NOTE: I'm in the United States so for me this question is mostly about 'is it legal' in the US...
I often drive down to one of the access roads outside the fence line of the international airport in my town and take pictures of the commercial jets taking off and landing, the control tower, the ground equipment, etc. Although my purpose is completely benign (just like aircraft and aircraft related things), I've done this on a number of occasions, and I've never had guys in black Kevlar with H&Ks show up to haul me in for threatening 'Homeland Security,' I have wondered if what I'm doing is actually legal, or if I just 'haven't been caught yet.' Thoughts?
Assuming it is legal, if I were to do the exact same thing taking pictures of the military aircraft outside the fence line at the Air Force base in my town, can I expect a visit from FBI agents sporting black suits, dark sunglasses, and no sense of humor?