Flicht chaos for hunners o thoosands was caused in a ‘millisecond’ by a saftware error

A saftware defect in a pairt o the UK’s air traffic control system corrupted flicht data “in the space o a millisecond”, leadin tae a sax-hour outage and mass airline cancellations and delays across the UK last week, National Air Traffic Services (Nats) has said.

But ministers said the Nats report intae the incident still left questions unanswered, sayin they needed “tae urgently understand why this issue wasna discovered and fixed afore it caused chaos”.

Accordin tae the report, the error first occurred at 10am and was notified tae engineers wha investigatit – but the system appeared tae be workin again, until 12.30pm whan a repeat occurred and a major incident was declared.

The transport secretary, Heidi Alexander, said the Civil Aviation Authority (CAA) industry regulator wad now “check their findins” and investigate Nats mair widely.

Hunners o thoosands o passengers had their travel disruptit after the Nats failure on Tuesday 8 September, which endit up delayin and cancellin flichts across the UK and ayont late intae the neist day.

Airlines hae cawed for compensation and a “credible plan”, wi Ryanair demandin the dismissal o the Nats chief executive officer, Martin Rolfe, after the third major air traffic control failure in the UK syne summer 2023.

A government source said the CAA review wad be “a chance tae fundamentally investigate” if Nats was fit for purpose.

Rolfe said the incident was unrelated tae the previous failures. He said he cud “confirm that it was a saftware issue and no caused by ony incorrect actions by either military or civil operators”.

The preliminary report said the failure was a “legacy and previously unknown saftware defect and a combination o verra specific events occurrin simultaneously” in pairt o the National Airspace System, which allocates codes tae individual aircraft tae identify flichts on radar.

Nats said the saftware error occurred at 10am, wi engineers first notified at 10.02am that the link atween the national system and London area control had droppit. The engineers reportit at 10.06am that the system had apparently recovered wi nae operational impact, but continued tae investigate.

The report said the fauut presentit whan a manual request for an aircraft code was bein processed but pausit for anither, unspecified “heicher priority activity” request. It said: “Whan processin o the aircraft code request resumed, the saftware defect meant it didna resume correctly and the resultin output was corrupted, and affectit some subsequent flicht data updates. This happened in the space o a millisecond.”

At 12.32pm the link atween the national and London airspace management droppit again and a major incident was declared, wi controllers haein tae conduct some tasks manually. By 12.45pm, Nats was restrictin flichts as the system continued tae glitch, afore failin completely at 1.32pm.

At 1.40pm airlines were advisit o restrictions, and atween 2.50pm and 4.09pm Nats rebootit the system, eventually resumin fu operations at 7.30pm – but leavin mass congestion, displacit aircraft and hunners o thoosands o delayit passengers in its wake.

It took mair than twa days for the backlog o passenger disruption tae be cleared, wi mair than 2,000 flichts cancelled in total and hunners o thoosands o fowk’s travel plans disruptit.

Rolfe said: “The issue has been identified and mitigation is in place while a permanent fix is safety testit and deployit.”

He addit: “I wad like tae apologise again, verra sincerely, tae everyone wha was affectit last week. It’s our job tae get fowk whaur they want tae gang, quickly and without delay and we are devastatit whan that gangs wrang. However, our primary role is tae keep our skies safe, and everyone wha flees through them. At nae point last week was safety in question.”

The transport secretary said: “The disruption we saw last week was completely unacceptable and I ken how frustratin it was for passengers, airlines and airports.”

Alexander said she had receivit Nats’ report, addin: “It’s clear we need tae urgently understand why this issue wasna discovered and fixed afore it caused chaos.

“I hae therefore taskit the CAA wi conductin an independent review tae check Nats’ findins and investigate their investment plans tae enhance resilience in the future, alang wi regulatory accountability.”

The CAA’s review will be publishit within sax months.

Tim Alderslade, the chief executive o Airlines UK, a lobby group representin the industry, said: “The CAA’s review must mandate real investment in Nats’ resilience so a single fauut can never again descend intae nationwide disruption.”

He said his members were writin tae Nats tae “demand immediate compensation for the costs incurrit and a credible plan tae improve resilience”.

The EasyJet chief executive, Kenton Jarvis, said: “Passengers deserve mair than just anither promise that lessons will be learnit. Firm actions must be taken … and there must be a fair solution tae ensure that airlines are no left tae pick up the bill.”

The Ryanair chief operations officer, Neil McMahon, said: “‘The saftware ate my homework’ is no an acceptable explanation … How mony times must the UK ATC system collapse afore Martin Rolfe accepts responsibility and resigns.”