| 5501 | SKB | Skybus Airlines | IATA: SX, Callsign: Skybus, Ceased operations | USA | AVCODES |
| 5502 | SKB | Skybus Airlines | IATA: SX | | ICAO1 |
| 5503 | SKB | Schleifkottenbahn GmbH | Halver | D | privat-bahn.de |
| 5504 | SKBA | SKIP BARBER RACING SCHOOL LLC | | | SCAC4 |
| 5505 | SKBB | SKYLINE CUSTOMS SERVICES LLC | | | SCAC4 |
| 5506 | SKBF | SNEAKER KING OF BUFFALO | | | SCAC4 |
| 5507 | SKBN | SKIPPER BROTHERS TANK LINES LLC | | | SCAC4 |
| 5508 | SKBO | SKEETER BROKERAGE | | | SCAC4 |
| 5509 | SKBP | SMOKY BURN TRANSPORT | | | SCAC4 |
| 5510 | SKBQ | STREET KINGS INC | | | SCAC4 |
| 5511 | SKBR | SHOKER BROTHERS INCORPORATED | | | SCAC4 |
| 5512 | SKBU | SWEDISH NUCLEAR FUEL AND WASTE MANAGEMENT | | S | BIC |
| 5513 | SKBY | SKY-BLUE LOGISTICS LLC | | | SCAC4 |
| 5514 | SKC | Skymaster Air Lines Ltda | Callsign: Skymaster Air, Established on 30 November 1995 and started operations in 1997. Ceased operations. | BR | AVCODES |
| 5515 | SKC | Skymaster Air Lines | | | ICAO1 |
| 5516 | SKCB | SENKO CO LTD | | | SCAC4 |
| 5517 | SKCC | SCHECKLA, CRAIG LLC | | | SCAC4 |
| 5518 | SKCE | STARLINK CONSOLIDATION SERVICE | | | SCAC4 |
| 5519 | SKCF | SITKA COURIER LLC | | | SCAC4 |
| 5520 | SKCG | STRICKLAND OIL CO INC | | | SCAC4 |
| 5521 | SKCI | SKIERS CHOICE INC | | | SCAC4 |
| 5522 | SKCJ | SKYTRUCK CONTAINER LINES | | | SCAC4 |
| 5523 | SKCO | SRA KARTING INTERNATIONAL | | | SCAC4 |
| 5524 | SKCQ | STICKY MEDIA INC | | | SCAC4 |
| 5525 | SKCR | SKY COURIER NETWORK | | | SCAC4 |
| 5526 | SKCU | MAMMOET EUROPE BV | | NL | BIC |
| 5527 | SKCU | ALE HEAVYLIFT LIMITED | | | SCAC4 |
| 5528 | SKCW | SOFILINK CONTINENTAL INC | | | SCAC4 |
| 5529 | SKCX | Spartan Co-operative Creamery Co. (North Western Refrigerator Line Co.) | 7/1935 | | NAKINA |
| 5530 | SKCX | Sinclair-Koppers Co. | added 1/1968; 4/1970; eliminated 1/1974 | | NAKINA |
| 5531 | SKCX | Arco Polymers, Inc. | added 1/1974; eliminated 10/1974 | | NAKINA |
| 5532 | SKCX | ARCO/Polymers, Inc. | added 10/1974; 1/1975; eliminated 10/1979 | | NAKINA |
| 5533 | SKCX | ARCO Polymers, Inc. | added 10/1979; 1/1980; eliminated 10/1982 | | NAKINA |
| 5534 | SKCX | ARCO Chemical Co. | added 10/1982; eliminated 1/1984; 1/1994-7/2005 (not listed) | | NAKINA |
| 5535 | SKCX | Sinclair-Koppers Co. | added 1/68; 4/70 | | NRHS |
| 5536 | SKCX | ARCO Polymers, Inc. | 1/75-1/80; eliminated 10/82 | | NRHS |
| 5537 | SKCX | ARCO Chemical Co. | added 10/82; 1/94-7/2000 | | NRHS |
| 5538 | SKCX | ARCO CHEMICAL CO. [SINCLAIR-KOPPERS CO.] | | | PWRC |
| 5539 | SKCX | ARCO Chemical | | | RSRV |
| 5540 | SKCY | SKY COUNTRY TRANSPORTATION SERVICES | | | SCAC4 |
| 5541 | SKD | Sky Harbor Air Service, Inc. | Callsign: Sky Dwag, | USA | AVCODES |
| 5542 | SKD | Skyguard Ltd. | Callsign: Skyguard, Ceased aviation business during 1990 | GB | AVCODES |
| 5543 | SKD | Sky Harbor Air Service | | | ICAO1 |
| 5544 | SKDA | SEMPER TRUCKING INC | | | SCAC4 |
| 5545 | SKDB | SILKROAD LOGISTICS | | | SCAC4 |
| 5546 | SKDE | SAN KARLOS S DE RL DE | | | SCAC4 |
| 5547 | SKDF | STOCKARD ENTERPRISES INC | | | SCAC4 |
| 5548 | SKDP | STRICKLAND & SONS PIPELINE INC | | | SCAC4 |
| 5549 | SKDQ | SOKIL TRUCKING INC | | | SCAC4 |
| 5550 | SKDR | SKANDACOR DIRECT INC | | | SCAC4 |
| 5551 | SKDT | STRUCTURES DEREK INTERNATIONAL S A | | | SCAC4 |
| 5552 | SKDY | SERHIENKO, DENNIS | | | SCAC4 |
| 5553 | SKE | Sky Tours, Inc. | Callsign: Skyisle, | USA | AVCODES |
| 5554 | SKE | Sky Tours | | | ICAO1 |
| 5555 | SKEA | SKY BROKERAGE | | | SCAC4 |
| 5556 | SKEC | STOKELY CREEK CARRIERS | | | SCAC4 |
| 5557 | SKEF | STARKE ENTERPRISES LLC | | | SCAC4 |
| 5558 | SKEG | SHEPARD AND KEMNA ENGINEERED TRANSP | | | SCAC4 |
| 5559 | SKEI | SHEIK HALAL FARMS INC | | | SCAC4 |
| 5560 | SKEI | Shin-Keisei Electric Railway | | J | TRAFFIC |
| 5561 | SKEJ | SAMEK ENTERPRISE LLC | | | SCAC4 |
| 5562 | SKEK | SKELTON TRUCKING LLC | | | SCAC4 |
| 5563 | SKEL | SIEDAK ENTERPRISES LLC | | | SCAC4 |
| 5564 | SKEM | SKEEM | | | SCAC4 |
| 5565 | SKEO | SKEE, K FUEL OIL | | | SCAC4 |
| 5566 | SKEP | SUPERIOR BROKERAGE SERVICES INC | | | SCAC4 |
| 5567 | SKEQ | SK TRANSPORT | | | SCAC4 |
| 5568 | SKER | SPECK ENTERPRISE TRANSPORTATION INC | | | SCAC4 |
| 5569 | SKES | SKE ENTERPRISES LTD | | | SCAC4 |
| 5570 | SKEV | SOLIE, KEVIN | | | SCAC4 |
| 5571 | SKEW | STEELMAN, | | | SCAC4 |
| 5572 | SKEY | SHARKEY TRANSPORT SERVICES INC | | | SCAC4 |
| 5573 | SKF | Skycraft, Inc. | Callsign: Skycraft, | USA | AVCODES |
| 5574 | SKF | Skycraft | | | ICAO1 |
| 5575 | SKFA | S & K TRANSPORTATION LLC | | | SCAC4 |
| 5576 | SKFC | SKINNER FURNITURE CORP | | | SCAC4 |
| 5577 | SKFG | SENKO FREIGHT LINES | | | SCAC4 |
| 5578 | SKFI | SUNRISE TRUCKING INC | | | SCAC4 |
| 5579 | SKFL | SPECIAL K FISHERIES LTD | | | SCAC4 |
| 5580 | SKFN | SKIF INC | | | SCAC4 |
| 5581 | SKFO | SUNTEK AMERICA INC | | | SCAC4 |
| 5582 | SKFS | SKYWAY FREIGHT SYSTEMS, INC | | | SCAC1 |
| 5583 | SKFS | STAR K TRANSPORTATION INC | | | SCAC4 |
| 5584 | SKFY | SHAMROCK FOODS COMPANY | | | SCAC4 |
| 5585 | SKG | Sky Gabon S.A. | IATA: GV, Callsign: Sky Gabon, IATA Prefix: 536, | G | AVCODES |
| 5586 | SKG | Skycraft Air Transport, Inc. | IATA: 9F, Callsign: Skycraft Canada, Designator recalled by IATA | CDN | AVCODES |
| 5587 | SKG | Skycraft Air Transport | | | ICAO1 |
| 5588 | SKG | Srbija Kargo | | SR | TRAFFIC |
| 5589 | SKGC | S&S TRUCKING CO | | | SCAC1 |
| 5590 | SKGC | SAMBRAILO PACKAGING | | | SCAC4 |
| 5591 | SKGE | SHAKER GROUP INC | | | SCAC4 |
| 5592 | SKGF | S-T TRUCKING INC | | | SCAC4 |
| 5593 | SKGF | Ground Forces of the Slovak Republic | | SK | TRAFFIC |
| 5594 | SKGH | SKYLIGHT TRANSPORT | | | SCAC4 |
| 5595 | SKGJ | SCK LOGISTICS | | | SCAC4 |
| 5596 | SKGK | SOUTHERN TRUCKING & TRANSPORTATION | | | SCAC4 |
| 5597 | SKGM | SEATANKERS MANAGEM | | | SCAC4 |
| 5598 | SKGO | SHAMROCK AIR CARGO | | | SCAC1 |
| 5599 | SKGP | SPT LTD | | | SCAC4 |
| 5600 | SKGR | STOCK GRAIN INC | | | SCAC4 |
