NEW : Oil slick experts argue against an in - flight accident , Brazilian official says . NEW : Determining where plane broke up will be difficult , U.S. aviation expert says . Air France flight disappeared over Atlantic Ocean after taking off from Brazil . Memorial for the victims of Flight AF 447 takes place in Paris at Notre Dame .
NEW : Oil slick may argue against an in-flight explosion , Brazilian official says . NEW : Determining where plane broke up will be difficult , U.S. aviation expert says . Air France flight disappeared over Atlantic Ocean after taking off from Brazil . Memorial for the victims of Flight AF 447 takes place in Paris at Notre Dame .