A squawk code is the four-digit number a pilot sets on an aircraft’s transponder so air traffic control can identify that flight on radar. Only three are standardized worldwide: 7500 for unlawful interference, 7600 for radio failure, and 7700 for a general emergency.
Everything else is national or regional convention — the 1200 default in the United States and Canada, Europe’s 7000, the 2000 fallback over oceanic airspace. Those codes are set by individual countries rather than by a single global standard, which is why no authoritative worldwide squawk code list exists.
Search for a complete list of aviation squawk codes and you’ll find dozens of pages that all look authoritative and none that quite agree.
Some stop at the three emergency codes. Some add a regional VFR default and call it a list. A few print numbers that trace back to no regulation anyone can point to.
There’s a reason for the mess. The four-digit system was never built around one master reference.
The emergency codes are the exception: 7500, 7600 and 7700 are reserved internationally and mean the same thing whether the aircraft is over Kansas or Cambodia. Everything else — the codes a flight actually squawks for most of its journey — lives in individual national rulebooks called Aeronautical Information Publications, and those documents have no obligation to match each other.
That distinction is the story here. What follows is a reference to what’s genuinely standardized, what’s regional convention, and where the trail of verification runs out — including one code that means military intercept in the United States and ground-radar monitoring in Bosnia. Underneath all of it runs a quieter change: as Mode S transponders broadcast their own identity, the assigned squawk code is slowly losing the identification job it was invented to do.
What a squawk code actually is
The number a pilot dials into the transponder panel is four digits long, and every one of them sits between 0 and 7. That isn’t a stylistic choice. The system runs on octal — base eight — which is why 8 and 9 never appear in a squawk code no matter which country’s list you’re reading.
It also means the range from 0000 to 7777 holds 4,096 possible codes, not the 10,000 the decimal-looking format suggests. That number matters more than it sounds, because every aircraft in a controller’s airspace wants a code of its own.
Which is why assignment is largely a machine’s job.
According to the Federal Aviation Administration, facilities rely on computer-assigned beacon codes unless a directive, agreement, or coordination says otherwise — the point being that the next controller has the code in hand before the aircraft reaches the sector boundary. Europe works from an allocation list that participating states agree among themselves and coordinate with their neighbors. Either way, the pilot usually just reads back whatever ATC says and sets it — a step that appears in no passenger-facing document anywhere.
The squawk codes list, and why no global version exists
The three reserved codes are the exception that proves the rule. 7500 means unlawful interference, 7600 a failure of two-way radio communication, and 7700 an aircraft in a state of emergency — engine failure, a medical crisis, decompression, anything in that family. According to the ICAO PANS-ATM Doc 4444 text published by VFR Europe, these are the internationally reserved codes, which is why they read identically to a controller in Frankfurt, Fiji, or Fresno.
Nothing else gets that treatment, and the framework is built to allow it. ICAO’s PANS-ATM procedures are written as complementary to the organization’s own standards rather than as one global rulebook, and regional procedures are permitted to supplement them. States whose practice diverges significantly are required to publish the difference in their own Aeronautical Information Publication.
The document governing squawk codes is designed to accommodate national variation, not erase it.
So the rest of the list comes from national rulebooks.
In the United States and Canada, 1200 is the default for VFR aircraft with no specific ATC assignment. Across many European regions, 7000 is set by aircraft not receiving air traffic service, so they show up more clearly on a controller’s display. And 2000 is the fallback where no ATC instruction or regional agreement applies — the Bosnia and Herzegovina Air Navigation Services Agency publishes it that way, subject to exceptions for other published codes, and it is the usual choice for a flight crossing into oceanic airspace.
| Code | Meaning/function | Region or authority that defines it | Internationally standardized or regionally defined |
|---|---|---|---|
| 7500 | Unlawful interference | ICAO PANS-ATM framework | Internationally standardized emergency code |
| 7600 | Air-ground radio-communications failure | ICAO PANS-ATM framework | Internationally standardized emergency code |
| 7700 | State of emergency | ICAO PANS-ATM framework | Internationally standardized emergency code |
| 1200 | Default Mode 3/A code for VFR aircraft unless ATC directs otherwise | FAA, United States | Regionally defined |
| 1202 | VFR gliders not in contact with ATC | FAA, United States | Regionally defined |
| 1277 | Certain authorized U.S. Air Force or U.S. Coast Guard search-and-rescue flights | FAA, United States | Regionally defined |
| 7777 | Reserved for military interceptor operations; civil aircraft are prohibited from selecting it | FAA, United States | Regionally defined |
| 0000 | General-purpose code available for local use by a State | Bosnia and Herzegovina AIP | Regionally defined |
| 2000 | Default when no ATC instruction or regional agreement applies, subject to exceptions for other published codes | Bosnia and Herzegovina AIP implementing ICAO procedures | Regionally defined or locally implemented |
| 7000 | Conspicuity code for aircraft not receiving ATC service in specified areas | Bosnia and Herzegovina AIP; European regional practice | Regionally defined |
| 7775 | Reserved for SSR ground-transponder monitoring | Bosnia and Herzegovina AIP | Regionally defined |
| A1000 | Conspicuity code for eligible civil aircraft identified through the Mode S/downlinked-identification process | Belgian AIP and European rules | Regionally defined |
| A7000 | Uncontrolled flights without a prior transponder-setting instruction | Belgian AIP | Regionally defined |
| A7601 | Radio-communications failure for IFR flights in VMC that remain in VMC and land at the nearest suitable aerodrome | Belgian AIP | Regionally defined |
| Source: International Civil Aviation Organization (ICAO); Federal Aviation Administration (FAA); Bosnia and Herzegovina Air Navigation Services Agency (BHANSA); SKEYES / Belgian AIP | |||
Then there are the codes that never leave one country. The FAA reserves 7777 for military interceptor operations and bars civil aircraft from selecting it. In Bosnia and Herzegovina, the same digits are set aside for SSR ground-transponder monitoring, alongside 7775.
Same code, two unrelated jobs.
Smaller national entries fill in the rest. The FAA keeps 1202 for VFR gliders out of contact with ATC and 1277 for authorized search-and-rescue flights by the U.S. Air Force or Coast Guard. The Belgian AIP published by SKEYES adds A1000 for civil aircraft identified through the Mode S process, A7000 for uncontrolled flights with no transponder instruction, and A7601 for an IFR flight that loses radio contact in visual conditions and plans to stay visual and land at the nearest suitable aerodrome.
The A prefix marks those as Mode A entries; the underlying values are 1000, 7000 and 7601.
One procedural detail is worth knowing about 7500 in particular. The Belgian AIP instructs controllers to seek confirmation from the pilot once it appears on screen — and lets the pilot decline to confirm when the circumstances justify it. That’s the reality behind a code everyone assumes is a silent alarm.
Superdeals cover departures from North America, Europe and Australia.
Flight deals most people never see
Air Traveler Club monitors thousands of routes for pricing anomalies that traditional search engines miss. With ATC Superdeals members save up to 80% on each flight vs. regular fares.
Too good to be true? Check it out yourself. It's free.
Delivered weekly. Unsubscribe anytime.
How the transponder reply works, and what Mode S changes
What happens between the panel and the controller’s screen is a short conversation, repeated every few seconds.
Ground secondary-surveillance radar sends out an interrogation. The transponder answers with the four-digit Mode A code, and if Mode C is running, it adds pressure altitude in 100-foot increments. That reply is what lets a controller tie a moving radar return to a specific flight instead of an anonymous dot.
Mode S changed the terms. A Mode S transponder downlinks an aircraft identification that can be matched against the filed flight plan.
Where the aircraft, the ground system, the surveillance coverage, the communications and the controller’s display all support that correlation, a flight can operate under a conspicuity code instead of drawing a discrete one off the allocation list. Under European Union Regulation 1206/2011, that substitution is permitted — but only under those conditions.
Where any of them fail, the old arrangement snaps back into place. A flight outside contiguous coverage, or one whose identification won’t correlate reliably, still takes a discrete code. And ADS-B doesn’t retire the transponder: FAA procedures still require an operable one, with the ATC-assigned beacon code forming a required element of the ADS-B Out message.
Reporting by
Key terms
- Mode S
- Mode S is a transponder standard that carries an aircraft’s identity in its replies to ground surveillance radar. That identity can be matched against the filed flight plan, which lets a qualifying aircraft fly under a conspicuity code instead of a discrete one. For travelers, the practical effect is that the code on the panel matters less than the aircraft’s own broadcast identity — though the code remains the fallback whenever that identity cannot be confirmed.
- Aeronautical Information Publication (AIP)
- An Aeronautical Information Publication is the national document in which a state publishes its aviation rules and procedures. Under ICAO’s framework, states whose practice diverges significantly from the standards are required to flag the difference in their AIP. That is why the non-emergency squawk codes in this article are cited to national AIPs — Bosnia and Herzegovina’s and Belgium’s — rather than to a single global source.
- Conspicuity code
- A conspicuity code is a shared SSR code that an aircraft can use instead of a discrete, individually assigned one. It works when the aircraft’s downlinked identification can be reliably matched to its flight plan, so the code itself no longer has to carry the identification job. In Europe, A1000 is the conspicuity code for eligible civil aircraft, and its use depends on that identification being reliably correlated.
- PANS-ATM (Doc 4444)
- PANS-ATM, published as ICAO Doc 4444, is the procedures document that governs air traffic management, including the international treatment of SSR codes. It frames its procedures as complementary to ICAO’s standards and allows regional procedures in Doc 7030 to supplement them. It also points states to Annex 15 for the publication of significant differences, which is how national variations in code use reach the public record.
- ADS-B
- ADS-B is a surveillance technology in which an aircraft broadcasts its position and identity rather than waiting to be interrogated by ground radar. It is one of the systems, alongside Mode S, that carries an aircraft’s identity independently of the four-digit code a controller assigns. For a traveler, that is the shift this article describes: identity increasingly broadcast by the aircraft rather than assigned to it by a controller.
Questions? Answers.
What is the 7777 squawk code?
In the United States, 7777 is reserved for military interceptor operations and civil aircraft are prohibited from selecting it. In Bosnia and Herzegovina, the same digits are set aside for SSR ground-transponder monitoring. It isn’t an emergency code in either case — it’s a jurisdiction-specific assignment.
What is the most serious squawk code?
There is no formal ranking among the internationally reserved codes. 7500 signals unlawful interference, 7600 a failure of two-way radio communication, and 7700 an aircraft in a state of emergency — all three are handled as urgent, and which one applies depends on what has actually gone wrong.
What is squawk 7500, 7600, and 7700?
They are the three codes reserved internationally under the ICAO framework. 7500 means unlawful interference, 7600 means a failure of two-way radio communication, and 7700 means the aircraft is in a state of emergency.
What does the 0000 squawk code mean?
0000 is not an emergency code. In Bosnia and Herzegovina, the national AIP makes it available as a general-purpose code for a state’s own local use — a reminder that a four-digit value can carry entirely different meanings depending on which authority published it.
What’s the difference between squawking 7600 and 7700?
7600 is specifically for a failure of two-way radio communication: the aircraft can still fly, but the crew cannot talk. 7700 is the broader general-emergency code, used for anything from engine failure to a medical crisis. Both are internationally reserved and read the same way in any country’s airspace.
