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Real world aviation transponder codes are issued to flights from a block or set of numbers allocated to each ATC zone, area, facility, or section, with some flights using codes reserved specifically for their aviation function.  In many cases the squawk code issued to a flight will stay with that aircraft for the duration of its flight.  The same codes can also be used in FSX if desired and indeed many FSX ATCO’s utilise real world aviation transponder codes.  However, while transponder (squawk) codes in FSX can be used to replicate real world aviation these numbers can be somewhat arbitrary and have little other use as such.  With 4096 possible numeric codes this simple function in FSX can be made to work a little harder if desired.


A recent upgrade to the radar client used by some UK317 ATCO's facilitates an enhanced feature whereby certain squawk codes indicate to any active ATC the nature of your flight.  Many of these are real world codes specifically reserved for certain flight regimes.  The use of these codes can alert active ATC what a particular aircraft is doing.  If you fly under ATC direction in the server you may be issued with a transponder code that may not immediately make sense but it does in fact have a function useful to any active ATC.  If you are a pilot and have not been issued with a squawk code, and have not filed a flight plan, you may use the codes below to indicate to any ATC present your intentions if you wish.

Code     Abbr.     Meaning / Intention

0000           IDENT       Squawk identification.  Used to help ATC identify your aircraft if your transponder does NOT have an Ident button.  [Real world aviation code (ICAO).]  # See Note 1.

0001           V LIST       VFR listening.  Use this code if you are a VFR flight and are monitoring active ATC transmissions.  # See Note 2.

0002           I LIST         IFR listening.  Use this code if you are an IFR flight and are monitoring active ATC transmissions.  # See Note 2.

0020           MED          Medevac.  Medical evacuation/airlift, air ambulance, humanitarian aid flights.  [Real world aviation code (UK).]

0023           SAR           Search and rescue operations.  [Real world aviation code (UK).]


0030           LOST         FIR lost.  Use this code if you require assistance from an active ATC facility.  [Real world aviation code (UK).]  # See Note 3.

0032           POL           Police operations.  [Real world aviation code (UK).]

0033           PARA        Para dropping.  [Real world aviation code (UK).]

0X00          MIL            NATO, military operations.  [Real world aviation code UK.]  # See Note 4.

1177           FIS              London FIR.  [Real world aviation code, (UK).]


1200           D *              Default FSX transponder code.  VFR conspicuity.  [Real world aviation code (US and Canada).]

2000           I *               IFR conspicuity.  [Real world aviation code, (UK).]

4010           I CCT         IFR circuits.  Flying IFR circuits at an ATC controlled airfield.  [Special code for use with UK317 server and UK317 Radar v2]  # See Note 5.

4011           I PAR         IFR flight being provided with a PAR (Precision Approach Radar) 'Talk-down' service.  # See Note 6.

41XX                   I BS            IFR flight being provided with a Basic Service.  # See Note 4.


42XX                   I TS            IFR flight being provided with a Traffic Service.  # See Note 4.

43XX                   I DS            IFR flight being provided with a Deconfliction Service.  # See Note 4.

6XXX         V                VFR (General ATCO use).  # See Note 4.

7XXX         V                VFR (General ATCO use).  # See Note 4.

7000           V *              Special code:  VFR Conspicuity.  [Real world aviation code (UK).]  # See Note 5.


7001           MIL LO     Military low level / climbout.  [Real world aviation code (UK).]

7002           DA             Danger area.  Flights within an activated military Danger Area.  [Real world aviation code (UK).]

7003           TEAM       Display team.

7004           AERO        Aerobatics / display.  [Real world aviation code (UK).]

7005           SPDY         High speed / high energy manoeuvres.  [Real world aviation code (UK).]


7010           V CCT       VFR Circuits.  Flying VFR circuits within an aerodrome traffic pattern (UK).  [Real world aviation code (UK).]  # See Note 5.

7011           V PAR       VFR flight being provided with a PAR (Precision Approach Radar) 'Talk-down' service.  # See Note 6.

71XX                   V BS           VFR Basic Service.  # See Note 4.

72XX                   V TS           VFR Traffic Service.  # See Note 4.

7300           FISH          Marine Protection Agency (MPA) / DEFRA / Fisheries protection.  [Real world aviation code (UK).]


73XX                   V DS          VFR Deconfliction Service.  # See Note 4.

7400           LINK         UAV lost link.  [Real world aviation code (UK).]

7401           FIS              Scottish FIR.  [Real world aviation code (UK).]

7500           HIJACK     Special code:  Hijack.  [Real world aviation code (ICAO).]

7600           RT FAIL    Special code:  Radio failure.  [Real world aviation code (ICAO).]


7601           ACK          Special code:  Radio failure.  Acknowledgement of instruction.  # See Note 7.

7602           UNABL     Special code:  Radio failure.  Unable to comply.  # See Note 7.

7603           CHAT        Special code:  Radio failure.  Message in chat box.  # See Note 8.

7700           EMERG     Special code:  Emergency.  [Real world aviation code (ICAO).]

7776           PAN          Special code:  Pan-Pan.


7777           MAYDAY Special code:  Mayday.  [Real world aviation code (US).]

XXXX        I                  IFR (General ATCO use).  All other codes not listed above will show up on radar that you are an IFR flight.  # See Note 4.



1.      Selecting code ‘0000’ (or pressing the ‘Ident’ button on your transponder if fitted) will cause your aircraft tag on FSX radar to flash red instead of yellow.  This will draws attention of ATC to your aircraft and helps ATC identify your aircraft on screen.  Note that it may unnecessarily distract ATC and you should not leave your transponder set to ‘0000’ unless specifically requested.  (A functioning ‘Ident’ button on a transponder will self cancel after several seconds.)

2.      Transponder codes 0001 and 0002 are the UK317 virtual equivalent of a 'listening squawk'.  This tells active ATCO's that you are monitoring their transmissions.  This is virtual replication of Real World (UK) transponder codes allocated to several UK airfields and control zones.

3.      Squawk code 0030 can be used to indicate to active ATC that you are lost or require assistance.  Retune your radio to 121.500 (Emergency) and active ATC may be able to help you.

4.      An 'X' in place of a number means that the 'X' number could be any number.  In the case of NATO / military flights that could be 0100, 0200, 0300, 0400, 0500, 0600, 0700.

5.      A standard circuit, that is:  Upwind/Runway, crosswind, downwind, base, final.

6.      Used where an active ATC is providing a 'talk-down' service in poor visibility where an ILS facility is unusable or unavailable.

7.      Radio failure.  Codes 7601 and 7602 are special provisions for aircraft radio failure but where the aircraft can hear active ATC.  Live ATC may issue instructions, an aircraft can then squawk 7601 for 'Yes', or 7602 for 'No'.

8.      Radio failure.  Code 7603 may be used by an aircraft that has a total comms failure and contact with pilots or ATC can be made via the chat box.

UK317 squawk code quick reference table


0XXX  IFR (General use)

1XXX  IFR (General use)

2XXX  IFR (General use)

3XXX  IFR (General use)

4XXX  IFR (General use)

5XXX  IFR (General use)

6XXX  VFR (General use)

7XXX  VFR (General use)

0000  Squawk Ident

1177  London FIS

2000  IFR conspicuity

4010  IFR circuit

7000  VFR Conspicuity

0001  VFR listening

1200  Default



4011  IFR PAR approach



7001  Military low-level / climbout

0002  IFR listening



41XX  IFR Basic service



7002  Danger Area operations

0020  Medevac




42XX  IFR Traffic service



7003  Display team

0023  Search and rescue




43XX  IFR Deconfliction service



7004  Aerobatics / display

0030  FIR lost






7005  High energy manoeuvres

0032  Police







7010  VFR circuits

0033  Para dropping







71XX  VFR Basic service

0100  NATO / military ops







72XX  VFR Traffic service

0200  NATO / military ops







7300  MPA / DEFRA / Fisheries

0300  NATO / military ops







73XX  VFR Deconfliction service

0400  NATO / military ops







7400  UAV lost link

0500  NATO / military ops







7401  Scottish FIS

0600  NATO / military ops







7500  Hijack

0700  NATO / military ops







7600  Radio failure







7601  Acknowledgement of instruction







7602  Unable to comply







7603  Message in chat box







7700  Emergency







7776  Pan-Pan







7777  Mayday


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