Pilot made U-turn two hours into 13-hour flight after they realized they forgot extremely important item

A United Airlines pilot was forced to turn his plane around two hours into a 13-hour flight after he realized he'd left behind one very important item.

Don't worry, this isn't a Home Alone kind of situation - he didn't forget his child.

But with Flight UA 198 set to travel all the way from Los Angeles to China, the thing he did forget was almost as vital.

The situation went down on board the United Airlines flight which departed from LAX airport at around 2pm on March 22, after 257 passengers and 13 crew members successfully boarded and settled in for the long-haul flight.

The flight was set to land in Shanghai, but customers barely had chance to get stuck in to an in-flight movie when the plane made a U-turn.

According to the website FlightAware, the plane was redirected to San Francisco after turning around, and it ended up landing back in the US at around 5pm local time.

Now, do a mental pat of your pockets and think about everything you need when traveling abroad. Wallet, keys, phone... ID?

You need more than just a driver's license when traveling overseas, but unfortunately, a passport is the one thing the pilot didn't have that day.

In a statement addressing the situation, United said: "The pilot did not have their passport onboard."

United said customers received a meal voucher (Justin Sullivan/Getty Images)

Yang Shuhan, a Chinese passenger who was on board flight UA 198, told CNN she heard the pilot sound 'very frustrated' when he admitted to customers over the speakerphone that he 'forgot' his passport.

Shuhan said she appreciated the pilot's 'honesty' over the situation, though other customers were less forgiving.

Writing on RedNote, China’s Instagram-like platform, other passengers said they were 'speechless' at the situation.

In response to complaints on social media, United's account said it 'sincerely apologize[d] for this unexpected travel disruption'.

In its statement, United added that customers were provided with meal vouchers and compensation for the mishap. Yang told CNN she received two meal vouchers totaling $30, which she used for a meal at the airport.

The pilot told passengers he didn't have his passport (JEFF HAYNES/AFP via Getty Images)

The customer has also filed a compensation claim on United’s website, and is expected to receive a response within 14 business days.

"We arranged for a new crew to take our customers to their destination that evening," the company said.

The new flight took off around 9pm local time, and landed in Shanghai about six hours later than originally planned.

The knock-on effect of the interrupted flight meant that customers in Shanghai who were waiting to travel to LA on the returning flight also faced delays.