LONDON -- British Airways canceled all flights from London's Heathrow and Gatwick airports Saturday as a global information technology failure upended the travel plans of tens of thousands of people on a busy U.K. holiday weekend.
The airline said it was suffering a "major IT systems failure" around the world. Chief Executive Officer Alex Cruz said "we believe the root cause was a power-supply issue and we have no evidence of any cyberattack."
He said the crash had affected "all of our check-in and operational systems" and said the airline is "extremely sorry for the huge inconvenience this is causing our customers."
British Airways operates hundreds of flights from the two London airports on a typical day -- and both are major hubs for worldwide travel.
Several hours after problems began cropping up Saturday morning, British Airways suspended flights up to 6 p.m. because the two airports had become severely congested. The airline later scrapped flights from Heathrow and Gatwick for the rest of the day.
The airline said it was working to restore services out of Heathrow and Gatwick beginning today, although some disruptions are expected. It said it expected that London-bound long-haul flights would land on schedule today.
The problem comes on a bank holiday weekend, when tens of thousands of Britons and their families are traveling.
Travelers took to Twitter to complain of flight postponements, long lines to check in, and waiting for long periods on the tarmac after boarding planes.
Once services were canceled, passengers from grounded planes or at gates at Heathrow endured large crowds at passport-control desks to re-enter the country.
British Airways said the crash also affected its call centers.
Airline staff told customers to find hotels on their own for reimbursement later by the airline. Payments will include $260 per night for lodging, about $64 round-trip between the airport and the hotel, and as much as about $32 for refreshments, according to leaflets from the company.
Passenger Phillip Norton tweeted video of an announcement from a pilot to passengers at Rome's Fiumicino airport, saying the problem affects the system that regulates what passengers and baggage go on which aircraft. The pilot said passengers on planes that have landed at Heathrow were unable to get off because there was nowhere to park.
One person posted a picture on Twitter of British Airways staff writing gate numbers on a white board.
"We've tried all of the self-check-in machines. None were working, apart from one," said Terry Page, booked on a flight to Texas. "There was a huge queue for it and it later transpired that it didn't actually work, but you didn't discover that until you got to the front."
Another traveler, public relations executive Melissa Davis, said her British Airways plane was held for more than 90 minutes on the tarmac at Heathrow on a flight arriving from Belfast.
She said passengers had been told that they could not transfer to other flights because "they can't bring up our details."
Some British Airways flights were still arriving at Heathrow on Saturday, although with delays.
American Airlines, which operates code-share flights with British Airways, said its operations were unaffected.
Air industry consultant John Strickland said Saturday's problems would have "a massive knock-on effect" for several days.
"Manpower, dealing with the backlog of aircraft out of position, parking spaces for the aircraft --it's a challenge and a choreographic nightmare," he said.
Airlines depend on expansive, overlapping and complex information technology systems to do just about everything, from operating flights to handling ticketing, boarding, websites and mobile-phone apps. Some critics say complex airline technology systems have not always kept up with the times.
And after years of rapid consolidation in the business, the computer systems may be a hodgepodge of parts of varying ages and from different merger partners, all layered on top of one another.
A union official, meanwhile, blamed British Airways cost-cutting for the travel chaos, saying the airline had laid off hundreds of IT staff last year and outsourced the work to India.
"This could have all been avoided," said Mick Rix, national officer for aviation at the GMB union.
While not that frequent, when airline computer failures do happen, the effects are widespread and high-profile, and they can hit travelers across the globe.
British Airways passengers were hit with severe delays in July and September because of problems with the airline's online check-in systems.
In August, 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. While the system moved to backup power, not all of the servers were connected to that source, which caused the cascading problem.
In January, United also grounded flights because of a computer problem.
Also in July, Southwest Airlines canceled more than 2,000 flights after a failure that it blamed on a failed network router.
After the recent failures, outside experts have questioned whether airlines have enough redundancy in their IT systems and test them frequently enough.
Information for this article was contributed by Alastair Marsh, Susan Warren and Sharon Smyth of Bloomberg News.
A Section on 05/28/2017