• 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.

• A United Airlines flight turned back to Newark, New Jersey, after 90 minutes.
• It's the latest example of a flight to nowhere — when flights return to their origin.
• Passengers eventually made it to London 12 hours later than scheduled.

United Airlines passengers faced a 12-hour delay after their transatlantic trip became a flight to nowhere.

Saturday's flight from Newark, New Jersey, to London was in the air for about 90 minutes when it U-turned just off the coast of Nova Scotia, according to data from FlightAware.

The flight-tracking website shows that after landing back in New Jersey at about 2:30 a.m. ET, the Boeing 767 didn't take off again for nearly five more hours.

Flight UA940 ultimately made it to London Heathrow at 7.29 p.m. local time on Sunday — 12 hours and 5 minutes after it was initially scheduled.

In a statement shared with Business Insider, a United Airlines spokesperson said the flight returned to Newark "to address a disruptive passenger."

The statement added that law enforcement removed the passenger before the flight continued to London that morning.

One Reddit user who said they were on the flight said the plane turned around after a business-class passenger threatened the aircraft's security.

They added that the delay at Newark was compounded by the flight crew reaching their maximum time on the clock, so new staff had to be brought in from standby.

The Port Authority of New York and New Jersey didn't immediately respond to a request for comment sent by BI outside US working hours.

Returning all the way to Newark rather than landing at a nearer airport in Canada may initially seem a strange decision, but so-called flights to nowhere aren't uncommon. Going back to an airline's hub airport usually means it's simpler to reroute passengers and solve any issues.

There have been several flights to nowhere in recent weeks.

Last month, a Delta Air Lines plane turned back over the coast of Newfoundland after the crew observed a potential engine issue.

Then, a KLM flight U-turned over the Atlantic Ocean and headed back to Amsterdam in a four-hour flight to nowhere as a precaution because of a technical malfunction.