Australian airline Qantas has said it has discovered oil leaks in three engines of its Airbus A380s and was keeping six passenger jets grounded for further checks.

Tests have uncovered oil leaks in three Rolls—Royce engines on Qantas’ grounded Airbus A380s, the airline’s CEO said on Monday, as engineers tried to zero in on the cause of an engine failure on board one of the carrier’s superjumbo jets last week.

Australia’s national carrier grounded its six double—decker A380s, the world’s newest and largest airliner, after an engine burst minutes into a flight from Singapore to Sydney last week, scattering debris over Indonesia’s Batam island. The plane made a safe emergency landing in Singapore.

Engineers conducted eight hours of extensive checks on each engine over the weekend.

On Monday, CEO Alan Joyce said engineers have discovered oil leaks in the turbine area of three engines on three different A380s.

“Oil leaks were beyond normal tolerances”

“The oil leaks were beyond normal tolerances,” Mr. Joyce told reporters. “So Rolls—Royce and our engineers have looked at what we have gathered as an accepted level and they have passed that threshold.”

“All of these engines are new engines on a new aircraft type,” he added. “The engines are not performing to the parameters that you would expect with this.”

Because of that, he said, all of the airline’s A380s will be grounded for at least an additional 72 hours.

“We are not going to take any risks whatsoever,” Mr. Joyce said. “We want to make sure we have a 100 percent safe operation.”

All three affected engines have been removed from the planes for further testing, and will be replaced with spare engines the airline has on hand, Mr. Joyce said.

“As a consequence, it’s now narrowing our focus on that issue,” he said.

Lufthansa and Singapore Airlines, the other airlines that fly A380s fitted with Rolls—Royce’s Trent 900 engines, also briefly grounded their planes last week but resumed services after completing checks.

The Qantas engineers are working with Rolls—Royce, who manufactured and maintains the engines, as well as Airbus.

Appeal to Batam island’s residents

The Australian Transport Safety Bureau, which is leading an international investigation into the blowout on the A380, appealed for help from residents of Indonesia’s Batam island to find a missing piece of a turbine disc.

The island was scattered with debris last Thursday when one of the A380’s four engines failed minutes into a flight to Sydney, with 466 people aboard. The engine was quickly shut down and the plane returned to Singapore and safely made an emergency landing.

“The recovery of that disk could be crucial to a full understanding of the nature of the engine failure, and may have implications for the prevention of future similar occurrences,” the bureau said in a statement.

It released a photograph of a jagged and bent piece of turbine disc from the Trent 900 engine and asked that anyone who might have found a similar piece should hand it to police.

It said one piece of the shattered engine that had been found on Batam was being sent to Britain for examination by Rolls—Royce engineers, under the supervision of bureau investigators. Extra experts were being sent from Australia to Singapore to examine other debris.

Rolls—Royce Group PLC, a London—based aerospace, power systems and defence company separate from the car manufacturer, has said the investigation is in its early stages and that it is too early to draw any conclusions.

Turbine disc may have failed

John Goglia, a former National Transportation Safety Board member and an expert on aircraft maintenance, said the photo showing the broken turbine disc indicates it was the disc that may have failed. The photo didn’t show any signs of discoloration on the disc that would indicate overheating.

There are several reasons why a disc might fail, but they usually involve the metal used to make the disc or the manufacturing method, Mr. Goglia said. He cautioned that he was looking at one photo, which was not enough information to make a definitive judgment.

Qantas passengers stranded by the grounding of the A380s are expected to be flown to their destinations within 24 hours, Mr. Joyce said. The airline is adding flights from London and Los Angeles to help clear the backlog.

Mr. Joyce would not specify how much the airline has lost since the engine explosion, nor would he comment on whether Qantas plans to seek compensation from Rolls—Royce.

“We are working with Airbus and Rolls—Royce to fix this issue, that’s our top priority and compensation talks will take place after the aircraft are back in the air,” he said.

Shares in Rolls—Royce PLC slumped almost 12 percent to 576.5 pence ($9.32) in early trading on Monday on the London Stock Exchange. They lost more than five percent last week after Thursday’s in—flight incident.