How A Single French Bee Flight Plan Error Delayed 700,000 Passengers

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  • A flight plan filed by French bee caused a UK ATC outage, impacting 700,000 passengers in August 2023.
  • The two systems’ failures resulted in them being disconnected within seconds.
  • Stakeholders complained of slow communication by NERL during outage, impacting airlines, airports, and passengers in UK airspace.

The United Kingdom Civil Aviation Authority (CAA) has published its preliminary report on the air traffic control (ATC) system outage over the country’s airspace in August 2023. According to the authority, a single French bee flight plan caused the failure, impacting hundreds of flights and hundreds of thousands of passengers.

Impacting 700,000 passengers

The CAA issued its report on March 14, detailing that when NATS, the company that provides ATC services in the UK, suffered its systems failure, over 700,00 passengers were affected by the outage. The panel provided its preliminary conclusions, having begun the investigatory work in October 2023.

Photo: French bee

According to the authority, the NATS flight planning system, known as NERL, failed when French bee filed its flight plan data for a specific service from Los Angeles International Airport (LAX) to Paris-Orly Airport (ORY). The flight’s planned route included overflights over American, Canadian, Oceanic, British, and French airspace before finally landing at ORY. It is important to note that NERL is an economically regulated NATS business that also provides ATC services outside the UK. As such, NERL is the de facto service provider for ATC for the country and its airspace.


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Two systems’ failure

The report detailed that after the airline filed its flight plan, the primary and secondary systems produced critical exception errors, causing each system to enter maintenance mode. As a result, this prevented the transfer of apparently corrupt flight plan data to ATC.

An Aerial View of London Heathrow Terminal 5.

Photo: EQRoy | Shutterstock

However, the report noted that French bee filed the plan in accordance with standard procedures, forwarding the plan to EUROCONTROL for processing. Subsequently, the flight plan data was converted to a European standard, ATS Data Exchange Presentation (ADEXP), adding supplementary waypoints, identifying states requiring flight information, and sharing the ADEXP-formatted file with those states.

“The action of supplementing the original flight plan increases the number of waypoints in the converted data file considerably. Most waypoints are identified using five-letter abbreviations, although some older waypoints use only three.”

Essentially, the flight plan data was then passed to NATS, namely to the FPRSA-R at Swanwick Area Control Centre (ACC). In a typical scenario, the ADEXP data is processed and further identifies the portion of the route flown in the country’s airspace, presenting that data to ATC.


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Mixing up North Dakota and France

The FPRSA-R, acting as the primary system, began searching for the entry point into the UK’s airspace. After identifying APSOV as a viable entry point, the system sought an exit waypoint, identifying two possibilities. However, since both (SITET and ETRAT) were not part of the original flight plan, they were dismissed, with the system selecting the third option: Deauville, which had the three-letter abbreviation of DVL.

“Deauville is one of the minority of waypoints that has a three-letter abbreviation, in this case DVL. As DVL was included in the original flight plan, FPRSA-R was able to identify it as a valid exit point.”

However, the DVL that French bee included in its original flight plan was in North Dakota, namely Devil’s Lake. As a result, FPRSA-R considered the exit waypoint unviable, generating a critical exception error and disconnecting it from the system, as it was designed to do.

The secondary system received the same flight plan and was undergoing the same process when it, too, generated a critical exception error and disconnected. Devils Lake Regional Airport (DVL) and Saint-Gatien Airport (DOL) are shown below, highlighting the huge distance between the two waypoints.

Devil's Lake and the nearest airport near the DVL exit point

Photo: Great Circle Mapper

The panel highlighted that after the primary system received the flight plan, both FPRSA-R systems shut down within 20 seconds. As a result, NATS could not automatically process flight plan data, forcing controllers to do so manually.


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Stakeholders’ complaints

The panel’s report also noted that after speaking with many stakeholders, including airports, airlines, consumer organizations, and others, many expressed dissatisfaction with the effectiveness of NERL’s communication.

One of the main issues expressed by the stakeholders was how slow NERL was in warning about the problem and describing it in detail. As a result, airlines and airports experienced more uncertainty, exacerbating the impact on passengers. The panel detailed that 300,000 passengers’ flights were canceled, while around 95,000 and 300,000 travelers suffered long and shorter delays, respectively.

A Ryanair Boeing 737 MAX Parked At A Remote Stand.

Photo: Ryanair

For example, Irish low-cost carrier Ryanair was highly critical of NATS after the failure and the company’s preliminary report, issued in September 2023. Ryanair’s chief executive officer (CEO), Michael O’Leary, alleged that NATS had made a number of false claims in its preliminary report.


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Moving forward following the systems’ failure

Moving toward the conclusion, the report stated that, compared with other European ATC providers, NATS has performed well in terms of average Air Traffic Flow Management (ATFM) delays. However, its two separate system failures in 2013 and 2023 highlighted the need to introduce incentives that ensure efficiency and address resilience-related problems.

“[…] the Panel has concerns about the measurement and incentivisation of NERL performance solely in terms of ATFM delay minutes, as opposed to the inclusion of passenger impact caused by cancellations as well as by knock-on delays.”

Still, the panel highlighted that it was inappropriate that despite achieving all of its performance targets in 2023, NERL will suffer very few financial consequences following the systems’ failure. As such, the report noted that using a performance incentive-based framework may not be measuring the right things.

Heathrow Tower

Photo: NATS

In conclusion, while the panel has only presented its preliminary findings, it also said it would make recommendations to fix various issues. These include the cause and management of the failure, resilience planning, systematic communication improvements, regulatory powers to seek information, a framework for consumer engagement and representation, and dispute resolution.


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