Footage on social media showed staff writing out the flight status of each flight and rubbing them off as updates came in.
In a tweet, the airport said: "We are sorry, but due to an IT issue our flight information is not displaying correctly".
Gatwick passengers were left furious after the boards, which display flight departure times and gate numbers, suddenly stopped working.
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Apologising to customers, he added that the airport's "manual contingency plan", which included having extra staff on hand to help direct passengers, had worked well.
"We are expecting to resolve the issue soon and apologise for the inconvenience".
London's Gatwick has resorted to using marking pens and whiteboards to post flight information after a technical failure at the United Kingdom airport caused electronic message boards to malfunction. Their statement also said "tens of thousands" of people still managed to depart on time.
Gatwick Airport didn't immediately respond to a request for further comment.
Vodafone provides the service, and said a damaged fibre cable was to blame.