| 1 | D | DampfPlus GmbH | Halle | D | privat-bahn.de |
| 2 | D | Rheinbahn AG | City: Düsseldorf | D | TRAFFIC |
| 3 | D&CI | Des Moines & Central Iowa R.R. | 7/1923-7/1936 | | NAKINA |
| 4 | D&CI | Des Moines & Central Iowa R.R. | 23-Jul | | NRHS |
| 5 | D&CI | DES MOINES & CENTRAL IOWA RAILROAD | | | PWRC |
| 6 | D&D | D & D Eisenbahngesellschaft mbH | Hagenow Land (D&D = Dehns und Dehns) | D | privat-bahn.de |
| 7 | D&H | Delaware and Hudson R.R. Corp. | 1/1941-10/1966 | | NAKINA |
| 8 | D&H | Delaware and Hudson R.R. Corp. | 1/52-10/66 | | NRHS |
| 9 | D&H | CANADIAN PACIFIC RAILWAY [DELAWARE & HUDSON RAILROAD CORP.] | | | PWRC |
| 10 | D&IM | Denver & Intermountain R.R. Co. | 8/1920-1/1946; 1/1952 | | NAKINA |
| 11 | D&IM | Denver & Intermountain R.R. Co. | 7/23-1/52 | | NRHS |
| 12 | D&IM | DENVER & INTERMOUNTAIN RAILROAD CORP. | | | PWRC |
| 13 | D&IR | (The) Duluth & Iron Range R.R. (Co.) | 8/1920-7/1954 | | NAKINA |
| 14 | D&IR | The Duluth & Iron Range R.R. Co. | 23-Jul | | NRHS |
| 15 | D&IR | Duluth & Iron Range R.R. | 4/38-1/52 | | NRHS |
| 16 | D&IR | DULUTH & IRON RANGE RAILROAD CO. | | | PWRC |
| 17 | D&M | Detroit & Mackinac Ry. | 8/1920-4/1961 | | NAKINA |
| 18 | D&M | Detroit & Mackinac Ry. | 7/23-4/61 | | NRHS |
| 19 | D&M | LAKE STATE RAILWAY CO. [DETROIT & MACKINAC RY] | | | PWRC |
| 20 | D&MM | (The) Dansville & Mount Morris R.R. (Co.) | 8/1920-4/1938 | | NAKINA |
| 21 | D&MM | The Dansville & Mount Morris R.R. Co. | 23-Jul | | NRHS |
| 22 | D&MM | Dansville & Mount Morris R.R. Co. | Apr-38 | | NRHS |
| 23 | D&MM | DANSVILLE & MT. MORRIS RAILROAD CO. | | | PWRC |
| 24 | D&N | Delaware & Northern Ry. | 1/1941 | | NAKINA |
| 25 | D&N | Delaware & Northern Ry. (Co.) | 7/1930-4/1938 | | NAKINA |
| 26 | D&N | Delaware & Northern R.R. Co. | 8/1920-7/1923 | | NAKINA |
| 27 | D&N | Delaware & Northern R.R. Co. | 23-Jul | | NRHS |
| 28 | D&N | Delaware & Northern R.R. | Apr-38 | | NRHS |
| 29 | D&N | *DELAWARE & NORTHERN RWY. | | | PWRC |
| 30 | D&N | *NEW YORK CENTRAL [DEXTER & NORTHERN RR] | | | PWRC |
| 31 | D&RG | Denver & Rio Grande Western R.R. Co. | 7/1932 | | NAKINA |
| 32 | D&RG | Denver & Rio Grande Western R.R. System | 7/1923 | | NAKINA |
| 33 | D&RG | Denver & Rio Grande Western R.R. System | 23-Jul | | NRHS |
| 34 | D&RG | DENVER & RIO GRANDE WESTERN RAILROAD | | | PWRC |
| 35 | D&RGW | Denver & Rio Grande Western R.R. (Co.) | 7/1930-10/1966 | | NAKINA |
| 36 | D&RGW | Denver & Rio Grande Western R.R. | 4/38-10/66 | | NRHS |
| 37 | D&RGW | DENVER & RIO GRANDE WESTERN RAILROAD | | | PWRC |
| 38 | D&S | DILLONVALE & SMITHFIELD RWY | | | PWRC |
| 39 | D&SL | Denver & Rio Grande Western R.R. | 4/1961-7/1965 | | NAKINA |
| 40 | D&SL | Denver & Salt Lake Ry. (Co.) | 8/1920-10/1957 | | NAKINA |
| 41 | D&SL | Denver & Salt Lake Ry. Co. | 23-Jul | | NRHS |
| 42 | D&SL | Denver & Salt Lake Ry. | 4/38-10/57 | | NRHS |
| 43 | D&SL | Denver & Rio Grande Western R.R. | 4/61-7/65 | | NRHS |
| 44 | D&SL | *DENVER & SALT LAKE rWY. CO. | | | PWRC |
| 45 | D&SL | *DENVER & RIO GRANDE WESTERN RAILROAD | | | PWRC |
| 46 | D&TS | Detroit & Toledo Shore Line R.R. (Co.) | 8/1920-4/1961 | | NAKINA |
| 47 | D&TS | Detroit & Toledo Shore Line R.R. Co. | 23-Jul | | NRHS |
| 48 | D&TS | Detroit & Toledo Shore Line R.R. | 4/38-4/61 | | NRHS |
| 49 | D&TS | DETROIT & TOLEDO SHORE LINE RAILROAD CO. | | | PWRC |
| 50 | D&W | Danville & Western Ry. | 4/1938-1/1950 | | NAKINA |
| 51 | D&W | Danville & Western Ry. Co. (Southern Ry. System) | 8/1920-7/1936 | | NAKINA |
| 52 | D&W | Danville & Western Ry. (Southern Ry. System) | 23-Jul | | NRHS |
| 53 | D&W | Danville & Western Ry. | Apr-38 | | NRHS |
| 54 | D&W | SOUTHERN RAILWAY {DANVILLE & WESTERN RAILWAY CO.} | | | PWRC |
| 55 | D0 | DHL Air Limited | ICAO: DHK, Callsign: World Express, IATA Prefix: 936, | GB | AVCODES |
| 56 | D1 | Alidaunia S.R.L. | ICAO: LID, Callsign: Alida, IATA designator changed to D4* | I | AVCODES |
| 57 | D1 | AIR4 Passenger Service Systems, LLC | Computer Reservation System | USA | AVCODES |
| 58 | D2 | Severstal Joint Stock Company | ICAO: SSF, Name changed to Severstal Aircompany Ltd. | RUS | AVCODES |
| 59 | D2 | Skyline NEPC Ltd. | ICAO: SKV, Callsign: Skyflyer, Designator D2 recalled by IATA | IND | AVCODES |
| 60 | D2 | Severstal Aircompany Ltd. | ICAO: SSF, Callsign: Severstal, Name changed from Severstal Joint Stock Company | RUS | AVCODES |
| 61 | D3 | Daallo Airlines | ICAO: DAO, Callsign: Dalo Airlines, IATA Prefix: 991, | DJI | AVCODES |
| 62 | D4 | Alidaunia S.R.L. | ICAO: LID, Callsign: Alida, IATA designator changed from D1 | I | AVCODES |
| 63 | D4 | Dart Limited Trust Distribution | ICAO: DAT, Callsign: Dartlimited, Suspended operations during February 2018. Assets requested to be transferred to new airline called LLC Alanna. | UA | AVCODES |
| 64 | D4 | Airline Geo Sky LLC | ICAO: GEL, Callsign: Sky Georgia, IATA Prefix: 330, | GE | AVCODES |
| 65 | D4 | Airline Geo Sky LLC | ICAO: GEL, Callsign: Sky Georgia, IATA Prefix: 330, | GE | AVCODES |
| 66 | D5 | DHL Aero Expreso, S.A. | ICAO: DAE, IATA Prefix: 992, Designator D5* recalled by IATA. IATA designator changed from DS* | PA | AVCODES |
| 67 | D5 | NEPC Airlines ( A Division of NEPC Micon Limited) | ICAO: NEP, Callsign: Nepcair, Designator D5 recalled by IATA | IND | AVCODES |
| 68 | D5 | Dau Air Verwaltungs AG | ICAO: DAU, Callsign: Dauair, Ceased operations on 16 August 2006. | D | AVCODES |
| 69 | D6 | Inter-Aviation Services d/b/a Inter-Air | ICAO: ILN, Callsign: Inline, IATA Prefix: 625, Name changed to Inter-Aviation Services d/b/a Interair South Africa | ZA | AVCODES |
| 70 | D6 | Inter-Aviation Services d/b/a Interair South Africa | ICAO: ILN, Callsign: Inline, IATA Prefix: 625, Name changed from Inter-Aviation Services d/b/a Inter-Air | ZA | AVCODES |
| 71 | D6 | Servicios Aereos GECA S.A. d/b/a GECA | ICAO: GCA, Callsign: Aerogeca, | DOM | AVCODES |
| 72 | D7 | Dinar Lineas Aereas, S.A. | ICAO: RDN, Callsign: Aero Dinar, IATA Prefix: 429, Ceased operations on 30 September 2002. | RA | AVCODES |
| 73 | D7 | Fly Asian Express Sdn Bhd | ICAO: XFA, IATA Prefix: 843, Name changed to AirAsia X Sdn Bhd. | MAL | AVCODES |
| 74 | D7 | Airasia X Berhad d/b/a Airasia X | ICAO: XAX, Callsign: Xanadu, IATA Prefix: 843, Name changed from Fly Asian Express Sdn Bhd | MAL | AVCODES |
| 75 | D8 | Djibouti Airlines | ICAO: DJB, Callsign: Djibouti Air, Designator D8 reinstated by IATA | DJI | AVCODES |
| 76 | D8 | Norwegian Air International Ltd. | ICAO: IBK, Callsign: Nortrans, IATA Prefix: 329, IATA designator changed to D8 | IRL | AVCODES |
| 77 | D8 | Norwegian Air International Ltd. | ICAO: IBK, Callsign: Nortrans, IATA Prefix: 329, IATA designator changed from D8* | IRL | AVCODES |
| 78 | D8 | Norwegian Air Sweden AOC AB | ICAO: NSZ, Callsign: Norlight, ICAO Callsign changed to Rednose. | S | AVCODES |
| 79 | D8 | Norwegian Air International Ltd. | ICAO: IBK, Callsign: Nortrans, IATA designator changed from D8* | IRL | AVCODES |
| 80 | D8 | Norwegian Air Sweden AOC AB | ICAO: NSZ, Callsign: Rednose, ICAO Callsign changed from Norlight. | S | AVCODES |
| 81 | D9 | Joint stock Aviation Company Donavia | ICAO: DNV, Callsign: Donavia, Operates as Aeroflot-Don. Name changed to Joint stock Company Donavia | RUS | AVCODES |
| 82 | D9 | Joint stock Company Donavia | ICAO: DNV, Callsign: Donavia, IATA Prefix: 733, Merged into Rossiya Airlines JSC (FV/SDM) w.e.f. 26 May 2016. Name changed from Joint stock Aviation Company Donavia operation as Aeroflot-Don | RUS | AVCODES |
| 83 | D9 | Dena Airways | ICAO: DAI, Callsign: Dena, IATA Prefix: 313, | IR | AVCODES |
| 84 | D9 | Daallo Airlines (Somalia) | ICAO: DMQ, Callsign: Dalo, | SO | AVCODES |
| 85 | DA | Air Georgia | ICAO: GEO, Callsign: Air Georgia, ICAO designator changed from DAN | GE | AVCODES |
| 86 | DA | Dan-Air Services Ltd. | ICAO: DAN, Callsign: Danair, Merged into British Airways European Operations Gatwick B.A.E.O.G. | GB | AVCODES |
| 87 | DA | Air Georgia | ICAO: DAN, Callsign: Air Georgia, Merged into Aircompany Airzena Georgian Airlines. Designator DA recalled by IATA | GE | AVCODES |
| 88 | DA | Canadian Pacific Ry. Co. | added 1/1997; 7/2000-7/2005 | | NAKINA |
| 89 | DA | CP Rail System | eliminated 1/1997 | | NAKINA |
| 90 | DA | CP Rail | 1/1994 | | NAKINA |
| 91 | DA | CP Rail (Dominion Atlantic Ry. Co.) | 1/1975-1/1980 | | NAKINA |
| 92 | DA | Dominion Atlantic Ry. Co. | 8/1920-10/1966 | | NAKINA |
| 93 | DA | Dominion Atlantic Ry. Co. | 7/23-10/66 | | NRHS |
| 94 | DA | CP Rail (Dominion Atlantic Ry. Co.) | 1/75-1/80 | | NRHS |
| 95 | DA | CP Rail | Jan-94 | | NRHS |
| 96 | DA | CP Rail System | eliminated 1/97 | | NRHS |
| 97 | DA | Canadian Pacific Ry. Co. | added 1/97; 7/2000 | | NRHS |
| 98 | DA | CP RAIL [DOMINION ATLANTIC RY.] | | | PWRC |
| 99 | DA | Dominion Atlantic Railway (Canadian Pacific Railway) | | | RSRV |
| 100 | DA | Dominion Atlantic Ry. Co. | | CDN | TRAFFIC |
