British Airways has provided more insight into the global IT outage that caused the cancellation of flights on Saturday, and long delays to flights out of Heathrow and Gatwick airports across the bank holiday weekend.
At the time, Willie Walsh, the CEO of British Airways' holding company IAG, claimed that a power surge affecting the company's data centre at Heathrow had caused systems to go down, while an attempt to restore systems from back-ups also failed.
"There was a loss of power to the UK data centre which was compounded by the uncontrolled return of power which caused a power surge taking out our IT systems. So we know what happened we just need to find out why," claimed BA in a new statement.
It continued: "It was not an IT failure and had nothing to do with outsourcing of IT, it was an electrical power supply which was interrupted. We are undertaking an exhaustive investigation to find out the exact circumstances and most importantly ensure that this can never happen again."
UK Power Networks, however, disputed Walsh's suggestion that there had been any kind of power problems in the area at the time.
Instead, the meltdown appears to have been triggered by overheating in the data centre, which had been designed in the 1980s, and claims that the data centre and its cooling systems have not been adequately maintained as the building has filled up with hardware.
Walsh suggested that the uninterruptible power supply (UPS) that ought to have protected the data centre from power outages failed and that, when the systems were rebooted, staff did not bring them "gradually" back up, causing "catastrophic damage" to servers.
But anecdotal evidence from staff working for BA suggests that the ageing data centre suffered from overheating for some years, with air conditioning equipment struggling to keep temperatures down and staff even resorting to hosing the roof of the building during particularly hot spells.
The building would have been designed in the era of mainframe and mini-computers, at a time when there was much less computerisation than there is today.
The GMB trade union had initially blamed outsourcing to India for the outage on Saturday, but has changed tack since the real cause became clear. Instead, it blames under-investment and the loss of skilled staff due to cost-cutting, of which the outsourcing is just one part.
Cotton seedling freezes to death as Chang'e-4 shuts down for the Moon's 14-day lunar night
Fortnite easily out-earns PUBG, Assassin's Creed Odyssey and Red Dead Redemption 2 in 2018
Meteor showers as a service will be visible for about 100 kilometres in all directions
Saturn's rings only formed in the past 100 million years, suggests analysis of Cassini space probe data
New findings contradict conventional belief that Saturn's rings were formed along with the planet about 4.5 billion years ago