Sun Country Airlines flights were temporarily grounded early Thursday when a key software program stopped working.

The software that manages Sun Country's crew schedules, from Dubai-based AIMS International, went down.

The program keeps track of legally-required checkoffs for flights, including federally-mandated rest requirements, duty limitations and other scheduling issues for flight crews.

By mid-morning, Twin Cities-based Sun Country — with the help of the U.S. Federal Aviation Administration — resumed operations by manually clearing crews for takeoff.

"However, this manual process is causing delays throughout our system. We appreciate the patience of our guests as we work to get them safely on their way as quickly as possible," a Sun Country spokeswoman said in a statement.

The system was partially restored by early afternoon as the airline worked through the flight backlog.

Sun Country canceled four of its 91 scheduled passengers flights for Thursday — a roundtrip from Dallas-Forth Worth to Cozumel and a roundtrip from Austin, Texas, to Cancun.

"We are working with those passengers now to get them meal vouchers, hotel accommodations if needed and alternative travel," the spokeswoman said.

The airline had an additional 48 cargo or charter flights planned for Thursday. All of these flights were affected by delay.

On Twitter, people complained Thursday morning of large crowds congregated in Minneapolis-St. Paul International Airport's Terminal 2, where Sun Country operates.

Passengers with trips scheduled for Thursday were allowed to reschedule their flights without a fee, Sun Country said.

A phone number listed for AIMS' North American office in Miami was disconnected Thursday.