36:
151:. Mode S transponders are compatible with transmitting the mode C signal, and have the capability to report in 25-foot increments; they receive information from a GPS receiver and also transmit location and speed. Without the pressure altitude reporting, the air traffic controller has no display of accurate altitude information, and must rely on the altitude reported by the pilot via radio. Similarly, the
227:(VFR), when in uncontrolled airspace, will "squawk VFR" (1200 in the US and Canada, 7000 in Europe). Upon contact with an ATC unit, they will be told to squawk a certain code. When changing frequency, for instance because the VFR flight leaves controlled airspace or changes to another ATC unit, the VFR flight will be told to "squawk VFR" again.
187:
Transponder codes are four-digit numbers transmitted by an aircraft transponder in response to a secondary surveillance radar interrogation signal to assist air traffic controllers with traffic separation. A discrete transponder code (often called a squawk code) is assigned by air traffic controllers
234:
Not all ATC units will use radar to identify aircraft, but they assign squawk codes nevertheless. As an example, London
Information—the flight information service station that covers the lower half of the UK—does not have access to radar images, but does assign squawk code 1177 to all aircraft that
123:
A pilot may be requested to squawk a given code by an air traffic controller, via the radio, using a phrase such as "Cessna 123AB, squawk 0363". The pilot then selects the 0363 code on their transponder and the track on the air traffic controller's radar screen will become correctly associated with
106:
Secondary surveillance radar (SSR) is referred to as "secondary", to distinguish it from the "primary radar" that works by passively reflecting a radio signal off the skin of the aircraft. Primary radar determines range and bearing to a target with reasonably high fidelity, but it cannot determine
163:
All mode A, C, and S transponders include an "IDENT" switch which activates a special thirteenth bit on the mode A reply known as IDENT, short for "identify". When ground-based radar equipment receives the IDENT bit, it results in the aircraft's blip "blossoming" on the radar scope. This is often
215:
Some codes can be selected by the pilot if and when the situation requires or allows it, without permission from air traffic control (ATC). Such codes are referred to as "conspicuity codes" in the UK. Other codes are generally assigned by ATC units. For flights on
107:
target elevation (altitude) reliably except at close range. SSR uses an active transponder (beacon) to transmit a response to an interrogation by a secondary radar. This response most often includes the aircraft's
199:
digits; the dials on a transponder read from zero to seven, inclusive. Four octal digits can represent up to 4096 different codes, which is why such transponders are sometimes described as "4096 code transponders."
230:
In order to avoid confusion over assigned squawk codes, ATC units will typically be allocated blocks of squawk codes, not overlapping with the blocks of nearby ATC units, to assign at their discretion.
239:(FIS) from them. This tells other radar-equipped ATC units that a specific aircraft is listening on the London Information radio frequency, in case they need to contact that aircraft.
59:
and sometimes abbreviated to XPDR, XPNDR, TPDR or TP) is an electronic device that produces a response when it receives a radio-frequency interrogation. Aircraft have
147:
there is often a regulatory requirement that all aircraft be equipped with altitude-reporting mode C or mode S transponders. In the United States, this is known as a
643:
171:
Ident can also be used in case of a reported or suspected radio failure to determine if the failure is only one way and whether the pilot can still transmit
131:
transponders also report pressure altitude. Mode C altitude information conventionally comes from the pilot's altimeter, and is transmitted using a modified
502:
701:
729:
769:
1346:
992:
343:
39:
Cessna ARC RT-359A transponder (beige box), beneath a VHF radio. In this example, the transponder code selected is 1200 for
330:
92:
The transponder receives interrogation from the
Secondary Surveillance Radar on 1030 MHz and replies on 1090 MHz.
71:
have been developed to use transponder transmissions as a means of detecting aircraft at risk of colliding with each other.
1386:
220:(IFR), the squawk code is typically assigned as part of the departure clearance and stays the same throughout the flight.
1341:
1286:
1151:
127:
Because primary radar generally gives bearing and range position information, but lacks altitude information, mode C and
68:
1406:
152:
762:
653:
556:
315: — July 3, 1988 (incorrect interpretation of transponder code, a factor in mistaken identity and shooting-down)
1176:
628:
506:
306:
333: — September 29, 2006 (midair collision; one of the aircraft had its transponder accidentally switched off)
1376:
974:
364:
164:
used by the controller to locate the aircraft amongst others by requesting the ident function from the pilot,
1669:
1720:
1659:
1500:
755:
622:
204:
101:
503:"TP 14371 — Transport Canada Aeronautical Information Manual (TC AIM) RAC 1.9 Transponder Operation"
318:
1381:
1336:
1027:
236:
1567:
1361:
294:
189:
677:"Air Traffic Services Surveillance Systems, Including An Explanation of Primary and Secondary Radar"
1351:
904:
834:
155:(TCAS) installed on some aircraft needs the altitude information supplied by transponder signals.
1679:
1654:
1416:
1396:
1321:
1211:
1181:
1156:
1022:
987:
309: — August 31, 1986 (one of the aircraft equipped with a Mode A, but not Mode C, transponder)
217:
596:
1694:
1495:
1391:
1216:
1032:
321: — July 30, 1998 (mid-air collision; one of the aircraft had its transponder switched off)
1674:
1592:
1582:
1087:
799:
1639:
1442:
1236:
1047:
1002:
324:
81:, "Squawk 7421". Squawk thus can be said to mean "select transponder code" or "squawking
8:
1618:
1525:
1241:
949:
778:
327: — September 11, 2001 (suspected hijack involving the transponder code, false alarm)
312:
224:
74:
40:
143:(which does not directly display altitude) is connected to the transponder. Around busy
1730:
1326:
1306:
1301:
1275:
1186:
1127:
899:
264:
1725:
1634:
1371:
1316:
1296:
1226:
1221:
1206:
894:
552:
108:
77:
units use the term "squawk" when they are assigning an aircraft a transponder code,
1689:
1572:
1246:
1141:
864:
839:
782:
747:
1699:
1664:
1515:
1436:
1401:
1366:
1161:
809:
35:
1067:
934:
676:
573:
551:(27th Revised ed.). Ottawa Ontario: Aviation Publishers. pp. 238–239.
203:
The use of the word "squawk" comes from the system's origin in the World War II
1684:
1544:
1261:
819:
814:
1465:
413:
139:. Where the pilot's altimeter does not contain a suitable altitude encoder, a
19:"Squawk code" redirects here. For the similarly named compression scheme, see
1714:
1613:
1552:
1356:
1291:
929:
909:
824:
435:
391:
1649:
1577:
1540:
1520:
1510:
1485:
1450:
1231:
1201:
1171:
1137:
1117:
1107:
1102:
1072:
1007:
874:
844:
804:
457:
136:
43:
flight (in North
American airspace). The green IDENT button is marked "ID".
1597:
1480:
1196:
1052:
148:
60:
27:
1587:
1475:
1470:
1426:
1421:
1256:
1191:
1166:
1122:
1097:
1082:
1017:
879:
869:
1644:
1562:
1490:
1455:
1311:
1092:
1077:
1057:
1012:
997:
954:
939:
924:
859:
829:
648:
132:
368:
1557:
1530:
1505:
1271:
1251:
1112:
1042:
959:
884:
854:
790:
144:
1331:
982:
964:
889:
1037:
944:
919:
849:
128:
20:
1460:
1062:
914:
276:
196:
192:(FIR). This allows easy identification of aircraft on radar.
112:
64:
679:. The Airways Museum & Civil Aviation Historical Society
576:. The Airways Museum & Civil Aviation Historical Society
727:
210:
297:
for list of country-specific and historic allocations.
63:
to assist in identifying them on air traffic control
777:
730:"JO 7110.66D, National Beacon Code Allocation Plan"
1712:
500:
300:
95:
247:The following codes are applicable worldwide.
763:
207:(IFF) system, which was code-named "Parrot".
179:, "Cessna 123AB, if you read, squawk ident".
723:
721:
719:
455:
433:
411:
389:
85:" to mean "I have selected transponder code
696:
694:
574:"Air Traffic Services Surveillance Systems"
770:
756:
624:Pilot's Handbook of Aeronautical Knowledge
716:
542:
540:
538:
536:
534:
532:
530:
528:
526:
524:
168:, "Cessna 123AB, squawk 0363 and ident".
26:For uses non related to aeronautics, see
691:
496:
494:
449:
427:
405:
383:
344:Aviation transponder interrogation modes
34:
641:
546:
492:
490:
488:
486:
484:
482:
480:
478:
476:
474:
362:
1713:
702:"ENR 1.6.2 — SSR Operating Procedures"
594:
521:
356:
188:to identify an aircraft uniquely in a
751:
588:
211:Codes assigned by air traffic control
644:"Ask the Captain: Strangle my WHAT?"
471:
182:
13:
621:"Chapter 14: Airport Operations".
331:Gol Transportes Aéreos Flight 1907
242:
153:traffic collision avoidance system
14:
1742:
732:. Federal Aviation Administration
728:Federal Aviation Administration.
674:
642:Getline, Meryl (April 17, 2006).
595:Rogers, Tom (September 6, 1998).
571:
501:Transport Canada (May 20, 2010).
668:
635:
629:Federal Aviation Administration
614:
307:1986 Cerritos mid-air collision
1680:In-flight entertainment system
1377:Horizontal situation indicator
565:
365:"The Truth About Transponders"
1:
349:
301:Transponder-related incidents
1660:Environmental control system
631:. July 17, 2023. p. 25.
205:identification friend or foe
118:
102:Secondary surveillance radar
96:Secondary surveillance radar
7:
627:(FAA-H-8083-25C ed.).
337:
319:Proteus Airlines Flight 706
69:Collision avoidance systems
10:
1747:
1337:Course deviation indicator
1028:Electro-hydraulic actuator
237:flight information service
99:
25:
18:
16:Airborne radio transponder
1627:
1606:
1568:Conventional landing gear
1539:
1435:
1270:
1136:
973:
789:
295:List of transponder codes
190:flight information region
1352:Flight management system
363:Mangine, Robert (2007).
158:
1655:Emergency oxygen system
1417:Turn and slip indicator
1212:Leading-edge droop flap
1182:Drag-reducing aerospike
1157:Adaptive compliant wing
1152:Active Aeroelastic Wing
547:Peppler, I. L. (1996).
218:instrument flight rules
195:Codes are made of four
175:receive, but not both,
1695:Passenger service unit
1496:Self-sealing fuel tank
1392:Multi-function display
44:
1675:Ice protection system
1593:Tricycle landing gear
1583:Landing gear extender
800:Aft pressure bulkhead
456:Farlex, Inc. (2008).
434:Farlex, Inc. (2008).
412:Farlex, Inc. (2008).
390:Farlex, Inc. (2008).
38:
1640:Auxiliary power unit
1048:Flight control modes
597:"Transponder Basics"
325:Korean Air Flight 85
1721:Air traffic control
1619:Escape crew capsule
1526:War emergency power
1397:Pitot–static system
1242:Variable-sweep wing
950:Vertical stabilizer
656:on January 23, 2009
313:Iran Air Flight 655
277:lost communications
225:visual flight rules
75:Air traffic control
1327:Attitude indicator
1307:Airspeed indicator
1302:Aircraft periscope
549:From The Ground Up
371:on August 16, 2011
265:Aircraft hijacking
45:
1708:
1707:
1635:Aircraft lavatory
1372:Heading indicator
1317:Annunciator panel
1297:Air data computer
1207:Leading-edge cuff
291:
290:
287:Emergency (ICAO)
183:Transponder codes
109:pressure altitude
1738:
1690:Navigation light
1670:Hydraulic system
1645:Bleed air system
1573:Drogue parachute
1247:Vortex generator
865:Interplane strut
772:
765:
758:
749:
748:
742:
741:
739:
737:
725:
714:
713:
711:
709:
698:
689:
688:
686:
684:
672:
666:
665:
663:
661:
652:. Archived from
639:
633:
632:
618:
612:
611:
609:
607:
592:
586:
585:
583:
581:
569:
563:
562:
544:
519:
518:
516:
514:
505:. Archived from
498:
469:
468:
466:
464:
453:
447:
446:
444:
442:
431:
425:
424:
422:
420:
409:
403:
402:
400:
398:
387:
381:
380:
378:
376:
367:. Archived from
360:
250:
249:
124:their identity.
1746:
1745:
1741:
1740:
1739:
1737:
1736:
1735:
1711:
1710:
1709:
1704:
1700:Ram air turbine
1665:Flight recorder
1623:
1602:
1535:
1516:Thrust reversal
1440:
1431:
1402:Radar altimeter
1367:Head-up display
1277:
1266:
1162:Anti-shock body
1144:
1132:
993:Artificial feel
975:Flight controls
969:
835:Fabric covering
785:
781:components and
776:
746:
745:
735:
733:
726:
717:
707:
705:
704:. July 29, 2021
700:
699:
692:
682:
680:
673:
669:
659:
657:
640:
636:
620:
619:
615:
605:
603:
593:
589:
579:
577:
570:
566:
559:
545:
522:
512:
510:
509:on July 9, 2010
499:
472:
462:
460:
454:
450:
440:
438:
432:
428:
418:
416:
410:
406:
396:
394:
388:
384:
374:
372:
361:
357:
352:
340:
303:
275:Radio failure (
245:
243:Emergency codes
213:
185:
161:
121:
104:
98:
31:
24:
17:
12:
11:
5:
1744:
1734:
1733:
1728:
1723:
1706:
1705:
1703:
1702:
1697:
1692:
1687:
1685:Landing lights
1682:
1677:
1672:
1667:
1662:
1657:
1652:
1647:
1642:
1637:
1631:
1629:
1625:
1624:
1622:
1621:
1616:
1610:
1608:
1607:Escape systems
1604:
1603:
1601:
1600:
1595:
1590:
1585:
1580:
1575:
1570:
1565:
1560:
1555:
1549:
1547:
1545:arresting gear
1537:
1536:
1534:
1533:
1528:
1523:
1518:
1513:
1508:
1503:
1501:Splitter plate
1498:
1493:
1488:
1483:
1478:
1473:
1468:
1463:
1458:
1453:
1447:
1445:
1433:
1432:
1430:
1429:
1424:
1419:
1414:
1409:
1404:
1399:
1394:
1389:
1384:
1379:
1374:
1369:
1364:
1359:
1354:
1349:
1344:
1339:
1334:
1329:
1324:
1319:
1314:
1309:
1304:
1299:
1294:
1289:
1283:
1281:
1268:
1267:
1265:
1264:
1259:
1254:
1249:
1244:
1239:
1234:
1229:
1224:
1219:
1214:
1209:
1204:
1199:
1194:
1189:
1184:
1179:
1174:
1169:
1164:
1159:
1154:
1148:
1146:
1134:
1133:
1131:
1130:
1125:
1120:
1115:
1110:
1105:
1100:
1095:
1090:
1085:
1080:
1075:
1070:
1065:
1060:
1055:
1050:
1045:
1040:
1035:
1030:
1025:
1020:
1015:
1010:
1005:
1000:
995:
990:
985:
979:
977:
971:
970:
968:
967:
962:
957:
952:
947:
942:
937:
932:
927:
922:
917:
912:
907:
902:
897:
892:
887:
882:
877:
872:
867:
862:
857:
852:
847:
842:
837:
832:
827:
822:
820:Cruciform tail
817:
815:Crack arrestor
812:
807:
802:
796:
794:
787:
786:
775:
774:
767:
760:
752:
744:
743:
715:
690:
667:
634:
613:
587:
564:
557:
520:
470:
448:
426:
404:
382:
354:
353:
351:
348:
347:
346:
339:
336:
335:
334:
328:
322:
316:
310:
302:
299:
289:
288:
285:
281:
280:
273:
269:
268:
262:
258:
257:
254:
244:
241:
212:
209:
184:
181:
160:
157:
120:
117:
111:and a 4-digit
100:Main article:
97:
94:
15:
9:
6:
4:
3:
2:
1743:
1732:
1729:
1727:
1724:
1722:
1719:
1718:
1716:
1701:
1698:
1696:
1693:
1691:
1688:
1686:
1683:
1681:
1678:
1676:
1673:
1671:
1668:
1666:
1663:
1661:
1658:
1656:
1653:
1651:
1648:
1646:
1643:
1641:
1638:
1636:
1633:
1632:
1630:
1628:Other systems
1626:
1620:
1617:
1615:
1614:Ejection seat
1612:
1611:
1609:
1605:
1599:
1596:
1594:
1591:
1589:
1586:
1584:
1581:
1579:
1576:
1574:
1571:
1569:
1566:
1564:
1561:
1559:
1558:Arrestor hook
1556:
1554:
1553:Aircraft tire
1551:
1550:
1548:
1546:
1542:
1538:
1532:
1529:
1527:
1524:
1522:
1519:
1517:
1514:
1512:
1509:
1507:
1504:
1502:
1499:
1497:
1494:
1492:
1489:
1487:
1484:
1482:
1479:
1477:
1474:
1472:
1469:
1467:
1464:
1462:
1459:
1457:
1454:
1452:
1449:
1448:
1446:
1444:
1438:
1434:
1428:
1425:
1423:
1420:
1418:
1415:
1413:
1410:
1408:
1405:
1403:
1400:
1398:
1395:
1393:
1390:
1388:
1385:
1383:
1380:
1378:
1375:
1373:
1370:
1368:
1365:
1363:
1360:
1358:
1357:Glass cockpit
1355:
1353:
1350:
1348:
1345:
1343:
1340:
1338:
1335:
1333:
1330:
1328:
1325:
1323:
1320:
1318:
1315:
1313:
1310:
1308:
1305:
1303:
1300:
1298:
1295:
1293:
1292:Air data boom
1290:
1288:
1285:
1284:
1282:
1279:
1273:
1269:
1263:
1260:
1258:
1255:
1253:
1250:
1248:
1245:
1243:
1240:
1238:
1235:
1233:
1230:
1228:
1225:
1223:
1220:
1218:
1215:
1213:
1210:
1208:
1205:
1203:
1200:
1198:
1195:
1193:
1190:
1188:
1185:
1183:
1180:
1178:
1175:
1173:
1170:
1168:
1165:
1163:
1160:
1158:
1155:
1153:
1150:
1149:
1147:
1143:
1139:
1135:
1129:
1126:
1124:
1121:
1119:
1116:
1114:
1111:
1109:
1106:
1104:
1101:
1099:
1096:
1094:
1091:
1089:
1086:
1084:
1081:
1079:
1076:
1074:
1073:Rudder pedals
1071:
1069:
1066:
1064:
1061:
1059:
1056:
1054:
1051:
1049:
1046:
1044:
1041:
1039:
1036:
1034:
1031:
1029:
1026:
1024:
1021:
1019:
1016:
1014:
1011:
1009:
1006:
1004:
1001:
999:
996:
994:
991:
989:
986:
984:
981:
980:
978:
976:
972:
966:
963:
961:
958:
956:
953:
951:
948:
946:
943:
941:
938:
936:
933:
931:
930:Trailing edge
928:
926:
923:
921:
918:
916:
913:
911:
910:Stressed skin
908:
906:
903:
901:
898:
896:
893:
891:
888:
886:
883:
881:
878:
876:
873:
871:
868:
866:
863:
861:
858:
856:
853:
851:
848:
846:
843:
841:
838:
836:
833:
831:
828:
826:
823:
821:
818:
816:
813:
811:
808:
806:
803:
801:
798:
797:
795:
792:
788:
784:
780:
773:
768:
766:
761:
759:
754:
753:
750:
736:September 23,
731:
724:
722:
720:
708:September 11,
703:
697:
695:
678:
675:Vabre, Phil.
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572:Vabre, Phil.
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558:0-9690054-9-0
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141:blind encoder
138:
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58:
54:
50:
42:
37:
33:
29:
22:
1650:Deicing boot
1578:Landing gear
1521:Townend ring
1511:Thrust lever
1486:NACA cowling
1451:Autothrottle
1443:fuel systems
1441:devices and
1411:
1232:Stall strips
1202:Krueger flap
1172:Channel wing
1118:Wing warping
1108:Stick shaker
1103:Stick pusher
1023:Dual control
1008:Centre stick
875:Leading edge
845:Flying wires
805:Cabane strut
734:. Retrieved
706:. Retrieved
681:. Retrieved
670:
658:. Retrieved
654:the original
647:
637:
623:
616:
604:. Retrieved
600:
590:
578:. Retrieved
567:
548:
511:. Retrieved
507:the original
463:December 24,
461:. Retrieved
451:
441:December 24,
439:. Retrieved
429:
419:December 24,
417:. Retrieved
407:
397:December 24,
395:. Retrieved
385:
373:. Retrieved
369:the original
358:
292:
246:
233:
229:
222:
214:
202:
194:
186:
176:
172:
170:
165:
162:
140:
137:Gillham code
126:
122:
115:identifier.
105:
91:
86:
82:
78:
73:
61:transponders
56:
52:
48:
46:
32:
1598:Tundra tire
1481:Intake ramp
1412:Transponder
1197:Gurney flap
1138:Aerodynamic
1053:Fly-by-wire
935:Triple tail
223:Flights on
149:Mode C veil
135:, called a
51:(short for
49:transponder
28:Transponder
1715:Categories
1588:Oleo strut
1476:Inlet cone
1471:Gascolator
1437:Propulsion
1427:Yaw string
1422:Variometer
1278:instrument
1257:Wing fence
1192:Gouge flap
1167:Blown flap
1123:Yaw damper
1098:Stabilator
1083:Side-stick
1018:Dive brake
905:Stabilizer
880:Lift strut
870:Jury strut
513:August 21,
350:References
235:receive a
55:mitter-res
1731:Encodings
1563:Autobrake
1491:NACA duct
1466:Fuel tank
1456:Drop tank
1439:controls,
1322:Astrodome
1312:Altimeter
1177:Dog-tooth
1142:high-lift
1093:Spoileron
1078:Servo tab
1058:Gust lock
1013:Deceleron
998:Autopilot
955:Wing root
940:Twin tail
925:Tailplane
860:Hardpoint
830:Empennage
793:structure
683:March 13,
660:March 13,
649:USA Today
606:March 18,
580:April 15,
279:) (ICAO)
133:Gray code
119:Operation
1726:Avionics
1531:Wet wing
1506:Throttle
1252:Vortilon
1113:Trim tab
1043:Flaperon
1033:Elevator
988:Airbrake
960:Wing tip
885:Longeron
855:Fuselage
791:Airframe
779:Aircraft
375:March 5,
338:See also
145:airspace
1541:Landing
1332:Compass
1280:systems
1272:Avionic
1262:Winglet
1145:devices
1088:Spoiler
983:Aileron
965:Wingbox
890:Nacelle
840:Fairing
783:systems
414:"XPNDR"
267:(ICAO)
1276:flight
1237:Strake
1068:Rudder
1038:Elevon
1003:Canard
945:V-tail
920:T-tail
850:Former
810:Canopy
555:
436:"TPDR"
392:"XPDR"
129:mode S
57:ponder
21:SQUOZE
1461:FADEC
1347:EICAS
1222:Slats
1063:HOTAS
915:Strut
601:AVweb
197:octal
159:IDENT
113:octal
65:radar
53:trans
1543:and
1407:TCAS
1387:ISIS
1342:EFIS
1287:ACAS
1274:and
1227:Slot
1187:Flap
1140:and
1128:Yoke
900:Spar
825:Dope
738:2023
710:2021
685:2008
662:2008
608:2014
582:2010
553:ISBN
515:2010
465:2008
458:"TP"
443:2008
421:2008
399:2008
377:2019
293:See
284:7700
272:7600
261:7500
256:Use
253:Code
177:e.g.
166:e.g.
87:xxxx
83:xxxx
79:e.g.
1382:INS
1362:GPS
1217:LEX
895:Rib
89:".
41:VFR
1717::
718:^
693:^
646:.
599:.
523:^
473:^
173:or
67:.
47:A
771:e
764:t
757:v
740:.
712:.
687:.
664:.
610:.
584:.
561:.
517:.
467:.
445:.
423:.
401:.
379:.
30:.
23:.
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