Between 9 p.m. CDT on Saturday, October 15, and 7 a.m. CDT on Sunday, October 16, United Airlines will be updating their MileagePlus account technology. During this time, customers will be unable to sign into their MileagePlus accounts or make transactions with miles or PlusPoints. The changeover is designed to be seamless, but the outage will affect some functions for MileagePlus customers, such as seat selection, inflight purchases, bag fees and other.