The aircraft affected are from the A320 family - which are used by numerous airlines - and need a systems update before they can fly again.

Airbus issued the alert after analysis of a flight involving an A320 showed "intense solar radiation may corrupt data critical to the functioning of flight controls".

It is understood the incident that triggered the warning involved a JetBlue flight from Cancun, Mexico, to Newark in the US on 30 October.

That flight was diverted to Tampa International Airport after it suffered a flight control issue and experienced a sharp loss of altitude, which injured at least 15 passengers.

An Airbus spokesperson told Sky News the software change would affect up to 6,000 planes.

The fix involves A320 aircraft reverting to an earlier software version and Airbus stressed it would only take two to three hours for most planes.

However, it said some jets would also need new hardware and therefore would be affected for longer. Industry sources estimated about 1,000 aircraft could be in this position.

America's aviation watchdog has issued an emergency order to immediately replace or modify the software, mirroring one from the European Union Aviation Safety Agency.

'Very concerning'

Gatwick said a "small number" of carriers based there were affected, but warned disruption was still possible. It urged passengers to contact their airline.

Heathrow said it wasn't expecting any disruption.

"The good news is it seems the impact on UK airlines seems limited, with a smaller number of aircraft requiring more complex software and hardware changes," said Transport Secretary Heidi Alexander.

She said it was "heartening this issue has been identified and will be addressed so swiftly".

Airbus is understood to have traced the issue to the ELAC (Elevator and Aileron Computer) system, which sends commands to elevators on the plane's tail. These in turn control the aircraft's pitch or nose angle.

Travel expert Simon Calder said the situation was "very concerning" but stressed "aviation remains extraordinarily safe".

He warned customers might not be entitled to compensation if they're delayed as the issue would be considered out of airlines' control.

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What have airlines said?

EasyJet said it had already completed the software update on many aircraft and was working closely with safety authorities.

"We plan to operate our flying programme normally on Saturday and ask that customers travelling continue to monitor their flights on flight tracker," it added.

The airline said passengers would be informed of any changes by email, SMS, or the flight tracker.

British Airways said it wasn't expecting any problems and that only three of its planes were affected.

For American Airlines - the world's largest operator of the A320 - the issue was more significant, with 209 aircraft needing an update.

It comes on a huge travel weekend stateside as many travel home after Thanksgiving. However, the US carrier said the fix would be completed for the vast majority of its planes on Friday.

Others affected include Japan's All Nippon Airways, which cancelled 65 domestic flights on Saturday, and Air France - which said it was cancelling 35 flights.

Ireland's Aer Lingus said a limited number of aircraft were impacted, while Wizz Air has started the software update but said some weekend flights could still be affected.

"Passengers who booked directly with Wizz Air via the website or mobile app will be notified of any schedule changes," the airline said.

The aircraft manufacturer is carrying out software updates for 6,000 of its jets - around half the global fleet - threatening travel disruption for airline passengers.

The UK's Civil Aviation Authority said it expects some disruptions to airlines and flights, with easyJet and Wizz Air saying they will take some planes briefly out of service to do the repairs.

But why have airlines been told to carry out a software update for the planes, and how is solar radiation involved?

Follow the latest updates on this story

What triggered the repair order?

It is understood the incident that triggered the unexpected repair order involved a JetBlue flight from Cancun, Mexico, to Newark, New Jersey, on 30 October.

The flight suffered a control problem and a sudden uncommanded drop in altitude, basically a sharp loss of height, which left 15 passengers with injuries and forced the flight to make an emergency landing in Tampa, Florida.

After investigating the incident, Airbus said "intense solar radiation" may corrupt data critical to the functioning of flight controls.

The issue is known as bit flip, where solar radiation can strike a computer's memory, changing its data from a 0 to a 1 and vice versa - a risk which also affects spacecraft.

Read more: Which airlines are affected by Airbus disruption?

'Very concerning' - but 'very low likelihood' of such an event

The situation was "very concerning", travel expert Simon Calder told Sky News presenter Gillian Joseph.

However, he said there was a "very low likelihood" of such an event happening, adding: "In aviation, nothing is taken for granted."

He said: "Aviation remains extraordinarily safe. And that is partly because as soon as a possible threat is identified, then action is taken immediately."

What is the fix?

The fix involves reverting to earlier software, but must be carried out before the planes can fly again, according to a bulletin to airlines.

Airbus said for most of the affected aircraft, the required update would only take between two to three hours.

However, some jets may need to have their hardware replaced to adopt the required software - a process which would take a longer time.

The Airbus bulletin traced the problem to a flight system called ELAC (Elevator and Aileron Computer), which sends commands from the pilot's side-stick to elevators at the rear of the plane, Reuters reported.

Those elevators control the aircraft's pitch or nose angle, determining which way it is flying.

The A320 was first launched in 1984 and is the main competitor to the Boeing 737 MAX, which was grounded worldwide between March 2019 and December 2020, as well as during January 2024, after fatal crashes in 2018 and 2019 caused by faulty flight-control software.

"Either they can't get pregnant, or they lose their [foetus] over time.

"So, women are afraid of getting pregnant."

For centuries, the indigenous Munduruku have lived in an area across what is now the states of Amazonas and Para in northern Brazil, especially around the Tapajos River.

But in recent decades, villagers had been plagued by curious symptoms that they didn't realise could be related: children unable to lift their heads, adults unable to walk any more, muscle tremors, memory loss, fading hearing and vision, miscarriages.

Now they are finally closing in on the cause.

The Tapajos river, their lifeblood, is laced with highly toxic mercury.

Mercury poisoning is hard to diagnose because symptoms resemble other degenerative illnesses like Parkinson's or Alzheimer's, says Gabriela Arrifano, professor of mercury toxicology at the Federal University of Para.

"But there is now enough evidence to relate the signs and symptoms found in people exposed to mercury."

And they have no doubts about where it's coming from.

"We have robust evidence that mercury emissions to the environment comes from illegal gold mining activity," says Prof Arrifano in her university lab, where she analyses hair and blood samples.

When researchers began studying the symptoms, Alessandra "didn't know what mercury was", she says.

Hand in hand with drugs

In Brazil, gold mining is outlawed in indigenous territory.

Yet swathes of it are pockmarked with red and orange craters from illicit gold projects - a trend fuelled by record-high prices around the world.

The underground trade works hand in hand with organised crime groups, sharing the same makeshift runways and roads through the Amazon rainforest, and using the gold to launder drug money.

The gold, once locked in the mountainside of the Andes, was gradually washed away by ancient rain into the Amazon basin.

To extract it, illegal miners churn up the riverbed and combine it with mercury because it binds to gold.

The process releases mercury into the air, water and soil.

Over time, the mercury coursing through the waterways accumulates in river fish, which indigenous communities eat for breakfast, lunch, dinner.

One study found one in five fish in markets in northern Brazil had dangerous levels of mercury (0.5 micrograms per gram).

Once in the guts, it enters the bloodstream and makes its way to the brain, where it can cause lesions.

Even low levels of exposure can disrupt most of the body's systems, whether reproductive, skin, or nervous systems.

Prof Arrifano says people's visual field shrinks so they lose their peripheral vision. "And then you can imagine this is very hard for people who live in the forest that need their complete senses."

The Munduruku have been fending off mining on their land since 1960s, Alessandra tells Sky News in Para's state capital Belem, as the city hosted international climate talks.

Her symptoms aren't so bad. "I feel tingling in my hands, brain fog, forgetfulness, that is because of the mercury."

But her niece can't walk or talk.

Alessandra suspects it's got something to do with the girl's grandfather being a fisherman.

"So maybe because of this, the mother ended up ingesting a lot of mercury in her body that went to the child."

The toxic metal also accumulates in placentas, breast milk and children, often two or three times the safe threshold for pregnant women.

One study across all of Brazil identified 668 cases of mercury poisoning, but that's thought to be a vast underestimate due to poor data collection and lack of access to healthcare.

How global gold prices fuel the problem

The current administration under President Luiz Inacio Lula da Silva has been attempting a widespread crackdown on illegal mining.

Its environmental protection agency, IBAMA, swoops in by helicopter, blows up equipment, torches makeshift buildings and flies out again.

It has also frozen assets and ended the presumption of "good faith" - that gold for sale was extracted from lawful sights.

In the Yanomami Indigenous Territory in the far north, federal government figures show a 94% reduction in active illegal mining areas between 2023 and 2025.

But some of these miners have set up camp elsewhere, and the ever-soaring price of gold is making it "harder" to combat, one of Brazil's top officials admits.

"We thought that the amount would be reduced, and initially it did," Adalberto Maluf, national secretary for water resources in the environment ministry, overseeing the crackdown, tells Sky News in Belem.

"But I think it's not going as fast as we wanted, or we thought it could happen, mainly because the price of gold continues rising."

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The problem is not unique to Brazil, but common across South America and parts of Africa.

Prices are surging as investors seek security from market turbulence and geopolitical tensions - upping the incentive for miners despite the risks, says Julia Yansara from the Financial Accountability and Corporate Transparency Coalition.

"It is driving illegal gold miners into new areas. And it's driving new criminal groups to get involved in this for the first time."

'If we don't fight, we are crushed'

The Munduruku were formerly known as an aggressive group, feared by neighbouring peoples, before being fought down by colonisers who annexed their territory.

This year, they capitalised on the global attention on Brazil as it hosted the UN climate talks (COP30) to fight for their land once again.

Halfway through the conference they peacefully blocked the entrance, forcing a meeting with officials that then won them the legal rights to two further portions of territory.

When the land is demarcated, it's easier to pressure the government to protect the land, says Alessandra.

"If we don't fight, we are crushed, we are taken over."

But she too knows they are fighting a rising tide.

"When the price increases, everyone wants to invade our land, to pollute the water, to destroy the forest, because they need to take the gold to sell to other countries."

But those buyers don't know "what is happening to our bodies, to our lives", she adds.

Monsoon rains over the past week caused rivers to burst their banks in North Sumatra province.

The deluge tore through mountainside villages, swept away people and submerged thousands of houses and buildings, the National Disaster Management Agency said.

Rescue workers have been struggling to reach some areas cut off by damaged roads, and where communications lines have come down. Authorities fear the number of dead will increase further.

Relief aircraft have been delivering aid and supplies to the hard-hit district of Central Tapanuli in North Sumatra and other provinces in the region.

The agency said West Sumatra's Agam district had also been affected. Some 76 people have died in that province.

Pictures of the rescue efforts show workers trudging through waist-deep mud and areas filled with tree trunks and debris, searching for any victims potentially trapped.

In Aceh province, flooded roads meant authorities struggled to get tractors and other heavy equipment to hilly hamlets which were hit by mud and rocks in the deluge.

Hundreds of police officers, soldiers and residents dug through the debris with their bare hands and spades as heavy rain hindered their efforts.

Meanwhile, a magnitude 6.3 earthquake hit Sumatra island near Aceh province on Thursday, the country's geophysics agency said.

Torrential rain triggered flash flooding and landslides in Sumatra earlier in the week. Videos posted on social media showed water streaming down from rooftops as panicked residents scrambled to safety.

Heavy seasonal rain from about October to March often causes flooding and landslides in Indonesia - an archipelago of more than 17,000 islands including Sumatra - where millions of people live in mountainous areas or near fertile floodplains.

Last week, almost 1,000 people from three villages on Java were forced to flee to shelters after the eruption of Mount Semeru, the island's highest volcano.

Speaking to Sky News on the eve of the conference, Mr Corbyn acknowledged "stresses and strains" in the set-up of the party but said it had become "a lot better in the last few days and weeks and we're going to get through this weekend".

The former Labour leader has publicly clashed with Ms Sultana, the MP for Coventry South, over the launch and structure of the new party.

Asked if they were friends, Mr Corbyn said they were "colleagues in parliament, and we obviously communicate and so on".

The pair appeared at separate events on the eve of the party's inaugural gathering.

Ms Sultana had previously claimed she was being "sidelined" by a "sexist boys' club" within the fledgling party.

Mr Corbyn said her comments were an "unfortunate choice of words" but added that he had been more involved in the organisation of the conference than she had.

The Islington North MP also said that Your Party was still waiting for Ms Sultana to transfer all of the funds she had raised from supporters.

"Obviously having money up front for a conference is a big help," he said.

Ms Sultana has insisted she is transferring the donations in stages.

The weekend gathering in Liverpool will see supporters choose between four options for a permanent party name: Your Party, Our Party, Popular Alliance, For the Many.

The preferred choice of Ms Sultana - The Left - did not make the ballot.

Similarly, the Coventry MP had said she favoured a co-leader approach, but members will only be able to pick between single leadership or collective leadership models.

Speaking at her own pre-conference rally, Ms Sultana blamed a "nameless, faceless bureaucrat" for restricting the choices.

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The meeting also risked being disrupted by a series of member expulsions. One of those ejected, Lewis Nielsen, accused a "clique" of trying to "take over".

Your Party sources said expulsions related to members of the Socialist Workers Party and that holding another national party membership was not allowed.

Ms Sultana blamed a "culture of paranoia at the top" and said she believed the same people who had been briefing against her were now also expelling members.

Mr Corbyn will open the conference on Saturday, while the results of the main decision-making votes will be announced on Sunday.