📡 Squawk Code Reference — EGPF ◀ Back to Map

📡 What is a Squawk Code?

A squawk code (formally a Mode A code) is a 4-digit number assigned by Air Traffic Control to uniquely identify an aircraft on radar. The aircraft's transponder transmits this code continuously, allowing controllers to distinguish it from every other aircraft in their airspace.

Each digit runs from 0–7 (octal, not decimal), giving 4,096 possible combinations. A small number of these are reserved for special purposes — the ones on this page. Everything else is a discrete code assigned uniquely to one flight.

7
0–7
7
0–7
0
0–7
0
0–7
Example: 7700 = General Emergency
Digits: 0, 1, 2, 3, 4, 5, 6, 7 only (no 8 or 9)
Total combinations: 8⁴ = 4,096
Reserved codes: ~30 with specific meanings
Discrete codes: Everything else, assigned by ATC

⚠ Emergency Codes — The Big Three

🚨

If you see 7500, 7600 or 7700 on the map — something serious is happening

These codes are internationally recognised and take absolute priority. ATC will immediately give the aircraft whatever it needs. Emergency services are alerted automatically.

Code Type Meaning
7700 EMERGENCY General Emergency (Mayday). The aircraft is in distress and requires immediate assistance. This is the catch-all emergency code — engine failure, medical emergency, fire, structural issue, fuel emergency or any other serious situation. ATC clears the airspace around the aircraft immediately.
7600 EMERGENCY Radio Failure (NORDO — No Radio). The aircraft has lost radio contact with ATC. The pilot will follow established lost-comms procedures: squawk 7600, continue on the filed flight plan, and look for light signals from the tower when approaching an airfield. Not necessarily dangerous, but ATC treats it seriously.
7500 EMERGENCY Unlawful Interference / Hijack. The aircraft is being subjected to unlawful interference. This triggers an immediate security response — military aircraft may be scrambled, and the flight is treated as a national security incident. Pilots sometimes set this accidentally; ATC will discretely verify.

📶 Conspicuity Codes — Standard Defaults

Code Type Meaning
7000 VFR UK VFR Conspicuity (UK & Europe). The default code for Visual Flight Rules aircraft in the UK and most of Europe that haven't been given a discrete code by ATC. Very commonly seen — small GA aircraft, flight training, private pilots. Think of it as "I'm here, I'm VFR, I haven't spoken to anyone yet."
2000 IFR UK IFR Conspicuity / Entering CAS. Used by Instrument Flight Rules aircraft entering controlled airspace without an ATC clearance, or as a default IFR conspicuity code. Also used in some countries as the standard IFR default. You'll see this on commercial flights in certain handoff situations.
1200 VFR USA VFR Conspicuity (North America). The North American equivalent of 7000. If you see this over Scotland it likely means a transatlantic visitor whose transponder hasn't been updated, or an aircraft in transit from North America.
0000 STANDBY Standby / Not assigned. Should not normally be transmitted. Occasionally seen when a transponder is powering up or has not yet been assigned a code. ATC treat this with some suspicion if sustained.
1000 MODE S Mode S default. Used by Mode S equipped aircraft in some European countries as a default code when no discrete squawk has been assigned. Mode S transponders also transmit the aircraft's unique 24-bit ICAO address, so the squawk code itself is less important for identification purposes.

🛩 Special Operations Codes (UK)

Code Type Meaning
0020 SPECIAL Glider / Sailplane. Unpowered glider in flight. May have limited ability to manoeuvre or change altitude quickly. ATC gives priority routing.
0021 SPECIAL Glider — Wave Operations. Glider exploiting mountain wave lift, often reaching significant altitudes.
0022 SPECIAL Glider Aerotow. A powered aircraft towing a glider. The combination behaves differently from a normal aircraft — slower, cannot turn sharply.
0023 SPECIAL Hang Glider / Paraglider. Very slow, very low, highly weather dependent. Rarely seen on ADS-B as these rarely carry transponders.
0024 SPECIAL Parachuting Operations. Aircraft dropping parachutists. Expect erratic altitude changes as the aircraft climbs, drops jumpers, and descends rapidly. A wide area around the drop zone is kept clear.
0025 SPECIAL Aerobatics. Aircraft performing aerobatic manoeuvres. Will deviate significantly from straight-and-level flight — expect unusual altitude and heading changes.
0026 SPECIAL Microlight. A microlight aircraft (very light, very slow). Often operating at low level.
0027 SPECIAL Fixed-wing aircraft below 1,000 ft AGL. Aircraft deliberately operating at very low level, e.g. crop spraying, survey, or pipeline patrol.
0030 SPECIAL Helicopter — Local Operations. Helicopter operating locally without a discrete ATC code assigned.
0033 SPECIAL Police Aircraft / Helicopter. Law enforcement aviation. May be conducting surveillance and will not always squawk this openly.
0034 SPECIAL Air Ambulance / HEMS. Helicopter Emergency Medical Services. Has priority over almost all other traffic. May operate at low level in built-up areas.
0035 SPECIAL HM Coastguard. Coastguard search and rescue operations. Operating around the Scottish coastline this is a common sight.
0037 SPECIAL Mountain Rescue / SAR. Search and rescue operations, often in mountainous or remote terrain.

🎖 Military Codes (UK)

Code Type Meaning
7001 MILITARY Military Low Flying. UK military aircraft conducting authorised low-level flying training. Common over Scotland — the low flying areas (LFAs) cover much of the Highlands.
7002 MILITARY Military — Formation Flying. Multiple military aircraft flying in formation, being treated as a single entity by ATC.
7003 MILITARY On Test / Air Display. Aircraft being tested or participating in an air display. Expect unusual manoeuvres.
7004 MILITARY Aerobatic Display. Military or civilian aircraft performing an aerobatic display at an airshow or event.
7777 INTERCEPT Military Interception. A military aircraft has been scrambled to intercept another aircraft. Seeing this is extremely rare and indicates a serious incident — an aircraft has violated restricted airspace, lost communication, or is behaving suspiciously. Essentially never seen on civilian trackers in normal operation.

💡 Interesting Notes

Why "squawk"? The term comes from the IFF (Identification Friend or Foe) system used in World War II. The early transponders were nicknamed "Parrot" (as in, they repeated back a signal), and to activate it, pilots were told to "squawk" — as a parrot would. The name stuck.

Digits 8 and 9 don't exist. Squawk codes are octal (base-8), so each digit only goes 0–7. You'll never see a squawk of 8 or 9 in any position. This means there are exactly 4,096 possible codes (8⁴), not 10,000 as you might expect.

7700 is more common than you'd think. Pilots sometimes set 7700 briefly by accident while dialling in a different code — "transponding through 7700." ATC are aware of this and will call the aircraft to verify before escalating.

Discrete codes are allocated regionally. Different blocks of codes are assigned to different countries and ATC centres. When you see a flight with a discrete code like 5342, that specific number was issued by a particular ATC unit and is only valid for that flight in that airspace.