Europe's Airbus ordered immediate repairs to 6,000 of its widely used A320 jets in a sweeping recall affecting more than half the global fleet, threatening upheaval during the busiest travel weekend of the year in the US and sparking disruption worldwide.

However, emergency repairs to some of the A320 jets affected by this major recall may be less burdensome than first thought, industry sources said.

Although some 6,000 jets remain impacted overall, a sub-set of jets needing a time-consuming hardware change rather than a quick software fix is smaller than the initial estimates of 1,000, they said.

Airlines around the world announced delayed or canceled flights following the alert.

Airbus instructed its clients on Friday to take "immediate precautionary action" after evaluating a technical malfunction on board a JetBlue flight in October.

"Intense solar radiation may corrupt data critical to the functioning of flight controls," it said, adding that "a significant number of A320 Family aircraft currently in-service" may be affected.

Customers affected

Replacing the software will take "a few hours" on most planes but for some aircraft, the process "will take weeks", a source close to the issue told reporters.

Air France said it was calculating how many more flights would be canceled on Saturday.

"Customers affected by cancellations are being notified individually by SMS and email," a spokesperson said.

It canceled 35 flights on Friday, while Colombian airline Avianca said 70 percent of its fleet had been impacted by a technical issue in the European plane-maker's software.

The European Union Aviation Safety Agency (EASA) said in a statement that Airbus had informed it about the issue.

"These measures may cause short-term disruption to flight schedules and therefore inconvenience to passengers," EASA said, adding that "safety is paramount."

Aerospace and defense giant Thales said that it makes the flight control computer, which it said was "fully compliant with the technical specifications issued by Airbus" and certified by the EASA and its U.S. equivalent, the Federal Aviation Administration (FAA).

But it added: "The functionality in question is supported by software that is not under Thales' responsibility."

Operational disruptions

The Airbus statement did not specify which company had designed the software.

"Airbus acknowledges these recommendations will lead to operational disruptions to passengers and customers," it said, apologising for the inconvenience.

On October 30, a JetBlue-operated A320 aircraft encountered an in-flight control issue due to a computer malfunction.

The plane suddenly nosedived as it traveled between Cancun in Mexico and Newark in the United States, and pilots had to land in Tampa, Florida.

US media quoted local firefighters saying that some passengers were injured.

Contacted by AFP news agency, JetBlue did not comment on the incident but said it had already begun necessary changes on some A320 and A321 models.

Its competitor, American Airlines, said it had already begun updating software following Friday's alert, and expected "the vast majority" of approximately 340 affected aircraft to be serviced by Saturday. "Several delays" would occur as a result, it added.

After initially saying it had not been affected, its competitor United Airlines said it had identified six affected aircraft and said it expected minor disruptions on a few flights.

Delta Air Lines said it expected to have made the necessary updates by Saturday morning.

Air India warned Saturday of delays, while an Avianca statement warned of "significant disruptions over the next 10 days."

In the Philippines, local carriers Philippine Airlines and Cebu Pacific were offering refunds or rebooked tickets after grounding at least 40 domestic flights on Saturday.

Produced since 1988, the A320 is the world's best-selling aeroplane. Airbus sold 12,257 of the aircraft by the end of September compared with the sale of 12,254 Boeing 737s.