Squawk code lookup
Type a transponder code to see what it means, or read the reserved codes below. Three emergency codes are universal. Almost everything else depends on the region.
Four digits, each one 0 to 7.
Worldwide
Reserved by ICAO. These three mean the same thing everywhere.
Hijacking. Controllers will not ask about it directly on frequency; the response happens on the ground.
Lost communications. The aircraft is still flying normally and is expected to follow the lost-comms procedure for its clearance.
Anything from an engine failure to a sick passenger. It gets priority handling and lights up every screen looking at that sector.
United States
Reserved in the US for active air-defence intercepts. Never assigned to ordinary traffic.
The standard code for VFR flight in the United States and Canada, and in Australia outside controlled airspace.
Glider operations not in contact with ATC, United States.
Aircraft working a fire, United States.
SAR aircraft on a mission, United States.
US military and some other operations conducted outside controlled airspace.
Europe
What you squawk in Europe when nobody has assigned you a code. The European equivalent of 1200. This is the single most common mix-up: the two regions chose different codes for the same idea.
The default when no code has been assigned, notably on entering European airspace from an oceanic sector.
Aerobatic and display flying, Europe.
United Kingdom
UK: used where an aircraft is lost or unsure of position and working it out.
UK: operating in the visual circuit at an aerodrome.
Australia
Australia, in controlled airspace. Outside it, Australian VFR uses 1200, so this is not a straight equivalent of the US or European code.
How this works
- Why octal — the hardware reason
- The original Mode A transponder reply is twelve pulses spaced across a 20.3-microsecond window. The pulses are grouped into four triplets, each triplet encoding one digit. Three pulses can represent 0 through 7 — octal. The encoding has not changed since the 1960s. Mode S still carries the same twelve-bit identity field inside its reply, which is why 8 and 9 remain impossible even on a modern transponder with a digital interface.
- Regional codes and the collision problem
- Outside the three emergency codes, nothing is coordinated globally. The US assigns 1200 for VFR; Europe assigns 7000. A US-registered aircraft flying VFR in European airspace on 1200 is not squawking the local conspicuity code — it reads as a discrete assignment to European controllers. With only 4,096 codes and hundreds of sectors worldwide, the same code is often active in multiple places at once. Mode S solves this with a unique 24-bit address per aircraft, but the four-digit code persists alongside it.
- Most codes are discrete assignments
- The majority of the 4,096 codes have no standing meaning. A controller assigns one to a particular aircraft for a particular flight so the radar can tell it apart. The code means nothing before or after that flight. Only the reserved codes carry meaning wherever you see them.
Reserved and common codes
The three emergency codes are the most important, but dozens of other codes carry standing assignments. These vary by region.
| Code | Region | Meaning |
|---|---|---|
| 0000 | US | Not assigned. Some military systems use it as a default. |
| 0033 | US | Parachute jump operations in progress. |
| 0100 | US | Department of Defense: VFR in uncontrolled airspace. |
| 1200 | US / Canada | VFR conspicuity. Default code for uncontrolled VFR flight. |
| 1201 | US | VFR operations above FL600 (U-2 and similar). |
| 1202 | US | VFR glider, no ATC contact. |
| 1255 | US | Firefighting aircraft (TFR operations). |
| 1276 | US | ADIZ penetration, no ATC contact yet. |
| 2000 | ICAO | Conspicuity code when entering a secondary surveillance area without an assigned code. |
| 3000 | Australia | VFR conspicuity inside controlled airspace. |
| 4000 | US | Discrete code placeholder: assigned temporarily during a radar handoff. |
| 7000 | Europe / ICAO | VFR conspicuity. Default code for European VFR flight. |
| 7001 | Europe | VFR conspicuity in some European states (supplementary). |
| 7500 | ICAO (worldwide) | Unlawful interference (hijacking). |
| 7600 | ICAO (worldwide) | Radio failure (NORDO). |
| 7700 | ICAO (worldwide) | General emergency. |
| 7777 | US | Military interceptor operations. Never assigned to civilian traffic. |
VFR conspicuity codes by region
The default VFR code depends on where you fly. Using the wrong conspicuity code is not dangerous, but it may confuse controllers.
| Region | Code | Note |
|---|---|---|
| United States | 1200 | Default for all VFR flight not in contact with ATC |
| Canada | 1200 | Same as the US |
| Europe (ICAO) | 7000 | Default VFR conspicuity across most European states |
| Australia | 1200 | Outside controlled airspace |
| Australia | 3000 | Inside controlled airspace (Class C, D, E) |
| United Kingdom | 7000 | Same as Europe |
| India | 2000 | ICAO default for secondary surveillance entry |
The three emergency codes
These are the only codes with the same meaning worldwide. Each one starts a specific controller procedure. A mnemonic for the order: 7-5, taken alive; 7-6, radio fix; 7-7, falling from heaven.
7700General emergency
This code applies to all airborne emergencies: engine failure, pressurization loss, fire, a medical event, or any condition the crew cannot solve with standard procedures. It is the most general of the three codes and the most frequently used.
What the pilot does
The pilot sets 7700 and declares the emergency on the active frequency. If the pilot already has contact with ATC, no other action is necessary. The controller sees the code on radar immediately. If the pilot has no ATC contact, the code alerts every radar facility that monitors the sector.
What ATC does
ATC moves other traffic out of the way and gives the shortest route to a suitable airport. The aircraft gets priority to land. Emergency services start on the ground. The controller asks for the type of emergency, the number of persons on board, and the fuel remaining.
FAR 91.3 gives the pilot in command full authority in an emergency. The pilot can deviate from any rule as necessary. AIM 6-1-2 describes the declaration procedure. ICAO Annex 10, Volume IV identifies 7700 as the worldwide distress code.
7600Radio failure (NORDO)
The aircraft radio does not work. The aircraft can still fly, navigate, and land normally. The pilot cannot talk to ATC. This code tells controllers that the silence is a known equipment failure, not a refusal to respond.
What the pilot does
The pilot sets 7600 and follows the lost-communications procedure for the active route and clearance. Under US IFR rules, this means: fly the route that was assigned or expected, hold the highest of the assigned, expected, or filed altitude, and land at the destination. VFR pilots usually fly to the nearest airport and land.
What ATC does
Controllers assume the pilot follows the lost-communications procedure. They keep other traffic clear of the expected route. They may try to reach the aircraft on 121.5 MHz (the guard frequency). At towered airports, the tower uses light gun signals: steady green means cleared to land, steady red means give way.
FAR 91.185 describes the IFR lost-communications procedure. AIM 6-4-1 gives the full procedure. ICAO Annex 10 identifies 7600 as the worldwide radio-failure code.
7500Unlawful interference (hijacking)
An unauthorized person has taken control of the aircraft. This code is the most sensitive of the three. It triggers the fastest response.
What the pilot does
The pilot sets 7500 silently. There is no voice call. The code alone is the signal. Controllers do not ask the pilot to confirm a hijacking on an open frequency, because that could put the crew at risk.
What ATC does
ATC changes the assigned squawk code and watches the transponder. If the pilot sets the code back to 7500, the hijacking is confirmed. The response then goes to law enforcement and, in some cases, military intercept. In the US, NORAD receives notification.
AIM 6-3-4 describes the US procedure. ICAO Annex 17 (Security) and Annex 2 (Rules of the Air) cover unlawful interference worldwide. FAR 91.3 applies: the pilot in command keeps final authority.
Real-world example: Korean Air 85
On September 11, 2001, Korean Air Flight 85 flew across the Pacific toward Anchorage. ATC asked the crew if an unauthorized person had taken control of the aircraft. The crew answered with “HJK” — their airline’s internal code for “negative.” They also set squawk 7500. They wanted to show they understood the question. But 7500 declares the opposite: a hijacking in progress. NORAD scrambled F-15 fighters. The flight diverted to Whitehorse, Yukon, and landed under military escort.
This incident shows how squawk codes work in practice. The code alone started a military response. What the crew said on frequency did not change the result. It also shows why 7500 does not need a voice call. Controllers must treat the code as fact, because in a real hijacking the crew may not be free to speak.
Transponder modes
The four-digit squawk code is older than GPS, ADS-B, and most of modern aviation. It was built for the simplest transponder design. It has not changed through three generations of technology.
| Mode | Data | Capability |
|---|---|---|
| Mode A | 12 bits (4 octal digits) | Identity only. Sends the four-digit squawk code. No altitude, no position. The oldest mode still in use. |
| Mode C | 12 bits | Altitude reporting. Sends the squawk code plus a pressure altitude in 100-foot steps, encoded in Gillham (Gray) code. |
| Mode S | 24-bit address + 56/112-bit messages | Selective interrogation. Each aircraft gets a unique 24-bit address. Supports ADS-B: position, velocity, callsign, and many other data fields. The squawk code still rides inside the Mode S reply. |
Frequently asked questions
- What does "squawk" mean in aviation?
- Squawk is the verb for setting a transponder code. When a controller says "squawk 4521," the pilot dials that four-digit code into the transponder. The word comes from the IFF (Identification, Friend or Foe) systems of World War II. Those systems used bird codenames. The transponder response was called Parrot, and the instruction to activate it was "squawk your parrot."
- What happens if I accidentally squawk 7500, 7600, or 7700?
- When you dial a code, the transponder passes through other codes on the way. This is called a "code pass-through." Controllers know this happens. They will verify before they take action. If you set an emergency code and leave it, ATC will ask you to confirm. Tell them it was not intentional and set the correct code. Pilots learn to avoid passing through 7500 or 7700 when they dial a new code. If you must pass through one, use 7600 — a brief radio-failure indication is the least disruptive.
- Why do squawk codes only use the digits 0 through 7?
- A transponder encodes each digit in three bits. Three bits can only show values 0 through 7 (octal). Four digits times three bits gives twelve bits total, which makes 4,096 possible codes. The constraint is physical. The early transponders used three-position switches per digit. The encoding has not changed since.
- What is squawk 1200?
- In the United States and Canada, 1200 is the default code for VFR (visual flight rules) flight. It tells controllers the aircraft flies VFR and has no assigned code. In Europe, the equivalent code is 7000. In Australia, the code depends on the airspace: 1200 outside controlled airspace, 3000 inside it.
- What is the difference between Mode A, Mode C, and Mode S?
- Mode A sends only the four-digit squawk code. Mode C adds pressure altitude. Mode S adds a unique 24-bit aircraft address and supports ADS-B, which broadcasts position, velocity, and other data. All three modes still use the same four-digit squawk code. Mode S carries much more data alongside it.
- Can two aircraft have the same squawk code at the same time?
- Yes. Controllers assign codes in their own sector. The same code can be active in different parts of the country at the same time. Mode S solves this problem with a unique 24-bit address for each aircraft.
- What does "squawk ident" mean?
- When a controller says "ident," the pilot presses the IDENT button on the transponder. This sends a pulse that makes the radar return flash on the controller's screen for a few seconds. It helps the controller find the aircraft among other targets. Ident does not change the four-digit code. It is a momentary highlight.
- What is squawk 7777?
- In the United States, 7777 is reserved for military interceptor operations. It is never assigned to civilian traffic. If you set it without authorization, it can cause a military response.
- Where does the FAA require a transponder?
- 14 CFR 91.215 requires a Mode C transponder in Class A, B, and C airspace, within the Mode C veil (30 NM of a Class B primary airport), above 10,000 ft MSL (except below 2,500 ft AGL), and in certain other areas. 14 CFR 91.413 requires an inspection every 24 calendar months. ADS-B Out (14 CFR 91.225) is required in the same airspace as the transponder, plus Class E above 3,000 ft in the Gulf of Mexico.
Every aircraft squawking one of these is broadcasting its position too.
A SkyPath print is composed from millions of them — real ADS-B position reports over a single airport, chosen and composed by hand, colored by altitude, then printed on aluminum.