Qantas initially said the plane returned for "operational reasons" and would later only admit there was an "issue" with one engine.
Qantas estimates that sparks may have been caused by overheating of an engine, but he denied that the engine was on fire, as Australian media reported.
"Friday night's QF94 A380 service from Los Angeles to Melbourne turned back to LA because of an issue with one of the aircraft's four engines", Woodward wrote.
Flight QF94 was two hours into its trip when the pilots had to shut down one of the A-380 plane's four engines.
The crew descended the aircraft, QF94, to 29,000ft and returned to Los Angeles and landed at 3am Saturday local time.
Qantas spokesman Thomas Woodward said the pilots turned the plane around and landed it safely back in LA.
He later tweeted a photo on board the replacement plane of the flight path, writing "lets try this again shall we". Loud noises may have been the sound of the engine being shut down. "We saw flames and sparks flying past the window", Sudgen said.
A Los Angeles to Melbourne flight carrying more than 300 passengers has finally touched down to the relief of frustrated travellers.
He said Qantas staff asked passengers to stay the night inside LAX as another flight could leave about lunchtime.