Qantas, Australia's national airline, grounded its Airbus A380 fleet indefinitely after part of a plane's engine cover fell off mid-flight on Thursday.
The airline said the twin-deck planes -- the world's largest airliners -- will remain suspended until an investigation into Thursday's incident is complete.
"As long as it takes," said airline CEO Alan Joyce, when a reporter asked him how long the suspension will last. "We are being very cautious until we know exactly what caused this."
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On Thursday, a Qantas airliner had one of its four engines shut down six minutes after takeoff from Singapore's Changi Airport, Joyce said.
The plane -- with 433 passengers and 26 crew members -- was headed to Sydney, Australia, but was forced to return to Changi.
While in the air above the western Indonesian island of Batam, part of the engine's covering, or cowling, tore off and fell.
"I am not sure what actually happened with the debris and why parts of the engine left the aircraft and fell into the ground," Joyce said. "We're still looking at what exactly was the cause of that."
Local television stations in Indonesia showed debris parts with red-white markings. Pictures of the Airbus A380 after it landed showed the cowling torn off in the back half.
Trifuadi, a security officer at an engineering firm in Batam, said he heard a loud explosion and saw smoke coming out of the engine of a plane flying overhead.
Shortly afterward, debris fell from the plane to the ground, said Trifuadi, who like many Indonesians go by one name.
The flight -- QF32 -- landed in Singapore safely, without injury to passenger or crew.
Ulf Waschbusch, who was on his way to Australia for the first time, said the crew kept passengers apprised of what was happening.
"We all stayed pretty calm," he told CNN. "It was an almost eerie calm."
The airline said it will work with the plane's manufacturer as well as Rolls-Royce, the maker of the engine, to determine what went wrong.
Qantas now has six A380s in its fleet of 191 planes. Airbus will at some point deliver another 14, the airline said.