Dan - when did the professor give you the suit to get into X16? I successfully escorted the guy to take the measurements, went back to the professor and then found the corpse by the helicopter but didn't receive a suit so can't get in to lab X16...
Watch from around 7:50. This is how I got in during my most recent playthrough. Note that I'm not anywhere near the helicopter by the swamp.
https://www.youtube.com/watch?v=lsrKkQXo2rg&index=21&list=PLpjJkR6CPffhDChRmbS5Sox1u5CFayl58