These solutions are sound but the most important part of this mission is the helicopter. It will leave and leave fast. You need to head straight there and tag it before you do much of anything else. I'd recommend a team of 4 or more and take out the guys on the cliff to the left 1st. Quickly make you way to the right towards the helicopter and get a dude or 2 to run in there n tag it. After that it's easy going.