A military aircraft entering “spurious” flight data into the UK’s air traffic control system led to an outage that caused thousands of planes to be grounded and unleashed a crisis that threatens to topple the head of the agency.
Four people briefed on Tuesday’s incident said a flight plan submitted by a UK military aircraft triggered a series of events that led to the shutdown of Britain’s skies for several hours.
The entry caused a meltdown within the wider air traffic control system that took hours — and several attempts — to restart, the people said.
The incident has strained relations between carriers and National Air Traffic Services (Nats), the air traffic control agency owned by airlines and the government, and puts the future of its longtime chief executive, Martin Rolfe, in doubt.
Transport secretary Heidi Alexander called Rolfe in for a meeting on Wednesday, while aviation minister Keir Mather hosted a call with airline executives. Afterwards, Alexander said the outage was “not unavoidable” and demanded a review by Nats within a week to determine the exact cause.
“I’m going to be looking very carefully at the report,” she told LBC on Friday. “We need to get to the bottom of this.”
While he can only be fired by the Nats board, led by former Rolls-Royce boss Warren East, the government owns 49 per cent and can withdraw its support for him.
The Civil Aviation Authority will carry out its own independent investigation, reporting in six months, but next week’s report from Nats is seen as crucial for Rolfe. “It would be wrong to fire anyone from a job when you don’t know what has happened,” said one person with knowledge of the process.
Others within the system are less circumspect. Rolfe is “toast”, said another person close to the process. “This is the beginning of the end.”
Airlines are particularly incensed by the latest disruption because they were promised that a Nats failure in 2023, caused by a rogue flight plan that caused the system to collapse, could never happen again.
“We were told the [recommendations after 2023] had been fully implemented, but to tell you the truth, we never saw the evidence,” one airline executive told the FT.
Tensions boiled over during a call on Tuesday evening between Nats operations director Kathryn Leahy and operations managers from airports and airlines.
On the call, Leahy informed them that flight plan data entry had sparked the problem. Some of the executives were flabbergasted. “You cannot be serious,” said one, according to three people with knowledge of the call.
Nats remains adamant the underlying problem is not a repeat of 2023’s outage, which was caused when the system confused two locations entered as part of the plan.
The agency has said the problem was within the “flight processing system”, a vast technical labyrinth that co-ordinates the thousands of flight plans it receives each day.
However, the FPS does not have a dedicated backup, partly because Nats is in the middle of a complete overhaul of its systems, and partly because its size means a duplicate service would cost vast amounts, according to people briefed on the outage.
The fact that the flight plan came from a military aircraft had no specific bearing on the problems that followed, two people briefed on the matter said. The Ministry of Defence declined to comment.
For airlines, Tuesday’s call capped a day of intense frustration, as promised fixes to the system failed to materialise and flight delays piled up at UK airports.
“It was a complete clusterfuck,” said Ryanair’s operations boss, Neal McMahon.
Warnings flashed up within the Nats control centre just outside Southampton before 1pm. Minutes later, airlines started receiving calls from airports, warning them of a problem with the Nats system. Within two minutes, take-offs were suspended from airports surrounding London.
“Nobody knew what it was, but within the space of two to three minutes everything was shutting down,” said one executive who was in their airline’s operations room at the time.
Within half an hour, Nats convened a call for the “air traffic incident communication and co-ordination cell” or ATICCC, its crisis response network.
More than 100 people joined; from airlines and airports to the UK’s regulator, the Department for Transport and air traffic control directors from neighbouring airspaces such as France and Ireland. It was to be the first of half a dozen such calls over the afternoon.
Shortly after 1.30pm, flights started to move — only to grind to a halt again. A separate fault, affecting several major airports, had been triggered by the restart.
“We were told the issue had reoccurred, Nats said they could only accept 30 aircraft per hour,” recalls Ryanair’s McMahon.
By 2pm, delays to flights sitting on the tarmac reached five hours. Frustrated passengers took to social media, saying they were stranded with little or no information. As airports filled up with delayed flights unable to leave, incoming planes were diverted to airports as far away as Bonn and Düsseldorf in Germany.
Shortly after 3pm, an email was sent by Nats to the ATICCC group. They now understood the problem, it would take 25 minutes to plan the fix, and perhaps another 30 to 40 minutes to implement it. But this timeframe proved far too optimistic.
The fix required a complete reboot of the Nats system, which happened just after 4pm. It was not until after 5pm that airlines were able to begin flying some aircraft and even then progress was painfully slow.
“They said it would be another 40 minutes but after another hour or so passed it still wasn’t resolved,” said easyJet’s chief commercial officer Sophie Dekkers.
“I think they were trying to manage us and trying to manage expectations but unfortunately the time that they gave us wasn’t actually met in reality, so it was very difficult to plan because it was a live ongoing situation.”
By 5.30pm, the delays for grounded planes hit 10 hours, some airlines said, and passengers waiting to board early evening flights were informed they might take off after 2am. At Heathrow, the queues to leave the airport stretched through the long corridors of its terminals.
In an attempt to prevent the next day’s schedule from completely disintegrating, British Airways decided to cancel all short-haul flights for the rest of the evening.
On a call just after 7pm, Leahy delivered the news to select operations managers that data from a flight plan had triggered the chaos.
Even once flights were restarted, progress in clearing the backlog was achingly slow. When arrivals finally resumed at 10pm, Gatwick was only able to receive four flights an hour, rising to eight in the final hour of operations.
Three days after the outage, airline schedules have only just recovered, but the industry is calling for significant change at Nats to prevent anything like this happening again.
Wizz Air’s UK boss Yvonne Moynihan said: “If the organisation wants to have any credibility, it has to demonstrate some kind of change.”
Additional reporting by Lucy Fisher
