Some Jetstar planes have been grounded due to a global recall of thousands of A320 aircraft, which are also used by Australian carriers Qantas and Virgin.
This morning, Airbus ordered immediate repairs to 6,000 of its A320 family of jets, more than half the global fleet.
About two-thirds of the affected aircraft will be briefly grounded as airlines revert to a previous software version, industry sources have told Reuters.
More than 1,000 of the affected aircraft may be grounded longer due to hardware changes, the sources said.
The repairs must be carried out before the next routine flight, according to a separate bulletin to airlines seen by Reuters, which could lead to cancellations or delays.
According to Jetstar's website, the carrier has 56 A320s in its main fleet and another 25 operating under Jetstar Japan.
It also has five A320neo planes in its main fleet.
A Jetstar spokesperson did not say how many of its planes are impacted, but said some had been immediately grounded and flights cancelled.
"Due to an issue affecting Airbus A320 operators globally, some of Jetstar's Airbus-operated flights are unable to depart at this stage," they said.
"Safety is our number one priority. To respond to a precautionary action from Airbus, we have cancelled some Jetstar Airways flights.
"Our teams are working on options to get customers on their way as quickly as possible, and are contacting affected customers directly.
"We will continue to provide updates."
A Qantas spokesperson said none of its fleet had been impacted.
Virgin Australia, which has five A320s in its fleet, has been contacted for comment.
In a statement, Sydney Airport said the global software outage was causing delays for some domestic Jetstar services operating from Sydney.
"We're supporting Jetstar as they work to resolve the issue, and strongly advise all Jetstar customers to check their flight status with the airline before travelling to the airport," it said.
"All other airlines and flights at Sydney Airport are operating as normal and are unaffected."
There was chaos at Melbourne Airport on Saturday morning with many travellers arriving to find their flights cancelled.
Three Jetstar flights scheduled from Adelaide to the Gold Coast, Sydney and Cairns have also been cancelled.
Sidney Dekker, a Griffith University professor and former pilot, said the software fix would be "fairly simple" and required impacted planes to be grounded for about two hours.
"But then you also need the right expertise when the airplane is in the hangar to do the software update, and that's a little bit of a crunch," Dr Dekker told ABC News Breakfast.
"We've had this problem in Australia for a while — not enough aviation maintenance engineers to go around.
"Worldwide, it will reverberate for a couple of weeks before it settles. It will cause a lot of disruptions."
The Civil Aviation Safety Authority told the ABC it was aware of the issue "affecting the A320 family of aircraft globally".
"All aircraft that are affected will need to be checked in accordance with advice issued by Airbus and the European Union Aviation Safety Agency," a spokesperson said.
"We are in contact with major airlines and confident they are acting quickly to minimise disruptions and ensure aircraft can be returned to service safely."
Recall linked to flight-control software issue
Airbus said a recent incident involving an A320-family aircraft had revealed that solar flares may corrupt data critical to the functioning of flight controls.
Industry sources have told Reuters that the incident that triggered the unexpected repairs involved a JetBlue flight from Cancun, Mexico, to Newark, New Jersey, on October 30.
Several passengers were hurt following a sharp loss of altitude, and the flight had to make an emergency landing at Tampa, Florida.
The setback appears to be among the largest recalls affecting Airbus in its 55-year history and comes weeks after the A320 overtook the Boeing 737 as the most-delivered model.
Some 3,000 A320-family jets were in the air worldwide shortly after Airbus's announcement on Saturday morning.
The world's largest A320 operator, American Airlines, said some 340 of its 480 A320 aircraft would need the fix.
It said it mostly expected repairs to be completed within a day, 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 UK-based easyJet.
Colombian carrier Avianca said the recall affected more than 70 per cent of its fleet, around 100 jets, causing significant disruption over the next 10 days and prompting the airline to close ticket sales for travel dates through December 8.
There are around 11,300 A320-family jets in operation, including 6,440 of the core A320 model, which first flew in 1987.
Four of the world's 10 biggest A320-family operators are major US airlines: American Airlines, Delta Air Lines, JetBlue and United Airlines.
Launched in 1984, the A320 was the first mainstream jetliner 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, when faulty flight-control software pushed the planes' noses down.
The Airbus 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' responsibility.
ABC/Reuters
