All Delta Air Lines flights worldwide were grounded Monday morning due to a “system outage.” A statement from the carrier said the issue began with a power outage in Atlanta around 2:30 a.m. According to one of the company’s Twitter postings, flights already in the air are operating normally but all others awaiting departure are delayed. “Large-scale cancellations are expected today,” the airline posted. The company still advised travelers to arrive on time for their flights, but at least one response to a customer on Twitter said, “Our systems are down everywhere” and that there was no way of knowing how quickly the problem would be resolved. By about 9 a.m. EST, the airline had lifted "limited" flights and some departures had resumed. Still, the company said cancellations would continue throughout the day.