Travellers were stranded at UK airports on Tuesday morning after dozens more flights were cancelled following a day of chaos caused by an air-traffic control glitch.
Transport Secretary Mark Harper said issues of this magnitude “haven’t happened for a decade” as he ruled out a cyber attack.
“Our technical experts have looked at it and are clear that it wasn’t a cyber security incident,” he told Sky News.
The Civil Aviation Authority has launched an “independent review” into the incident and is due to deliver a report to Mr Harper “in days”. The government will examine whether lessons can be learnt.
A technical fault was detected in the UK’s air-traffic control system on Monday morning and resolved by early afternoon. Airports had to resort to a backup system, meaning fewer flights could be processed.
Hundreds of flights were cancelled, leaving thousands stranded at airports in Britain and overseas.
About 790 departures and 785 arrivals across all UK airports were scrapped on Monday, aviation analytics company Cirium said. This equated to around 27 per cent of planned journeys.
On Tuesday, data from Flightradar24 showed 78 flights at Heathrow were delayed, while at least 32 departures and 31 arrivals were cancelled. That compares to more than 170 axed flights on Monday.
At Gatwick Airport, the second major hub in London, 23 departures were cancelled on Tuesday while 51 arrivals were called off, according to the data.
Manchester Airport reported delays and cancellations and urged people to check their flight status with their airline.
Mr Harper tried to reassure travellers, stressing that airlines had a legal responsibility to provide accommodation and food to passengers who had their journeys cancelled.
It remains unclear when travel will return to normal but passengers reported cancellations at UK airports on Tuesday morning.
British Airways, which operates the most flights to and from Heathrow, was the worst affected airline.
A man travelling to Dubai shared a video showing a crammed terminal at the West London airport on X, formerly known as Twitter.
“This is awful,” he wrote. “I can’t move in Heathrow Airport, there is no room. I have been here for 27 hours now. I want to get back to Dubai and nobody from customer service is helping. They’re ignoring everyone.”
On Monday evening, Heathrow said “schedules remain significantly disrupted” following the technical issues. It advised passengers to check with their airlines before travelling to the airport on Tuesday.
National Air Traffic Services, the country's leading air traffic control provider, said at 3.15pm on Monday it had “identified and remedied” the technical issue affecting its systems and it was working with airlines and airports to support affected flights.
Mr Harper on Tuesday told GB News: “It's nearly a decade since there was a significant issue like this.
“We want to make sure it doesn't happen again because of all the disruption that's been caused to passengers across the country.”
Juliet Kennedy, operations director at the air traffic services, said the issue meant the automatic system that provides controllers with details of every aircraft and its route stopped working.
“To manage safety, we had to limit the number of flights we could manage,” she added.