The majority of Delta flights are taking off once again Monday, after a systems outage caused delays and 170 cancellations on Sunday.

Delta claimed that “essential IT systems” went down at about 6:30 pm ET on Sunday. The systems were restored shortly after midnight, according to a statement from Delta. The Federal Aviation Administration said “automation issues” led to the problem. Flights in the air were not affected by the outage.

About 110 flights were cancelled on Monday as well, and a few more are possible, according to the statement from Delta. This compounded stress at airports around the nation, where immigration and customs officials were also working to interpret an executive order from US President Donald Trump that put a four-month hold on allowing refugees into the US, and temporarily banned travelers from seven Muslim-majority countries.

SEE: Trump travel ban still in place despite court ruling, DHS says (CBS News)

“I want to apologize to all of our customers who have been impacted by this frustrating situation,” said CEO Ed Bastian in the statement. “This type of disruption is not acceptable to the Delta family, which prides itself on reliability and customer service. I also want to thank our employees who are working tirelessly to accommodate our customers.”

Unfortunately, Delta is no stranger to outages: In August, a power outage at the airline’s Atlanta hub delayed and cancelled hundreds of flights worldwide. That outage resulted in a $150 million loss to the company’s third quarter operating profits.

And it’s far from the only airline to experience such issues. Last Sunday night, all United Airlines domestic flights were grounded for about two hours due to what the airline called “an IT issue.” In July, Southwest Airlines cancelled 1,150 flights after a system outage, and hundreds more were backlogged. That month, United Airlines also delayed or cancelled hundreds of flights due to network connectivity issues.

Businesses should view these incidents as cautionary tales. About 57% of small and mid-sized businesses have no recovery plan in the event of a network outage, data loss, or other IT disaster, according to a Symantec study.

To avoid shutdowns, companies need to ensure that they have quality data centers and disaster control systems in place. “Planning and executing disaster recovery exercises is something that should be done on a regular basis to find out these issues before they may be impactful,” Mark Jaggers, a Gartner data center recovery and continuity analyst, told TechRepublic after the August Delta outage.

Those traveling on Delta on Monday should check their flight status at or on the Fly Delta app. The company said a change fee waiver has been issued for those scheduled to travel on Sunday or Monday, for rebooking by February 3.

The 3 big takeaways for TechRepublic readers

1. On Sunday night, Delta Airlines experienced an outage of “essential IT systems,” causing delays and 170 cancellations.

2. The airline experienced a power outage at its Atlanta hub in August, and similar tech issues have recently plagued United Airlines and Southwest Airlines as well.

3. To avoid these issues, companies should ensure they have strong disaster recovery plans in place, and quality data centers, experts said.