An engineer who forgot their password potentially added hours to chaos caused after melted down.

Nearly three quarters of a million passengers were disrupted when were grounded at UK airports on August 28 last year after air traffic control (ATC) provider National Air Traffic Services (Nats) suffered a technical glitch while processing a flight plan.

An inquiry has now revealed that the resolution of an ATC meltdown in August 2023 was complicated due to delays in verifying the password of a remote-working engineer. The technical glitch resulted in more than 700,000 passengers experiencing disruption when flights were grounded at UK airports on August 28 last year.

The Civil Aviation Authority (CAA) found that Nats had scheduled a Level 2 engineer to be on call rather than on site that day, despite it being one of the busiest days for passenger numbers. A junior Level 1 engineer, who was on site at Nats’ headquarters in Swanwick, Hampshire, began checks immediately after automatic flight planning systems failed at 8.32am.

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However, the Level 2 engineer's password login details "could not be readily verified due to the architecture of the system", according to the report. After all remote intervention options were exhausted, it was agreed that they would attend the control centre, but their arrival took an additional one-and-a-half hours, three hours and 15 minutes after the incident began.

The inquiry suggested that Nats should consider having a Level 2 engineer on site during busy periods such as the summer. The report conceded that the necessary fix following the August 28, 2023 UK air traffic control system failure would incur a "significant" cost which could reach an eye-watering £100 million.

EasyJet boss Johan Lundgren blasted Nats for severely failing airlines and travellers, insisting such a catastrophic failure "can never be allowed to happen again". Meanwhile, Ryanair's boss Michael O’Leary has demanded that Transport Secretary Louise Haigh urgently rectify Nats' “hopeless service” and called for Nat's CEO Martin Rolfe to be fired.

The inquiry uncovered that an automatic flight planning system plus its backup crashed within mere seconds after receiving a plan for a Los Angeles to Paris (Orly) flight. The cause was a "unique set of circumstances not previously encountered", with the key issue being a pair of identical three-letter waypoints used to pinpoint locations.

With over 15 million flight plans smoothly processed before this glitch, its rare nature was emphasized. This technical blunder led to a manual crunching of flight plans, plummeting the processing rate from a swift 800 per hour to a mere 60.

UK airports had to enforce restrictions on the number of flights taking off from 11am until 6.03pm on August 28, yet the fallout continued for days due to misplaced aircraft and crew. A spokesperson from Nats expressed regret for the trouble fliers faced amid what was termed a "very unusual technical incident".

They said: "Our own internal investigation made 48 recommendations, most of which we have already implemented; these include improving our engagement with our airline and airport customers, our wider contingency and crisis response, and our engineering support processes. We fixed the specific issue that caused the problem last year as our first priority and it cannot reocur."