UN aviation officials cautioned anyone Friday who might want to leave a gift of a drone under the Christmas tree this season, to learn how to safely operate it first. “Drones can pose a serious threat to manned flights and people and property on the ground,” the International Civil Aviation Organization (ICAO) said in a statement. In reaction to their growing popularity, the UN agency put out basic information on its website explaining what pilots of the unmanned aerial vehicles need to know before chasing Santa's sled.