United Airlines is set to upgrade its reservation system. Here’s what that means for travelers.

United Airlines is set to undergo a significant technology update that will temporarily take down its online reservation system early Wednesday morning. The airline is advising passengers with flights scheduled to depart on Wednesday to check in via United’s website or mobile app on Tuesday to avoid any issues. The scheduled outage is expected to last approximately four and a half hours, starting at 2:30 a.m. EDT and ending at 6 a.m. EDT.

A notice on United’s homepage informs travelers that the airline is “conducting a planned technology upgrade” and that many of its web and app services will be unavailable during this time, including for employees of the airline. United is working on modernizing its aging mainframe flight reservation system, Shares, by transferring reservation data from its current data center in North Carolina to a more advanced facility in Chicago, which will enhance reliability.

For passengers flying on Wednesday, United’s flight schedule will be temporarily unavailable, and they will not be able to make new reservations, cancel bookings, check in for flights, or access their itineraries. The airline advises travelers scheduled to fly on Wednesday morning to check in on Tuesday and to check their bags at that time as well. The reservation system upgrade was planned in advance, with United canceling affected flights months ago and notifying customers of the changes.

United has conducted rehearsals of the data migration process to ensure a smooth transition, and travel experts anticipate minimal disruption. However, in the event that the upgrade encounters issues, it could potentially cause headaches for customers. Southwest Airlines experienced a computer outage a decade ago that resulted in numerous flight cancellations and delays, highlighting the importance of a seamless upgrade process.

In conclusion, United customers should be aware of the temporary outage of the reservation system on Wednesday and take necessary precautions by checking in early. The airline is working to improve its technology infrastructure for better reliability and efficiency. As the upgrade progresses, passengers are advised to stay informed and patient during this transition period.

This article was edited by Alain Sherter and contributed to by Kris Van Cleave.