premise: At 9:39 , the FAA 's Cleveland Air Route Traffic Control Center overheard a second announcement indicating that there was a bomb on board , that the plane was returning to the airport , and that they should remain seated and true is true and true is true and true is true and true is true and true is true .
hypothesis: The FAA 's Cleveland Air Route Traffic Control Center heard an announcement about a bomb being on the plane , but none was ever discovered .