Flights at Gatwick Airport were cancelled, delayed or diverted at short notice on Thursday due to a shortage of air traffic controllers.
Gatwick confirmed 22 cancellations as of 22:00 BST, while the website FlightRadar24 said hundreds of flights in and out of the airport were delayed.
The National Air Traffic Services (Nats) apologised for its staffing shortages.
Gatwick Airport said it expected a normal service on Friday.
The disruption comes just over two weeks after a technical issue at Nats led to 2,000 flights being cancelled across the UK.
EasyJet expressed frustration at Thursday’s delays and cancellations, while Ryanair boss Michael O’Leary called on Nats’ boss to resign.
Mr O’Leary said: “It is unacceptable that more flights and hundreds of passengers are suffering delays to/from Gatwick Airport due to Nats CEO, Martin Rolfe’s blatant failure to adequately staff UK ATC.
“Airlines are paying millions of pounds to Nats each and every year and should not have to see their passengers suffer avoidable delays due to UK ATC staff shortages.”
Laura Neary, 29, had her flight from Gatwick to Dublin diverted to London Stansted instead – which she had to travel to by coach.
“I don’t even know if I can get back to Dublin tonight,” Ms Neary said.
Paul Treloar, who planned on landing at Gatwick airport on Thursday, posted on social media: “It’s now four hours later and our flight from Samos has been diverted to Bournemouth. Can you give us any idea if/when we’re likely to be able to land at Gatwick this evening?”
Mike Reed, another traveller, wrote on social media that he had been in Bari, Italy, “sat on hot plane for ‘up to an hour'”
“The situation at Gatwick is unacceptable,” Julia Lo Blue-Said, chief executive of Advantage Travel Partnership, said.
She explained that the disruption has “huge financial implications” for the sector, as well as causing “havoc for travellers”.
In a statement Gatwick Airport said: “Nats are a world-class provider of air traffic services and London Gatwick’s senior management recognises how hard the airport’s air traffic controllers are working to keep the operation moving.
“We are working closely with Nats to build resilience in the airport’s control tower to ensure disruption is kept to a minimum.”
Nats apologised to people who had been inconvenienced, adding: “Airlines operating at London Gatwick were aware of the situation when Nats was appointed, but that does not dilute the apology we offer sincerely to them and their passengers who have been inconvenienced by recent disruption.”