Sun Country Airlines couldn't complete its systemwide technology upgrade Tuesday and Wednesday after one of its critical flight tools failed to work when it went live.

The problem arose a few hours into the transition Tuesday evening and forced the Eagan-based airline to continue on with its old system.

Such a development is not unusual when companies attempt major technology overhauls. Engineers frequently discover that systems don't always function in the real world like they do in simulations and tests.

"After months of testing and the hard work of many of our team members and partners, we unfortunately reached a critical barrier during the transition and were forced to make the hard decision to postpone," the airline said in a statement Wednesday. "Despite many successful tests, our connection to a critical flight operation tool was unsuccessful in the live environment."

The airline said it reverted to its existing system "in the interest of not disrupting our operation and our guests' travel plans" and that everything was functioning normally Wednesday. The airline is rescheduling the transition, though it didn't offer a target date.

Sun Country has been working for a year with Minneapolis-based Navitaire to build a new point-of-sale and departure-control system. The airline is also building a new website that will integrate with the system. Executives said the new technology will allow Sun Country to offer better service with ticket kiosks at airports and greater customer control over online reservations.

A new team of executives arrived at the airline in 2017 and found its tech systems to be outdated and a source of inconvenience for customers. A Sun Country spokeswoman said executives are still excited about the upgrade and the improvements it will bring to its operations.