Heathrow Airport is "fully operational", a spokesperson said, a day after a fire at a power station shut down Europe's busiest air hub and caused travel mayhem.
"We can confirm that Heathrow is open and fully operational today. Teams across the airport continue to do everything they can to support passengers impacted by yesterday's outage at an off-airport power substation," the spokesperson said.
"We have hundreds of additional colleagues on hand in our terminals and we have added flights to today's schedule to facilitate an extra 10,000 passengers travelling through the airport.
"Passengers travelling today should check with their airline for the latest information regarding their flight."
Flights resumed yesterday evening following hours of closure after a blaze knocked out an electricity substation in Hayes late on Thursday evening.
The Metropolitan Police are not treating the incident at the sub-station as suspicious and the London Fire Brigade's investigation is focusing on the electrical distribution equipment.
The airport had been due to handle 1,351 flights yesterday, flying up to 291,000 passengers, but planes were diverted to other airports in Britain and across Europe, while many long-haul flights returned to their point of departure.
Heathrow Airport's chief executive Thomas Woldbye told reporters that he expected the airport to be back in full operation today "so 100% operation as a normal day".
He added: "(Passengers) should come to the airport as they normally would. There's no reason to come earlier."
According to flight tracking website FlightRadar24, British Airways (BA) flight BA56 from Johannesburg, South Africa was the first regular passenger flight to land at Heathrow since Thursday evening, touching down at 4.37am.
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, but it is understood cancellations will be made, where possible, to high-frequency routes.
A 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."
Restrictions on overnight flights were temporarily lifted to help ease congestion, the Department of Transport said.
According to Heathrow's website, there is no formal ban on night flights, but since the 1960s, the government has placed restrictions on them.
There is an annual limit of 5,800 night-time take-offs and landings between the hours of 11.30pm and 6am as well as a nightly limit, which caps the amount of noise the airport can make at night.
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 to power what is described as a "mid-sized city".
He apologised to stranded passengers and defended the airport's response to the situation, saying the incident is as "as big as it gets for our airport" and that "we cannot guard ourselves 100%".
After announcing early yesterday that it would be closed until 11.59pm, Heathrow later reopened with a focus on repatriation flights for passengers diverted to other airports in Europe.
Following that announcement, several airlines said they would restart scheduled flights both to and from Heathrow, including British Airways, Air Canada and United Airlines.
Around 200,000 passengers have been affected by the closure of what is Europe's busiest airport.
Heathrow is Europe's largest airport, with more than 83.9 million passengers travelling through its terminals in 2024.
Read more: What we know about events leading to Heathrow Airport closure
The airline industry, facing the prospect of a financial hit costing tens of millions of pounds and a likely fight over who should pay, questioned how such crucial infrastructure could fail without backup.
"It is a clear planning failure by the airport," said Willie Walsh, head of global airlines body IATA, who, as former head of British Airways, has for years been a fierce critic of the crowded hub.
Aviation experts said the last time European airports experienced disruption on such a large scale was the 2010 Icelandic volcanic ash cloud that grounded some 100,000 flights.
They warned that some passengers forced to land in Europe may have to stay in transit lounges if they lack the paperwork to leave the airport.
Heathrow and London's other major airports have been hit by other outages in recent years, most recently by an automated gate failure and an air traffic system meltdown, both in 2023.
Flights between Ireland and Heathrow have resumed
The daa, which operates Dublin Airport, says 30 of the 32 flights scheduled between the Dublin and Heathrow today "are expected to operate."
The Heathrow route is the busiest for Dublin Airport and it is also the second busiest airline route in Europe.
Yesterday, 34 Aer Lingus and British Airways flights between the two airports were cancelled.
The daa said that as of 8.30am, British Airways had cancelled one service from Dublin at 1.05pm and one inbound service from Heathrow, which had been due to arrive at 12pm.
Aer Lingus said it is "planning to operate its normal schedule to and from London Heathrow today".
For passengers impacted by the cancellation of flights yesterday, the airline said customers can either apply for a refund or change their flight for free online, while people affected who need to travel urgently are asked to contact the Aer Lingus customer care centre.
The daa said some disruption at Heathrow Airport is possible and it's advice is "as always, passengers seeking updates regarding specific flights should contact their airline directly."
Shannon Airport has also confirmed that its schedules have returned to normal.
Flights departing Shannon today include some of the diverted planes which landed at the Co Clare airport yesterday.
Cork Airport and Ireland West Airport have also returned to normal service.
Additional reporting Tommy Meskill, Fergal O'Brien, Reuters
