Qantas will fly a replacement aircraft engine to the United States after a mid-air explosion forced one of its 747s carrying 230 people to make an emergency landing.
The 747-400 departed San Francisco about 11.30pm local time on Monday (Tuesday afternoon AEST) with 212 passengers and 18 crew on board.
"About 15 minutes into the flight, the flight crew picked up on some excessive vibration in the number four engine," a Qantas spokesman told AAP.
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The captain shut down the engine and informed San Francisco air traffic control of the problem.
An apparent explosion in the number four engine ripped a hole through its outer shell.
"I've certainly seen the images of holes," the spokesman said.
"Certainly the engine failed, but what caused that failure is something that's going to take some time to determine."
Passengers seated in view of the engine would have noticed a problem.
"It's possible, particularly at night, if the engine surged or when it failed, some passengers might have seen sparks or a flare of some description particularly coming from the rear of the engine," the spokesman said.
The plane returned to San Francisco and made a normal landing.
Passengers were not required to assume the emergency brace position, the spokesman said.
Qantas will fly the replacement engine to San Francisco on Wednesday.
Affected passengers have been offered seats on any of three Qantas flights scheduled to depart Los Angeles on Tuesday evening local time (Wednesday afternoon AEST).
The Federal Aviation Administration (FAA) in the US said Qantas will prepare a report into the incident for the FAA and the National Transportation Safety Board.
"Whatever Qantas does is going to have to meet with our approval too," an FAA spokesman told AAP.
"The bottom line is we want to make sure and know that that aircraft is airworthy when they are saying they want to put it back on line."
The Qantas spokesman said the Australian Transport Safety Bureau will also receive a report on the incident.
