A look at some of history's worst air travel disruptions before a fire shut Heathrow

LONDON (AP) — A fire that closed London's Heathrow Airport has sparked one of the most serious disruptions to air travel in years.

More than 1,300 flights were canceled and hundreds of thousands of journeys were disrupted following the blaze at an electrical substation, whose cause is under investigation.

Here is a look at some past incidents:

A faulty software update sent to millions of Microsoft customers by cybersecurity firm CrowdStrike caused technological havoc worldwide. Airlines lost access to their booking systems, thousands of flights were canceled and tens of thousands were delayed, leading to long lines at airports in the U.S., Europe, Asia and Latin America.

A glitch at Britain’s National Air Traffic Services in August 2023 meant flight plans had to be processed manually, rather than automatically. Hundreds of flights were delayed or canceled at the height of the summer holidays. The NATS system had already suffered several software-related failures in the years after it opened in 2002.

As a new coronavirus spread around the globe in early 2020, the world’s airports shut down. Many governments closed national borders and imposed travel restrictions. By April, the number of flights around the world had fallen by 80%. When air travel resumed, it was with masks, mandatory coronavirus tests and other measures that made flying more onerous and expensive. It wasn’t until 2024 that global passenger numbers reached 2019 levels again.

More than 140,000 travelers were stranded or delayed after dozens of drone sightings shut down London Gatwick, south of the U.K. capital and Britain’s second-busiest airport, for parts of three consecutive days before Christmas. A monthslong police investigation failed to identify the culprits or determine how many of the sightings were real.

A computer failure at a British Airways data center forced the airline to cancel all flights from Heathrow and Gatwick on a holiday weekend. The airline blamed a power-supply issue for the incident which affected some 75,000 travelers.

Delta Air Lines planes around the world were grounded when an electrical component failed and led to a shutdown of the transformer that provides power to the carrier’s data center. Delta said that it canceled more than 2,000 flights and lost $100 million in revenue as a result of the outage.

People around the world learned how to pronounce the name of Iceland’s tongue-twisting Eyjafjallajökull volcano (ay-yah-FYAH-lah-yer-kuhl) after it roared to life, sending plumes of ash and dust into the atmosphere. Airspace over northern Europe was shut for several days and airlines canceled flights between Europe and North America because of concerns the ash could damage jet engines. More than 100,000 flights were canceled, stranding millions of passengers, at an estimated cost of $3 billion.

U.S. airspace was closed to commercial flights on Sept. 11, 2011 after hijackers crashed planes into the World Trade Center towers, the Pentagon and a field in Pennsylvania. Thousands of planes were grounded and flights in the air heading for the U.S. were diverted to Canada and Mexico. Flights began to resume two days later, but air travel was forever altered, with passengers facing more rigorous security, more intrusive scrutiny and longer lines.

FILE - Licensed vocational nurse Caren Williams, left, collects a nasal swab sample from a traveler at a COVID-19 testing site at the Los Angeles International Airport in Los Angeles, Monday, Nov. 23, 2020. (AP Photo/Jae C. Hong, File)

FILE - Travelers wear face coverings in the line for the north security checkpoint in the main terminal of Denver International Airport Tuesday, Aug. 24, 2021, in Denver. (AP Photo/David Zalubowski, File)

FILE - Passengers waiting for a flight to Helsinki rest at Lisbon's international Portela Airport on May 10, 2010, as flights were disrupted due to an ash cloud drifting over from a volcano in Iceland that caused major air travel chaos. (AP Photo/Francisco Seco, File)

A traveller arrives with his lugage at Terminal 4 as Britain's Heathrow Airport has closed for the full day Friday after an electrical substation fire knocked out its power, disrupting flights for hundreds of thousands of passengers at one of Europe's biggest travel hubs in London, Friday, March 21, 2025.(AP Photo/Kin Cheung)

British travellers Rajih Alshibli and Michele planning to go to Bahrain to see their daughter are stranded after Britain's Heathrow Airport has closed for the full day Friday after an electrical substation fire knocked out its power, disrupting flights for hundreds of thousands of passengers at one of Europe's biggest travel hubs in London, Friday, March 21, 2025.(AP Photo/Kin Cheung)

Traveller Lauren Clark, left, and Shahin Jade Ali wait at Chhatrapati Shivaji Maharaj International Airport after a fire at Heathrow Airport in London forced its closure, leading to numerous flight cancellations, in Mumbai, India, Friday, March 21, 2025. (AP Photo/Rajanish Kakade)

LONDON (AP) — Heathrow Airport was up and running Saturday and airlines worked to clear the backlog after a fire at a nearby electricity substation knocked out power to Europe's busiest airport, disrupting travel plans for hundreds of thousands of people around the world.

The airport said it had made space for extra flights, but it is expected to take days to get stranded passengers to their destinations and displaced aircraft into the proper locations.

Here's a look at what happened and its impact on air travel.

A fire at an electrical substation in west London, about 2 miles (3.2 kilometers) from the airport, cut power to Heathrow Airport late on Thursday.

Residents reported an explosion and a fireball just before midnight. The London Fire Brigade said a transformer holding 25,000 liters (5,000 gallons) of cooling oil caught fire. It said 10 fire engines and 70 firefighters brought the blaze under control after seven hours, but isolated hotspots were still alight 24 hours after the fire started.

National Grid, which maintains energy infrastructure in Britain, said the blaze damaged equipment at the substation and cut power to 67,000 properties, including Heathrow. It said power was restored to all of them by Saturday morning.

The “significant power outage” initially forced Heathrow officials to announce that the airport would be closed until 11:59 p.m. on Friday, but some flights began to resume on Friday evening.

Officials said there was no suggestion of foul play, but the cause is still under investigation. The fire brigade said its investigation would focus on the electrical distribution equipment at the substation.

Even so, London's Metropolitan Police Service said counterterrorism detectives were leading the investigation because of the fire's impact on critical national infrastructure.

Energy Secretary Ed Miliband said it was "an unprecedented event.”

“Obviously, with any incident like this we will want to understand why it happened and what if any lessons it has for our infrastructure,” he told Sky News.

The closure disrupted the travel plans of around 200,000 people who were expected to travel through Heathrow on Friday. Heathrow advised passengers not to travel to the airport and to contact their airlines to rebook flights.

With all takeoffs and landings canceled, the first impact was on dozens of long-haul flights from North America and Asia that were in the air when the airport was shut down. Some were forced to turn around, while others were diverted to airports around the United Kingdom and Europe.

Heathrow-bound aircraft landed at Schiphol Airport in Amsterdam; Shannon Airport in western Ireland; Glasgow, Scotland; Manchester, England; Charles de Gaulle in Paris; Lyon, France; and Frankfurt, Germany, among others.

About 4,000 tons of cargo were also stranded by the closure, according to Anita Mendiratta, an aviation and leadership consultant.

The disruptions are expected to last for days as airlines move stranded aircraft and flight crews back into position and work to accommodate passengers whose flights were canceled. Mendiratta estimated that it would take two to four days to clear all the backlogs.

“This is an extreme situation where the entire aviation ecosystem is impacted,” she said.

“There will be two things that will be happening as a priority No. 1. First is airport operations and understanding, from an electrical system point of view, what has been impacted, if anything,” she said. “Did anything short out, for instance? What needs to be reactivated? And then how do you literally turn the airport back on again?"

Heathrow was Europe’s busiest airport last year, with 83.6 million passengers traveling through it. Its closure will have far-reaching impacts because it's a major hub for connecting flights to cities throughout the U.K. and around the world, as well as for travel to London.

Yes. Five other air hubs in southeastern England identify themselves as London airports, but they are much smaller than Heathrow. London Gatwick, Britain’s second-biggest airport, handled 43.2 million passengers last year. It's located in the town of Crawley, 28 miles (45 kilometers) south of London.

The fire raises concerns about the U.K.’s ability to withstand attacks or natural disasters that damage critical infrastructure such as communications and power networks, analysts said.

The incident is particularly worrisome given recent comments by Britain’s security services that Russia is conducting a reckless campaign of sabotage across Europe, said Alan Mendoza, the executive director of the Henry Jackson Society, a London-based security think tank.

“The U.K.’s critical national infrastructure is not sufficiently hardened for anywhere near the level it would need to be at to give us confidence this won’t happen again,” he said. “I mean, if one fire can shut down Heathrow’s primary systems ... it tells you something’s badly wrong with our system of management of such disasters.”

Robin Potter, an expert on resilience at London-based think tank Chatham House, said that successive governments have been slow to respond to repeated recommendations from the National Infrastructure Commission to strengthen the ability of Britain’s power, communications, transport and water networks to withstand major shocks.

“We still have yet to see a kind of clear response from the government to those recommendations,” he said. “And we hope that maybe in the government’s upcoming resilience review, which we expect will be published at some point this year, it might seek to address some of those questions.”

Heathrow defended its response. Its CEO Thomas Woldbye said “the same would happen in other airports” faced with a similar fire.

A plane takes off as Heathrow Airport slowly resumes flights after a fire cut power to Europe's busiest airport in London, Saturday, March 22, 2025.(AP Photo/Kirsty Wigglesworth)

Passengers on a bus look at a parked plane as Britain's Heathrow Airport has closed for the full day Friday after an electrical substation fire knocked out its power, disrupting flights for hundreds of thousands of passengers at one of Europe's biggest travel hubs in London, Friday, March 21, 2025.(AP Photo/Kin Cheung)

Planes are parked at the Terminal as Britain's Heathrow Airport has closed for the full day Friday after an electrical substation fire knocked out its power, disrupting flights for hundreds of thousands of passengers at one of Europe's biggest travel hubs in London, Friday, March 21, 2025.(AP Photo/Kin Cheung)

This image taken from video shows parked planes at Heathrow airport, as a fire at the North Hyde electrical substation on Thursday night has led to a closure of Heathrow Airport in London, Friday, March 21, 2025. (Sky News via AP)

Omar Sheikh from Pakistan checks his phone whilst standing beside his lugage at Terminal 4 as Britain's Heathrow Airport has closed for the full day Friday after an electrical substation fire knocked out its power, disrupting flights for hundreds of thousands of passengers at one of Europe's biggest travel hubs in London, Friday, March 21, 2025.(AP Photo/Kin Cheung)

No travellers are seen inside Terminal 4 as Britain's Heathrow Airport has closed for the full day Friday after an electrical substation fire knocked out its power, disrupting flights for hundreds of thousands of passengers at one of Europe's biggest travel hubs in London, Friday, March 21, 2025.(AP Photo/Kin Cheung)

Smoke still rises as firefighters inspect the site of the fire at the North Hyde electrical substation, which caught fire Thursday night and lead to the closure of Heathrow Airport in London, Friday, March 21, 2025.(AP Photo/Kirsty Wigglesworth)

This image taken from video shows firefighters working to secure the area of a fire at the North Hyde electrical substation, which caught fire Thursday night and lead to a closure of Heathrow Airport in London, Friday, March 21, 2025. (Sky News via AP)