Many people were left stranded in airports for days on end because of the chaos (Picture: AFP)

A technical glitch which caused widespread disruption to flights last week was a ‘one in 15 million’ occurrence, according to an air traffic control boss.

Many impacted travellers waited days for flights home which were either severely disrupted or cancelled.

It meant more than a quarter of flights were cancelled on Bank Holiday Monday, affecting around 250,000 people over a two-day period.

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

He said: ‘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.’

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.

Passengers wait at Stansted Airport, north of London, on August 29, 2023 after UK flights were delayed over a technical issue (Picture: AFP via Getty Images)

Many people were left confused and stranded with no help from any airlines (Picture: AFP via Getty Images)

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. in a report shared with transport secretary Mark Harper.

The flight plan 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.

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

The back up system stopped working and followed the same steps.

A ‘permanent software change’ is expected to be implemented in the coming days to prevent something similar happening again.

Many people were forced to sleep at the airport because they were not placed in hotels (Picture: AFP via Getty Images)

An ‘operating instruction’ has also been put in place to allow the ‘prompt recovery’ of the system if it happens again.

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

An independent review into the meltdown has now been launched by the Civil Aviation Authority (CAA).

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Details will be published at the end of September and the inquiry is expected to take 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.’

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The chaos affected around 250,000 people.