PATUXENT RIVER, Md. - An F-35C Joint Strike Fighter test aircraft returns from a flutter envelope expansion flight. Marine Corps test pilot Lt. Col. Matt Kelly flew the aircraft faster than the speed of sound for the first time, reaching Mach 1.02 at 30,000 feet. The F-35B short take off and vertical landing (STOVL) variant and F-35C carrier variant are undergoing flight test and evaluation at the integrated test facility at Naval Air Station Patuxent River.