[{"data":1,"prerenderedAt":373},["ShallowReactive",2],{"learn-\u002Flearn\u002Fsquawk-codes-and-transponders":3,"learn-nav-\u002Flearn\u002Fsquawk-codes-and-transponders":346},{"id":4,"title":5,"body":6,"date":273,"description":274,"draft":275,"extension":276,"faqs":277,"howTo":287,"keyTakeaways":295,"meta":300,"navigation":301,"path":302,"quiz":303,"seo":328,"series":329,"seriesOrder":329,"sources":330,"stem":343,"topic":344,"__hash__":345},"learn\u002Flearn\u002Fsquawk-codes-and-transponders.md","Squawk codes and transponders explained",{"type":7,"value":8,"toc":263},"minimark",[9,21,27,32,40,55,59,62,115,134,138,147,167,170,174,185,213,222,226,252,256],[10,11,12,13,20],"p",{},"A transponder is what turns your aircraft from an anonymous blip into a labelled, altitude-tagged target on a controller's screen, and the ",[14,15,19],"a",{"href":16,"className":17},"\u002Flearn\u002Fglossary#gt-squawk-code",[18],"glossary-link","squawk code"," is how you and air traffic control agree which target is you.",[22,23,24],"blockquote",{},[10,25,26],{},"This is general educational information, not operational, legal, or regulatory advice. Rules differ by authority and change over time. Always verify against current official sources and follow your operator's approved procedures.",[28,29,31],"h2",{"id":30},"what-a-transponder-actually-does","What a transponder actually does",[10,33,34,35,39],{},"A transponder is the airborne half of ",[36,37,38],"strong",{},"Secondary Surveillance Radar (SSR)",". A ground station sends an interrogation, and the transponder replies with a coded pulse train. Unlike primary radar, which just bounces energy off the airframe, SSR gets a cooperative reply that carries information, which is why a controller can see your identity and altitude rather than only your position.",[10,41,42,43,46,47,50,51,54],{},"The four-digit code you set is the ",[36,44,45],{},"Mode A"," identity. Each digit runs from ",[36,48,49],{},"0 to 7"," (the code is octal), so there are ",[36,52,53],{},"4096"," possible codes, which is why Mode A is sometimes called the 4096-code mode. Set 4321 and your reply carries 4321.",[28,56,58],{"id":57},"mode-a-mode-c-and-mode-s","Mode A, Mode C and Mode S",[10,60,61],{},"The modes build on each other:",[63,64,65,71,93],"ul",{},[66,67,68,70],"li",{},[36,69,45],{}," returns only the identity code you have set.",[66,72,73,76,77,80,81,86,87,92],{},[36,74,75],{},"Mode C"," adds your ",[36,78,79],{},"pressure altitude",", always referenced to the standard 1013.25 hPa setting, so the controller sees a ",[14,82,85],{"href":83,"className":84},"\u002Flearn\u002Fglossary#gt-flight-level",[18],"flight level"," regardless of the local ",[14,88,91],{"href":89,"className":90},"\u002Flearn\u002Fglossary#gt-qnh",[18],"QNH",".",[66,94,95,102,103,106,107,114],{},[36,96,97],{},[14,98,101],{"href":99,"className":100},"\u002Flearn\u002Fglossary#gt-mode-s",[18],"Mode S"," adds a permanent ",[36,104,105],{},"24-bit aircraft address"," unique to the airframe, allows a radar to interrogate one specific aircraft (selective interrogation, the \"S\"), and carries a data link. Mode S is the foundation for ",[36,108,109],{},[14,110,113],{"href":111,"className":112},"\u002Flearn\u002Fglossary#gt-ads-b",[18],"ADS-B",", where the aircraft broadcasts its own GPS position.",[10,116,117,118,121,122,128,129,92],{},"Most modern installations combine these and are described as ",[36,119,120],{},"Mode A\u002FC\u002FS",". The procedures for how codes are assigned and used are set out in ",[14,123,127],{"href":124,"rel":125},"https:\u002F\u002Fstore.icao.int\u002Fen\u002Fprocedures-for-air-navigation-services-air-traffic-management-doc-4444",[126],"nofollow","ICAO Doc 4444 (PANS-ATM)"," and, for the United States, the ",[14,130,133],{"href":131,"rel":132},"https:\u002F\u002Fwww.faa.gov\u002Fair_traffic\u002Fpublications\u002Fatpubs\u002Faim_html\u002Fchap4_section_1.html",[126],"FAA AIM",[28,135,137],{"id":136},"the-three-codes-every-pilot-must-know","The three codes every pilot must know",[10,139,140,141,146],{},"Three codes are reserved internationally in ",[14,142,145],{"href":143,"rel":144},"https:\u002F\u002Fstore.icao.int\u002Fen\u002Fannex-2-rules-of-the-air",[126],"ICAO Annex 2"," and recognised by air traffic services everywhere:",[63,148,149,155,161],{},[66,150,151,154],{},[36,152,153],{},"7700: a general emergency."," Setting it alerts every SSR station in range.",[66,156,157,160],{},[36,158,159],{},"7600: radio communication failure."," It tells ATC you can probably still hear or be seen, but cannot talk.",[66,162,163,166],{},[36,164,165],{},"7500: unlawful interference",", such as a hijack.",[10,168,169],{},"These never change between countries, and most training uses a memory aid for them. Setting one of these draws immediate attention, so they are used deliberately, not tested in the air.",[28,171,173],{"id":172},"conspicuity-and-no-code-assigned","Conspicuity and \"no code assigned\"",[10,175,176,177,180,181,184],{},"When ATC has not given you a discrete code, you use a ",[36,178,179],{},"conspicuity code",", and these are ",[36,182,183],{},"regional",", not universal:",[63,186,187,194,207],{},[66,188,189,190,193],{},"In much of Europe, ",[36,191,192],{},"7000"," is the general conspicuity code.",[66,195,196,197,200,201,206],{},"In the United States, ",[36,198,199],{},"1200"," is the ",[14,202,205],{"href":203,"className":204},"\u002Flearn\u002Fglossary#gt-vfr",[18],"VFR"," code.",[66,208,209,212],{},[36,210,211],{},"2000"," is commonly used when entering an area from one without SSR code assignment.",[10,214,215,216,221],{},"Because these vary by country and are revised from time to time, always set the code current for where you are flying, as published in the local ",[14,217,220],{"href":218,"className":219},"\u002Flearn\u002Fglossary#gt-aip",[18],"AIP",", rather than relying on memory of another region's value.",[28,223,225],{"id":224},"common-pitfalls","Common pitfalls",[63,227,228,234,240,246],{},[66,229,230,233],{},[36,231,232],{},"Codes are octal."," There is no 8 or 9 in a squawk code; every digit is 0 to 7.",[66,235,236,239],{},[36,237,238],{},"Mode C altitude is pressure altitude."," It is always on the standard setting, so it will not match your QNH altitude readout, and that is normal.",[66,241,242,245],{},[36,243,244],{},"Conspicuity codes are local."," A code that is correct at home may mean something else abroad, so check the AIP.",[66,247,248,251],{},[36,249,250],{},"Squawk only when told, except in an emergency."," Changing to a discrete code you were not assigned can confuse the picture.",[28,253,255],{"id":254},"in-pilot-efb","In Pilot EFB",[10,257,258,259,262],{},"Pilot EFB keeps a quick ",[36,260,261],{},"squawk-code reference",", including the reserved emergency codes, so the value you need is a tap away rather than a memory test on a busy frequency. It is a personal reference held on your device; Pilot EFB is offline-first and is not a certified Electronic Flight Bag, so follow ATC instructions and current official procedures as the authority on what to set and when.",{"title":264,"searchDepth":265,"depth":265,"links":266},"",2,[267,268,269,270,271,272],{"id":30,"depth":265,"text":31},{"id":57,"depth":265,"text":58},{"id":136,"depth":265,"text":137},{"id":172,"depth":265,"text":173},{"id":224,"depth":265,"text":225},{"id":254,"depth":265,"text":255},"2026-06-20","What a transponder squawk code is, the difference between Mode A, C and S, and the emergency codes 7500, 7600 and 7700 every pilot must know.",false,"md",[278,281,284],{"q":279,"a":280},"What do 7500, 7600 and 7700 mean?","They are the three internationally reserved transponder codes. 7700 signals a general emergency, 7600 signals a radio communication failure, and 7500 signals unlawful interference such as a hijack. They are defined in ICAO Annex 2 and the PANS-ATM (Doc 4444) and recognised by air traffic services worldwide.",{"q":282,"a":283},"What is the difference between Mode A, Mode C and Mode S?","Mode A returns only the four-digit identity code you set. Mode C adds the aircraft's pressure altitude. Mode S adds a unique 24-bit aircraft address and a data link, lets a radar interrogate one aircraft selectively, and is the basis for ADS-B. Most modern transponders combine these, often described as Mode A\u002FC\u002FS.",{"q":285,"a":286},"Why is it called a squawk?","The term is generally traced to the wartime IFF (Identification Friend or Foe) systems that transponders grew out of, which were reportedly code-named 'Parrot', so to transmit a code was to 'squawk'. The exact origin is anecdotal, but the usage stuck: today 'squawk 4321' simply means set 4321 on the transponder, and the code itself is often called a squawk code.",{"name":288,"steps":289},"Respond to a transponder instruction",[290,291,292,293,294],"Set the four-digit code (each digit is 0 to 7) on the transponder when ATC says 'squawk' followed by the code.","Select the mode ATC needs, normally an altitude-reporting mode so your pressure altitude is sent as well.","Press IDENT only when asked to 'squawk ident', which flags your return on the controller's display.","In an emergency, set the reserved code that fits: 7700 for a general emergency, 7600 for radio failure, 7500 for unlawful interference.","Use the conspicuity code for your region when no discrete code is assigned, and always follow current local procedures.",[296,297,298,299],"A squawk code is four octal digits (each 0 to 7), giving 4096 possible codes.","Mode A sends the code, Mode C adds pressure altitude, and Mode S adds a unique address and data link and underpins ADS-B.","Three codes are reserved worldwide: 7700 emergency, 7600 radio failure, 7500 unlawful interference.","Conspicuity codes such as 7000 in much of Europe or 1200 for VFR in the United States are regional, so always use the current local code.",{},true,"\u002Flearn\u002Fsquawk-codes-and-transponders",[304,312,320],{"q":305,"options":306,"answer":310,"explanation":311},"Which transponder code signals a radio communication failure?",[307,308,309,192],"7500","7600","7700",1,"7600 is the reserved code for radio communication failure; 7700 is a general emergency and 7500 is unlawful interference.",{"q":313,"options":314,"answer":310,"explanation":319},"What does Mode C add over Mode A?",[315,316,317,318],"A unique 24-bit aircraft address","The aircraft's pressure altitude","A data link for ADS-B","Nothing, they are the same","Mode A returns only the identity code; Mode C adds the aircraft's pressure altitude. The 24-bit address and data link belong to Mode S.",{"q":321,"options":322,"answer":310,"explanation":327},"How many digits does a transponder code have, and what values can each take?",[323,324,325,326],"Three digits, 0 to 9","Four digits, 0 to 7","Four digits, 0 to 9","Five digits, 0 to 7","A code is four octal digits, each 0 to 7, giving 4096 possible codes (which is why Mode A is sometimes called the 4096-code mode).",{"title":5,"description":274},null,[331,333,335,337,340],{"label":332,"url":143},"ICAO Annex 2: Rules of the Air",{"label":334,"url":124},"ICAO Doc 4444: PANS-ATM (Air Traffic Management)",{"label":336,"url":131},"FAA Aeronautical Information Manual, Chapter 4 Section 1 (Services Available to Pilots)",{"label":338,"url":339},"SKYbrary: discrete and non-discrete SSR codes","https:\u002F\u002Fskybrary.aero\u002Farticles\u002Fdiscrete-and-non-discrete-ssr-codes",{"label":341,"url":342},"SKYbrary: Mode S","https:\u002F\u002Fskybrary.aero\u002Farticles\u002Fmode-s","learn\u002Fsquawk-codes-and-transponders","Operations","RyBeefhz0ujVC_X3FBeo4qfAkCzUrdtO5ESrFzIAmeA",{"related":347,"newer":363,"older":369,"series":329},[348,354,358],{"path":349,"title":350,"description":351,"date":352,"topic":344,"draft":275,"minutes":353,"series":329,"seriesOrder":329},"\u002Flearn\u002Fcold-temperature-altimeter-corrections","Cold-temperature altimeter corrections","Why a pressure altimeter over-reads in cold air, leaving you lower than indicated, and how to correct minimum altitudes for temperature on an approach in mountainous or freezing conditions.","2026-06-21",4,{"path":355,"title":356,"description":357,"date":352,"topic":344,"draft":275,"minutes":353,"series":329,"seriesOrder":329},"\u002Flearn\u002Fmode-s-and-ads-b-explained","Mode S and ADS-B explained","How Mode S adds a 24-bit address, selective interrogation and a data link to the transponder, the difference between elementary and enhanced surveillance, and how ADS-B broadcasts your GPS position.",{"path":359,"title":360,"description":361,"date":352,"topic":344,"draft":275,"minutes":362,"series":329,"seriesOrder":329},"\u002Flearn\u002Fthe-global-reporting-format-for-runway-conditions","The Global Reporting Format for runway conditions","How the Global Reporting Format (GRF) describes a contaminated runway, including the runway condition code (RWYCC) from 6 to 0, the assessment matrix (RCAM), and how the report is split into thirds.",5,{"path":364,"title":365,"description":366,"date":273,"topic":367,"draft":275,"minutes":368,"series":329,"seriesOrder":329},"\u002Flearn\u002Freading-a-surface-analysis-chart","How to read a surface analysis chart","Decode a surface analysis chart: isobars and the pressure gradient, highs and lows, warm, cold and occluded fronts, and what the big picture tells you before you read the METAR.","Weather",3,{"path":370,"title":371,"description":372,"date":273,"topic":367,"draft":275,"minutes":368,"series":329,"seriesOrder":329},"\u002Flearn\u002Fthe-international-standard-atmosphere","The International Standard Atmosphere (ISA)","What the ICAO International Standard Atmosphere is, its sea-level values and lapse rate, and how ISA deviation underpins altimetry, performance and density altitude.",1781989193031]