Can't Remeber a Movie Title?

I was talking about a movie that I had seen a while back and could not remember the title of it. The main character finds out that Los Angeles is about to be nuked by the US Govt. He tries to tell people about it and receives a varied level of responses, which leads to some adventurous sub-plots. He manages to hire a helicopter and convinces some people to come with him, including what I thought was his girlfriend. Anyway, the big day comes and all hell breaks loose on the streets of L.A. shootings, s, pure anarchy. Well just after take-off in the helicopter, the explosion goes off and the pilot I think is killed and the chopper goes down in the La Brea tar pits or something like that. Does anyone know the movie name?