possible values from 0000 through 7777. Digits 8 and 9 are not valid.

What does an unlisted valid octal code mean?

Usually it is a discrete code that ATC assigned to one flight so radar can identify it, such as 2403 or 4521. Its meaning comes from that assignment, not the number, and blocks of codes are allocated differently by each country and facility.

Does this reference replace ATC instructions or flight manuals?

No. Code allocations vary by country, flight information region (FIR) and facility. Always follow current ATC instructions and the applicable national publications.

Aviation Transponder Code Reference

Type any 4-digit squawk code to see what it means and where it applies. 7500 = hijack, 7600 = radio failure, 7700 = emergency worldwide; 1200 is US VFR and 7000 is European VFR.

Squawk 7500 means unlawful interference (hijacking), 7600 means radio communication failure, and 7700 means a general emergency; ICAO, the FAA and EU SERA all use these three.

Aviation Operational Notice: For study and flight briefing only. Code allocations vary by Flight Information Region (FIR) and national authority. Always follow ATC instructions and current aeronautical publications. Lookups run in your browser.

Squawk Code Decoder

Enter a 4-digit octal code (Mode A/3A: digits 0–7 only).

Quick Presets

Enter any 4-digit code above or select a preset to evaluate.

Safe Code-Change Helper

The FAA AIM warns against passing through 7500, 7600 or 7700 when changing codes. Find a knob order that avoids them.

Current code

New code

Mode A Technical Framing

Total Combinations:: 4,096 (8^4)
Register Layout:: 4 octal digits
Valid Octal Range:: 0000 – 7777
Emergency Codes:: 7500, 7600, 7700

Squawk Codes List by Region

Sources: FAA AIM 4-1-20, FAA JO 7110.65/7110.66, EU SERA.13005, UK AIP ENR 1.6, Transport Canada AIM, ICAO.

Code	Type	Meaning	Region / Source
7500	Emergency	Unlawful Interference (Hijack) For an aircraft subject to unlawful interference. Under EU SERA.13005 the pilot attempts to select 7500 and may use 7700 instead if circumstances warrant.	Worldwide (ICAO) ICAO / FAA AIM / SERA.13005
7600	Emergency	Radio Communication Failure For an aircraft that has lost two-way radio communication. In the US, IFR flights then follow the 14 CFR 91.185 lost-communication rules.	Worldwide (ICAO) ICAO / FAA AIM / SERA.13005
7700	Emergency	General Emergency For an aircraft in a state of emergency. SERA.13005: select 7700 unless ATC has already directed the pilot to keep a specific code.	Worldwide (ICAO) ICAO / FAA AIM / SERA.13005
2000	IFR	No ATC Code Instruction Selected when ATS has given no code instruction (SERA.13005), when entering secondary-radar coverage from an area without it, and by default in North Atlantic airspace.	Worldwide (ICAO) SERA.13005 / ICAO regional
7000	VFR	VFR Conspicuity (Europe) Selected by pilots not receiving air traffic services, unless the competent authority prescribes another code. The European equivalent of US 1200.	Europe EU SERA.13005 / UK AIP
1000	IFR	Mode S Conspicuity (Europe) Non-discrete code assigned to IFR flights where radar identifies the aircraft by its downlinked Mode S aircraft identification instead of a discrete code.	Europe ICAO Doc 4444 / Eurocontrol
0000	Regional	Not a Standard Assignment Left to states for regional allocation in some ICAO regional plans; not a universal standby or VFR code.	Worldwide (ICAO) ICAO SAM / Regional
1200	VFR	VFR, No Assigned Code (US) Standard US code for VFR flight when not using an ATC-assigned code. Transport Canada uses 1200 the same way.	United States FAA AIM 4-1-20
1202	VFR	VFR Glider Operations Gliders operating VFR and not in contact with ATC use 1202 instead of 1200.	United States FAA AIM 4-1-20
1255	Special	Firefighting Aircraft Authorized firefighting aircraft not in contact with ATC, en route to, from or within a designated firefighting area.	United States FAA AIM 4-1-20
1276	Special	ADIZ Entry, No Radio Contact Aircraft entering an Air Defense Identification Zone that cannot establish communication with ATC or an aeronautical facility.	United States FAA JO 7110.66
1277	Special	Search and Rescue (SAR) VFR aircraft on authorized USAF or USCG search-and-rescue missions within a designated search area.	United States FAA AIM 4-1-20
4000	Special	Military Training Routes / Warning Areas Military aircraft on VFR military training routes or in restricted or warning areas, unless ATC assigns a discrete code.	United States FAA AIM / JO 7110.65
7400	Special	UAS Lost Control Link May be transmitted by an unmanned aircraft system after loss of the control link between aircraft and pilot. Also allocated in the UK (2026).	United States FAA JO 7110.65 / UK CAA
7777	Special	Military Interceptor (Not for Civil Use) Reserved for military interceptor operations in the US system; civil aircraft must never operate a transponder on 7777. Also used by fixed radar test transponders.	United States FAA AIM 4-1-20
7001	Special	Military Low-Level Climb-Out Military aircraft making a sudden climb out of low-level operations into airspace where they may conflict with other traffic.	United Kingdom UK AIP ENR 1.6
7004	Special	Aerobatics and Display Civil or military aircraft flying solo or formation aerobatics while displaying, practising or training for a display, when no discrete code is assigned.	United Kingdom UK AIP ENR 1.6
0033	Special	Parachute Dropping Aircraft engaged in parachute dropping in UK airspace.	United Kingdom UK AIP ENR 1.6
1000	IFR	IFR Below 18,000 ft, No Code Canadian IFR flights below 18,000 ft ASL when no other code has been assigned.	Canada Transport Canada AIM
2000	IFR	Uncontrolled IFR at or above 18,000 ft Canadian uncontrolled IFR flights at or above 18,000 ft when no other code has been assigned.	Canada Transport Canada AIM

What to Do with Each Emergency Code

7700 — emergency: select it unless ATC has already given you a code to keep; if you are talking to ATC on a discrete code, they may ask you to stay on it.
7600 — radio failure: squawk 7600 and follow the lost-communication procedure (in the US, 14 CFR 91.185 for IFR: route, altitude and approach timing).
7500 — unlawful interference: attempt to select 7500; EU SERA allows 7700 instead if circumstances warrant. Controllers will confirm the code discreetly.
Changing codes: avoid passing through 7500, 7600 or 7700, even for a moment. Example: from 0700 to 7200, change the second digit first (0700 → 0200 → 7200); changing the first digit first would briefly show 7700.

Primary Authorities Reviewed: October 2026

Quick answer

Squawk 7500 means unlawful interference (hijacking), 7600 means radio communication failure, and 7700 means a general emergency; ICAO, the FAA and EU SERA all use these three. VFR pilots not talking to ATC squawk 1200 in the US and 7000 in Europe. Most other codes, such as 2403, are discrete codes ATC assigns to one flight.

Examples

Code	Meaning	Where
7500	Unlawful interference (hijack)	Worldwide (ICAO)
7600	Radio communication failure	Worldwide (ICAO)
7700	General emergency	Worldwide (ICAO)
1200	VFR, no ATC-assigned code	US, Canada
7000	VFR, not receiving ATS	Europe (SERA), UK
2000	No code instruction from ATC	Europe (SERA), ICAO areas
7400	Drone (UAS) lost control link	US, UK

Type any 4-digit code to check that it is valid octal and see every region where it is a special-purpose code.

Summary

Client-side reference and validator for Mode A transponder squawk codes based on the FAA AIM and Order JO 7110.65, EU SERA.13005, the UK AIP and Transport Canada, with a helper that orders knob changes to avoid the emergency codes.

How it works

Enter any 4-digit octal squawk code (digits 0–7) or tap a preset.
See every region where the code has a special meaning, with the governing source (ICAO, FAA, EU SERA, UK AIP or Transport Canada).
Filter the reference table by region or by text such as "VFR" or "emergency".
Enter your current and new codes in the code-change helper to get a knob order that never passes through 7500, 7600 or 7700.
Check Mode A syntax: four positions using digits 0–7 give 4,096 possible values from 0000 to 7777.

Use cases

Quick cross-referencing of emergency and special-purpose squawk codes against FAA, ICAO and EASA publications.
Checking the right VFR code before flying in the US (1200), Europe (7000) or Canada.
Flight crew and dispatcher preflight briefing review.
Aviation students and flight simulator users verifying Mode A octal numbering.
ADS-B receiver and flight-tracker users decoding a squawk they see on screen.

Frequently Asked Questions

Last updated: 2026-10-09 · Reviewed by Nham Vu