Squawk Codes Reference
Standard transponder codes used by pilots and ATC worldwide, from emergency squawks to routine assignments.
Last reviewed: March 2026
A squawk code is a four-digit octal number (each digit ranges from 0 to 7) that a pilot sets on the aircraft's transponder. ATC assigns these codes to identify and track aircraft on radar. When a controller says "squawk 4521," the pilot dials that code into the transponder, and the aircraft appears on radar with that unique identifier. Certain codes are reserved worldwide for emergency situations and must never be set accidentally.
Emergency Squawk Codes
Three squawk codes are reserved internationally for emergency use. These codes trigger immediate alerts on ATC radar displays and initiate specific response procedures. Pilots must memorise all three.
Squawk 7700 is the universal transponder code for any emergency situation. It alerts ATC that the aircraft requires immediate assistance, whether due to engine failure, medical emergency, structural damage, fire, fuel emergency, or any other condition threatening the safety of the flight.
When to use
- Any situation that constitutes a distress or urgency condition
- When declaring a MAYDAY or PAN-PAN on the radio
- When unable to communicate but experiencing an emergency
- Anytime the pilot-in-command determines the safety of the aircraft or persons on board is in jeopardy
ATC response
- The code triggers a prominent alert on radar screens — typically a flashing or highlighted target with "EMRG" or equivalent annotation
- The controller will attempt to establish communication, provide priority handling, and clear conflicting traffic
- Emergency services may be alerted automatically at the destination or nearest suitable airport
Pilot procedure
- Set transponder to 7700
- Declare the emergency on the current frequency (or 121.5 MHz if unable)
- State the nature of the emergency, souls on board, and fuel remaining
- Follow ATC instructions or exercise pilot-in-command authority as needed
Squawk 7600 indicates that the aircraft has lost the ability to communicate by radio. This is known as a communications failure or NORDO (no radio) condition. The code alerts ATC that the pilot cannot hear or transmit on any frequency, so the controller must provide separation without two-way communication.
When to use
- Complete loss of radio transmit and receive capability
- When attempts to contact ATC on all available frequencies (including 121.5 MHz emergency) have failed
- After completing the standard troubleshooting steps (check volume, frequency, headset connections, circuit breakers)
ATC response
- The radar display shows a "RDOF" or communications failure indicator
- ATC will attempt contact on multiple frequencies, including 121.5 MHz
- Controllers will provide separation from other traffic based on the expected route and altitude
- ATC may attempt to relay messages through other aircraft
Pilot procedure (IFR)
- Set transponder to 7600
- Follow the memory aid: A-V-E-F — fly the route in this priority order: Assigned, Vectored, Expected, Filed
- For altitude, fly the highest of: assigned altitude, expected altitude, or minimum en-route altitude (MEA)
- In VMC conditions, continue the flight under VFR and land as soon as practicable
Squawk 7500 is the code for unlawful interference — commonly known as a hijack code. This is an extremely sensitive code that triggers immediate security protocols. It allows the crew to silently alert ATC to the situation without making a radio call that could be overheard in the cockpit.
When to use
- When the aircraft is subject to unlawful interference, hijacking, or any act of violence or threat against the flight
- Only when a genuine unlawful interference event is occurring
ATC response
- ATC will discreetly attempt to confirm the situation, typically by asking the pilot to verify the squawk code
- If the code is confirmed or no response is received, security and law enforcement agencies are immediately notified
- Military intercept may be initiated depending on the jurisdiction and circumstances
- The aircraft is given priority handling and a clear path to the designated airport
Important notes
- Never set 7500 accidentally — if ATC asks you to confirm a 7500 squawk and the situation is not a hijack, immediately change to the correct code and advise ATC it was set in error
- When cycling through codes on the transponder, avoid passing through 7500 (go from 74xx directly to 76xx if possible)
Memory aid for emergency codes: A common mnemonic is "75 — taken alive, 76 — need a fix (radio fix), 77 — going to heaven." While informal, it helps pilots recall which code matches which situation under stress.
Complete Squawk Codes Reference Table
A squawk code is a four-digit octal transponder code (0000–7777) assigned by ATC or set by the pilot to identify an aircraft on radar. Emergency codes are internationally standardised: 7700 for general emergency, 7600 for radio failure, and 7500 for unlawful interference (hijack). Standard codes are assigned by ATC for each flight.
| Code | Name | Meaning/Use |
|---|---|---|
| 7700 | General Emergency | Universal code for any emergency — distress, MAYDAY, engine failure, medical emergency. Triggers immediate ATC alert and priority handling. |
| 7600 | Radio Failure (NORDO) | Communications failure — aircraft cannot transmit or receive. ATC provides separation without two-way radio contact. Pilot follows AVEF procedure (IFR). |
| 7500 | Hijack / Unlawful Interference | Silently alerts ATC to unlawful interference. Triggers security protocols and possible military intercept. Never set accidentally. |
| 1200 | VFR Conspicuity (US / Canada) | Default code for VFR flights in US and Canadian airspace not receiving ATC radar services. Squawk 1200 when flying VFR without a discrete code assignment. |
| 7000 | VFR Conspicuity (ICAO / Europe) | Standard VFR conspicuity code in most ICAO member states outside North America, including Europe. Equivalent in purpose to 1200 in the US. |
| 2000 | Entering FIR (no assigned code) | Used when entering a Flight Information Region and no specific code has been assigned. A temporary code — expect a discrete code shortly after ATC contact. |
| 1000 | Mode S (no assigned code) | In some ICAO regions (primarily Europe), Mode S-equipped aircraft may use 1000 when no other code is assigned. Aircraft still identified via unique Mode S address. |
| 0000 | Reserved — Do Not Use | Generally reserved and should not be selected by pilots. May indicate transponder malfunction in some systems. Avoid setting this code. |
| 0033 | Parachute Operations (US) | Used by aircraft conducting parachute jump operations in the United States, per FAA guidance. |
Discrete Codes
ATC assigns discrete (unique) squawk codes to individual flights to positively identify each aircraft on radar. These codes are four-digit octal numbers in the range 0001 to 7777, excluding the reserved emergency and standard codes listed above. Since each digit ranges from 0 to 7 (octal), there are 4,096 possible codes in total (8 x 8 x 8 x 8).
When a controller issues an instruction like "Squawk 3412," the pilot enters that code on the transponder. The code then appears next to the aircraft's radar return, allowing the controller to correlate the target with the flight plan. Discrete codes are typically assigned upon initial contact with a radar-equipped ATC facility or during departure clearance.
How Transponder Modes Work
Aircraft transponders operate in several modes, each providing different levels of information to ATC radar systems. Understanding these modes helps pilots know what data their transponder is transmitting.
| Mode | Data Transmitted | Description |
|---|---|---|
| Mode A | Squawk code only | The most basic mode. The transponder replies to radar interrogations with only the four-digit identification code. ATC can see the aircraft's position and assigned code, but not its altitude. This mode is now considered legacy and is rarely used alone in modern aviation. |
| Mode C | Squawk code + pressure altitude | Adds automatic altitude reporting to the Mode A response. The transponder transmits the aircraft's pressure altitude (from the altimeter's encoding mechanism) along with the squawk code. ATC can see the aircraft's position, code, and altitude on the radar display. Mode C is required in most controlled airspace. |
| Mode S | Squawk code + altitude + aircraft data | An advanced mode that transmits the squawk code, altitude, and additional data via a unique 24-bit aircraft address. Mode S enables selective interrogation (the radar queries specific aircraft rather than all at once), reducing frequency congestion. It also supports Enhanced Surveillance (EHS), which can transmit heading, speed, and vertical rate. Mode S is the basis for ADS-B Out. |
ADS-B and Mode S: Automatic Dependent Surveillance-Broadcast (ADS-B) builds on Mode S technology. ADS-B Out broadcasts the aircraft's GPS-derived position, altitude, velocity, and identification continuously, without requiring radar interrogation. Many countries now mandate ADS-B Out equipage in controlled airspace.
Squawk Procedures
ATC uses specific phraseology when issuing transponder instructions. Pilots should understand each instruction and respond promptly.
Setting a Squawk Code
When ATC instructs "Squawk 4521", enter the four digits on the transponder. Read back the code to confirm: "Squawk 4521, Golf Alpha Bravo Charlie Delta." Ensure the transponder is in the ALT (altitude reporting) position unless otherwise instructed.
ATC: "Golf-Alpha Bravo Charlie Delta, squawk 4521."
Pilot: "Squawk 4521, Golf-Alpha Bravo Charlie Delta."
# ATC requests ident:
ATC: "Golf-Alpha Bravo Charlie Delta, squawk ident."
Pilot: "Squawk ident, Golf-Alpha Bravo Charlie Delta."
(Pilot presses the IDENT button once)
"Squawk Ident"
When a controller says "squawk ident," the pilot presses the IDENT (or ID) button on the transponder exactly once. This causes the aircraft's radar return to "bloom" or flash distinctively on the controller's screen for approximately 15 to 30 seconds, allowing the controller to positively identify which target corresponds to that aircraft. Do not press IDENT repeatedly — a single press is sufficient.
"Squawk Standby"
The instruction "squawk standby" means the pilot should switch the transponder to standby mode (SBY). In standby, the transponder is powered on but does not reply to radar interrogations. This is typically requested when the aircraft is on the ground or when ATC temporarily does not need the transponder response (for example, to reduce clutter in a congested area). The pilot should be ready to return to normal operation when instructed.
"Squawk Normal"
If ATC instructs "squawk normal", the pilot should return the transponder to its normal operating mode — typically ALT (Mode C or Mode S with altitude reporting). This is usually given after a period on standby or after the ident function has been used. It means resume normal transponder operation with altitude reporting enabled.
"Stop Squawk"
In some regions, ATC may instruct "stop squawk" which means turn the transponder to standby or off. This is more common in military operations or in non-radar environments where transponder replies are not needed.
Historical Context
The term "squawk" originates from the IFF (Identification Friend or Foe) systems developed during World War II. The military IFF system used the codename "Parrot," and the instruction to activate it was "squawk your parrot." Over time, the term "squawk" became standard aviation parlance for setting a transponder code.
Why 7700, 7600, and 7500?
Transponder codes use the octal number system (base-8), where each of the four digits ranges from 0 to 7. The emergency codes were deliberately chosen from the 7x00 range for practical reasons:
- Easy to set under stress: In older transponder designs with individual digit dials, the 7x00 codes required turning the first dial to 7, the second dial to the distinguishing digit (7, 6, or 5), and leaving the last two dials at 0. This minimised the number of actions needed in an emergency.
- Distinctive on radar: The 7x00 family of codes was reserved early in the development of secondary surveillance radar (SSR), ensuring that radar processing systems could flag them with high priority.
- Memorable pattern: The descending sequence (7700, 7600, 7500) makes the codes easier to memorise as a group. Each represents a progressively different type of emergency — general distress, communications failure, and unlawful interference.
The adoption of these codes was formalised through ICAO Annex 10 (Aeronautical Telecommunications) and has remained unchanged since the 1960s, providing a universal standard that all pilots and ATC facilities worldwide recognise.
Regional Differences
While the emergency codes (7700, 7600, 7500) are universal, some standard codes vary by region. Pilots operating internationally must be aware of these differences.
| Region | VFR Default Code | Notes |
|---|---|---|
| United States | 1200 | The standard VFR conspicuity code. Used when flying VFR without ATC radar services. All VFR aircraft in the US National Airspace System should squawk 1200 unless otherwise assigned. |
| Canada | 1200 | Same as the United States. Canadian VFR traffic uses 1200 as the default conspicuity code. |
| Europe (ICAO) | 7000 | The ICAO standard VFR conspicuity code used across most European countries. Eurocontrol and national ANSPs recognise 7000 as the default VFR squawk. |
| United Kingdom | 7000 | Standard VFR conspicuity code. The UK also uses additional conspicuity codes: 7010 for flights in the Lower Airspace Radar Service (LARS) and specific codes for certain services. |
| France | 7000 | Standard ICAO VFR conspicuity code. French ATC may assign specific codes in certain zones or for specific information services. |
| Australia | 1200 | Australia uses 1200 for VFR, consistent with US practice. ADS-B is mandated in most controlled airspace above 10,000 ft AMSL. |
| India | 7000 | Follows the ICAO standard. VFR flights squawk 7000 unless assigned a discrete code by ATC. |
Tip for international flights: When planning a flight that crosses between regions with different VFR default codes (e.g., transiting from US to European airspace), be aware of the change and listen for ATC instructions. In most cases, ATC will assign you a discrete code for oceanic and international crossings, so the VFR default becomes relevant mainly for local operations within each region.