British Airways has ordered an independent investigation into the systems meltdown that left 75,000 passengers stranded over the bank holiday weekend.

The actions of a technician who switched off and then reconnected the power supply to BA’s data centre are expected to form the centre of the inquiry, which will be carried out by an as-yet-unnamed external company.

Willie Walsh, the chief executive of the airline’s parent company, IAG, said the technician responsible was “authorised to be in the room, but wasn’t authorised to do what he did”.

He added: “You could cause a mistake to disconnect the power – it’s difficult for me to understand how you can mistakenly reconnect the power.”

The power was restored to the data centre in “an uncontrolled and uncommanded fashion that caused physical damage to the servers and distribution panels”, Walsh said.

If that had not been the case BA could have quickly recovered from the power outage, Walsh claimed. “That in itself was a problem that we could have overcome probably in a couple of hours, I don’t think it would have led to any cancellations.”

Walsh said BA’s communications had been poor after the incident, in which thousands of passengers were stranded at Heathrow before having to queue to leave the airport. “I wouldn’t suggest for one minute we got communications right at BA – we didn’t.”

He added: “It’s damaged us, but it hasn’t destroyed us in any way. We’ve recovered from worse. The BA brand is incredibly resilient.”

Speaking at the International Air Transport Associationglobal summit in Mexico, Walsh said of the fiasco: “It’s something I wouldn’t wish on anybody or any airline, when you see the customers who have suffered. I’m hoping people will be able to learn from the experience we’ve had and we’ll all be better as a result.”

But the IAG chief defended cost-cutting at the airline, which has been criticised by unions as well as some City analysts. Hundreds of IT staff have been made redundant, while the airline’s mixed fleet cabin crew are going on strike again this month in a dispute over “poverty pay”.

Walsh said the system meltdown “was not a failure of IT” and denied cost-cutting had become counterproductive.

“I don’t believe so – in many cases I don’t believe there is any correlation ... But without question if we had not embarked on an efficiency improvement programme we wouldn’t be in business today,” he said.

BA has faced a barrage of criticism over the last week over customer service and compensation. The airline has also this year stopped offering free food and drink on short-haul flights, as well as squeezing in more seats on some planes.

Walsh said it was a natural reaction to focus on negative changes, but added: “If you look at the advances in technology – trillions of dollars invested in new aircraft, lounges and equipment – there needs to be balance about the changes that are beneficial to business and consumers and those that are regarded as retrograde. We invest a lot of money in new aircraft, we’ve got to fund that through profitability.”

BA’s system meltdown came after other highly disruptive failures at airlines such as Delta.

Alexandre de Juniac, director general of Iata, said that the aviation industry’s problems had “nothing to do with cost-cutting”, but bigger and more complex IT systems. He added: “It’s a miracle it works so well.”