Air Traffic System Failure Was Caused by One in 15 Million Chance Error

The National Air Traffic Services reveals why thousands of UK passengers were left stranded as 1,500 flights were cancelled and 575 delayed.

Passengers wait at Stansted Airport, north of London, after UK flights were delayed over a technical issue, on Aug. 29, 2023. Daniel Leal/AFP via Getty Images

An air travel chaos that hit Britain last week was caused by an issue with a flight plan processing system, the National Air Traffic Services (NATS) has reported.

Thousands of passengers were stranded on Aug. 28, as their flights to and from the UK were cancelled owing to the “network-wide failure.”

The issue was identified and fixed on the same day, but has ultimately disrupted travel for the next days.

A preliminary investigation by NATS has confirmed that the outage was caused by an “extremely rare set of circumstances.” The organisation’s flight plan processing sub-system encountered a flight plan that included two identically named, but separate waypoint markers outside of UK airspace.

This caused the entire air traffic system to enter a fail-safe mode.

“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,” NATS said in a statement on Wednesday.

The route of the flight plan has not been named, but the aircraft in question was scheduled to depart at around 4:00 a.m. on Aug. 28 and arrive at its destination at 15:00 p.m. An 11-hour flight was at some point to enter UK airspace.

According to the air traffic services, a failure of this kind has never happened before to the system that previously processed 15 million flight plans in its five years of operation.

NATS said that on the day it isolated and removed the problem in a controlled way. The system was then tested to ensure it could safely return to operation.

Independent Review

The preliminary report (pdf) by NATS was submitted to the UK Civil Aviation Authority (CAA) and shared with the transport secretary Mark Harper and the aviation minister Charlotte Vere.

The report has estimated that more than 1,500 flights were cancelled and around 575 were delayed on Monday due to the incident.

NATS chief executive Martin Rolfe has issued an apology to affected passengers, airlines and airport customers.

“Incidents like this are extremely rare and we have put measures in place to ensure it does not happen again,” Mr. Rolfe said.

Mr. Harper welcomed the report and the confirmation that there were no safety issues as a result of the outage.

In a statement, released on Tuesday, he confirmed that the CAA will conduct and independent review of the air traffic system failure and how NATS’ responded to it.

If the review find that NATS has breached its statutory and licensing obligations, the CAA will then “consider whether any further action is necessary.”

This could mean that NATS will have to uphold some of the financial responsibility for the disruption caused by its system failure. The cost of the outage for the airlines could add up to £100 million, according to the global airline group IATA.

“NATS has crucial questions to answer about their responsibility for this fiasco. The failure of this essential service is unacceptable and brings into question the oversight of the CAA who are required to review the NATS resilience plan under the terms of its licence,” said IATA’s director general Willie Walsh.

He suggested that while the airlines will bear the brunt of costs for the air traffic system failure, “it will cost NATS nothing.”

Mr. Walsh called on policymakers to take note and improve the passenger rights system.

Last week, shadow transport minister Louise Haigh criticised the government for having “sat on their hands for too long” while airline passengers were denied basic rights and compensation.

Ms. Haigh suggested that Downing Street has failed to grant new enforcement powers for the CAA to hold airlines to account.

The CAA said that the preliminary report on the incident will be examined to find answers for passengers and the industry.

Mr. Harper will chair a meeting between NATS, the CAA and the aviation industry on Thursday, where NATS will present its findings and the airlines will give feedback.