Aircraft squawk codes explained
Squawk codes are four-digit transponder codes (0000–7777, octal) that identify an aircraft to radar. Three are universal emergencies: 7500 signals hijacking, 7600 radio failure, and 7700 a general emergency. Air traffic control assigns most other codes, while a few are conspicuity defaults (1200 for VFR in the US, 7000 for VFR in Europe). AeroScope highlights emergency squawks in real time as they appear over your area.
WHAT ARE SQUAWK CODES?
Squawk codes are four-digit octal codes assigned to aircraft by Air Traffic Control (ATC). Each code is set on the aircraft's transponder and broadcast continuously, allowing ATC radar systems to identify and track individual aircraft. The term "squawk" originates from the World War II-era IFF (Identification Friend or Foe) system codenamed "Parrot", controllers would tell pilots to "squawk your parrot."
Each digit in a squawk code ranges from 0 to 7 (octal notation), creating 4,096 possible combinations from 0000 to 7777. Certain codes are reserved internationally for emergency situations, while others have specific meanings depending on the region and airspace. ATC assigns discrete squawk codes to aircraft entering controlled airspace, enabling positive identification on radar displays.
How squawk codes work
Squawk codes are transmitted by an aircraft's transponder, a radio transmitter/receiver that operates on 1030 MHz (interrogation) and 1090 MHz (reply). There are three primary transponder modes used in aviation:
MODE A
The original transponder mode that transmits only the four-digit squawk code. When interrogated by Secondary Surveillance Radar (SSR), the transponder replies with the assigned squawk code. This allows ATC to identify the aircraft but provides no altitude information.
MODE C
An extension of Mode A that adds pressure altitude reporting. The transponder transmits both the squawk code and the aircraft's barometric altitude (in 100-foot increments). Most controlled airspace requires at least Mode C capability for separation assurance.
Mode S / ADS-B
The modern standard used by ADS-B (Automatic Dependent Surveillance-Broadcast). Mode S transponders transmit a unique 24-bit ICAO address, squawk code, altitude, GPS position, velocity, callsign, and additional data. This is the data that AeroScope captures and analyzes in real-time.
Emergency squawk codes
Three squawk codes are reserved internationally for emergency situations. These codes trigger immediate attention from ATC and are monitored by military and security services worldwide.
| Code | Meaning | Description | Response |
|---|---|---|---|
| 7700 | General Emergency | Used for any in-flight emergency including engine failure, fire, medical emergency, fuel emergency, structural damage, or any situation requiring immediate assistance. | ATC provides priority handling, clears airspace, alerts emergency services, and coordinates with the nearest suitable airport for landing. |
| 7600 | Radio Failure (COMMS Lost) | Indicates the pilot has lost the ability to communicate with ATC via radio. The transponder is still functioning, so ATC can see the aircraft but cannot talk to it. | ATC provides separation based on last known intentions. The pilot follows lost communication procedures (squawk 7600, fly last assigned altitude and route, then proceed to destination). |
| 7500 | Hijack / Unlawful Interference | The most serious squawk code, indicating the aircraft is being hijacked or subject to unlawful interference. ATC will first attempt to confirm the code is intentional. | Security protocols activated immediately. Military intercept may be scrambled. ATC clears surrounding airspace and coordinates with national security agencies. |
A common mnemonic for remembering emergency codes: 75, taken alive (hijack), 76, radio fix (comms lost), 77, going to heaven (emergency).
Common squawk codes
| Code | Usage | Description |
|---|---|---|
| 1200 | VFR (US/Canada) | Standard code for Visual Flight Rules traffic in the United States and Canada. Aircraft flying VFR without ATC services use this code. |
| 1000 | IFR (some regions) | Used in some European and international regions for Instrument Flight Rules traffic. In ICAO regions, 1000 indicates an IFR flight receiving ATC services with Mode S. |
| 2000 | Entering controlled airspace | Used by aircraft entering controlled airspace from an area where no squawk code was previously assigned. Often used as a default before ATC assigns a discrete code. |
| 7777 | Military interceptor | Reserved for military interceptor aircraft on active intercept missions. This code should never be assigned to civilian aircraft under any circumstances. |
| 4000 | Military (restricted areas) | Used by military aircraft operating within designated restricted or military operating areas. The specific usage varies by country and military branch. |
| 0000 | Not yet assigned | Indicates that no discrete code has been assigned by ATC. Aircraft may briefly display 0000 during startup or when transitioning between ATC facilities. |
Conspicuity codes by country
Different countries and regions use specific "conspicuity" squawk codes for various types of uncontrolled traffic. These help ATC identify the type of operation being conducted.
United states
1200. VFR traffic (the universal US VFR code)
1277. Search and Rescue (SAR)
1255. Firefighting aircraft
0100. FAA flight inspection
4400-4477. Reserved for NORAD/ADIZ operations
United kingdom
7000. VFR conspicuity (equivalent of US 1200)
2000. Entering controlled airspace (no prior code)
0030. Parachute dropping
7001. VFR conspicuity (Mode S equipped)
0033. Aerobatic displays
EUROPE (EUROCONTROL)
7000. VFR conspicuity (standard across Europe)
2000. Entering controlled airspace
1000. Mode S equipped IFR (no discrete code needed)
0021-0027. Reserved for specific national uses
7010. Used in some regions for VFR in TMAs
How AeroScope tracks squawk codes
AeroScope reads squawk codes in its enrichment pipeline and feeds them into the attention score and the behavioral baselines. There is no reinforcement-learning classifier: that code was removed, and the anomaly layer is a consensus of established detectors.
Squawk Codes in Threat Scoring v2
Emergency squawk codes carry specific point values in the weighted threat scoring system:
- 7500 (Hijack): +20 points, the highest squawk-derived threat elevation. A 7500 code immediately pushes an aircraft into HIGH attention territory and is surfaced for a human to look at.
- 7700 (Emergency): +18 points, general emergencies receive near-maximum squawk scoring. The system distinguishes between aircraft that were already in a high-threat state (potential causal correlation) vs. those that transition to 7700 from normal operations.
- 7600 (Radio Failure): +12 points, comms loss elevates threat but at a lower weight, since radio failure alone is more commonly benign. However, a 7600 combined with other threat indicators (unusual flight path, proximity to restricted airspace) compounds multiplicatively.
- Military codes (4000 range, 7777): Military squawk codes feed into the RL surveillance classifier as one of its 20 state dimensions, contributing to the MILITARY_ISR or LEO classification decision.
Flow Through the 27-Stage Pipeline
Squawk data is read at ingestion, survives de-duplication on the ICAO address, and is evaluated during scoring: the code is checked against the emergency table and its points are added to the attention score.
- Real-time monitoring: Every aircraft's squawk code is captured from ADS-B data and displayed on the dashboard. Squawk codes are updated every 12 seconds as new data arrives from community receiver networks.
- Behavioral baseline context: The system tracks squawk code changes over time. An aircraft that cycles through multiple squawk codes in a short period deviates from its behavioral baseline, contributing additional anomaly points independent of the specific code values.
- Historical analysis: Squawk code changes are recorded in AeroScope's database, allowing post-event analysis of when emergency codes were activated and deactivated.
You can launch AeroScope to see live squawk codes for all aircraft in your area right now.
Frequently asked questions
What does squawk 7700 mean?
Squawk 7700 indicates a general emergency. When a pilot sets their transponder to 7700, it alerts air traffic control and triggers priority handling. This code is used for any in-flight emergency including engine failure, medical emergencies, fuel emergencies, and other critical situations.
What does squawk 7600 mean?
Squawk 7600 indicates radio failure (COMMS lost). The pilot can no longer communicate with air traffic control via radio but the aircraft transponder is still functioning. ATC will provide separation and the pilot follows lost communication procedures.
What does squawk 7500 mean?
Squawk 7500 indicates hijacking or unlawful interference. This is the most serious squawk code and immediately triggers security protocols. ATC will attempt to confirm the code is intentional to rule out accidental selection.
What is the normal VFR squawk code?
In the United States, the standard VFR (Visual Flight Rules) squawk code is 1200. In Europe and the UK, the VFR conspicuity code is 7000. Aircraft flying VFR without specific ATC-assigned codes use these to indicate they are operating under visual flight rules.
How many squawk codes are there?
There are 4,096 possible squawk codes, ranging from 0000 to 7777 in octal notation. Each digit can be 0-7, giving 8 x 8 x 8 x 8 = 4,096 combinations. Many codes are reserved for specific purposes while others are assigned dynamically by ATC.
Can AeroScope detect emergency squawk codes?
Yes. AeroScope monitors all aircraft squawk codes in real-time. When an aircraft transmits 7700, 7600, or 7500, AeroScope's threat scoring engine automatically flags the aircraft, raises its threat score, and generates an alert for monitoring operators.