Denver airport workers initially missed a security breach by a man who scaled an 8-foot perimeter fence and crossed a runway where he was hit and killed by a plane with 231 people on board. Authorities said Tuesday that the 41-year-old man entered the airport and crossed a runway as a Frontier Airlines plane attempted to take off. The medical examiner said he died by suicide, but no note was immediately recovered. The collision sparked an engine fire, and the plane was evacuated after the cabin filled with smoke. Twelve passengers suffered minor injuries during the evacuation and five were taken to hospitals.