Two historic military planes collided and crashed to the ground Saturday during a Dallas air show, exploding into a ball of flame and sending black smoke billowing into the sky. The collision killed six people. It was unclear how many people were on board each aircraft, but the B-17 Flying Fortress bomber typically has a crew of four to five people and the P-63 Kingcobra fighter plane, has a single pilot. It occurred at the Dallas Executive Airport, about ten miles from downtown Dallas. The collision happened during the Commemorative Air Force Wings Over Dallas show. Several videos posted on Twitter showed the fighter plane appearing to fly into the bomber.