| 1 | NK | Spirit Airlines, Inc. | ICAO: NKS, Callsign: Spirit Wings, IATA Prefix: 487, | USA | AVCODES |
| 2 | NK | Norcanair | IATA designator changed from SQ | CDN | AVCODES |
| 3 | NK | Air Vanuatu | ICAO: AVN, Callsign: Air Van, | VAN | AVCODES |
| 4 | NK | Niigata Kotsu Ltd. | | J | TRAFFIC |
| 5 | NK | Nordkalk AB | | SE | VKM |
| 6 | NKA | Northern Dene Airways Ltd. | IATA: U7, Callsign: Norcanair, Designator U7* recalled by IATA. Name changed from Norcanair | CDN | AVCODES |
| 7 | NKA | Anka Aviation Cargo | Callsign: Anka Cargo, | ET | AVCODES |
| 8 | NKAKR | Nadgoplańska Bus Transport in Kruszwica | City: Kruszwica | PL | TRAFFIC |
| 9 | NKAL | N | | | SCAC4 |
| 10 | NKAM | NK AMERICA INC | | | SCAC4 |
| 11 | NKAN | Nishitetsu Kanko Bus | | J | TRAFFIC |
| 12 | NKAR | NOR-AM GO KARTS INC | | | SCAC4 |
| 13 | NKAT | NKA TRANSPORTATION INC | | | SCAC4 |
| 14 | NKCK | NICKELS CARTAGE CO LTD | | | SCAC4 |
| 15 | NKCL | NIPPO KISEN CO LTD | | | SCAC3 |
| 16 | NKCM | NAKAMOTO, C MOVERS | | | SCAC3 |
| 17 | NKCM | NOBEK B V | | | SCAC4 |
| 18 | NKCN | N K C TRANSPORTATION LLC | | | SCAC4 |
| 19 | NKCO | NIELSEN, KNUD CO INC | | | SCAC3 |
| 20 | NKCR | Nebraska, Kansas & Colorado RailNet, Inc. | added 1/1999; 7/2000-7/2005 | | NAKINA |
| 21 | NKCR | Nebraska, Kansas & Colorado RailNet, Inc. | added 1/99; 7/2000 | | NRHS |
| 22 | NKCR | NEBRASKA, KANSAS & COLORADO RAILNET INC | | | PWRC |
| 23 | NKCR | Nebraska, Kansas and Colorado Railnet | | | RSRV |
| 24 | NKCR | NEBRASKA KANSAS & COLORADO RAILNET | | | SCAC4 |
| 25 | NKCU | NINGXIA KING CHEMICAL CO LTD | | | SCAC4 |
| 26 | NKE | Napkelet Airlines | Callsign: Sun East, | H | AVCODES |
| 27 | NKEIB | New Keisei Bus | | J | TRAFFIC |
| 28 | NKEL | NUNEZ TRUCKING | | | SCAC4 |
| 29 | NKEQ | NICKY WAREHOUSES INC | | | SCAC3 |
| 30 | NKF | Nordkalottflyg AB | IATA: 8N, Callsign: Nordflight, Designator 8N* recalled by IATA. Designator 8N* reinstated by IATA | S | AVCODES |
| 31 | NKF | Barents AirLink | IATA: 8N | | ICAO1 |
| 32 | NKFA | NEUDORF, KARL FARMS | | | SCAC4 |
| 33 | NKFI | NORTHUP, FREDERICK INC | | | SCAC4 |
| 34 | NKFL | NORSK FLYFRAKT A S | | | SCAC3 |
| 35 | NKH | Norsk Helikopterservice AS | Callsign: Helinor, | N | AVCODES |
| 36 | NKIA | NORM KERKHOF INCORPORATED | | | SCAC4 |
| 37 | NKIC | NOLTE KITCHENS INC | | | SCAC4 |
| 38 | NKIE | NICKI ENTERPRISES INC | | | SCAC3 |
| 39 | NKIE | NORTH RIVER TRUCKING INC | | | SCAC4 |
| 40 | NKIM | NORKIM DISTRIBUTORS LTD | | | SCAC4 |
| 41 | NKIT | NORMAC KITCHENS LTD | | | SCAC4 |
| 42 | NKIX | Nipak, Inc. | added 4/1966; 10/1966-1/1980; eliminated 10/1980 | | NAKINA |
| 43 | NKIX | Nipak, Inc. | added 4/66; 10/66-1/80; eliminated 10/80 | | NRHS |
| 44 | NKIX | NIPAK, INC. | | | PWRC |
| 45 | NKJ | Nakskov - Kragenæs Jernbane (Kragenæsbanen) | 1915 - 1967 | DK | jernbanen.dk |
| 46 | NKJ | Nora - Karlskoga Järnväg | 1874 - 1905 | S | svenska-lok.se |
| 47 | NKJ | Nakskov - Kragenæs Jernbane (Kragenæsbanen) | 1915 - 1967 | DK | TRAFFIC |
| 48 | NKJT | NEAL, K J TRUCKING INC | | | SCAC4 |
| 49 | NKK | Nihon Kinkyori Airways | IATA: WJ, Callsign: Kinkyiro, Name changed to Air Nippon Co. Ltd. | J | AVCODES |
| 50 | NKK | Air Nippon Co. Ltd. | IATA: WJ, Callsign: Ank Air, ICAO designator changed to ANK. Name changed from Nihon Kinkyori Airways. | J | AVCODES |
| 51 | NKKU | NOK SHIPPING LINE LLC | | UAE | BIC |
| 52 | NKL | Istithmar World Aviation | Callsign: Nakheel, | UAE | AVCODES |
| 53 | NKL | Nakheel Aviation | | | ICAO1 |
| 54 | NKLB | NICKELS BROKERAGE INC | | | SCAC4 |
| 55 | NKLC | NYKCOOL USA INC | | | SCAC4 |
| 56 | NKLL | NICKEY LOGISTICS LLC | | | SCAC4 |
| 57 | NKLU | NORTHERN LIGHTS SHIPPING | | GR | BIC |
| 58 | NKLU | NORTHERN LIGHTS SHIPPING CO. | | | SCAC3 |
| 59 | NKLU | NORTHERN LIGHTS SHIPPING | | | SCAC4 |
| 60 | NKLV | NICKERSON LIVESTOCK | | | SCAC4 |
| 61 | NKMQ | NIKOLAY MALAKHOV SHIPPING CO LTD, T | | | SCAC3 |
| 62 | NKMS | NEWHOUSE | | | SCAC4 |
| 63 | NKMT | N K M TRUCKING | | | SCAC4 |
| 64 | NKNO | NAKANO EXPRESS SERVICE, Nakano Warehouse and Transportation Corp | | | SCAC1 |
| 65 | NKNO | NAKANO EXPRESS SERVICE | | | SCAC4 |
| 66 | NKNU | PJSC NIZHNEKAMSKNEFTEKHIM | | RUS | BIC |
| 67 | NKOR | NONNEMAN, KORY | | | SCAC4 |
| 68 | NKOU | NIKOU SHIPPING | | | SCAC3 |
| 69 | NKP | Abakan Air LLC | IATA: S5, Callsign: Abakan Air, IATA Prefix: 917, | RUS | AVCODES |
| 70 | NKP | Norfolk Southern Ry. Co. (Norfolk Southern) | 7/2005 | | NAKINA |
| 71 | NKP | Norfolk Southern Ry. Co. | added 1/1991; 1/1994-7/2000 | | NAKINA |
| 72 | NKP | Norfolk and Western Ry. Co. | 1/1975-1/1980; eliminated 1/1991 | | NAKINA |
| 73 | NKP | New York, Chicago & St. Louis R.R. (Norfolk and Western Ry. Co.) | 7/1965-10/1966 | | NAKINA |
| 74 | NKP | New York, Chicago & St. Louis R.R. | 7/1954-4/1961 | | NAKINA |
| 75 | NKP | New York, Chicago & St. Louis R.R. (Nickel Plate Road) | 4/1938-1/1952 | | NAKINA |
| 76 | NKP | New York, Chicago & St. Louis R.R. Co. (Nickel Plate Road) | 7/1923-7/1936 | | NAKINA |
| 77 | NKP | New York, Chicago & St. Louis R.R. Co. | 8/1920 | | NAKINA |
| 78 | NKP | New York, Chicago & St. Louis R.R. (Nickel Plate Road) | 4/38-1/52 | | NRHS |
| 79 | NKP | New York, Chicago & St. Louis R.R. | 10/57-4/61 | | NRHS |
| 80 | NKP | New York, Chicago & St. Louis R.R. (Norfolk and Western Ry. Co.) | 7/65-10/66 | | NRHS |
| 81 | NKP | Norfolk and Western Ry. Co. | 1/75-1/80; eliminated 1/91 | | NRHS |
| 82 | NKP | Norfolk Southern Ry. Co. | added 1/91; 1/94-7/2000 | | NRHS |
| 83 | NKP | NORFOLK SOUTHERN RWY. [NORFOLK & WESTERN RY.; NEW YORK, CHICAGO & ST. LOUIS RR (NICKEL PLATE ROAD)] | | | PWRC |
| 84 | NKP | New York, Chicago and St. Louis Railroad (Norfolk Southern) | | | RSRV |
| 85 | NKP | New York, Chicago & St. Louis R.R. (Nickel Plate Road) | | USA | TRAFFIC |
| 86 | NKPE | NICKLE PLATE EXPRESS | | | SCAC3 |
| 87 | NKPE | NICKLE PLATE EXPRESS | | | SCAC4 |
| 88 | NKRA | NICKSON-RAMPLEY INC | | | SCAC3 |
| 89 | NKRD | NIKRANDT, ROBERT C.&DAUGHTERS TRUCKING CO | | | SCAC3 |
| 90 | NKRI | NJIRICH, KENNETH R INC | | | SCAC3 |
| 91 | NKRI | NANKAI TRANSPORT INTERNATIONAL USA | | | SCAC4 |
| 92 | NKRS | N K R S | | | SCAC4 |
| 93 | NKS | Spirit Airlines, Inc. | IATA: NK, Callsign: Spirit Wings, IATA Prefix: 487, | USA | AVCODES |
| 94 | NKS | Spirit Airlines | IATA: NK | | ICAO1 |
| 95 | NKSC | NIKEA SHIPPING COMPANY LTD CYPRUS | | | SCAC3 |
| 96 | NKSC | NAKKAS SHIPPING & TRADING CO LTD | | | SCAC4 |
| 97 | NKSK | NEKOROSKI OIL COMPANY INC | | | SCAC4 |
| 98 | NKSL | NORTHERN KING SHIPPING CO, LTD. | | | SCAC3 |
| 99 | NKSL | NORTHERN KING SHIPPING CO, LTD. | | | SCAC4 |
| 100 | NKSM | NICKS MOVERS | | | SCAC3 |
