Htydjtk

I love aviation and I love learning new things about it.

I was wondering if anyone knew all of the squawk codes and in particular what squawk 7500 means.

Here is a list of all the squawk codes (there's 4096 of them). Very few of them have a specific fixed meaning. Probably the only three that always, globally, have the exact same meaning are 7500 (unlawful interference), 7600 (communication failure) and 7700 (emergency).

1200 is used for uncontrolled VFR in the USA. 2000 and 7000 are used for uncontrolled traffic in other areas, VFR or IFR depending on the territory. 7777 is used for test transponders.

If you want to know what squawk codes are used for, you should check out this question: How does ATC know if you have been assigned a squawk or not?

Anyway, without further ado:

0000, 0001, 0002, 0003, 0004, 0005, 0006, 0007, 0010, 0011, 0012, 0013, 0014, 0015, 0016, 0017, 0020, 0021, 0022, 0023, 0024, 0025, 0026, 0027, 0030, 0031, 0032, 0033, 0034, 0035, 0036, 0037, 0040, 0041, 0042, 0043, 0044, 0045, 0046, 0047, 0050, 0051, 0052, 0053, 0054, 0055, 0056, 0057, 0060, 0061, 0062, 0063, 0064, 0065, 0066, 0067, 0070, 0071, 0072, 0073, 0074, 0075, 0076, 0077, 0100, 0101, 0102, 0103, 0104, 0105, 0106, 0107, 0110, 0111, 0112, 0113, 0114, 0115, 0116, 0117, 0120, 0121, 0122, 0123, 0124, 0125, 0126, 0127, 0130, 0131, 0132, 0133, 0134, 0135, 0136, 0137, 0140, 0141, 0142, 0143, 0144, 0145, 0146, 0147, 0150, 0151, 0152, 0153, 0154, 0155, 0156, 0157, 0160, 0161, 0162, 0163, 0164, 0165, 0166, 0167, 0170, 0171, 0172, 0173, 0174, 0175, 0176, 0177, 0200, 0201, 0202, 0203, 0204, 0205, 0206, 0207, 0210, 0211, 0212, 0213, 0214, 0215, 0216, 0217, 0220, 0221, 0222, 0223, 0224, 0225, 0226, 0227, 0230, 0231, 0232, 0233, 0234, 0235, 0236, 0237, 0240, 0241, 0242, 0243, 0244, 0245, 0246, 0247, 0250, 0251, 0252, 0253, 0254, 0255, 0256, 0257, 0260, 0261, 0262, 0263, 0264, 0265, 0266, 0267, 0270, 0271, 0272, 0273, 0274, 0275, 0276, 0277, 0300, 0301, 0302, 0303, 0304, 0305, 0306, 0307, 0310, 0311, 0312, 0313, 0314, 0315, 0316, 0317, 0320, 0321, 0322, 0323, 0324, 0325, 0326, 0327, 0330, 0331, 0332, 0333, 0334, 0335, 0336, 0337, 0340, 0341, 0342, 0343, 0344, 0345, 0346, 0347, 0350, 0351, 0352, 0353, 0354, 0355, 0356, 0357, 0360, 0361, 0362, 0363, 0364, 0365, 0366, 0367, 0370, 0371, 0372, 0373, 0374, 0375, 0376, 0377, 0400, 0401, 0402, 0403, 0404, 0405, 0406, 0407, 0410, 0411, 0412, 0413, 0414, 0415, 0416, 0417, 0420, 0421, 0422, 0423, 0424, 0425, 0426, 0427, 0430, 0431, 0432, 0433, 0434, 0435, 0436, 0437, 0440, 0441, 0442, 0443, 0444, 0445, 0446, 0447, 0450, 0451, 0452, 0453, 0454, 0455, 0456, 0457, 0460, 0461, 0462, 0463, 0464, 0465, 0466, 0467, 0470, 0471, 0472, 0473, 0474, 0475, 0476, 0477, 0500, 0501, 0502, 0503, 0504, 0505, 0506, 0507, 0510, 0511, 0512, 0513, 0514, 0515, 0516, 0517, 0520, 0521, 0522, 0523, 0524, 0525, 0526, 0527, 0530, 0531, 0532, 0533, 0534, 0535, 0536, 0537, 0540, 0541, 0542, 0543, 0544, 0545, 0546, 0547, 0550, 0551, 0552, 0553, 0554, 0555, 0556, 0557, 0560, 0561, 0562, 0563, 0564, 0565, 0566, 0567, 0570, 0571, 0572, 0573, 0574, 0575, 0576, 0577, 0600, 0601, 0602, 0603, 0604, 0605, 0606, 0607, 0610, 0611, 0612, 0613, 0614, 0615, 0616, 0617, 0620, 0621, 0622, 0623, 0624, 0625, 0626, 0627, 0630, 0631, 0632, 0633, 0634, 0635, 0636, 0637, 0640, 0641, 0642, 0643, 0644, 0645, 0646, 0647, 0650, 0651, 0652, 0653, 0654, 0655, 0656, 0657, 0660, 0661, 0662, 0663, 0664, 0665, 0666, 0667, 0670, 0671, 0672, 0673, 0674, 0675, 0676, 0677, 0700, 0701, 0702, 0703, 0704, 0705, 0706, 0707, 0710, 0711, 0712, 0713, 0714, 0715, 0716, 0717, 0720, 0721, 0722, 0723, 0724, 0725, 0726, 0727, 0730, 0731, 0732, 0733, 0734, 0735, 0736, 0737, 0740, 0741, 0742, 0743, 0744, 0745, 0746, 0747, 0750, 0751, 0752, 0753, 0754, 0755, 0756, 0757, 0760, 0761, 0762, 0763, 0764, 0765, 0766, 0767, 0770, 0771, 0772, 0773, 0774, 0775, 0776, 0777, 1000, 1001, 1002, 1003, 1004, 1005, 1006, 1007, 1010, 1011, 1012, 1013, 1014, 1015, 1016, 1017, 1020, 1021, 1022, 1023, 1024, 1025, 1026, 1027, 1030, 1031, 1032, 1033, 1034, 1035, 1036, 1037, 1040, 1041, 1042, 1043, 1044, 1045, 1046, 1047, 1050, 1051, 1052, 1053, 1054, 1055, 1056, 1057, 1060, 1061, 1062, 1063, 1064, 1065, 1066, 1067, 1070, 1071, 1072, 1073, 1074, 1075, 1076, 1077, 1100, 1101, 1102, 1103, 1104, 1105, 1106, 1107, 1110, 1111, 1112, 1113, 1114, 1115, 1116, 1117, 1120, 1121, 1122, 1123, 1124, 1125, 1126, 1127, 1130, 1131, 1132, 1133, 1134, 1135, 1136, 1137, 1140, 1141, 1142, 1143, 1144, 1145, 1146, 1147, 1150, 1151, 1152, 1153, 1154, 1155, 1156, 1157, 1160, 1161, 1162, 1163, 1164, 1165, 1166, 1167, 1170, 1171, 1172, 1173, 1174, 1175, 1176, 1177, 1200, 1201, 1202, 1203, 1204, 1205, 1206, 1207, 1210, 1211, 1212, 1213, 1214, 1215, 1216, 1217, 1220, 1221, 1222, 1223, 1224, 1225, 1226, 1227, 1230, 1231, 1232, 1233, 1234, 1235, 1236, 1237, 1240, 1241, 1242, 1243, 1244, 1245, 1246, 1247, 1250, 1251, 1252, 1253, 1254, 1255, 1256, 1257, 1260, 1261, 1262, 1263, 1264, 1265, 1266, 1267, 1270, 1271, 1272, 1273, 1274, 1275, 1276, 1277, 1300, 1301, 1302, 1303, 1304, 1305, 1306, 1307, 1310, 1311, 1312, 1313, 1314, 1315, 1316, 1317, 1320, 1321, 1322, 1323, 1324, 1325, 1326, 1327, 1330, 1331, 1332, 1333, 1334, 1335, 1336, 1337, 1340, 1341, 1342, 1343, 1344, 1345, 1346, 1347, 1350, 1351, 1352, 1353, 1354, 1355, 1356, 1357, 1360, 1361, 1362, 1363, 1364, 1365, 1366, 1367, 1370, 1371, 1372, 1373, 1374, 1375, 1376, 1377, 1400, 1401, 1402, 1403, 1404, 1405, 1406, 1407, 1410, 1411, 1412, 1413, 1414, 1415, 1416, 1417, 1420, 1421, 1422, 1423, 1424, 1425, 1426, 1427, 1430, 1431, 1432, 1433, 1434, 1435, 1436, 1437, 1440, 1441, 1442, 1443, 1444, 1445, 1446, 1447, 1450, 1451, 1452, 1453, 1454, 1455, 1456, 1457, 1460, 1461, 1462, 1463, 1464, 1465, 1466, 1467, 1470, 1471, 1472, 1473, 1474, 1475, 1476, 1477, 1500, 1501, 1502, 1503, 1504, 1505, 1506, 1507, 1510, 1511, 1512, 1513, 1514, 1515, 1516, 1517, 1520, 1521, 1522, 1523, 1524, 1525, 1526, 1527, 1530, 1531, 1532, 1533, 1534, 1535, 1536, 1537, 1540, 1541, 1542, 1543, 1544, 1545, 1546, 1547, 1550, 1551, 1552, 1553, 1554, 1555, 1556, 1557, 1560, 1561, 1562, 1563, 1564, 1565, 1566, 1567, 1570, 1571, 1572, 1573, 1574, 1575, 1576, 1577, 1600, 1601, 1602, 1603, 1604, 1605, 1606, 1607, 1610, 1611, 1612, 1613, 1614, 1615, 1616, 1617, 1620, 1621, 1622, 1623, 1624, 1625, 1626, 1627, 1630, 1631, 1632, 1633, 1634, 1635, 1636, 1637, 1640, 1641, 1642, 1643, 1644, 1645, 1646, 1647, 1650, 1651, 1652, 1653, 1654, 1655, 1656, 1657, 1660, 1661, 1662, 1663, 1664, 1665, 1666, 1667, 1670, 1671, 1672, 1673, 1674, 1675, 1676, 1677, 1700, 1701, 1702, 1703, 1704, 1705, 1706, 1707, 1710, 1711, 1712, 1713, 1714, 1715, 1716, 1717, 1720, 1721, 1722, 1723, 1724, 1725, 1726, 1727, 1730, 1731, 1732, 1733, 1734, 1735, 1736, 1737, 1740, 1741, 1742, 1743, 1744, 1745, 1746, 1747, 1750, 1751, 1752, 1753, 1754, 1755, 1756, 1757, 1760, 1761, 1762, 1763, 1764, 1765, 1766, 1767, 1770, 1771, 1772, 1773, 1774, 1775, 1776, 1777, 2000, 2001, 2002, 2003, 2004, 2005, 2006, 2007, 2010, 2011, 2012, 2013, 2014, 2015, 2016, 2017, 2020, 2021, 2022, 2023, 2024, 2025, 2026, 2027, 2030, 2031, 2032, 2033, 2034, 2035, 2036, 2037, 2040, 2041, 2042, 2043, 2044, 2045, 2046, 2047, 2050, 2051, 2052, 2053, 2054, 2055, 2056, 2057, 2060, 2061, 2062, 2063, 2064, 2065, 2066, 2067, 2070, 2071, 2072, 2073, 2074, 2075, 2076, 2077, 2100, 2101, 2102, 2103, 2104, 2105, 2106, 2107, 2110, 2111, 2112, 2113, 2114, 2115, 2116, 2117, 2120, 2121, 2122, 2123, 2124, 2125, 2126, 2127, 2130, 2131, 2132, 2133, 2134, 2135, 2136, 2137, 2140, 2141, 2142, 2143, 2144, 2145, 2146, 2147, 2150, 2151, 2152, 2153, 2154, 2155, 2156, 2157, 2160, 2161, 2162, 2163, 2164, 2165, 2166, 2167, 2170, 2171, 2172, 2173, 2174, 2175, 2176, 2177, 2200, 2201, 2202, 2203, 2204, 2205, 2206, 2207, 2210, 2211, 2212, 2213, 2214, 2215, 2216, 2217, 2220, 2221, 2222, 2223, 2224, 2225, 2226, 2227, 2230, 2231, 2232, 2233, 2234, 2235, 2236, 2237, 2240, 2241, 2242, 2243, 2244, 2245, 2246, 2247, 2250, 2251, 2252, 2253, 2254, 2255, 2256, 2257, 2260, 2261, 2262, 2263, 2264, 2265, 2266, 2267, 2270, 2271, 2272, 2273, 2274, 2275, 2276, 2277, 2300, 2301, 2302, 2303, 2304, 2305, 2306, 2307, 2310, 2311, 2312, 2313, 2314, 2315, 2316, 2317, 2320, 2321, 2322, 2323, 2324, 2325, 2326, 2327, 2330, 2331, 2332, 2333, 2334, 2335, 2336, 2337, 2340, 2341, 2342, 2343, 2344, 2345, 2346, 2347, 2350, 2351, 2352, 2353, 2354, 2355, 2356, 2357, 2360, 2361, 2362, 2363, 2364, 2365, 2366, 2367, 2370, 2371, 2372, 2373, 2374, 2375, 2376, 2377, 2400, 2401, 2402, 2403, 2404, 2405, 2406, 2407, 2410, 2411, 2412, 2413, 2414, 2415, 2416, 2417, 2420, 2421, 2422, 2423, 2424, 2425, 2426, 2427, 2430, 2431, 2432, 2433, 2434, 2435, 2436, 2437, 2440, 2441, 2442, 2443, 2444, 2445, 2446, 2447, 2450, 2451, 2452, 2453, 2454, 2455, 2456, 2457, 2460, 2461, 2462, 2463, 2464, 2465, 2466, 2467, 2470, 2471, 2472, 2473, 2474, 2475, 2476, 2477, 2500, 2501, 2502, 2503, 2504, 2505, 2506, 2507, 2510, 2511, 2512, 2513, 2514, 2515, 2516, 2517, 2520, 2521, 2522, 2523, 2524, 2525, 2526, 2527, 2530, 2531, 2532, 2533, 2534, 2535, 2536, 2537, 2540, 2541, 2542, 2543, 2544, 2545, 2546, 2547, 2550, 2551, 2552, 2553, 2554, 2555, 2556, 2557, 2560, 2561, 2562, 2563, 2564, 2565, 2566, 2567, 2570, 2571, 2572, 2573, 2574, 2575, 2576, 2577, 2600, 2601, 2602, 2603, 2604, 2605, 2606, 2607, 2610, 2611, 2612, 2613, 2614, 2615, 2616, 2617, 2620, 2621, 2622, 2623, 2624, 2625, 2626, 2627, 2630, 2631, 2632, 2633, 2634, 2635, 2636, 2637, 2640, 2641, 2642, 2643, 2644, 2645, 2646, 2647, 2650, 2651, 2652, 2653, 2654, 2655, 2656, 2657, 2660, 2661, 2662, 2663, 2664, 2665, 2666, 2667, 2670, 2671, 2672, 2673, 2674, 2675, 2676, 2677, 2700, 2701, 2702, 2703, 2704, 2705, 2706, 2707, 2710, 2711, 2712, 2713, 2714, 2715, 2716, 2717, 2720, 2721, 2722, 2723, 2724, 2725, 2726, 2727, 2730, 2731, 2732, 2733, 2734, 2735, 2736, 2737, 2740, 2741, 2742, 2743, 2744, 2745, 2746, 2747, 2750, 2751, 2752, 2753, 2754, 2755, 2756, 2757, 2760, 2761, 2762, 2763, 2764, 2765, 2766, 2767, 2770, 2771, 2772, 2773, 2774, 2775, 2776, 2777, 3000, 3001, 3002, 3003, 3004, 3005, 3006, 3007, 3010, 3011, 3012, 3013, 3014, 3015, 3016, 3017, 3020, 3021, 3022, 3023, 3024, 3025, 3026, 3027, 3030, 3031, 3032, 3033, 3034, 3035, 3036, 3037, 3040, 3041, 3042, 3043, 3044, 3045, 3046, 3047, 3050, 3051, 3052, 3053, 3054, 3055, 3056, 3057, 3060, 3061, 3062, 3063, 3064, 3065, 3066, 3067, 3070, 3071, 3072, 3073, 3074, 3075, 3076, 3077, 3100, 3101, 3102, 3103, 3104, 3105, 3106, 3107, 3110, 3111, 3112, 3113, 3114, 3115, 3116, 3117, 3120, 3121, 3122, 3123, 3124, 3125, 3126, 3127, 3130, 3131, 3132, 3133, 3134, 3135, 3136, 3137, 3140, 3141, 3142, 3143, 3144, 3145, 3146, 3147, 3150, 3151, 3152, 3153, 3154, 3155, 3156, 3157, 3160, 3161, 3162, 3163, 3164, 3165, 3166, 3167, 3170, 3171, 3172, 3173, 3174, 3175, 3176, 3177, 3200, 3201, 3202, 3203, 3204, 3205, 3206, 3207, 3210, 3211, 3212, 3213, 3214, 3215, 3216, 3217, 3220, 3221, 3222, 3223, 3224, 3225, 3226, 3227, 3230, 3231, 3232, 3233, 3234, 3235, 3236, 3237, 3240, 3241, 3242, 3243, 3244, 3245, 3246, 3247, 3250, 3251, 3252, 3253, 3254, 3255, 3256, 3257, 3260, 3261, 3262, 3263, 3264, 3265, 3266, 3267, 3270, 3271, 3272, 3273, 3274, 3275, 3276, 3277, 3300, 3301, 3302, 3303, 3304, 3305, 3306, 3307, 3310, 3311, 3312, 3313, 3314, 3315, 3316, 3317, 3320, 3321, 3322, 3323, 3324, 3325, 3326, 3327, 3330, 3331, 3332, 3333, 3334, 3335, 3336, 3337, 3340, 3341, 3342, 3343, 3344, 3345, 3346, 3347, 3350, 3351, 3352, 3353, 3354, 3355, 3356, 3357, 3360, 3361, 3362, 3363, 3364, 3365, 3366, 3367, 3370, 3371, 3372, 3373, 3374, 3375, 3376, 3377, 3400, 3401, 3402, 3403, 3404, 3405, 3406, 3407, 3410, 3411, 3412, 3413, 3414, 3415, 3416, 3417, 3420, 3421, 3422, 3423, 3424, 3425, 3426, 3427, 3430, 3431, 3432, 3433, 3434, 3435, 3436, 3437, 3440, 3441, 3442, 3443, 3444, 3445, 3446, 3447, 3450, 3451, 3452, 3453, 3454, 3455, 3456, 3457, 3460, 3461, 3462, 3463, 3464, 3465, 3466, 3467, 3470, 3471, 3472, 3473, 3474, 3475, 3476, 3477, 3500, 3501, 3502, 3503, 3504, 3505, 3506, 3507, 3510, 3511, 3512, 3513, 3514, 3515, 3516, 3517, 3520, 3521, 3522, 3523, 3524, 3525, 3526, 3527, 3530, 3531, 3532, 3533, 3534, 3535, 3536, 3537, 3540, 3541, 3542, 3543, 3544, 3545, 3546, 3547, 3550, 3551, 3552, 3553, 3554, 3555, 3556, 3557, 3560, 3561, 3562, 3563, 3564, 3565, 3566, 3567, 3570, 3571, 3572, 3573, 3574, 3575, 3576, 3577, 3600, 3601, 3602, 3603, 3604, 3605, 3606, 3607, 3610, 3611, 3612, 3613, 3614, 3615, 3616, 3617, 3620, 3621, 3622, 3623, 3624, 3625, 3626, 3627, 3630, 3631, 3632, 3633, 3634, 3635, 3636, 3637, 3640, 3641, 3642, 3643, 3644, 3645, 3646, 3647, 3650, 3651, 3652, 3653, 3654, 3655, 3656, 3657, 3660, 3661, 3662, 3663, 3664, 3665, 3666, 3667, 3670, 3671, 3672, 3673, 3674, 3675, 3676, 3677, 3700, 3701, 3702, 3703, 3704, 3705, 3706, 3707, 3710, 3711, 3712, 3713, 3714, 3715, 3716, 3717, 3720, 3721, 3722, 3723, 3724, 3725, 3726, 3727, 3730, 3731, 3732, 3733, 3734, 3735, 3736, 3737, 3740, 3741, 3742, 3743, 3744, 3745, 3746, 3747, 3750, 3751, 3752, 3753, 3754, 3755, 3756, 3757, 3760, 3761, 3762, 3763, 3764, 3765, 3766, 3767, 3770, 3771, 3772, 3773, 3774, 3775, 3776, 3777, 4000, 4001, 4002, 4003, 4004, 4005, 4006, 4007, 4010, 4011, 4012, 4013, 4014, 4015, 4016, 4017, 4020, 4021, 4022, 4023, 4024, 4025, 4026, 4027, 4030, 4031, 4032, 4033, 4034, 4035, 4036, 4037, 4040, 4041, 4042, 4043, 4044, 4045, 4046, 4047, 4050, 4051, 4052, 4053, 4054, 4055, 4056, 4057, 4060, 4061, 4062, 4063, 4064, 4065, 4066, 4067, 4070, 4071, 4072, 4073, 4074, 4075, 4076, 4077, 4100, 4101, 4102, 4103, 4104, 4105, 4106, 4107, 4110, 4111, 4112, 4113, 4114, 4115, 4116, 4117, 4120, 4121, 4122, 4123, 4124, 4125, 4126, 4127, 4130, 4131, 4132, 4133, 4134, 4135, 4136, 4137, 4140, 4141, 4142, 4143, 4144, 4145, 4146, 4147, 4150, 4151, 4152, 4153, 4154, 4155, 4156, 4157, 4160, 4161, 4162, 4163, 4164, 4165, 4166, 4167, 4170, 4171, 4172, 4173, 4174, 4175, 4176, 4177, 4200, 4201, 4202, 4203, 4204, 4205, 4206, 4207, 4210, 4211, 4212, 4213, 4214, 4215, 4216, 4217, 4220, 4221, 4222, 4223, 4224, 4225, 4226, 4227, 4230, 4231, 4232, 4233, 4234, 4235, 4236, 4237, 4240, 4241, 4242, 4243, 4244, 4245, 4246, 4247, 4250, 4251, 4252, 4253, 4254, 4255, 4256, 4257, 4260, 4261, 4262, 4263, 4264, 4265, 4266, 4267, 4270, 4271, 4272, 4273, 4274, 4275, 4276, 4277, 4300, 4301, 4302, 4303, 4304, 4305, 4306, 4307, 4310, 4311, 4312, 4313, 4314, 4315, 4316, 4317, 4320, 4321, 4322, 4323, 4324, 4325, 4326, 4327, 4330, 4331, 4332, 4333, 4334, 4335, 4336, 4337, 4340, 4341, 4342, 4343, 4344, 4345, 4346, 4347, 4350, 4351, 4352, 4353, 4354, 4355, 4356, 4357, 4360, 4361, 4362, 4363, 4364, 4365, 4366, 4367, 4370, 4371, 4372, 4373, 4374, 4375, 4376, 4377, 4400, 4401, 4402, 4403, 4404, 4405, 4406, 4407, 4410, 4411, 4412, 4413, 4414, 4415, 4416, 4417, 4420, 4421, 4422, 4423, 4424, 4425, 4426, 4427, 4430, 4431, 4432, 4433, 4434, 4435, 4436, 4437, 4440, 4441, 4442, 4443, 4444, 4445, 4446, 4447, 4450, 4451, 4452, 4453, 4454, 4455, 4456, 4457, 4460, 4461, 4462, 4463, 4464, 4465, 4466, 4467, 4470, 4471, 4472, 4473, 4474, 4475, 4476, 4477, 4500, 4501, 4502, 4503, 4504, 4505, 4506, 4507, 4510, 4511, 4512, 4513, 4514, 4515, 4516, 4517, 4520, 4521, 4522, 4523, 4524, 4525, 4526, 4527, 4530, 4531, 4532, 4533, 4534, 4535, 4536, 4537, 4540, 4541, 4542, 4543, 4544, 4545, 4546, 4547, 4550, 4551, 4552, 4553, 4554, 4555, 4556, 4557, 4560, 4561, 4562, 4563, 4564, 4565, 4566, 4567, 4570, 4571, 4572, 4573, 4574, 4575, 4576, 4577, 4600, 4601, 4602, 4603, 4604, 4605, 4606, 4607, 4610, 4611, 4612, 4613, 4614, 4615, 4616, 4617, 4620, 4621, 4622, 4623, 4624, 4625, 4626, 4627, 4630, 4631, 4632, 4633, 4634, 4635, 4636, 4637, 4640, 4641, 4642, 4643, 4644, 4645, 4646, 4647, 4650, 4651, 4652, 4653, 4654, 4655, 4656, 4657, 4660, 4661, 4662, 4663, 4664, 4665, 4666, 4667, 4670, 4671, 4672, 4673, 4674, 4675, 4676, 4677, 4700, 4701, 4702, 4703, 4704, 4705, 4706, 4707, 4710, 4711, 4712, 4713, 4714, 4715, 4716, 4717, 4720, 4721, 4722, 4723, 4724, 4725, 4726, 4727, 4730, 4731, 4732, 4733, 4734, 4735, 4736, 4737, 4740, 4741, 4742, 4743, 4744, 4745, 4746, 4747, 4750, 4751, 4752, 4753, 4754, 4755, 4756, 4757, 4760, 4761, 4762, 4763, 4764, 4765, 4766, 4767, 4770, 4771, 4772, 4773, 4774, 4775, 4776, 4777, 5000, 5001, 5002, 5003, 5004, 5005, 5006, 5007, 5010, 5011, 5012, 5013, 5014, 5015, 5016, 5017, 5020, 5021, 5022, 5023, 5024, 5025, 5026, 5027, 5030, 5031, 5032, 5033, 5034, 5035, 5036, 5037, 5040, 5041, 5042, 5043, 5044, 5045, 5046, 5047, 5050, 5051, 5052, 5053, 5054, 5055, 5056, 5057, 5060, 5061, 5062, 5063, 5064, 5065, 5066, 5067, 5070, 5071, 5072, 5073, 5074, 5075, 5076, 5077, 5100, 5101, 5102, 5103, 5104, 5105, 5106, 5107, 5110, 5111, 5112, 5113, 5114, 5115, 5116, 5117, 5120, 5121, 5122, 5123, 5124, 5125, 5126, 5127, 5130, 5131, 5132, 5133, 5134, 5135, 5136, 5137, 5140, 5141, 5142, 5143, 5144, 5145, 5146, 5147, 5150, 5151, 5152, 5153, 5154, 5155, 5156, 5157, 5160, 5161, 5162, 5163, 5164, 5165, 5166, 5167, 5170, 5171, 5172, 5173, 5174, 5175, 5176, 5177, 5200, 5201, 5202, 5203, 5204, 5205, 5206, 5207, 5210, 5211, 5212, 5213, 5214, 5215, 5216, 5217, 5220, 5221, 5222, 5223, 5224, 5225, 5226, 5227, 5230, 5231, 5232, 5233, 5234, 5235, 5236, 5237, 5240, 5241, 5242, 5243, 5244, 5245, 5246, 5247, 5250, 5251, 5252, 5253, 5254, 5255, 5256, 5257, 5260, 5261, 5262, 5263, 5264, 5265, 5266, 5267, 5270, 5271, 5272, 5273, 5274, 5275, 5276, 5277, 5300, 5301, 5302, 5303, 5304, 5305, 5306, 5307, 5310, 5311, 5312, 5313, 5314, 5315, 5316, 5317, 5320, 5321, 5322, 5323, 5324, 5325, 5326, 5327, 5330, 5331, 5332, 5333, 5334, 5335, 5336, 5337, 5340, 5341, 5342, 5343, 5344, 5345, 5346, 5347, 5350, 5351, 5352, 5353, 5354, 5355, 5356, 5357, 5360, 5361, 5362, 5363, 5364, 5365, 5366, 5367, 5370, 5371, 5372, 5373, 5374, 5375, 5376, 5377, 5400, 5401, 5402, 5403, 5404, 5405, 5406, 5407, 5410, 5411, 5412, 5413, 5414, 5415, 5416, 5417, 5420, 5421, 5422, 5423, 5424, 5425, 5426, 5427, 5430, 5431, 5432, 5433, 5434, 5435, 5436, 5437, 5440, 5441, 5442, 5443, 5444, 5445, 5446, 5447, 5450, 5451, 5452, 5453, 5454, 5455, 5456, 5457, 5460, 5461, 5462, 5463, 5464, 5465, 5466, 5467, 5470, 5471, 5472, 5473, 5474, 5475, 5476, 5477, 5500, 5501, 5502, 5503, 5504, 5505, 5506, 5507, 5510, 5511, 5512, 5513, 5514, 5515, 5516, 5517, 5520, 5521, 5522, 5523, 5524, 5525, 5526, 5527, 5530, 5531, 5532, 5533, 5534, 5535, 5536, 5537, 5540, 5541, 5542, 5543, 5544, 5545, 5546, 5547, 5550, 5551, 5552, 5553, 5554, 5555, 5556, 5557, 5560, 5561, 5562, 5563, 5564, 5565, 5566, 5567, 5570, 5571, 5572, 5573, 5574, 5575, 5576, 5577, 5600, 5601, 5602, 5603, 5604, 5605, 5606, 5607, 5610, 5611, 5612, 5613, 5614, 5615, 5616, 5617, 5620, 5621, 5622, 5623, 5624, 5625, 5626, 5627, 5630, 5631, 5632, 5633, 5634, 5635, 5636, 5637, 5640, 5641, 5642, 5643, 5644, 5645, 5646, 5647, 5650, 5651, 5652, 5653, 5654, 5655, 5656, 5657, 5660, 5661, 5662, 5663, 5664, 5665, 5666, 5667, 5670, 5671, 5672, 5673, 5674, 5675, 5676, 5677, 5700, 5701, 5702, 5703, 5704, 5705, 5706, 5707, 5710, 5711, 5712, 5713, 5714, 5715, 5716, 5717, 5720, 5721, 5722, 5723, 5724, 5725, 5726, 5727, 5730, 5731, 5732, 5733, 5734, 5735, 5736, 5737, 5740, 5741, 5742, 5743, 5744, 5745, 5746, 5747, 5750, 5751, 5752, 5753, 5754, 5755, 5756, 5757, 5760, 5761, 5762, 5763, 5764, 5765, 5766, 5767, 5770, 5771, 5772, 5773, 5774, 5775, 5776, 5777, 6000, 6001, 6002, 6003, 6004, 6005, 6006, 6007, 6010, 6011, 6012, 6013, 6014, 6015, 6016, 6017, 6020, 6021, 6022, 6023, 6024, 6025, 6026, 6027, 6030, 6031, 6032, 6033, 6034, 6035, 6036, 6037, 6040, 6041, 6042, 6043, 6044, 6045, 6046, 6047, 6050, 6051, 6052, 6053, 6054, 6055, 6056, 6057, 6060, 6061, 6062, 6063, 6064, 6065, 6066, 6067, 6070, 6071, 6072, 6073, 6074, 6075, 6076, 6077, 6100, 6101, 6102, 6103, 6104, 6105, 6106, 6107, 6110, 6111, 6112, 6113, 6114, 6115, 6116, 6117, 6120, 6121, 6122, 6123, 6124, 6125, 6126, 6127, 6130, 6131, 6132, 6133, 6134, 6135, 6136, 6137, 6140, 6141, 6142, 6143, 6144, 6145, 6146, 6147, 6150, 6151, 6152, 6153, 6154, 6155, 6156, 6157, 6160, 6161, 6162, 6163, 6164, 6165, 6166, 6167, 6170, 6171, 6172, 6173, 6174, 6175, 6176, 6177, 6200, 6201, 6202, 6203, 6204, 6205, 6206, 6207, 6210, 6211, 6212, 6213, 6214, 6215, 6216, 6217, 6220, 6221, 6222, 6223, 6224, 6225, 6226, 6227, 6230, 6231, 6232, 6233, 6234, 6235, 6236, 6237, 6240, 6241, 6242, 6243, 6244, 6245, 6246, 6247, 6250, 6251, 6252, 6253, 6254, 6255, 6256, 6257, 6260, 6261, 6262, 6263, 6264, 6265, 6266, 6267, 6270, 6271, 6272, 6273, 6274, 6275, 6276, 6277, 6300, 6301, 6302, 6303, 6304, 6305, 6306, 6307, 6310, 6311, 6312, 6313, 6314, 6315, 6316, 6317, 6320, 6321, 6322, 6323, 6324, 6325, 6326, 6327, 6330, 6331, 6332, 6333, 6334, 6335, 6336, 6337, 6340, 6341, 6342, 6343, 6344, 6345, 6346, 6347, 6350, 6351, 6352, 6353, 6354, 6355, 6356, 6357, 6360, 6361, 6362, 6363, 6364, 6365, 6366, 6367, 6370, 6371, 6372, 6373, 6374, 6375, 6376, 6377, 6400, 6401, 6402, 6403, 6404, 6405, 6406, 6407, 6410, 6411, 6412, 6413, 6414, 6415, 6416, 6417, 6420, 6421, 6422, 6423, 6424, 6425, 6426, 6427, 6430, 6431, 6432, 6433, 6434, 6435, 6436, 6437, 6440, 6441, 6442, 6443, 6444, 6445, 6446, 6447, 6450, 6451, 6452, 6453, 6454, 6455, 6456, 6457, 6460, 6461, 6462, 6463, 6464, 6465, 6466, 6467, 6470, 6471, 6472, 6473, 6474, 6475, 6476, 6477, 6500, 6501, 6502, 6503, 6504, 6505, 6506, 6507, 6510, 6511, 6512, 6513, 6514, 6515, 6516, 6517, 6520, 6521, 6522, 6523, 6524, 6525, 6526, 6527, 6530, 6531, 6532, 6533, 6534, 6535, 6536, 6537, 6540, 6541, 6542, 6543, 6544, 6545, 6546, 6547, 6550, 6551, 6552, 6553, 6554, 6555, 6556, 6557, 6560, 6561, 6562, 6563, 6564, 6565, 6566, 6567, 6570, 6571, 6572, 6573, 6574, 6575, 6576, 6577, 6600, 6601, 6602, 6603, 6604, 6605, 6606, 6607, 6610, 6611, 6612, 6613, 6614, 6615, 6616, 6617, 6620, 6621, 6622, 6623, 6624, 6625, 6626, 6627, 6630, 6631, 6632, 6633, 6634, 6635, 6636, 6637, 6640, 6641, 6642, 6643, 6644, 6645, 6646, 6647, 6650, 6651, 6652, 6653, 6654, 6655, 6656, 6657, 6660, 6661, 6662, 6663, 6664, 6665, 6666, 6667, 6670, 6671, 6672, 6673, 6674, 6675, 6676, 6677, 6700, 6701, 6702, 6703, 6704, 6705, 6706, 6707, 6710, 6711, 6712, 6713, 6714, 6715, 6716, 6717, 6720, 6721, 6722, 6723, 6724, 6725, 6726, 6727, 6730, 6731, 6732, 6733, 6734, 6735, 6736, 6737, 6740, 6741, 6742, 6743, 6744, 6745, 6746, 6747, 6750, 6751, 6752, 6753, 6754, 6755, 6756, 6757, 6760, 6761, 6762, 6763, 6764, 6765, 6766, 6767, 6770, 6771, 6772, 6773, 6774, 6775, 6776, 6777, 7000, 7001, 7002, 7003, 7004, 7005, 7006, 7007, 7010, 7011, 7012, 7013, 7014, 7015, 7016, 7017, 7020, 7021, 7022, 7023, 7024, 7025, 7026, 7027, 7030, 7031, 7032, 7033, 7034, 7035, 7036, 7037, 7040, 7041, 7042, 7043, 7044, 7045, 7046, 7047, 7050, 7051, 7052, 7053, 7054, 7055, 7056, 7057, 7060, 7061, 7062, 7063, 7064, 7065, 7066, 7067, 7070, 7071, 7072, 7073, 7074, 7075, 7076, 7077, 7100, 7101, 7102, 7103, 7104, 7105, 7106, 7107, 7110, 7111, 7112, 7113, 7114, 7115, 7116, 7117, 7120, 7121, 7122, 7123, 7124, 7125, 7126, 7127, 7130, 7131, 7132, 7133, 7134, 7135, 7136, 7137, 7140, 7141, 7142, 7143, 7144, 7145, 7146, 7147, 7150, 7151, 7152, 7153, 7154, 7155, 7156, 7157, 7160, 7161, 7162, 7163, 7164, 7165, 7166, 7167, 7170, 7171, 7172, 7173, 7174, 7175, 7176, 7177, 7200, 7201, 7202, 7203, 7204, 7205, 7206, 7207, 7210, 7211, 7212, 7213, 7214, 7215, 7216, 7217, 7220, 7221, 7222, 7223, 7224, 7225, 7226, 7227, 7230, 7231, 7232, 7233, 7234, 7235, 7236, 7237, 7240, 7241, 7242, 7243, 7244, 7245, 7246, 7247, 7250, 7251, 7252, 7253, 7254, 7255, 7256, 7257, 7260, 7261, 7262, 7263, 7264, 7265, 7266, 7267, 7270, 7271, 7272, 7273, 7274, 7275, 7276, 7277, 7300, 7301, 7302, 7303, 7304, 7305, 7306, 7307, 7310, 7311, 7312, 7313, 7314, 7315, 7316, 7317, 7320, 7321, 7322, 7323, 7324, 7325, 7326, 7327, 7330, 7331, 7332, 7333, 7334, 7335, 7336, 7337, 7340, 7341, 7342, 7343, 7344, 7345, 7346, 7347, 7350, 7351, 7352, 7353, 7354, 7355, 7356, 7357, 7360, 7361, 7362, 7363, 7364, 7365, 7366, 7367, 7370, 7371, 7372, 7373, 7374, 7375, 7376, 7377, 7400, 7401, 7402, 7403, 7404, 7405, 7406, 7407, 7410, 7411, 7412, 7413, 7414, 7415, 7416, 7417, 7420, 7421, 7422, 7423, 7424, 7425, 7426, 7427, 7430, 7431, 7432, 7433, 7434, 7435, 7436, 7437, 7440, 7441, 7442, 7443, 7444, 7445, 7446, 7447, 7450, 7451, 7452, 7453, 7454, 7455, 7456, 7457, 7460, 7461, 7462, 7463, 7464, 7465, 7466, 7467, 7470, 7471, 7472, 7473, 7474, 7475, 7476, 7477, **7500**, 7501, 7502, 7503, 7504, 7505, 7506, 7507, 7510, 7511, 7512, 7513, 7514, 7515, 7516, 7517, 7520, 7521, 7522, 7523, 7524, 7525, 7526, 7527, 7530, 7531, 7532, 7533, 7534, 7535, 7536, 7537, 7540, 7541, 7542, 7543, 7544, 7545, 7546, 7547, 7550, 7551, 7552, 7553, 7554, 7555, 7556, 7557, 7560, 7561, 7562, 7563, 7564, 7565, 7566, 7567, 7570, 7571, 7572, 7573, 7574, 7575, 7576, 7577, **7600**, 7601, 7602, 7603, 7604, 7605, 7606, 7607, 7610, 7611, 7612, 7613, 7614, 7615, 7616, 7617, 7620, 7621, 7622, 7623, 7624, 7625, 7626, 7627, 7630, 7631, 7632, 7633, 7634, 7635, 7636, 7637, 7640, 7641, 7642, 7643, 7644, 7645, 7646, 7647, 7650, 7651, 7652, 7653, 7654, 7655, 7656, 7657, 7660, 7661, 7662, 7663, 7664, 7665, 7666, 7667, 7670, 7671, 7672, 7673, 7674, 7675, 7676, 7677, **7700**, 7701, 7702, 7703, 7704, 7705, 7706, 7707, 7710, 7711, 7712, 7713, 7714, 7715, 7716, 7717, 7720, 7721, 7722, 7723, 7724, 7725, 7726, 7727, 7730, 7731, 7732, 7733, 7734, 7735, 7736, 7737, 7740, 7741, 7742, 7743, 7744, 7745, 7746, 7747, 7750, 7751, 7752, 7753, 7754, 7755, 7756, 7757, 7760, 7761, 7762, 7763, 7764, 7765, 7766, 7767, 7770, 7771, 7772, 7773, 7774, 7775, 7776, 7777

Squawk codes are used by air traffic control to identify aircraft on the secondary surveillance radar. Flights are being given a squawk code by an air traffic controller, the pilot dials it into the radar transponder panel, and the radar reads that number out of the transponder and gives it back to the air traffic control system.

In the air traffic control system, information such as the flight plan, call-sign and given clearances can be associated to the radar track, and this is (partly) done based on the squawk code. The squawk code is a non-unique identifier. Typically flights that are under air traffic control are given a code that is unique in that control area. Non-controlled flights are given a generic code, so there may be many with the same code in a single air traffic control area. For example, for uncontrolled VFR in the USA code 1200 is used. On the oceans (where there is no radar control) code 2000 is used. Wikipedia has a list of many transponder codes and their uses. It does not contain all codes; for a list of all codes I refer the ultimate squawk code list by @J.Hougaard.

Three codes are designated as emergency code; their meaning is the same anywhere in the world:

• 7500: unlawful interference; used in hijacking situation


• 7600: lost communication; used when no radio contact can be established


• 7700: general emergency code

7500 hijack

7600 no radio

7700 emergency

If you really want to learn, reading the FAR and AIM will really get you up to speed

http://www.faraim.org/

One might wonder why 8 and 9 are not used. I imagine it is to save on bits of data. 0 to 7 can be done in 3 bits - 000, 001, 010, 011, 100, 101, 110, 111. 8 and 9 need another bit: 1000, 1001. Save a bit on each number simplifies the rotary knob a little bit, and saves 4 bits on the overall transmission. As it is, the four 0-7 digits allow 4096 codes in any one area, which might seem like plenty for any one controller to keep track of. 0000 to 9999 would mean really crowded skies!

Octal was popular for a while. 4 knobs to send 12 bits has been around quite a while. So even tho the latest transponders use push buttons instead of knobs, the 8 numbers are with us for a while more. Maybe self flying taxis will drive up the range eventually.

In addition to the other great answers, you might be wondering why the squawk codes are the way they are — why each digit only goes up to 7 before rolling around to 0. I'm not an aviation expert but I do know about computing so I can answer this question. This is because the transponder is a simple electronic system sending binary information (ie what can be thought of as strings of just 1s or 0s). But long strings of 1s and 0s are hard for humans to remember, so we almost always represent binary strings in a different form.

Now, you may think binary is just a number, so we can just convert binary to our normal decimal numbers and use those. But this is actually quite tricky; because 10 isn't a power of 2, converting a binary number to decimal is non-trivial; it requires relatively complex circuitry to do so. If you think about this logically it makes sense; if I have a four digit decimal number, say 1000, that translates to 01111101000 in binary. But if I then change it to 1100, the binary is now 10001001100 — you see there have been changes throughout almost the whole number.

But if our base is a power of 2, like 8 for instance, we can split the number into useful chunks (for base 8, chunks of 3, because 2^3 is 8), which are entirely self-contained. For instance, base 8 (octal) 1000 translates to binary 001,000,000,000 (I'm using commas as digit separators so you can clearly see the groups of binary digits which correspond to each number), whereas octal 1100 translates to binary 001,001,000,000 — you see that each octal number corresponds 1:1 with a group of three binary digits. Octal 7777 would be 111,111,111,111.

Now, this is useful for both electrical circuitry, because it makes it simpler, and for humans who need to have a good understanding of how the binary works under the hood, because it's easier to do the mental mapping.

Octal was quite popular for a time, when the standard size of a group of binary digits was not generally fixed, so there's no reason it shouldn't have been a multiple of three. But in modern computing, we tend to use groups of eight binary digits as the smallest unit we generally care about, known as a byte. Three doesn't go into 8, so for that reason octal has generally fallen out of favour. Nowadays we tend to use hexadecimal (base 16), which uses numbers 0-9 and A-F, and each digit represents a group of four binary digits. But because of its age, octal lives on in aircraft transponders.

In addition to those globally recognized special values, and locally valid special values (uncontrolled VR, IFR) you will be assigned the code by the ATC. They will usually assign you a code in sequence from some block they were assigned for this purpose. The exact procedure is highly specific to local procedures.

There is some very incomplete (mostly in the UK) list here http://www.flightradars.eu/squawkcodes.html

For example in the LKAA FIR (Czech Republic) it should work like this (completely unofficial, but likely fairly accurate, it is just an illustration):

0040 = search and rescue (if not assigned otherwise)

0041 - 0044 = search and rescue (assigned by ATC)

0045 = flights connected with human life saving (if not assigned otherwise)

0046 - 0047 = flights connected with human life saving (assigned by ATC)

0052 - 0053 = police helicopters daytime (if not assigned otherwise)

0054 - 0055 = police helicopters nighttime (if not assigned otherwise)

0056 - 0057 = flights of the civil aviation authority (assigned by ATC)

then

• blocks for IFR flights, transit, arrivals, departures, domestic


• IFR blocks inside local CTAs 0020 - 0037


• VFR flights following airways 3330 - 3344


• military flights - several blocks, depending on who is controlling


• local flights
  
  
  
  
  • each airport has its own block, for example LKPR 3310 - 3317