Tower to control: ''The Aviator'' is cleared for takeoff. Finally. Over the years, several director-actor pairs have toyed with bringing the life of mogul Howard Hughes to the screen -- among them, Christopher Nolan and Jim Carrey, Milos Forman and Edward Norton, and Warren Beatty and...Warren Beatty. But the first team to take flight is Martin Scorsese and Leonardo DiCaprio, reuniting after winning critical plaudits with ''Gangs of New York.'' ''We tend to think of Howard Hughes near the end of his life in Las Vegas, the recluse, et cetera,'' says Scorsese, referring to Hughes' final career incarnation as a casino boss. ''This deals with him as a vibrant young man changing the world and fighting a disease that he didn't know he had: obsessive-compulsive disorder.'' The film also promises to detail Hughes' famous romantic conquests: Cate Blanchett plays Katharine Hepburn and Kate Beckinsale appears as Ava Gardner (Jude Law, meanwhile, shows up as Errol Flynn). ''It's terrifying to play a real person, especially one as beloved as Ava Gardner,'' Beckinsale says, ''because you know there's going to be 15 billion people going 'You completely got it wrong!'''The film's time span means we'll see DiCaprio age from 26 to 46. ''He goes from this extraordinarily handsome young man, full of life, to a man who's tortured by his own shortcomings,'' says Scorsese, who adds that he and DiCaprio now have a special shorthand together. ''It's almost getting like telepathy,'' says the director. The two other actors with whom Scorsese says he shares such a bond? ''De Niro and Keitel.''