Thousands of travellers faced further chaos on Sunday as British Airways cancelled around 40 flights from London's Heathrow Airport following an IT system failure.
Around one quarter of Sunday's flights set to depart from London's key hub before 1.00 pm (1200 GMT) were cancelled as the airline battled to contain the "knock-on disruption" to schedules, with aircraft and crews out of position around the world.
British Airways said it was hoping to operate a near-normal schedule of flights from Gatwick, London's other major airport, and the majority of its Heathrow services.
More flights left Heathrow as the day wore on, but most were operating with delays. Travellers also faced hold-ups at Gatwick, but no flights were cancelled.
The airline advised passengers not to come to the two airports unless they had confirmed bookings, with disruption expected throughout the holiday weekend.
BA cancelled all its flights out of Heathrow and Gatwick on Saturday after the IT failure, which shut down all of the carrier's check-in and operational systems and affected call centres and its website.
Power supply issue
However, it did not appear to be a cyber-attack, according to a video statement by chairman and chief executive Alex Cruz.
Britain is still recovering from a ransomware attack that crippled crucial infrastructure earlier this month, including computer systems at the National Health Service.
"We believe the root cause was a power supply issue," said Cruz, adding that IT teams were working "tirelessly" to fix the problems.
Full refunds will be given to customers who decide they no longer wish to travel, Cruz said.
The outage came on a busy weekend in Britain, where Monday is a public holiday and many schoolchildren are beginning their half-term break.
An AFP photographer at Heathrow's Terminal 5 on Saturday said many travellers were waiting outside the departure area with their luggage in "chaotic" scenes.
They were not being allowed inside the terminal for health and safety reasons, prompting some of them to leave in taxis.
"None of your staff know what the heck is going on. Nor do your passengers. Can we have some info please? Chaos here," tweeted Chris Ship, royal editor for ITV News, to BA.
Passengers were asked to contact the airline in order to locate their luggage, after many were forced to leave Heathrow without claiming their bags.
The carrier said it was "extremely sorry" for causing inconvenience over the holiday period.
British Airways has suffered other IT glitches recently, leading to severe delays for passengers in July and September last year.
IAG, the parent group of British Airways and Spanish carrier Iberia, earlier this month reported a 74-percent slump in first-quarter net profit to 27 million euros ($30 million), due in large part to a weak pound.
Explore further: BA aims to restore normal flight service after IT failure
