I'm playing Just Cause 2, but can't figure out how I should take down the helicopter in the mission where I need to protect the technichian. Any help?
Faction takeover missions, the ones that require you to protect a technician while trying he goes about hacking into the site's systems, usually end with a 'boss battle', where the site's commander comes attacking in a helicopter or armored vehicle.
At this point, look around for a mounted minigun, which can be detached by tapping the jump key (default: Space), so that you can aim upwards at the helicopter. This is the best option, as the minigun is extremely powerful and has unlimited ammo. If you can't find one, then you just have to make use with whatever is at hand. There should be a lot of dead guards around the area whose machine guns should be useful in taking down the helicopter. If you have the time (which you usually wouldn't), you can also look around to see if there's a helicopter nearby which you can use.