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Heathrow is coming under growing scrutiny over its decision to close for nearly 24 hours following a fire at a nearby electrical substation, even though it was still able to receive power from other parts of the grid.
Senior management at Europe’s busiest airport took the decision to close on Friday as they battled to restore full power to a complex that uses the same amount of electricity as a small city.
But John Pettigrew, chief executive of National Grid which operates Britain’s high-voltage transmission network, told the Financial Times that two other substations serving Heathrow were working throughout the incident, meaning the airport never lost potential access to power.
As concerns grow over the resilience of the UK’s critical infrastructure, Prime Minister Sir Keir Starmer on Monday said “there are questions” for airport executives to answer over the scale of disruption.
Why wasn’t there enough backup power to run the airport?
Heathrow has enough diesel generators to power critical operations, including its control tower and runway lights, and passengers were able to safely leave the airport late on Thursday night after the outage was first reported. But its generators do not have the capacity to run the whole airport.
Simon Gallagher, managing director of UK Networks Services, a consultancy specialising in power grids, said few other airports have better backup supplies than Heathrow.
But he said other industries “are far more resilient”.
“The airport industry as a whole has this issue with resilience . . . other industries with even bigger connections ensure they never go off supply,” he said.
How does Heathrow’s resilience compare?
A nearby data centre run by Ark Data Centres, which is equipped with 12 emergency generators, was also affected by Friday’s substation fire, but says it managed to avoid disruption by switching on its backup supply.
“I don’t think that the people buying services off me would buy them without this resilience built in,” said Huw Owen, Ark’s chief executive.
A 2023 US government report found one large hub airport reported having 10 diesel fuel generators and enough fuel on site to power the entire airport for three weeks. The airport was seen as an outlier, analysts said.
Resilience must “strike the right balance between risks and costs”, said Olivier Jankovec, director-general of trade group Airports Council International Europe. “Ensuring minimum disruptions and keeping operations going as much as possible is simply not always possible — especially when faced with rare and extreme events.”
Why did it take so long to restart if power was available?
While the fire took North Hyde substation out of operation, two others remained capable of providing power to the airport. But in order to access the power from the remaining two substations, Heathrow said it had to “reconfigure” its internal electrical networks.
In practice, this meant the airport had to send technicians to its own power distribution points, where they physically toggled circuit breakers to disconnect Heathrow from North Hyde and reconnect it to the other stations.
The airport also had to shut down, restart and systematically test hundreds of its systems before it could resume operations.
Heathrow said: “Given Heathrow’s size and operational complexity, safely restarting operations after a disruption of this magnitude was a significant challenge.”
It is unclear how long each step of the process took, and some experts said they were surprised by the length of time it took to return the airport to normal operation.
Heathrow announced at 4.30am on Friday that it would close until midnight, and by 12.30pm it had begun restarting its systems. By 4pm the airport was “100 per cent confident that all systems were safely operating”, said transport secretary Heidi Alexander. The first flights restarted around 7pm.
“In some ways, this seems to [have been] a process failure,” said David Wallom, professor of informatics at Oxford university. “It seems like Heathrow had never considered the possibility of this scale of failure.”
Should Heathrow have been better prepared?
All contingency planning requires a “weighing up of the economics”, said Malte Jansen, an energy policy researcher at Sussex university.
“No technical system will be 100 per cent fail-proof,” he said. “I didn’t get the feeling this was a reckless design — the system is designed to be reliable and a very unlikely case has come to fruition.”
Nevertheless, power industry executives said Heathrow should have been better prepared given its status as Europe’s busiest airport. The ability to switch power quickly “should be a minimum standard”, said one executive.
A 2014 report by consultancy Jacobs, prepared as part of an earlier Heathrow expansion push, said “even a brief interruption to electricity supplies could have a long-lasting impact”.
But it concluded “Heathrow is equipped with on-site generation and appears to have resilient electricity supplies that are compliant with regulations and standards”.
Heathrow has spent a total of £7.4bn in capital expenditure on the airport since 2014, including on new security scanners. But at a time when landing fees have risen, airlines have criticised its owners for spending this money inefficiently, leaving the airport with ageing infrastructure.
Additional reporting by Clara Murray in London. Illustrations by Ian Bott
