The chief executive of NATS, the UK's main air traffic control provider, says he has not considered resigning after two technical failures in September disrupted flights across the UK. Speaking at the Airlines 2026 conference in London on 11 November, Martin Rolfe said the causes of both events had been fixed and "will never recur", but added that "nobody standing on a stage like this can credibly promise that a complex technical system will never experience another fault"1. Ryanair, which has called for his resignation after each failure, repeated its criticism at the same conference1.

For crews, the episode shows how quickly a fault deep inside an air traffic system turns into departure stops, slot delays and diversions. It also comes with a regulatory review that will test how far the lessons of the August 2023 failure were applied.

What failed on 8 September

According to NATS's preliminary investigation report, the failure began at 10:00 local time on 8 September inside the National Airspace System (NAS), the core flight data system behind London Area Control at Swanwick, which handles traffic mainly above 24,500 ft over England and Wales. A valid manual request to allocate a squawk code was paused while the system handled a higher priority message. Because of a legacy software defect with an exposure window of about one millisecond, the request did not resume correctly and corrupted flight data2.

The first link drop between the London Area Control system and the NAS cleared itself after 45 seconds and was logged as a routine engineering incident. At 12:32 the link started dropping repeatedly, and at 13:32 it failed and did not recover. Controllers switched to fallback procedures and coordinated handovers with neighbouring units by hand, a task that is normally automatic. NATS says controllers could talk to and see every aircraft on radar throughout, and that all aircraft stayed safely separated2.

How it reached the flight deck

The extra manual workload meant fewer aircraft per sector. From 12:45 the duty supervisor limited sector entries and stopped departures from UK airfields, with airlines and airports told through the EUROCONTROL portal. At 13:38 NATS aimed to restrict entries into London Area Control sectors to 30 an hour and capped arrivals at some UK airports, which in turn held departures at foreign airports. From 15:20, with more aircraft arriving than leaving, airports ran short of ground space and inbound flights already airborne were diverted2.

The NAS was restarted between 15:17 and 16:09, and reconciling duplicate flight plans and squawk and callsign mismatches took until 18:50. All airspace restrictions were lifted at 19:30. In total UK departures were stopped for about four and a half hours over a six hour period2. NATS had forecast around 8,000 flights that day and handled 6,094, with more than 2,000 flights delayed, cancelled or diverted2.

On the line, restrictions like these arrive as ATFM regulations. A regulated flight receives a slot in the form of a Calculated Take Off Time (CTOT), which forms part of the ATC clearance, and the aircraft must not depart outside a tolerance of five minutes before to ten minutes after it13. British Airways said on the day that the disruption left "aircraft and crews ending up out of place"12, and Ryanair said more than 65,000 of its passengers were delayed by up to eight hours and over 50 flights were cancelled8.

A second failure at Prestwick

On 21 September a fault in the network infrastructure at the NATS Prestwick Centre disrupted the automatic distribution of data between systems and controller positions. NATS reduced Prestwick capacity to 60 per cent from 06:20 and to 40 per cent from 07:40, and began lifting restrictions from 10:00. All Scottish airports had aircraft held on the ground, and Cirium data cited by NATS showed 117 departures cancelled. NATS handled 7,933 of the 8,151 flights expected that day, reported no losses of separation and said the fault was unrelated to 8 September3.

Ryanair disputed that reading. It said the Prestwick event was another failure of NATS flight data processing three days after the preliminary report, that more than 140 of its flights were delayed, and that the permanent software fix for 8 September was still under test at the time9. The preliminary report itself said the fix had been delivered by the supplier and was being tested, with mitigations in place until deployment2.

Lessons from August 2023

Both September events are being measured against the failure of 28 August 2023. In that case a flight plan from Los Angeles to Paris Orly contained two waypoints with the same identifier, DVL, one at Devil's Lake in North Dakota and one at Deauville in France. The flight plan processing system FPRSA-R generated a critical exception and put itself into maintenance mode, and the backup did the same within about 20 seconds. Manual processing cut capacity from a typical 800 flight plans an hour to about 60, and UK slot rates fell to 20 an hour for Swanwick and 10 for Prestwick at the low point6.

The Independent Review Panel commissioned by the Civil Aviation Authority (CAA) found that recovery took longer than necessary. The on call system expert needed 1.5 hours to reach the site, a senior design expert was not involved for more than three hours, the manufacturer was not called for more than four hours, and there was no single person accountable for managing the incident6. The panel estimated airline costs at about £65 million, and the CAA put the number of affected passengers above 700,00067. Its 34 recommendations included earlier warnings to airlines and airports of possible disruption, a review of NATS contingency and engineering resource arrangements, and an industry forum to rehearse major incident management7.

NATS says those recommendations have been implemented and independently verified by the CAA, and that a dedicated Major Incident Manager, a role created after 2023, led the response on 8 September. Its timeline shows departures stopped and airlines notified at 12:45, with the first industry coordination call at 13:402.

What the government and the CAA are doing

Transport Secretary Heidi Alexander told the House of Commons on 9 September that a cyber attack had been ruled out, but that she did "not believe this issue was unavoidable"10. After reading the NATS report she said the government needed "to urgently understand why this issue was not discovered and fixed before it caused chaos"11. At the conference on 11 November she called the failure "simply unacceptable" and said she would not "jump the gun" before the regulator reports1.

The CAA review will check the NATS findings and look at its plans to renew and replace critical operational systems, how earlier recommendations were implemented, the CAA's own oversight and international practice on resilience. It will also take account of the Prestwick event. An initial report is due to the Secretary of State by the end of January 2027 and the final report by 8 March 20274. Airlines, airports and their representative groups can submit evidence until 23 November5.

Ryanair chief operating officer Neal McMahon was unconvinced by NATS pointing to its usual reliability. "It's like listening to the captain of the Titanic saying that 99% of the time it sailed just fine," he told the conference1. Rolfe said NATS had expected to handle about 8,000 flights on 8 September and that 6,000 had flown, without putting a figure on the delays1.

Air traffic services and air traffic management are part of the air law syllabus in ATPL theory, as our overview of ATPL theory subjects sets out. The Ryanair UK, British Airways and easyJet pages cover pilot recruitment at three of the airlines hit by the September disruption. For a comparable modernisation story across the Atlantic, see how the FAA is replacing legacy air traffic control systems.