Maker sure you're fully stocked on Frags and Plasmas before you go down (there's a cache of frags on the floor with the hunters. The elites on the bottom floor should drop plenty of grenades as well.) Assuming you killed everything before activating the map, there should be no enemies on this floor. On your way up to the next floor, you’ll be stormed by 2 jackals on the rampway. Usually a frag makes good work of them. After leaving the ramp room, a door to the right will lead down another ramp and a camo should be just at the exit. Use it and you can easily bypass the entire floor - just make sure you beat down any pesky elites you run into on your way. On the next floor you’ll have an elite and a few grunts. A frag is good for that followed with a melee to put the elite down for good. Go up the final ramp to the top floor and immediately to your right will be your exit blocked by an elite. Pop a grenade in there and make a run for the tunnel (if he doesn't die, he shouldn't follow you.) Go around the next turn and you'll be blocked by a Gold Sword Elite. As he taunts you quickly stick him with a plasma grenade. All you have left now is a few invisible elites at the very top of the structure. Lure them over one at a time and beat or grenade them to death and you’re path to the pelican will be open!
Grenade Jump trick: IF you're any good at grenade jumping, instead of going up to the second floor from the map room, there will be a small room across the way. Two jackals will be on the platform above. Take them out with a grenade, than grenade jump up and you'll be right next to the aforementioned camo pickup. This is a good way to prevent the entire room from being alerted.
Note: If you've got it, Grunt Funeral skull is excellent for this scene because a single frag can set off a decent chain reaction of grunts if time it right.