FlyUS (stylised as flyUS) is a prominent airline featured in the GTA IV Era and is also seen advertised in the second Grand Theft Auto V trailer. The company's slogan & motto tagline is: "Live a Little, Fly with US".
At Francis International Airport, there are many airlines promoting flights to Los Santos, Las Venturas and Vice City and FlyUS cars driving along such as the Feroci and the Perennial, as well as the Ripley and the Airtug. There are also taxis and buses which bear FlyUS advertisments. The airline's livery appears to be based off the United Airlines 1993-1997 "Battleship Grey" livery, though the name could be a joke towards US Airways. The design of the letters and colours also has a huge resemblance of that on FedEx's planes. Furthermore, the airline's resemblance might be a cross between Delta Air Lines and American Airlines, both in real life.A company named FlyUs does exist, however it is not a passenger airliner, and operates in the Netherlands and Belgium - Yet, the real life FlyUs logo does bear a stunning resemblance to the GTA FlyUS logo.
The FlyUS fleet includes a large amount of planes based off the 747-300 Boeing 747-300 jumbo jet and there are also some Shamal-like planes around Francis International Airport with the Fly US logo- Although only the Jumbo jets are seen flying (and also roaming around runways and taxiways) around Liberty City.
The name could be trying to say 'Fly US', a slang term for "Have Sex with US".
Trivia
There are five keychain viewfinders with pictures of Los Santos acquirable by pre-ordering the gamThe keychain viewfinders with the FlyUS logo.