London's Heathrow Airport 'fully operational' after fire causes travel chaos

LONDON -- London's Heathrow Airport said Saturday that flights have resumed after a fire at an electrical substation knocked out power to Europe's busiest hub.

"Flights have resumed at Heathrow, and we are open and fully operational," Heathrow Airport said on X. "Teams across the airport continue to do everything they can to support passengers impacted by yesterday's outage at an off-airport power substation."

Ed Miliband, the UK's secretary of state for energy security and net zero, announced Saturday that he is ordering an investigation into the substation fire.

The investigation will be led by National Energy System Operator "to understand any wider lessons to be learned on energy resilience for critical national infrastructure," the secretary said in a statement.

"The loss of power to the Heathrow area has caused major disruption to thousands of people and many businesses. We are determined to properly understand what happened and what lessons need to be learned," the secretary said.

Heathrow CEO Thomas Woldbye said he welcomed the news of the investigation.

"We will support every effort to understand the causes and impacts of yesterday's off-airport incident and we are committed to working closely with all stakeholders to ensure a thorough investigation to help strengthen the airport's future resilience," Woldbye said in a statement.

A Heathrow spokesperson said that hundreds of additional colleagues are on hand in their terminals on Saturday and that the airport has added flights to the schedule to facilitate an extra 10,000 passengers traveling through the airport.

"Power supplies have been restored to all customers connected to our North Hyde substation, including Heathrow, allowing operations to resume at the airport. We are now implementing measures to help further improve the resilience levels of our network," read a statement from the U.K.'s National Grid.

"We are deeply sorry for the disruption caused and are continuing to work closely with the government, Heathrow and the police to understand the cause of the incident," the statement continued.

Heathrow Chairman Lord Paul Deighton said an internal review will also be launched, chaired by former transport secretary and independent board member Ruth Kelly.

"The Kelly Review will analyse all of the relevant material concerning the robustness and execution of Heathrow’s crisis management plans, the airport’s response during the incident and how the airport recovered the operation with the objective of identifying any improvements that could be made to our future resilience," Deighton said in a statement.

An analysis said as many as 290,000 passengers had been impacted by the closure Friday, according to Cirium, an aviation analytics company. There were 669 flights scheduled to depart to Heathrow on Friday, with 145,836 seats, according to Cirium. The fire could affect another 270,000 passengers on Saturday, Cirium said.

The cause of the fire is still not known and currently under investigation but authorities have confirmed that they are not treating the blaze as suspicious.

"After initial assessment, we are not treating this incident as suspicious, although enquiries do remain ongoing," a statement from London's Metropolitan Police said. Because of the location of the substation "and the impact this incident has had on critical national infrastructure," the Met's Counter Terrorism Command was leading the investigation, authorities said.

ABC News' Morgan Winsor and Mike Trew contributed to the report.