Thousands of Airbus planes have been grounded after it was discovered that intense solar radiation could interfere with onboard flight control computers, leading to delays around the world.
Around 6,000 A320 planes are thought to be affected, half the European firm's global fleet, but it is understood most will be able to fly again after undergoing a quick software update.
The UK's aviation regulator said there would be "some disruption and cancellations to flights" though the impact at airports appears to be limited.
Airbus said it discovered the issue after an investigation into an incident in which a plane flying between the US and Mexico suddenly lost altitude in October.
The JetBlue Airways flight made an emergency landing in Florida after at least 15 people were injured.
As well as the A320, the company's best-selling aircraft, the vulnerability also impacts the A318, A319 and the A321 models.
It is understood that on around 5,100 Airbus planes, the issue can be addressed using a relatively simple software update which would typically take about three hours.
However, the remaining 900 aircraft, which are older versions, will need to have onboard computers physically replaced, and will not be allowed to carry passengers again until the job has been completed.
The length of time that takes will depend on the availability of replacement computers.
Airbus said it acknowledged this will lead to "operational disruption to passengers and customers" and has apologised.
Aviation analyst Sally Gethin told BBC News the situation is "very much out of the ordinary", saying the disruption to passengers will depend on the "different approaches" airlines take to upgrade their software.
In the UK, disruption at airports has been limited so far. London's Gatwick Airport reported "some disruption", while Heathrow said it had not experienced any cancellations. Manchester Airport said it did not anticipate significant problems.
The extent of the disruption varies between airlines: British Airways is understood not to be heavily impacted by the issue, while Wizz Air and Air India said it was undertaking the updates already.
Publicly available data suggested Air France was impacted more than any other airline, with 50 of its flights to and from its Paris hub that were scheduled for Saturday morning cancelled, travel journalist Simon Calder told the BBC.
Meanwhile Easyjet said it was "expecting this to result in some disruption" but later added it had started and "already completed the software update on many aircraft" and was planning a full service on Saturday.
In the US, the software issue emerged on the same weekend as Thanksgiving, one of the busiest travel periods of the year.
American Airlines said 340 of its planes were affected and that it expected "some operational delays", but added the vast majority of updates would be completed on Friday or Saturday. Delta Airlines said it believed the impact on its operations would be "limited".
In Australia, budget airline Jetstar cancelled 90 flights after confirming around a third of its fleet was impacted, with disruption expected to continue all weekend despite the majority of aircraft having already undergone the update.
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Tim Johnson, policy director at the UK's Civil Aviation Authority, said the notice from Airbus "unfortunately may mean there is some disruption, some delays or cancellations over the coming days".
He added that aviation was still "one of the safest forms of transport" due to the rigorous maintenance programs airlines have in place, and described the mass-grounding of flights as a "a very rare event".
Transport Secretary Heidi Alexander said "the impact on UK airlines seems limited", adding: "It is heartening this issue has been identified and will be addressed so swiftly, demonstrating the high aviation safety standards globally."
'Precautionary action'
The problem identified with A320 aircrafts relates to a piece of computing software which calculates a plane's elevation.
Airbus discovered that at high altitudes its data could be corrupted by intense radiation released by periodically by the sun.
That led to the October incident in which an aircraft suddenly lost altitude - though the manufacturer said this was the only time an incident of its kind had occurred.
The European Union Aviation Safety Agency (EASA) has issued an emergency airworthiness directive, ordering the problem be addressed before each plane can carry passengers again.
They will be allowed to make so-called "ferry flights", without passengers, in order to reach a maintenance facility.
The A320 family are what is known as "fly by wire" planes. This means there is no direct mechanical link between the controls in the cockpit and the parts of the aircraft that actually govern flight, with the pilot's actions processed by a computer.
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