It is understood only one lane at the security gate was open from around 6pm until 8pm on Thursday.The airport said normally "a couple" of lanes would be open during what is its peak period.Management said passengers were "upset" at the delays.Uel Hoey from the airport apologised and said an investigation was underway to determine how the delays came about to ensure it doesn't happen again.He said: "During the peak period we had some delays in the passenger process."That was due to the fact that normally we would have a couple of security channels open during the night and last night due to circumstances we only had one open for a period of time."Passengers experienced delays and we apologise to anybody who was disrupted."We only had one channel open for the peak period and for between an hour-and-a-half to two hours."The problem was fixed at around 8pm and everything has been running smoothly since then."Obviously it is regrettable and we do apologise to anyone affected and we are investigating to ensure it doesn't happen again."Mr Hoey said he was not fully aware of how the delay occurred.He added: "I'm not sure how long passengers had to wait, that will be something we will look at again in the investigation."But we are very aware passengers were upset, we are very sorry and we will endeavour to make sure it doesn't happen again."