A small plane headed to Key West for the Christmas holiday crashed Sunday at the end of a runway at a Florida airport, killing five people, authorities said. The twin-engine Cessna 340 crashed shortly after takeoff at Bartow Municipal Airport, immediately killing the 70-year-old pilot and his four adult passengers, according to a statement from Polk County Sheriff’s Office spokeswoman Carrie Horstman. It wasn’t immediately clear what caused the crash. The sheriff’s office identified the pilot as Lakeland attorney John Shannon. He had filed a flight plan to fly Sunday from Bartow to Key West, Horstman said. Shannon’s passengers included his two daughters, his son-in-law and a family friend.