Nov 7: Australia's Qantas Airways has ruled out sabotage after passenger jets on two consecutive days experienced engine failures that forced them to return to Singapore shortly after takeoff.

"We don't believe this is sabotage," Qantas chief Alan Joyce said Saturday of what his airline called a coincidence. "It looks like a mechanical failure of the engine."

He said a "contained engine failure" six minutes after takeoff accounted for a Boeing 747-400 aborting its flight to Sydney Friday and making an emergency landing at Changi Airport.

Among those on board the 747 were members of the crew of the A380 that a day earlier had aborted Flight QF32 to Sydney after an engine blew up four minutes after taking off from Changi.

Debris from the incinerated engine cowling rained down on Indonesia's Batam Island.

Both engines were manufactured by Rolls Royce. An investigation into the two cases was under way, the manufacturer said, but a spokesman in London declined to go into details.

"There was smoke and sparks coming from the engine, so the pilot followed procedure and landed safely in Singapore," Joyce said.

Passengers aboard Flight QF6 told of an explosion followed by a shower of sparks and flames.

Tourism Australia managing director Andrew McEvoy said he doubted Qantas' troubles would deter people from boarding its planes.

"They've had some trouble of late, but they're a great airline," he said. "People will have confidence in Qantas because they've such a long and strong history with safety."

Qantas, famously, has yet to record a fatality in 90 years of flying.

Joyce contrasted the two incidents, saying the earlier one involving the world's largest passenger plane was far more serious because the engine failure was "uncontained", meaning the cowling came apart and shards of metal punctured the fuselage.

"We're not concerned about our 747 fleet," he said. "Those engines have a long life. ... We've seen in-flight shutdowns take place before. ... It's a liability, not a safety issue."

Qantas Thursday grounded its fleet of A380s, a jet that began commercial flights in 2007, but Joyce said the same step was unnecessary in the case of the 747.

Joyce earlier ascribed the A380 engine blowout to a material failure or design fault rather than lax maintenance.

The two-year-old superjumbo involved had recently been serviced by Lufthansa in Germany. The 747, also fitted with Rolls-Royce engines, had been serviced locally.

In comments after the first mid-air scare, Joyce acknowledged the airline had received directives from the European Aviation Safety Agency concerning the Rolls-Royce Trent 900 engines fitted to the six A380s flown by Qantas.

"It's not an uncommon practice for these [directives] to occur," Joyce said. "It's a good practice, and particularly as you're getting new aircraft in, ... you're discovering ways of actually improving the way you maintain and operate the aircraft.

"This issue does not relate to maintenance," he said. "We believe this is most likely a material failure or some sort of design issue."

The A380 landed safely in Singapore nearly two hours after taking off despite the second engine on the left wing failing to shut down and tyres blowing as it touched the tarmac.