United Airlines added 50 76-seat Embraer 175 aircraft to operate under the United Express brand

through an amended agreement with regional carrier Shuttle America, United announced Tuesday. United earlier this year began delivery of 70 of the aircraft, which have 12 first-class seats, 16 premium-economy seats and 48 standard economy seats. The additional 50 aircraft will be delivered beginning in July 2015 through the summer of 2017, according to United. Shuttle America parent company Republic Airways Holdings will decide which regional carriers operate the new aircraft as a replacement to larger turboprop planes and other less-efficient models.