How did a single fire bring down Europe's busiest airport?

It seems astounding that a single fire at an electricity source shut down one of the world's busiest airports.

The disruption to the journeys of thousands of passengers and millions of tonnes of trade goods on Friday has prompted a series of questions over the resilience of the UK's major infrastructure.

Disaster recovery plans keep the top brass of many organisations awake at night.

Banks, data centres, stock exchanges, hospitals, all have contingency plans.

"How is it that critical infrastructure - of national and global importance - is totally dependent on a single power source without an alternative?", said Willie Walsh, the director general of the International Air Transport Association, which represents airlines.

He said the shutdown was the result of a "clear planning failure".

Heathrow does in fact have more than one source of electricity, however, as one National Grid insider told the BBC, but the fire that broke out damaged a "particularly important bit".

That meant the back-up systems in place for a scenario like this proved ineffective when the blaze ripped through the substation, which is used by the National Grid to transform high voltage electricity to a lower and safer voltage for use.

This is a process which generates a lot of heat which is dissipated using flammable cooling oils. This is what caught light in this instance. The exact cause is not yet known, but counter terrorism police are looking into whether there was any foul play.

Internationally embarrassing

Heathrow uses as much energy as a small city, so it is not possible for it to have the back-up power by itself to run its operation safely.

A source at Heathrow said it did however have back-up options for certain key systems, but kickstarting the alternative power supplies for the whole airport took time.

The systems need to be checked to ensure they are working properly.

A Heathrow source said its back-up diesel generators and uninterruptable power supplies in place all operated as expected.

The problem lay with the National Grid, the source said, pointing out thousands of homes had been left without power, not just the airport.

There are two National Grid substations close to Heathrow: one at North Hyde, north of the airport, and one at Laleham, south of the airport, according to energy analysis firm Montel Group.

It appears that only the North Hyde substation is connected to Heathrow through the local distribution network, said Phil Hewitt, director at the firm.

"This potential lack of resilience at a critical national and international infrastructure site is worrying," he said. "An airport as large and as important as Heathrow should not be vulnerable to a single point of failure."

However, Robin Potter, a research fellow at Chatham House, said Heathrow was one of only two UK airports – Gatwick is the other – that has any level of regulation around its resilience standards.

"These are actually the better airports in the UK for how their resilience is assessed and regulated," he said.

In 2023, the National Infrastructure Commission recommended to the government that it should set standards for some key sectors of infrastructure such as telecoms, water, transport and energy by 2025.

It followed up with a further report at the end of last year detailing how the government could do that for those sectors.

"Those have effectively been on the government's desk since October 2023," he added.

A Heathrow source said questions over why its back-up system failed would be investigated.

Sometimes - like now - a chain is only important as its weakest link. The cost of having a whole extra power supply to run the airport just in case would cost huge amounts of money and resources for a privately-owned business like Heathrow.

Questions over whether additional back-ups are worth the additional cost will continue long after the passengers and cargo delayed by Friday's disruptive, and internationally embarrassing, failure have got where they are going.

Reporting by Tom Espiner, Theo Leggett, Ben King, and Oliver Smith.