Heathrow's bad weather plan just before Christmas failed due to the wrong amount of snow, the airport's boss told MPs today.
Heathrow had planned for 6cm (2.4in) of snow "but got far more than that", Colin Matthews, chief executive of airport operator BAA, told the House of Commons Transport Committee.
He went on: "In retrospect we should have had a plan for more snow than 6cm."
Mr Matthews apologised for the disruption to passengers and airlines which saw Heathrow operations come to almost a complete halt, with thousands of Christmas getaway travellers jamming the terminals and sleeping there overnight.
He said BAA did "all we possibly could" for passengers but the bad weather "totally overwhelmed the ability of resources at Heathrow to cope with passengers".
Before Mr Matthews gave evidence, the committee heard from representatives of British Airways and Virgin Atlantic, who told MPs of the lack of communication between BAA and airlines during the pre-Christmas disruption.
They were particularly upset about not getting news of the reopening of the second runway on Tuesday December 21.
Virgin chief executive Steve Ridgway told the committee: "It was pretty galling on that Tuesday to hear from the Prime Minister on the media that the runway was reopening that afternoon."
Virgin operations, safety and security director Corneel Koster said communications at times had been "absent".
He went on: "We had passengers waiting to depart and hearing from the media that the airport was shut. We had passengers told not to go to a terminal, but we had passengers leaving from that terminal.
"The second runway reopened on the 21st but for a good part of that morning we were told that it would not open."
BA operations director Andrew Lord said that the weather on Saturday December 18 was "extremely severe" but nevertheless BA had expected the second runway at Heathrow to "close and reopen very quickly".
He went on: "At the end of the day, if the airport operators do not provide a service to us it is our customers that suffer and that is a situation that is not acceptable to us."
Mr Matthews said: "I am very sorry indeed for the thousands of disrupted passengers and for the thousands of Christmas holidays affected and for the airlines and the company."
He said the snow disruption had cost BAA £20 million at Heathrow and a total of £24 million across its six UK airports.
Mr Matthews said BAA needed to "dramatically improve" its ability to communicate and that the company could "certainly have done better and will do better in the future".
He said a change of wind direction had led to the decision to reopen the second runway on December 21. Asked how the Prime Minister knew about the reopening before the airlines, Mr Matthews replied: "I don't know how that came about."
He added that Transport Secretary Philip Hammond had visited Heathrow on the morning of December 21 and that BAA had kept in touch with the Government during the disruption.
Mr Matthews said he had declined the Government's "welcome offer" of use of the Army to clear the runway at Heathrow as "it had already been cleared".
Powers to hold airport operators more to account for passenger-related performance are currently being considered in an airport economic regulation Bill.
Mr Matthews told MPs today: "I think it would be good to have a sweep of measures to reflect the customer experience and make sure that an airport operator does less well if it performs poorly."
He said BAA had done a number of things for stranded passengers last December, including providing food, accommodation, laptops and free parking.
But he admitted many passengers had had "extremely uncomfortable nights" at Heathrow.
Mr Matthews announced just before Christmas that he was foregoing his 2010 bonus. He has ordered an external inquiry into Heathrow's handling of the pre-Christmas disruption. The inquiry report is expected later this month and will be made public.
Gatwick airport chief executive Stewart Wingate told MPs the West Sussex airport had had 10cm of snow in the pre-Christmas spell of severe weather but had been able to operate again "within five hours".
Mr Wingate said it was important for airports to be in close contact with rail and road authorities. He said it had taken him 13 hours to reach Gatwick after getting stuck on the M25 during the bad weather.