No doubt, you've heard of old elephants that stray off to die in a particular public location, sort of an elephant cemetery. Similar ideas apply in south central Tucson, the boneyard, the center of the Sonoran Desert, where obsolete planes repose in place of old pachyderms. Almost everyone in the aviation community is aware of the Air Force's "Boneyard," a 2,600-acre desert area in Arizona where thousands of retired military aircraft wait out their final days in silence.