Investigation into air traffic chaos identifies cause 'that had never been encountered before'

Officials have said that changes are being made to make sure the cause of the chaos does not surface again, but some are not convinced by what they have heard, as ITV News Consumer Editor Chris Choi reports

A preliminary investigation into last week's air traffic control chaos by Nats (National Air Traffic Services) confirmed the root cause was an extremely rare set of circumstances that had never been encountered before.  

The technical glitch which caused widespread disruption to flights last week was a “one in 15 million” occurrence.

National Air Traffic Services (Nats) chief executive Martin Rolfe said one of its systems failed after it “didn’t process (a) flight plan properly”.

The plan submitted by the airline – which has not been named – was “not faulty”, he added.

The problem led to Nats being unable to process flight plans automatically for several hours on August 28, a bank holiday Monday and a peak period for air travel.

The subsequent switch to manual processing meant the average number of plans it could handle dropped from around 400 per hour to as few as 60, leading to restrictions on flights to and from UK airports.

More than a quarter of flights were cancelled that day, affecting around 250,000 people.

The air traffic control problem caused widespread delays. Credit: PA Wire

Cancellations continued for two more days as planes and crews were out of position.

Asked what the odds of this happening were, Mr Rolfe replied: “We know it’s at least one in 15 million, because we’ve had 15 million flight plans through this system and we can be absolutely certain that we’ve never seen this set of circumstances before.”

In a preliminary report shared with Transport Secretary Mark Harper, Nats did not identify the route of the flight plan which led to the chaos but stated the aircraft was scheduled to enter UK airspace during an 11-hour journey.

Airlines’ flight plans feature waypoints, which represent locations and are identified by a combination of letters and numbers.

The flight plan which caused last week’s disruption was submitted to Eurocontrol – which oversees ATC across Europe – before being passed on to Nats.

The process led to the plan featuring two waypoints around 4,000 nautical miles apart but with identical names.

This meant Nats’ software was unable to extract a valid UK portion of the flight plan and reacted by shutting down.

A back-up system followed the same steps and also stopped working.

Nats said an “operating instruction” has been put in place to allow the “prompt recovery” of the system if there is a repeat of these circumstances. A “permanent software change” to prevent it shutting down in such an event is expected to be implemented in the coming days.

Mr Rolfe said: “I’m very confident that the changes we’re making here will prevent this incident from happening ever again.

“Keeping the sky safe is what guides every action we take, and that was our priority during last week’s incident.

"I would like to reiterate my apology for the effects it had on so many people, including our airline and airport customers.

What caused the system to go down?

Last week Nats said the system went down due to flight data that it received.

Here is a step by step of what happened, according to Mr Rolfe:

  • Flight data was received by Nats;

  • A technical issue began, which was 'complex and difficult to resolve';

  • Nats' primary and back-up systems suspended automatic processing - this was to ensure that no incorrect safety-related information could be presented to an air traffic controller or impact the rest of the air traffic system.

Initial reports suggested an inputting error from a French airline was to blame for the ATC issue, but this was not addressed in the last report.

Speaking to ITV News last week, Melanie Waite said she feels 'disappointed and let down' by airline Jet2 after her flight home from Mallorca was cancelled

Independent review announced

Hundreds of flights were cancelled across several days as a knock-on effect from the technical fault, which grounded flights and left thousands of passengers stranded.

The Civil Aviation Authority (CAA) announced it will launch an independent review into the meltdown.

Details of this will be published by the end of September and the inquiry is expected to take around three months.

CAA joint-interim chief executive Rob Bishton said: “The initial report by Nats raises several important questions and as the regulator we want to make sure these are answered for passengers and industry.

“If there is evidence to suggest Nats may have breached its statutory and licensing obligations we will consider whether any further action is necessary.”

Last week Ryanair boss Michael O’Leary slammed air traffic control (ATC) provider Nats for the “unacceptable” disruption caused over the glitch.

In a video message posted on X, the chief executive described the first day of the chaos as “a very difficult day” with 250 flights cancelled, while a further 70 were axed the following Tuesday.

He said: “It’s not acceptable that UK Nats simply allow their computer systems to be taken down and everybody’s flights get cancelled.”

'Absolute chaos'

Passengers stuck in the UK and abroad described the "absolute chaos" they had endured as a result of flight cancellations.

Melanie Waite told ITV News herself and her 11-year-old son were left stranded on the Spanish island of Mallorca when their Jet2 flight to England was cancelled on Monday.

Melanie Waite's 11-year-old son sleeping on the airport floor in Mallorca. Credit: Melanie Waite

She said they received "not much" help from the airline and were informed their flight had been scrapped by staff only when they arrived at their departure airport.

"There was a couple of ground crew there that some people from our flight approached and they told us 'just go to the luggage carousel, collect your luggage, your flight's cancelled'," she added.

Others who were left stranded by the travel chaos told of how it had disrupted honeymoons and end of summer getaway plans.

The disruption also left round 40 British athletes and staff stranded in Budapest, following the World Championships.

Some are now travelling from Hungary's capital directly to Zurich for the Diamond League meeting on Thursday, while UK Athletics is working to get other athletes back home, but do not yet know when they will return.

Travel expert Paul Charles explains what your rights are if you've had your flight delayed or cancelled

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