Passengers heading to China aboard a United Airlines flight faced an unexpected travel headache after a pilot forgot his passport prompting a midair U-turn back to the United States.

Flight UA198 from Los Angeles to Shanghai was over the Pacific Ocean when it made a U-turn and headed to San Francisco, tracking data showed.

United Airlines issued a brief statement, confirming that the pilot lacked a passport, which led to the decision to return the plane to California.

A replacement crew was then assigned to fly the passengers to their planned destination.

The flight finally departed about six hours behind its original schedule.

Passengers received meal vouchers and compensation, in compensation for the disruption and delay.