Heathrow shutdown caused by problem found seven years ago

Issues at an electrical substation which caused a fire that resulted in Heathrow Airport closing were first detected seven years ago but not fixed, a report has found.

The National Energy System Operator (NESO) said moisture entering electrical components at the North Hyde substation caused the blaze at the site that supplies the UK’s biggest airport with power.

It revealed an elevated moisture reading had been first detected in July 2018, but that the issue went “unaddressed”, with basic maintenance by National Grid cancelled.

Heathrow shut down the following day as a result of the power cut, which led to thousands of cancelled flights and stranded passengers.

Neso’s report said previously that the the power outage affected 66,919 domestic and commercial customers, including Heathrow Airport. Around 270,000 journeys were affected.

Its report said the fire was “most likely” caused by moisture entering the bushing causing a short circuit. The electricity likely then sparked, which ignited oil and caused a fire.

Bushing is insulating material used around electrical parts for safe operation of equipment.

The report said under National Grid’s guidance, such moisture readings indicate “an imminent fault and that the bushing should be replaced”.

But it said while the reading was recorded in National Grid’s online system, the mitigations appropriate to its severity were “not actioned”.

It said the controls in place were “not effective and failed to identify subsequently that action had not been taken” to fix the problem, which included an opportunity in 2022 when a decision was taken to “defer basic maintenance”.

The power failure resulting in the closure of Heathrow raised wider questions about the UK’s major infrastructure resilience.

Neso said the impact beyond the airport was “significant”, with “essential services” including road, rail and Hillingdon Hospital affected, as well as businesses and thousands of homes, some of which had to be evacuated.

Energy Secretary Ed Miliband said the report detailing how risks were not addressed was “deeply concerning”.

He added that Ofgem, the energy watchdog, had opened an official enforcement investigation “to consider any possible licence breaches” relating to the development and maintenance of its substation in North Hyde, which was built in the 1960s.

National Grid said it had a “comprehensive asset inspection and maintenance programme in place” and that it had “taken further action since the fire”.

It said this included “re-testing the resilience of substations that serve strategic infrastructure”.

In response to the report, Heathrow Airport said a “combination of outdated regulation, inadequate safety mechanisms, and National Grid’s failure to maintain its infrastructure” that led to this “catastrophic power outage”.

“We expect National Grid to be carefully considering what steps they can take to ensure this isn’t repeated,” it added.

Akshay Kaul, director general for Infrastructure at Ofgem, said it expected energy companies to “properly maintain their equipment and networks to prevent events like this happening”.

“Where there is evidence that they have not, we will take action and hold companies fully to account,” he added.

Neso said that “it was not known to the energy companies” that the loss of one of the electrical supply points – of which Heathrow has three – would result in a power outage to some of the airport’s critical systems.

“The review also found that energy network operators are not generally aware whether customers connected to their networks are Critical National Infrastructure,” it said.

While power was restored to Heathrow by 06:25 on 21 March using circuits from another nearby substation, the flow of electricity to all four of Heathrow’s passenger terminals was not restored until 10:56.

Flights did not resume until after 18:00 that day, once safety checks were completed. Planes were able to land and take off through the night to enable Heathrow to get back up to full capacity.

Nigel Wicking, chief executive of Heathrow Airline Operators’ Committee, told the BBC that Heathrow’s closure cost airlines between £80m-£100m.