Well, anyone who wants some quiet time living on the departure or arrival path now has a very easy way to do that. Simply home build your own multicopter/flying wing and program a flightpath close to the airport. Not traceable since not actually radio controlled, and GPS is not necessary either, there is always GLONASS and Galileo, not to mention Baidu. Or simply terrain recognition, a childs play with todays system, a simply raspy can do that.