Staff shortages in air-traffic control at London Gatwick Airport forced flights to be cancelled, delayed or diverted on Thursday evening.
The airport confirmed a short-notice staff absence in its air-traffic control tower, which meant 42 flights were cancelled or diverted as far away as Brussels and Cardiff, while dozens more were badly delayed.
On Friday, Gatwick said the airport was operating normally again, and that any delays were not related.
In a statement issued to The National it said: "The tower is fully staffed and the airport is operating as normal today."
Stanstead also said it was operating as normal on Friday morning, after reports of "manic" queues forming overnight due to flight diversions from Gatwick.
EasyJet, which had spoken of its "disappointment" about the impact on its customers on Thursday, told The National its schedule was "running as normal" on Friday.
However, the airline's chief executive said air traffic control provider National Air Traffic Services (Nats) has “let down customers all summer” after the latest period of disruption on Thursday.
Johan Lundgren said: “Persistent staff shortages at Nats have plagued the industry and repeatedly let down customers all summer, having caused more than a month’s worth of disruption.
“This cannot be allowed to continue.
“Immediate action must be taken to fix the staffing shortages now while a more wide-ranging review examines broader issues to ensure Nats delivers robust services to passengers now and in the future.”
More than 6,000 passengers are likely to have been affected by cancellations on Thursday and overnight.
Passengers complained on social media of delays of up to five or six hours.
Laura Neary, 29, was due to catch a Ryanair flight to Dublin at 5.30pm, but it diverted to London Stansted, which she had to travel by coach to make her flight.
Ms Neary, who was travelling on her own, said some passengers received text messages saying they needed to take a coach to Stansted, in Essex, while others were told they could still board the flight from Gatwick.
The sales worker, who is from the Irish capital, said: “I don't even know if I can get back to Dublin tonight.”
Nats said new air-traffic controllers had been recruited since last summer, “increasing our presence by 17 per cent”, and others were due to start after completing their training.
“London Gatwick’s senior management understands that we are working hard to keep the operation moving,” it added.
“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.”
Gatwick Airport through the years – in pictures
“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,” the Sussex airport said in a statement.
“We are working closely with Nats to build resilience in the airport’s control tower to ensure disruption is kept to a minimum.”
Thursday's events came just over two weeks after an air-traffic control technical glitch caused widespread disruption at airports across the UK, leaving thousands of holidaymakers stranded overseas for several days.
More than a quarter of flights to and from UK airports were cancelled that day, affecting about 250,000 people.
Cancellations continued for two more days because planes and crews were out of position.
Ryanair boss Michael O'Leary has called on Nats' chief executive to resign, while easyJet said it is “very disappointed” its customers have been affected again.
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.”
An easyJet representative said: “We are very disappointed that customers are once again impacted by this and while this is outside of our control, we are sorry for the inconvenience caused to our customers.
“We are doing all possible to minimise the impact of the disruption, notifying those on cancelled flights of options to rebook or receive a refund and provided hotel accommodation and meals where required.”
Julia Lo Bue-Said, chief executive of Advantage Travel Partnership – a network of independent travel agents, said: “The situation at Gatwick is unacceptable. This kind of disruption causes havoc for travellers and has huge financial implications for airlines, travel agents and the entire ecosystem.
“There needs to be an urgent inquiry into why there appear to be staff shortages in this crucial area, and measures implemented to stop these incidents occurring again.”