Done on mission Russia and Roxxon (mission 2.) Obviously done on the easiest difficulty will make this easy. However if your still having problems, run through with War Machine and Two mini guns. Fly as far ahead of the convoy as you can and take down anything and everything. Keep an eye on the radar incase some enemies show up behind you. The ground based missles are more important to destroy than the helicopters. If you stay out in front you shouldn't have a big problem.