BA chief executive Alex Cruz says he will not resign and that flight disruption had nothing to do with cutting costs.
He told the BBC a power surge, had "only lasted a few minutes", but the back-up system had not worked properly.
He said the IT failure was not due to technical staff being outsourced from the UK to India.
Mr Cruz said "I am profusely sorry" to the 75,000 passengers affected across 170 airports in 70 countries.
He said two thirds of passengers will have reached their destination by the end of the day.
There was no evidence of a cyber attack, he added.
"There was a power surge and there was a back up system, which did not work at that particular point in time. It was restored after a few hours in terms of some hardware changes... we will make sure that it doesn't happen again," Mr Cruz said in his first interview.