The National Transportation Safety Board says altimeter in the Black Hawk helicopter may have malfunctioned before the DCA mid-air collision with an American Airlines jet. All 67 people aboard died.
Among the unanswered questions about the crash near Washington, D.C., are the flight pattern of the Black Hawk helicopter and the exact nature of its training exercise.
A missing Black Hawk carrying 10 crew members is believed to have crashed into the sea off a southern island after objects appearing to be aircraft parts were spotted in the area, an official said.