United Airlines will disable many of its app and website functions between 2:30 a.m. and 6:00 a.m. Wednesday morning for an update of its reservation system.
Flyers should plan to book, complete check-in, or make trip changes either before or after those hours, a banner on the United.com website reads.
"We've removed all departures from the schedule during those early morning hours to create the right conditions to complete the upgrade as seamlessly as possible for our customers," the airline said in a statement.
The system to be updated, called Shares, is a mainframe reservation system that United inherited from Continental at the time of their merger in 2012.