Federal law requires that all airplanes, helicopters, blimps, and other airborne craft file a flight plan before leaving the ground. Joe farmer has been using his airplane to dust crops for years and has never filed a flight plan. Last year he was approached by a federal aviation officer and warned that failure to comply could result in a fine or imprisonment or both. Joe's response was "Ah'm only flyin' over mah own land, so you can go fly a kite!" Is the federal law valid?