British Airways' parent company has confirmed that human error caused an IT meltdown that left 75,000 passengers stranded over a holiday weekend last month.
Willie Walsh, boss of IAG, said an electrical engineer disconnected the uninterruptible power supply which shut down British Airway's (BA) data centre.
A leaked BA email last week had pointed the finger at a single contractor.
Mr Walsh said on Monday there would now be an independent investigation "to learn from the experience".
Appearing at an annual airline industry conference in Mexico, Mr Walsh said: "It's very clear to me that you can make a mistake in disconnecting the power.
"It's difficult for me to understand how to make a mistake in reconnecting the power."
IAG has commissioned an "independent company to conduct a full investigation" into the IT crash and is "happy to disclose details" of its findings, Mr Walsh said.
The BBC reported last week that senior company executives at IAG were pushing for an external probe into the computer meltdown.
BA has already launched its own investigation, led by its chief executive Alex Cruz.
Following the computer crash, which caused travel chaos for people travelling from Heathrow and Gatwick, Mr Walsh gave his full backing to Mr Cruz.
BA and IAG also rejected claims that the incident was due to Mr Cruz's decision to outsource the airline's IT department to India as part of cost-cutting measures.
On Monday, Mr Walsh apologised again for the incident, saying: "When you see customers who suffered, you wouldn't want it to happen to any airline or any business."