08 September, 2023

NATS publishes its Major Incident Preliminary Report on the events of 28 August.

NATS (En Route) Plc's preliminary investigation has confirmed the root cause that led to last Monday’s air traffic control incident, and the company has reiterated its apology for the associated disruption to passengers, airlines and airports.

The report confirms that safety was maintained throughout the incident and that a solution has been implemented to avoid any possible recurrence.

The report, submitted earlier this week to the Civil Aviation Authority, identified an issue with a flight plan processing sub-system called Flight Plan Reception Suite Automated – Replacement (FPRSA-R).

A small but important part of NATS’ overall air traffic control technical infrastructure, it was found to have encountered an extremely rare set of circumstances presented by a flight plan that included two identically named, but separate waypoint markers outside of UK airspace.

This led to a ‘critical exception’ whereby both the primary system and its backup entered a fail-safe mode. The report details how, in these circumstances, the system could not reject the flight plan without a clear understanding of what possible impact it may have had. Nor could it be allowed through and risk presenting air traffic controllers with incorrect safety critical information. On the day, the time taken to recover was driven by the need to identify the problem and the specific data, isolate and remove it in a controlled way, and then test it to ensure it could be returned safely into operation.

This scenario had never been encountered before, with the system having previously processed more than 15 million flight plans over the 5 years it has been in service. Steps have been taken to ensure the incident cannot be repeated.

Martin Rolfe, CEO of NATS said: “Keeping the sky safe is what guides every action we take, and that was our priority during last week’s incident. I would like to reiterate my apology for the effects it had on so many people, including our airline and airport customers. Incidents like this are extremely rare and we have put measures in place to ensure it does not happen again.

“Our preliminary report, provided to the CAA this week, details what caused the incident, how we responded and the steps already taken to prevent recurrence. We welcome any further review of the incident that the CAA wishes to conduct.”

Flight plan process
Operators, usually airlines, wishing to fly through controlled airspace within participating European Countries must submit a flight plan, either directly or through third parties.

This flight plan will contain key information such as aircraft type, speed, callsign and intended routing that enables air traffic control to plan for, safely control and communicate with the aircraft.

For flights that will operate within the European flight regions, they submit the plan into Eurocontrol. If the submitted flight plan is accepted, it will be sent to all relevant air traffic services who need to manage the flight. Within NATS the data is passed to FPRSA-R. The FPRSA-R sub-system exists to convert the data received from Eurocontrol into a format that is compatible with our flight data processing system.