Travelers walk through the United Airlines terminal at O'Hare International Airport on April 12, 2017 in Chicago, Illinois. United Airlines has been criticized in recent days after airport police officers physically removed passenger Dr. David Dao from his seat and dragged him off the airplane, after he was requested to give up his seat for United Airline crew members on a flight from Chicago to Louisville, Kentucky Sunday night.  / AFP PHOTO / Joshua LOTT        (Photo credit should read JOSHUA