U.S. aviation regulators were looking into whether a U.S. pilot broke any rules when he entered Cuban airspace with a small rented plane and dropped leaflets over Havana that called President Fidel Castro an "old dinosaur." The South Vietnamese-born pilot, Ly Vong, voluntarily surrendered his pilot's certificate after Saturday's incident, the Federal Aviation Administration said. "That does not constitute an official enforcement action," FAA spokeswoman Kathleen Bergen said. "We are still investigating." Vong took off from the Tamiami Airport southwest of Miami and buzzed Havana Saturday morning, flying low across the Florida Straits in a failed attempt to avoid radar detection.