Flights at Gatwick Airport were suspended for about two hours due to what it says was an issue in its control tower.
A total of 25 flights were diverted to other UK airports when the problems began shortly after 17:00 BST.
The airport said it had experienced a problem with its air traffic control systems.
Passengers due to travel to or from the airport have been advised to check for updates with their airline.
Colin Franks, who was due to board an EasyJet flight to Palma, Spain, at 18:00 said he was “trapped between the boarding gate and the air bridge”.
He said the plane’s pilot had spoken to passengers, adding: “He said they had been given a provisional [take off] time of 10pm.
“At the moment, everybody is talking to one another and it’s quite cheery. There is a lot of children here.”
In December flights were suspended for 30 hours after drone sightings, causing chaos for 140,000 passengers.
A senior Sussex Police officer said the airport was not prepared for an attack by more than one drone.