• A Qantas flight U-turned over the Pacific Ocean — 1,100 miles after leaving Los Angeles.
• Investigators said sparks were seen coming from an engine, and Qantas confirmed a "mechanical issue."
• Passengers were left with a six-hour flight to nowhere.

Qantas passengers endured a six-hour flight to nowhere when their flight turned around over the Pacific Ocean.

Flight 16 from Los Angeles to Brisbane, Australia, on December 3 U-turned after 2 ½ hours, about 1,100 miles off the California coast, per FlightAware data.

It landed back at LAX at about 2:45 a.m. the next day in Los Angeles.

The Australian Transport Safety Bureau, which is investigating the incident, said the Airbus A330 suffered an engine malfunction.

From initial reports, it said, sparks were seen coming from one of the engines, prompting the Qantas pilots to return to Los Angeles.

It added that a bang was heard during the approach, followed by stall indications for the engine. After landing, an inspection found evidence of metal in the engine's tailpipe.

FlightAware's data shows that the A330, registered under the tail number VH-EBQ, has been grounded since the incident.

A Qantas spokesperson confirmed the plane returned because of a "mechanical issue with one of the engines."

"The pilots followed normal procedures and returned to LA where the aircraft landed normally," they added.

"We apologize for the inconvenience and recognize this would have been unsettling for some passengers. We'll work closely with the regulators on their investigation."

So-called flights to nowhere can be frustrating for passengers and costly for airlines — but typically less so than other diversions. It is generally easier to repair problems and reroute passengers where airlines have bases. Qantas has a maintenance facility at LAX.

The airline spokesperson said the engine would be repaired before it returned to the fleet. In the meantime, a replacement is being sent to Los Angeles from Melbourne.

It isn't especially rare for planes to turn back to where they came from when an issue arises.

On Saturday, a United Airlines flight to London returned to Newark, New Jersey, where a 24-year-old was arrested on suspicion of interference with transportation.

Earlier this month, a KLM Boeing 777 U-turned over the Atlantic, leaving passengers with a four-hour flight to nowhere.