Suicide by a plane? [spoilers for Stealth]

Watched the movie Stealth yesterday. Exceptional special effects. That's the most memorable thing about the movie. Beside the fact that the AI plane committed suicide. Why ah? The plane could actually just shoot down the helicopter. No need to ram into it. If the 'machine gun' [dunno exact name of weapon] on the plane can be used to shoot down fighter jets, why not use it on a helicopter? Ish ish...