Martin Scorsese is probably the closest thing we have to an American filmmaking icon, particularly since Francis Ford Coppola has apparently retired to his vineyards and his Belize resort, but it's hard to put a finger on just why. In the course of a thirty-five year career he seems to have alternated between brilliance and tedium, from the powerful "Alice Doesn't Live Here Anymore" and "Taxi Driver" to the tedious "New York, New York;" from the force of "Raging Bull" to the turgid "Last Temptation of Christ;" from the dark wit of "Goodfellas" to the dull lives of "The Age of Innocence;" and finally from the brilliance of "Casino" to the unwatchable "Gangs of New York." All of them, good or bad, seem to show a kind of edginess, what might be called a filmmaker's insecurity about his work; you're never quite sure that Scorsese himself is confident about what he's doing. Sometimes that insecurity gives his films power, sometimes it drags them down.

His new film, "The Aviator," though, seems more relaxed and secure than any others I can recall. And that may be because it turns out not to be a 'Scorsese' film at all; it's a contract job for Warner Bros. and Miramax, which jointly own the film. It was written by John Logan ("Gladiator," "The Last Samurai"), who had never worked with Scorsese, and it was originally to be directed by Michael Mann, who had other commitments and asked Scorsese to take his place. I point this out because Scorsese, taking over someone else's film, has done a beautiful job with a movie that is unlike anything he's ever done before.

If people know Howard Hughes today it's because of his death and not his life: the well-publicized years of madness, of isolated luxury on the top floors of a Las Vegas casino, never emerging, growing endless fingernails and eating nothing but peas and milk, protected by Mormon cohorts who denied access to any outsider. But the film, starring the unlikely Leonardo DiCaprio as Hughes, begins with a suggestively incestuous scene of the child Howard (a bit too old, being bathed intimately by his mother), then cuts to the wealthy Texas playboy - he inherited millions at the age of eighteen - who moves to Los Angeles because he wants to make movies.

And so he does, starting with "Hell's Angels," a World War I aviation film, begun as a silent in 1928 but converted at his great expense into a sound film and released in 1930. Scorsese fills the screen with Hughes's dogfight footage, projected behind him as he directs the editing in what will become his manic, compulsively controlling style; it's the beginning stages of a madness that so far is seen only in his work, where in fact it is useful. In the Hollywood years he's all over town with Jean Harlow and then with Katharine Hepburn (Cate Blanchett, who looks nothing like Hepburn but has captured that tall, mannish, free-swinging style and voice). He's designing new airplanes, test-piloting them - including a CGI crash into some Beverly Hills homes that nearly kills him - setting a new airspeed record, and, when World War II comes, trying for government contracts to build warplanes. What would be his monument, he hopes, is the enormous Hercules transport plane, but it becomes a millstone around his neck. And by this time he's trying to control the life of his last lover, Ava Gardner (Kate Beckinsale), with bugs in her house and on her phone, promising her jewels (she tells him "I'm not for sale; buy me dinner.").

The film follows him into his confrontations with Juan Trippe (Alec Baldwin), the head of Pan Am, who tries to destroy Hughes's TWA with the help of a senator on his payroll (Alan Alda). And increasingly the demons are attacking Hughes, giving him Tourette-like repetitions of speech, phobias about cleanliness and more.

All of this is in the film, but the brilliance of "The Aviator," and it is a brilliant film, lies in Scorsese's direction and the exquisite editing of his longtime collaborator Thelma Schoonmaker, who can combine images and reveal subtleties like no one else working today. The film, though it covers more than twenty years, is seamless and always clear; there are shots in screening rooms where we can take in both what's being projected and what's live in front of the screen, and each enhances the other. Scorsese has always had a tendency to rely on conventional cross-cutting in conversational scenes, going back and forth from one person to the other, rather than trusting his camera to hold on one key player at important moments; but Schoonmaker has minimized it here.