The problems at Terminal 5 have led to criticism of BAA and BA
British Airways' chief executive Willie Walsh has said the company failed to predict the problems that blighted the opening of Heathrow's Terminal 5.
Mr Walsh told MPs he had believed the terminal was ready for its opening in March, but with hindsight, he would have done things differently.
He said "a combination of factors" had caused the fiasco, including a lack of training for staff.
The chaotic T5 opening saw many flights cancelled and thousands of bags lost.
Mr Walsh told the House of Commons Transport Select Committee that he was aware of some problems beforehand, but decided to go ahead with the move after scaling it down.
The airline had initially planned to move 92% of its operations to Terminal 5 on March 30, but subsequently decided to split the move into four stages.
He admitted that the airline had compromised on testing the new building and said that BA staff were not given enough training.
"Our staff weren't as familiar as they should have been and that impacted on their performance," Mr Walsh said.
"If we were to do it again, we would do things differently," he added.
Earlier, the chief executive of airport operator BAA said he "was unaware" that Heathrow's Terminal 5 was not ready when it opened for business in March.
Baggage systems had not been tested sufficiently and lifts were out of order, Colin Matthews told the committee.
MPs accused Mr Matthews of being "complacent" and said the debacle had made a "fool out of this country".
Other problems at the terminal included paintwork not being finished, toilets being unavailable and staff facing security delays.
The BAA boss said that there had, as yet, been no inquiry into exactly who was responsible for the woes that beset the airport.
"We have put all resources towards fixing things for passengers," Mr Matthews said.
The next priority was helping BA move all its Heathrow flights to the terminal, he added.
Huge problems with baggage handling led to thousands of items being delayed when the terminal opened.
Mr Matthews added that the baggage system had been tested at full load about 20 times.
But admitted that "the totality of the testing regime did not adequately replicate the reality of the first days of operations".
The baggage system was now "good", he said, adding he was unaware of any baggage which was still missing.
BAA's non-executive chairman, Sir Nigel Rudd, said he was "bitterly disappointed" about the opening of the terminal.
"It was clearly a huge embarrassment to the company, me personally and the board.
"Nothing can take away that failure. We had all believed genuinely that it would be a great opening, which clearly it wasn't."
Sir Nigel added: "We have apologised, but my view of the matter is that there were a number of problems that might have been foreseen, but none that would have led to the stopping of the opening of the terminal."
He added: "In a project as huge as Terminal 5, the problems had a cumulative effect."