Sorry for the length. I live in a very rural town. It's in a valley maybe two miles wide where The Green Mtns and Appalachian Mountains flank both sides. There is one tiny, old runway in town where I would guess a plane takes off once a month. You can always hear when a plane is nearby because the sound bounces off the mountains. Once in a while a military plane will also fly overhead. The lowest flying plane I have ever seen is probably a 1000ft. Usually very small prop planes taking off or going to the airport or an airport in a neighboring town. Until today I never thought for a second I would need to worry or even think about it. I know we have pilots here on these forums and I hope one of them can chime in. I was standing in the living room of a customer's house house today when she said" Oh look, there's Bob!!" (not real name). From the window, I see a big green plane, flying very LOW! I would definitely say below 500ft no doubt. I run to the window in an adjacent room to see the plane bank hard right and continue up the valley and out of sight. I turned around and asked, "Who?" She told me he was a Civil Air Pilot that grew up in the town. Apparently his father was also a pilot who crashed in a freak storm years and years ago and when ever he's in the area he flies over his mother's house and tips a wing. Touching story but he was LOW, and what makes this crazy to me is that this is a place I frequently fly. I guarantee I have flown within 100ft of his line today. Now I know I'm not supposed to fly above 400ft and I thought "they" weren't supposed to fly below 1000ft. What am I missing? What I really want to know is the legality of this. He was absolutely not taking off or landing anywhere within 50 miles of where I saw him. Is he allowed to fly that low? There are no NFZ's anywhere around me. He was flying pretty fast and came out of nowhere. Can anyone clarify the laws as it pertains to this? Thanks.