The British Airways website and app have been down for several hours due to “planned improvements”.
People hoping to book tickets, check in online or monitor flight arrivals and departures on ba.com are being told: “We’ll be back soon. Both ba.com and our apps are temporarily unavailable while we make some planned improvements to our systems.
“Everything should be back up and running by 14:30 BST.
“You can still check in at the airport as normal if you’re travelling in the next few hours.”
BA recommends people seek flight information “from the website of your departure airport”.
One prospective user, Robin Page, tweeted: “Your website is down again. Can you update please?”
He was told by BA’s social media team: “Hi Robin, the website should be up and running now as the issue has been resolved.
“If you’re still having trouble, we would recommend deleting cookies from your browser via your browser settings, or using a different internet browser for now.”
Users of the airline’s app were told: “We are unable to log you in. Please try again. If the problem persists visit ba.com or call your local contact centre.”
A spokesperson for British Airways said: “Our website is temporarily unavailable due to planned maintenance, and will be available again soon.
“We apologise for any inconvenience caused.”
British Airways has suffered repeatedly from IT failures in recent years.
In May 2017, around 75,000 passengers were stranded after a power problem disabled the departure control system. BA cancelled about 800 flights from Gatwick and Heathrow as a result of the failure, incurring losses of £58m.
The following year, cyber criminals hacked the payment details of hundreds of thousands of customers who had booked direct with the airline.