LONDON >>British Airways said many of its IT systems were back up and running today, but some travelers will likely face cancellations and delays for a third straight day after a global computer failure grounded hundreds of flights.

BA chief executive Alex Cruz said the airline was running a “near-full operation” at London’s Gatwick Airport and planned to operate all scheduled long-haul services from Heathrow. But he said there would still be delays, as well as some canceled short-haul flights.

The airline said it will run a full schedule at Gatwick on Monday and intends to run its full long-haul flight schedule and a “high proportion” of its shorter flights at Heathrow.

BA canceled all flights from Heathrow and Gatwick Saturday after the IT outage, which it blamed on a power-supply problem. The glitch threw the plans of thousands of travelers into disarray, on what is a holiday weekend in Britain.

BA operates hundreds of flights from Heathrow and Gatwick on a typical day — and both are major hubs for worldwide travel.

Cruz apologized in a video statement, saying: “I know this has been a horrible time for customers.”

Passengers faced hours-long lines to check in, reclaim lost luggage or rebook flights at Terminal 5, BA’s hub at Heathrow. Cruz said that to reduce overcrowding travelers will only be let into the terminal 90 minutes before their flights.

Passengers — some of whom had spent the night at the airport — faced frustrating waits to learn if and when they could fly out.

“Everyone is upset. There’s people in tears,” said Melanie Ware, who flew in from Los Angeles and was trying to get to Venice on her honeymoon.

“We rebooked for Venice for tonight, which they also have canceled now,” she told Sky News. “So we have no way of getting out of Heathrow and they haven’t compensated us for anything, and we’re stuck and this is the worst honeymoon ever.

“British Airways has ruined our honeymoon.”

Tonda Sallee, who was trying to fly to Frankfurt, said she has been in line for five hours, “and we have no idea how long we’ll be in line. The rest of the day I’m sure, and we probably won’t fly out today either.”

Many passengers complained about a lack of information from the airline.

“Some 80-year-old lady was standing around waiting for announcements, et cetera, and she fell over,” said Londoner Terry Page, who managed to get on one of the last flights from Heathrow to Dallas-Fort Worth on Saturday. He and other passengers arrived, but their luggage did not.

“We helped her up and she said ‘I’m just so tired,’ ” Page said. “It’s been a terrible, terrible day.”

While not that frequent, when airline outages do happen, the effects are widespread, high-profile and can hit travelers across the globe.

BA passengers were hit with severe delays in July and September 2016 because of problems with the airline’s online check-in systems.

In August 2016, Delta planes around the world were grounded when an electrical component failed and led to a shutdown of the transformer that provides power to the airline’s data center. Delta said it lost $100 million in revenue as a result of the outage.