| 1 | SZ | China Southwest Airlines | ICAO: CXN, Callsign: China Southwest, IATA Prefix: 785, Founded on 15 October 1987. Ceased operations on 28 October 2002 (merged with Air China). Formerly CAAC Southwest region | PRC | AVCODES |
| 2 | SZ | Air Southwest Ltd. | ICAO: WOW, Callsign: Swallow, IATA Prefix: 429, Air Southwest was a British airline founded by Sutton Harbour Holdings in 2003. Ownership was transferred to Eastern Airways in September 2010 but operations ceased 12 months later on 30 September 2011. | GB | AVCODES |
| 3 | SZ | Aerolineas de El Salvador, S.A. | ICAO: SZA, Callsign: AESA, Designator SZ recalled by IATA | ES | AVCODES |
| 4 | SZ | Air Nepal International Pvt. Ltd. | ICAO: NPL, Callsign: Air Nepal, IATA Prefix: 855, All of its flights were suspended from 22 December 2005. | NEP | AVCODES |
| 5 | SZ | Aircompany Somon Air LLC | ICAO: SMR, Callsign: Somon Air, IATA Prefix: 413, IATA designator changed from 4J. | TJ | AVCODES |
| 6 | SZ | SMUCKERS | | | PWRC |
| 7 | SZ | Slowenia | | SLO | TRAFFIC |
| 8 | SZ | Slovenske Zeleznice D.D. | | SI | VKM |
| 9 | SZA | Shenzhen Astro General Aviation Co., Ltd. | Callsign: Air Astro, Name changed to Astro Air Co., Ltd. | PRC | AVCODES |
| 10 | SZA | Aerolineas de El Salvador, S.A. | IATA: SZ, Callsign: AESA, Designator SZ recalled by IATA | ES | AVCODES |
| 11 | SZA | Astro Air Co., Ltd. | Callsign: Air Astro, Name changed from Shenzhen Astro General Aviation Co., Ltd. | PRC | AVCODES |
| 12 | SZA | Aerolineas De El Salvador | | | ICAO1 |
| 13 | SZA | \"Sviloza\" AD / \"Свилоза\" АД | | BG | VKM |
| 14 | SZAB | Szabolcs Volán | | H | TRAFFIC |
| 15 | SZAE | SANCHEZ AGUIRRE, EDUARDO | | | SCAC4 |
| 16 | SZBB | SCHWARTZ, BEN B AND SONS INC | | | SCAC4 |
| 17 | SZBP | SWARTZ, B TRANSPORT | | | SCAC4 |
| 18 | SZBT | SITZER, BRENT E TRUCKING INCORPORAT | | | SCAC4 |
| 19 | SZCH | SALAZAR, CHRIS | | | SCAC4 |
| 20 | SZCZ | MZK Szczecin | Real: MZK, City: Szczecin | PL | TRAFFIC |
| 21 | SZD | | | SU | TRAFFIC |
| 22 | SZDA | SEILTZ, WILLIAM TRUCKING | | | SCAC4 |
| 23 | SZDC | Správa železniční dopravní cesty, státní organizace | | CZ | VKM |
| 24 | SZDF | SZADO FISHING LTD | | | SCAC4 |
| 25 | SZDM | SUAREZ, JORGE LUIS | | | SCAC4 |
| 26 | SZDS | SCHATZ, DONNY MOTORSPORTS | | | SCAC4 |
| 27 | SZDS | Slovenská železničná dopravná spoločnosť, a.s. | | SK | VKM |
| 28 | SZEC | SANZO ENTERPRISE CO LTD | | | SCAC4 |
| 29 | SZEL | SANCHEZ ESTRADA, LUIS ENRIQUE | | | SCAC4 |
| 30 | SZET | SZETO TECHNOLOGIES INC | | | SCAC4 |
| 31 | SZEVA | Szentesi Vasútépítö | | HU | VKM |
| 32 | SZF | Skyforce Aviation Pty Ltd. | Callsign: Skyforce, ICAO Designator changed to SFZ | AUS | AVCODES |
| 33 | SZFA | SCHULTZ, FLOYD A | | | SCAC1 |
| 34 | SZFN | SANCHEZ ZORRILLA, FRANCISCO | | | SCAC4 |
| 35 | SZFV | Alba Volán Székesfehérvár | City: Székesfehérvár | H | TRAFFIC |
| 36 | SZG | Shtotz Agro Service | Callsign: Stotz Agro, | BY | AVCODES |
| 37 | SZGS | SANCHEZ GAMBOA, LUIS LAURO | | | SCAC4 |
| 38 | SZHE | SHANGHAI ZHENHUA SHIPPING CO LTD | | | SCAC4 |
| 39 | SZHN | SOLUTIONS HANZO SOLUTIONS INC | | | SCAC4 |
| 40 | SZIA | STOLTZFUS, IVAN | | | SCAC4 |
| 41 | SZID | SNOOZIES INDUSTRIES | | | SCAC4 |
| 42 | SZIL | Szilvásvárad | Real: H-SAEV | H | TRAFFIC |
| 43 | SZIN | SOLDADURAS ZELECTA SA DE CV | | | SCAC4 |
| 44 | SZKI | SCHWARTZ TRUCKING INC | | | SCAC4 |
| 45 | SZKT | SMYCZAK TRUCKING | | | SCAC4 |
| 46 | SZKT | Szeged | City: Szeged | H | TRAFFIC |
| 47 | SZL | Airlink Swaziland | Callsign: Swazilink, | SD | AVCODES |
| 48 | SZL | Royal Eswatini National Airways Corporation | IATA: RN, Callsign: Eswatini, | SD | AVCODES |
| 49 | SZL | Swaziland Airlink | | | ICAO1 |
| 50 | SZLB | SPECIALIZED LOGISTICS & BROKERAGE L | | | SCAC4 |
| 51 | SZLC | STARZZ LOGISTICS | | | SCAC4 |
| 52 | SZLD | SAMCO ZETA LTD | | | SCAC4 |
| 53 | SZLI | SZL INC | | | SCAC4 |
| 54 | SZLU | SEACUBE CONTAINERS LLC | | USA | BIC |
| 55 | SZLU | Seacube Container Leasing | | | RSRV |
| 56 | SZLU | SEACASTLE CONTAINER LEASING | | | SCAC4 |
| 57 | SZMA | STUZMAN TRUCKING LLC | | | SCAC4 |
| 58 | SZMC | Shenzhen Metro Group | City: Shenzhen | PRC | TRAFFIC |
| 59 | SZMG | ST MICHAELS TRUCKING | | | SCAC4 |
| 60 | SZMH | SMH | | | SCAC4 |
| 61 | SZMN | SCOTT, MASON | | | SCAC4 |
| 62 | SZMT | SPECIALIZED MACHINERY TRANSPORT INC | | | SCAC4 |
| 63 | SZN | Air Senegal S.A. | IATA: HC, Callsign: Sensa, | SN | AVCODES |
| 64 | SZNT | SCHULTZ & SONS TRANSPORT LLC | | | SCAC4 |
| 65 | SZOB | Szobi kisvasút | Real: BKNK | H | TRAFFIC |
| 66 | SZOD | SALZILLO SA DE CV | | | SCAC4 |
| 67 | SZOL | Szolnok | | H | TRAFFIC |
| 68 | SZOS | SIX ZERO ONE SEVEN TWO NINE ONE (60 | | | SCAC4 |
| 69 | SZOSTEK | Prywatna Komunikacja Samochodowa, A. Szostek | | PL | TRAFFIC |
| 70 | SZPH | SANCHEZ PATRON, HUGO | | | SCAC4 |
| 71 | SZPS | SEVEN THREE ZERO (730) PERMIT SERVI | | | SCAC4 |
| 72 | SZPT | SZAWLOWSKI POTATO FARMS INC | | | SCAC4 |
| 73 | SZQV | SPECIALIZED EQUIPMENT SERVICES LTD | | | SCAC4 |
| 74 | SZR | Śląskie Zaplecze Remontowe Sp. z o.o. | | PL | VKM |
| 75 | SZRO | SANCHEZ, RIGOBERTO | | | SCAC4 |
| 76 | SZRP | Polish Armed Forces - Siły Zbrojne Rzeczypospolitej Polskiej | | PL | TRAFFIC |
| 77 | SZRT | SWITZER TANK LINES INC | | | SCAC4 |
| 78 | SZRU | LLC SYNTEZRAIL | | RUS | BIC |
| 79 | SZS | Scandinavian Airlines Ireland Limited | IATA: SL, Callsign: Spinnaker, Name changed to Scandinavian Airlines Ireland Limited d/b/a SAS Connect w.e.f. 28 September 2021. | IRL | AVCODES |
| 80 | SZS | Scandinavian Airlines Ireland Limited d/b/a SAS Connect | IATA: SL, Callsign: Spinnaker, Name changed from Scandinavian Airlines Ireland Limited w.e.f. 28 September 2021. | IRL | AVCODES |
| 81 | SZSB | SCHNITZER STEEL BC INC | | | SCAC4 |
| 82 | SZSD | SEVEN ZERO SEVEN SIX TWO ZERO SEVEN | | | SCAC4 |
| 83 | SZSE | SPECIALIZED SERVICES TRANSPORTATION | | | SCAC4 |
| 84 | SZSO | SHENZHEN SHINING OCEAN INTERNATIONA | | | SCAC4 |
| 85 | SZSR | SANCHEZ, SALVADOR | | | SCAC4 |
| 86 | SZSV | SPECIALIZED SERVICES INC | | | SCAC4 |
| 87 | SZSW | SIX ZERO SEVEN TWO THREE SEVEN (607 | | | SCAC4 |
| 88 | SZT | Servicios Aeronauticos Z, S.A. de C.V. | Callsign: Aero Zee, | MEX | AVCODES |
| 89 | SZT | Servicios Aeronauticos Z | | | ICAO1 |
| 90 | SZTE | SPECIALIZED TANK SERVICES INC | | | SCAC4 |
| 91 | SZTG | SPEEDY TRANSPORT GROUP INC | | | SCAC4 |
| 92 | SZTH | SEVEN ZERO TWO ZERO SIX THREE FIVE | | | SCAC4 |
| 93 | SZTI | SUB ZERO TRANSPORTATION INC | | | SCAC4 |
| 94 | SZTK | SANCHEZ TRUCKING | | | SCAC4 |
| 95 | SZTL | SARZA TOWING LLC | | | SCAC4 |
| 96 | SZTP | STOLTZFUS TRUCKING | | | SCAC4 |
| 97 | SZTQ | SPECIALIZE TRANSPORTATION INC | | | SCAC4 |
| 98 | SZTR | SCHULZ & SONS TRUCKING, INC | | | SCAC1 |
| 99 | SZTR | SEUZ TRANSPORTES TRANSFRONTERIZOS | | | SCAC4 |
| 100 | SZTS | SPECIALIZED TRANSPORTATION SERVICES | | | SCAC4 |
