The blaze triggered a “significant power outage” that resulted in more than 1,000 flights to and from the airport being cancelled.
Heathrow Airport has reopened for a limited number of flights after a large fire at a nearby electrical substation disrupted travel for around 200,000 passengers.
Counter-terror police were leading the investigation into the cause of the blaze, which triggered a “significant power outage” that led to more than 1,000 flights to and from the airport being cancelled.
Heathrow’s boss apologised to passengers, describing the disruption “as big as it gets for our airport” and admitting “we cannot guard ourselves 100%”.
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) announced its investigation will focus on the electrical distribution equipment.
Heathrow is expected to run a full schedule on Saturday.
The fire that caused the power outage is at the North Hyde substation in Hayes, about 1.5 miles to the north of the west London airport.
LFB received the first reports of the fire at 11.23pm on Thursday.
Heathrow initially announced the airport would be closed until 11.59pm on Friday but later said repatriation flights for passengers diverted to other airports in Europe would resume on Friday evening.
Several airlines announced they would restart scheduled flights both to and from Heathrow, including British Airways (BA), Air Canada and United Airlines.
A BA flight to Riyadh, in Saudi Arabia, took off just before 9pm after a slight delay to its expected departure time.
Restrictions on overnight flights have also been temporarily lifted to help ease congestion, the Department of Transport said.
Airport disruption nearly ‘as big as it gets’
Heathrow Airport’s chief executive Thomas Woldbye told reporters the flights taking off on Friday evening would help make sure the airport has “operations in place” for Saturday morning.
He continued: “Tomorrow morning we expect to be back in full operation, so 100% operation as a normal day.”
Mr Woldbye added that passengers who were planning to fly from Heathrow on Saturday should arrive at the airport in time for their flight as normal.
The chief executive also apologised to the passengers whose journeys had been disrupted but said he would not have closed down the airport unless there were “severe safety concerns”.
