LONDON — Delta Air Lines has grounded flights and predicted widespread cancellations Monday, disrupting the travel plans of thousands of passengers, after a power outage hit its computer systems globally.

The Atlanta-based carrier said the outage began at around 2:30 a.m, though it was unclear how that affected the company’s global computer systems. Eastern. Flights which were already en route were operating normally, but others were delayed or cancelled.

The massive outage threw the airline back to the days of yore in aviation travel, where many things were done manually. In Richmond, Virgina, boarding passes were written out by hand. In Tokyo, a dot-matrix printer was resurrected to keep track of passengers on a flight to Shanghai. In New York, self service check-in kiosks were dark.

And the technology that was working was giving inaccurate information. Flight status systems, including airport screens, were incorrectly showing flights on time, something the company was trying address.