Experts ask why Black Hawk helicopter may have been flying above allowed altitude before crash

The military Black Hawk helicopter that crashed into a passenger plane near Reagan National Airport Wednesday appears to have been flying above the permitted altitude, publicly available flight data analyzed by CBS News shows.

This data point is one of several key mysteries investigators are exploring as they seek to explain what caused the nation's worst air disaster in more than a decade, aviation experts said.

"That's the $64 million question that needs to be answered," said Greg Feith, a former senior air safety investigator with the National Transportation Safety Board, in an interview with CBS News.