United Airlines is testing blocked middle seats on its Airbus A321XLRs. This could secure more revenue while simultaneously saving on labor costs. Joe Raedle/Getty Images United Airlines plans to block some middle seats on Airbus A321XLR aircraft. The seats resemble "Eurobusiness" and will likely come at an upcharge. Blocking middle seats ensures it staffs the minimum number of flight attendants possible. United Airlines is testing something new in economy class: blocked middle seats. A vir...