Heathrow is expecting a full day of normal operation today after the airport was shut over a loss of power, as passengers have been warned of further disruption.

Overnight, a limited number of flights resumed at the west London airport following hours of closure after a large fire at a nearby electricity substation triggered a “significant power outage”.

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The closure of Europe’s busiest airport yesterday led to more than 1,000 flights being cancelled and disrupted the travel plans of more than 200,000 passengers.

In an update on Friday evening, the Metropolitan Police said the cause of the fire is believed to be non-suspicious, while the London Fire Brigade (LFB) said its investigation will focus on electrical distribution equipment.

Heathrow‘s boss Thomas Woldbye said the flights that took off on Friday night would help make sure the airport had “operations in place” for Saturday morning.

Several airlines, including British Airways (BA), Air Canada and United Airlines, said late on Friday that they would restart scheduled flights both to and from Heathrow.

A BA flight to Riyadh, in Saudi Arabia, took off just before 9pm after a slight delay to its expected departure time.

Mr Woldbye said passengers who were planning to fly from Heathrow on Saturday should arrive at the airport in time for their flight as normal, adding “there’s no reason to come earlier”.

He said: “We expect to be back in full operation (Saturday), so 100% operation as a normal day.”

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The chief executive also apologised to passengers whose journeys had been disrupted, describing the delays “as big as it gets for our airport” and admitting “we cannot guard ourselves 100%”.

But he said he would not have closed down the airport unless there were “severe safety concerns”.

Of the power outage, Mr Woldbye said a back-up transformer failed, meaning systems had to be closed down in accordance with safety procedures so that power supplies could be restructured from two remaining substations to restore enough electricity.

BA, which has a major presence at Heathrow, said it expects to operate around 85% of its scheduled flights at the airport today.

The airline would usually expect to run nearly 600 departures and arrivals on Saturday but it is understood cancellations will be made, where possible, to high-frequency routes.

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An airline spokesman said: “We are planning to operate as many flights as possible to and from Heathrow on Saturday, but to recover an operation of our size after such a significant incident is extremely complex.

“We expect around 85% of our Saturday Heathrow schedule to run, but it is likely that all travelling customers will experience delays as we continue to navigate the challenges posed by Friday’s power outage at the airport.”

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The disruption began late on Thursday night when fire crews were called to a blaze in Hayes, west London, at the electricity substation serving Heathrow and local properties.

LFB deputy commissioner Jonathan Smith told reporters on Friday that the fire involved a transformer – a key part of the substation – with 25,000 litres of cooling oil “fully alight”.

Pictures from the scene showed large flames and plumes of thick black smoke, with around 70 firefighters and 10 engines working to extinguish the blaze.

Crews evacuated 29 people from neighbouring properties but there were no casualties.

In all, 67,000 households were left without power after the fire at the substation, but all supplies have been restored.

Transport Secretary Heidi Alexander said she was in close contact with the energy secretary, the home secretary and with Heathrow to “make sure that any lessons we need to learn from the systems that the airport has in place are learned”.