Airlines — U
- DOIU.S. Department of the Interior
- UCOUcoaviacion
- UESUes-Avia Aircompany
- UFSUFS
- UCCUganda Air Cargo
- UGAUganda Airlines
- RAUUganda Royal Airways
- HLEUK HEMS
- UKIUK International Airlines
- LPDUK Royal/HRH Duke of York
- UKLUkraine Air Alliance
- UKNUkraine Air Enterprise
- UATUkraine Atlantic
- AUIUkraine International Airlines
- TRBUkraine Transavia
- UKSUkrainian Cargo Airways
- UHLUkrainian Helicopters
- UPLUkrainian Pilot School
- UTSUkrainian State Air Traffic Service Enterprise
- ULTUltrair
- UHSUlyanovsk Higher Civil Aviation School
- UKMUM Airlines
- UIAUni Air
- UNCUni-Fly
- UNUUnifly Servizi Aerei
- LEAUnijet
- UAIUnion Africaine des Transports
- GIHUnion des Transports Africains de Guinee
- UNFUnion Flights
- UACUnited Air Charters
- UALUnited Airlines
- UBDUnited Airways
- UAFUnited Arab Emirates Air Force
- UABUnited Arabian Airlines
- UVNUnited Aviation
- SAUUnited Aviation Services
- UCSUnited Carriers Systems
- UEAUnited Eagle Airlines
- SDSUnited Kingdom Civil Aviation Authority
- UKPUnited Kingdom Home Office
- KRHUnited Kingdom Royal VIP Flight
- TQFUnited Kingdom Royal VIP Flights
- UPSUnited Parcel Service
- AIOUnited States Air Force
- CGXUnited States Coast Guard Auxiliary
- AGRUnited States Department Of Agriculture
- UMSUnitemp-M
- WECUniversal Airlines
- UVAUniversal Airways
- HBUUniversal Avia
- UNJUniversal Jet
- UJTUniversal Jet Aviation
- UJRUniversal Jet Rental de Mexico
- UAJUniversity Air Squadron
- UAYUniversity of Birmingham Air Squadron (RAF)
- NDUUniversity of North Dakota
- UNSUnsped Paket Servisi
- URVUraiavia
- SVRUral Airlines
- UTUUrartu-Air
- UGCUrgemer Canarias
- UCHUS Airports Air Charter
- USAUS Airways
- GKAUS Army Parachute Team
- USCUS Check Airlines
- USXUS Express
- USHUS Helicopter
- USJUS Jet
- MSHUS Marshals Service
- UBGUS-Bangla Airlines
- JUSUSA Jet Airlines
- ES2Usa Sky Cargo
- GWYUSA3000 Airlines
- DODUSAF Air Mobility Operations Control Center
- USFUSAfrica Airways
- UTGUTAGE
- UTAUTair Aviation
- UTRUtair South Africa
- UVMUvavemex
- UZBUzbekistan Airways