I always laugh at this title :) This is really easy. Your only aim is to go back down the way you just came, to get to the ship which is now waiting for you in the hangar area. Go right back down the same passageways to get to the big hangar area. You can now press X to activate the ship, and he flies you out. There's a cool video of him squishing 2 enemies with the ship before flying away to safety.

Master Halo Walkthrough