Sheila Marie Evans Widnall (born July 13, 1938) is an American aerospace researcher and Institute Professor at the Massachusetts Institute of Technology. She served as United States Secretary of the Air Force between 1993 and 1997, making her the first female Secretary of the Air Force and first woman to lead an entire branch of the U.S. military in the Department of Defense. Widnall was a member of the board of investigation into the Space Shuttle Columbia disaster. She currently works with the Lean Advancement Initiative.