People arrive for the British Airways check-in desk at Gatwick Airport in southern England, Britain, May 28, 2017. REUTERS/Hannah McKay

LONDON (Reuters) - A contractor doing maintenance work at a British Airways data center inadvertently switched off the power supply, knocking out the airline’s computer systems and leaving 75,000 people stranded last weekend, the Times newspaper reported on Friday.

Quoting a BA source, the newspaper said the power supply unit that sparked the I.T. failure was working perfectly but was accidentally shut down by a worker. An investigation into the power outage is likely to focus on human error rather than any equipment failure, it said.

BA had to cancel all flights from London’s Heathrow and Gatwick airports last Saturday. It blamed a power surge that knocked out its computer system, disrupting flight operations, call centers and its website.