The Head of Communications for daa has said "well over 1,000 passengers" missed their flights at Dublin Airport due to lengthy queues on Sunday.
Speaking on RTE's Morning Ireland, Kevin Cullinane said an updated figure on how many people were unable to get through security in time for their departure flight will be issued later today.
He said: "At this stage, we estimate over 1,000 passengers... we will be doing a final tally with all our airline partners and customers again this morning to ascertain the final number".
READ MORE: Dublin Airport LIVE updates as queues snake outside departures for second day running
He added: "But certainly at this stage, it's well over 1,000 passengers, and we unreservedly apologise".
Officials from daa are to meet Minister for International Transport Hildegarde Naughton this morning to better understand the cause of the situation and what needs to be done to resolve the problem.
More than 50,000 passengers were expected to depart the airport yesterday.
Operations at Dublin Airport appear to be running a little faster today, with no queues currently reported outside the terminal buildings.
However, some queues did form for a period earlier this morning outside terminal one, with a temporary set down zone in operation briefly.
To combat queues today, extra security lanes have been opened this morning to cater for the anticipated early arrival of passengers, with 45,000 people due to depart from Dublin airport today.
Asked why the airport did not have enough staff to deal with yesterday's numbers, Mr Cullinane said the airport is operating on "very fine margins" and is "running to the max" of available staffing levels.
Mr Cullinane said an additional 370 additional officers are due to start in July.
He said: "Yesterday morning when we opened security in terminal one and terminal two, we clearly didn't have enough security lanes open due to resourcing challenges, and at the moment, any absenteeism impacts on our ability to operate lanes."
Mr Cullinane said the problem began at around 4.30am yesterday morning and got worse until, eventually, the system was overwhelmed.
He said the airport did not become aware of the scale of the problem until "literally people report for duty at 3am, and 4am", and when it became apparent, the airport did its best to open the optimum number of lanes.
He added that although the airport is aware of the number of passengers due to fly that day, they do not have access to airline passengers' manifests.
The same amount of passengers presented on Saturday, he explained, and daa was able to manage that situation, but there were not enough lanes open or staff available on Sunday.
Mr Cullinane said all available staff would be deployed this week and over the bank holiday weekend to avoid the situation arising again.
"We will have all the staff available - including our task force - deployed again this weekend. And we'll be doing our level best to make sure that everyone makes their flight this weekend.
"We're conscious that we let ourselves and we let the nation down yesterday, and we certainly don't want to repeat of that on our watch this week," he added.
Mr Cullinane said anyone who lost money as a result of yesterday's queues will be reimbursed as quickly as possible and should email customerexperience@dublinairport.com.
He added: "We will obviously ensure that anyone who's out of pocket as a result of yesterday is reimbursed as quickly as possible. Some of our airline partners are facilitating re-booking on the next available flights free of charge no additional cost.
"In some instances, there may be an additional cost because the airline fare is different, but they won't be charged for making that change of booking.
"And in some instances, people will have travel insurance that may provide some recompense also."
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