| ICAO | IATA | NAME |
|---|
| DOI | | U.S. Department of the Interior |
| UCO | | Ucoaviacion |
| UES | | Ues-Avia Aircompany |
| UFS | | UFS |
| UCC | | Uganda Air Cargo |
| UGA | | Uganda Airlines |
| RAU | | Uganda Royal Airways |
| HLE | | UK HEMS |
| UKI | | UK International Airlines |
| LPD | | UK Royal/HRH Duke of York |
| UKL | | Ukraine Air Alliance |
| UKN | | Ukraine Air Enterprise |
| AUI | PS | Ukraine International Airlines |
| TRB | | Ukraine Transavia |
| UKS | 6Z | Ukrainian Cargo Airways |
| UHL | | Ukrainian Helicopters |
| UPL | | Ukrainian Pilot School |
| UTS | | Ukrainian State Air Traffic Service Enterprise |
| ULT | | Ultrair |
| UHS | | Ulyanovsk Higher Civil Aviation School |
| UKM | UF | UM Airlines |
| US | Unavia Suisse |
| UNC | | Uni-Fly |
| UNU | | Unifly Servizi Aerei |
| LEA | | Unijet |
| UAI | | Union Africaine des Transports |
| GIH | | Union des Transports Africains de Guinee |
| UNF | | Union Flights |
| UAC | | United Air Charters |
| UAL | UA | United Airlines |
| UAF | | United Arab Emirates Air Force |
| UAB | | United Arabian Airlines |
| UVN | | United Aviation |
| SAU | | United Aviation Services |
| UCS | | United Carriers Systems |
| UEA | | United Eagle Airlines |
| U2 | United Feeder Service |
| SDS | | United Kingdom Civil Aviation Authority |
| EXM | | United Kingdom Civil Aviation Authority |
| CFU | | United Kingdom Civil Aviation Authority |
| UKP | | United Kingdom Home Office |
| KRH | | United Kingdom Royal VIP Flight |
| KRF | | United Kingdom Royal VIP Flights |
| TQF | | United Kingdom Royal VIP Flights |
| UPS | 5X | United Parcel Service |
| AIO | | United States Air Force |
| CGX | | United States Coast Guard Auxiliary |
| AGR | | United States Department Of Agriculture |
| UMS | | Unitemp-M |
| WEC | | Universal Airlines |
| PNA | | Universal Airlines |
| UVG | | Universal Airlines |
| UVA | | Universal Airways |
| HBU | | Universal Avia |
| UNJ | | Universal Jet |
| UJT | | Universal Jet Aviation |
| UJR | | Universal Jet Rental de Mexico |
| UAD | | University Air Squadron |
| UAJ | | University Air Squadron |
| UAA | | University Air Squadron |
| UAH | | University Air Squadron |
| NDU | | University of North Dakota |
| UNS | | Unsped Paket Servisi |
| URV | | Uraiavia |
| SVR | U6 | Ural Airlines |
| UTU | | Urartu-Air |
| UGC | | Urgemer Canarias |
| UCH | | US Airports Air Charter |
| AWE | US | US Airways |
| GKA | | US Army Parachute Team |
| USC | | US Check Airlines |
| USX | | US Express |
| USH | | US Helicopter |
| UH | US Helicopter Corporation |
| USJ | | US Jet |
| MSH | | US Marshals Service |
| JUS | U7 | USA Jet Airlines |
| GWY | U5 | USA3000 Airlines |
| QID | | USAF 100th Air Refuelling Wing |
| DOD | | USAF Air Mobility Operations Control Center |
| USF | | USAfrica Airways |
| US | USAir |
| US* | USAir Express |
| UTG | | UTAGE |
| UTA | UT | UTair Aviation |
| UTR | | Utair South Africa |
| UVM | | Uvavemex |
| UZB | HY | Uzbekistan Airways |
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