Well, it's hard to say for sure. 'Aviator' could be entirely fictional, or it might be loosely based on some true events or real-life aviators, but with significant alterations for the sake of the story.
The Aviator does have a basis in truth. It tells the story of Howard Hughes, though some artistic liberties were likely taken to make it more engaging for the audience.
In fact, 'Aviator' draws heavily from true events, though some artistic liberties might have been taken for dramatic effect. But the core elements are based on reality.
The movie blends fact and fiction by basing the main story on Hughes' real life in aviation but adding fictional elements for drama. For example, his real flights are there, but some of the in - flight tensions could be fictional.
One major fact is Howard Hughes' real achievements in aviation. He really built innovative planes. In fiction, some of the more dramatic personal relationships might be exaggerated for the movie. For example, the way his relationships with certain characters are depicted might not be entirely as they were in real life.