Air traffic control: flight chaos over August bank holiday caused by error ‘never encountered’ before

Hundreds of flights were delayed or cancelled over the August bank holiday due to a  "one in 15 million" event that has never happened before, according to the company that controls the UK’s air traffic services.

The chief executive of Nats, Martin Rolf, said the system shut itself down after receiving highly unusual duplicate "markers" on a flight plan.

He added that the system did "what it was designed to do, i.e. fail safely when it receives data that it can’t process" but it was"a one in 15 million flight plan that we received" causing engineers to take a few hours to work out what they were not familiar with.

Nats, formerly known as National Air Traffic Services, said it had taken measures to prevent the situation from happening again while the UK’s aviation regulator, the Civil Aviation Authority (CAA), has also announced an independent review which is expected to report in a few months’ time.

The watchdog said it could take action if Nats had breached "statutory and licensing obligations".

Nats published its initial report today (Wednesday 6 September), confirming that on 28 August at 08:32 its system received details of a flight which was due to cross UK airspace later that day and the system detected that two markers along the planned route had the same name - even though they were in different places.

As a result, it could not understand the UK portion of the flight plan which triggered the system to automatically stop working for safety reasons.

The backup system then did the same thing. Engineers struggled to fix the problem, and called in the manufacturer for help.

The situation unfolded in just 20 seconds and Mr Rolfe said it was the first time this had happened in the five years the software had been operating.

Speaking to the BBC’s Today programme, he apologised to customers whose holidays were affected, saying “we absolutely understand how disruptive the events over the bank holiday were for people."

Many British holidaymakers found themselves stuck abroad and facing long waits to get home.

One family was left stranded in Egypt after a two week holiday, and ended up having to pay £6k more to get home due to the air traffic control chaos.

The system was back online just before 14:30 BST but it wasn’t until just after 18:00 that restrictions on air traffic were fully removed.

Nats has said that a software update will mean its system will no longer react in the way it did if the same situation happened again.

The CAA said “this scenario has never been encountered before” but the event "is now understood and should it reoccur would be fixed quickly with no effect to the aviation system".

Transport Secretary Mark Harper said that he was pleased to receive confirmation that there were no safety issues, adding that the independent review from the aviation watchdog will "dig deeper into this event and understand whether there are any further steps to be taken to improve the resilience of the air traffic control system".