Speaking from a avid plane spotter experience, you can use camera or camcorder within the terminal common area.
If you point your equipment towards staff entrance etc, or record a single location for prolong period of time with no particular subject in view, then they will tell you off or even escort you to their security office.
Using of camera or camcorder around the perimeter is strictly prohibited and may also send you into their security office as well. I've been there done that. :bsmilie: