Delta Air Lines has said that a fire was the cause of the major IT meltdown that grounded all of its flights earlier this week.
Delta CEO Ed Bastian told the Atlanta Journal-Constitution that the fire occurred after a power control module at its command centre failed, which led to an electrical surge and a loss of power.
Bastian also told the newspaper that the incident revealed to the company that around 300 of its 7,000 servers weren't wired to backup power.
The major outage first hit Delta on Monday, and saw flights cancelled until Wednesday.
"We are aware that flight status systems, including airport screens, are incorrectly showing flights on time. We apologise to customers who are affected by this issue, and our teams are working to resolve the problem as quickly as possible," the firm said in a statement at the time.
Delta is the third largest airline in the US, carrying 180 million passengers a year, and the incident left thousands stuck at airports and terminal gates with little information on what would happen next.
It was the second outage in a month for a major US airline after SouthWest was forced to cancel over 2,000 flights in July owing to a computer glitch.
As Twitter filled with pictures of departure boards and passengers camped out in airport lounges, Delta staff were said to be using a local terminal-based system in some locations, rather than the global cloud-based one that has gone down.
Some Virgin flights were also cancelled as they 'codeshared' with Delta aircraft. Air France and KLM were also affected.
UK air traffic control suffered a major IT glitch in October that trapped passengers in Scottish airspace, while a major incident in October 2014 prompted MPs to criticise the UK's air traffic management authority for failing to invest in its IT infrastructure.
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