I've been flying at my local park, always keeping the quad-copter under 400ft. Unlike many pilots (!), I am pretty cautious because I don't want to kill anyone. However, twice now low-flying small planes have buzzed by my quad-copter, appearing to be uncomfortably close. It seems they like to fly around this particular park, probably for its views of the lake, etc... Today one buzzed by, didn't hear it until it was right above me. It looked about the same altitude as the quadcopter. It was really scary. Are small aircraft pilots required to stay above 400ft altitude? Or is it up their discretion? I just want to make sure I'm the heck out of their way, as I fear they may not be able to see a quad-copter in the daylight.