Europe’s Airbus is ordering an immediate software change on a “significant number” of its best-selling A320 family of jets, in a move that industry sources said would bring disruption to half the global fleet, or thousands of jets.

The move to a different software, announced on Friday, which will affect 6,000 of its widely used A320 family of jets, must be carried out before the next routine flight, threatening cancellations or delays during one of the busiest travel weekends of the year in the United States and beyond.

Airbus said in a statement that a recent incident involving an A320-family aircraft had revealed that intense solar radiation may corrupt data critical to the functioning of flight controls.

“Airbus acknowledges these recommendations will lead to operational disruptions to passengers and customers,” it said.

Industry sources said the incident that triggered the unexpected repair action involved a JetBlue flight from Cancun, Mexico, to Newark, New Jersey, on October 30, in which several passengers were hurt following a sharp loss of altitude.

Flight 1230 made an emergency landing at Tampa, Florida, after a flight control problem and a sudden uncommanded drop in altitude, prompting an investigation by the US Federal Aviation Administration (FAA).

JetBlue and the FAA had no immediate comment.

The European Union Aviation Safety Agency is due to issue an emergency directive mandating the fix, Airbus said.

Two-hour repair

For about two-thirds of the affected jets, the recall will result in a relatively brief grounding as airlines revert to a previous software version, industry sources said.

Still, that comes at a time of intense demands on airline repair shops, already plagued by shortages of maintenance capacity and the grounding of hundreds of Airbus jets due to long waiting times for separate engine repairs or inspections.

Hundreds of the affected jets may also need hardware changed, threatening much longer waits, the sources said.

Some 3,000 A320-family jets were in the air worldwide shortly after the Airbus announcement.

American Airlines and Hungary’s Wizz Air said they had already identified which of their aircraft would need the software fix. United Airlines said it was not affected.

The world’s largest A320 operator, American, in a statement, said that about 340 of its 480 A320 aircraft require the software replacement, and it expects the majority of those fixes to be “complete today and tomorrow”, with about two hours required for each plane.

Other airlines said they would take planes briefly out of service to do the repairs, including Germany’s Lufthansa, India’s IndiGo and United Kingdom-based easyJet.

Colombian carrier Avianca said the recall affected more than 70 percent of its fleet, about 100 jets, causing significant disruption over the next 10 days and prompting the airline to close ticket sales for travel dates through December 8.

An Airbus spokesperson estimated the repairs would affect some 6,000 jets in total, mixed between several variants, confirming an earlier report by the Reuters news agency.

The temporary groundings for repairs for some airlines could be much longer, since more than 1,000 of the affected jets may also have to have hardware changed, the sources said.

The abrupt recall sent ripples around the world. In northern Europe, a Finnair flight was delayed almost an hour as pilots established which software version they had, a passenger said.

In Paris, Air France-KLM said it was cancelling 38 flights, 5 percent of the airline’s daily total. Mexico’s Volaris said it would be hit by delays or cancellations for up to 72 hours.

Largest mass recall

There are about 11,300 A320-family aircraft in operation, including 6,440 of the core A320 model, which first flew in 1987.

The setback appears to be among the largest mass recalls affecting Airbus in its 55-year history and comes weeks after the A320 overtook the Boeing 737 as the most-delivered model.

The A320 was the first mainstream airliner to introduce fly-by-wire computer controls.

The bulletin, seen by Reuters, 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. These, in turn, control the aircraft’s pitch or nose angle.

The computer’s manufacturer, France’s Thales, said in response to a Reuters query that the computer complies with Airbus specifications, and the functionality in question is supported by software that is not under Thales’s responsibility.

Launched in 1984, the A320 was the first mainstream plane to introduce fly-by-wire computer controls.

It competes with the Boeing 737 MAX, which suffered a lengthy worldwide grounding after fatal crashes in 2018 and 2019, blamed on poorly designed flight-control software.

Demand for the two main brands of workhorse jets has surged in recent years as economic growth led by Asia brought tens of millions of new travellers into the skies.

Originally designed to serve hubs, the single-aisle models were later widely adopted by low-cost carriers. The connections they provide now represent a significant slice of the economy.