Photo courtesy of American Airlines

An American Airlines flight was forced to make an emergency landing in London Wednesday after several passengers and crew members fell ill.

According to Erin Dooley of ABC News, American Airlines Flight 109 from London’s Heathrow Airport to Los Angeles International Airport was carrying 172 passengers and 16 crew members when two passengers and four flight attendants became ill with an unknown sickness.

Passenger Kris Evans witnessed the incidents unfolding, and told ABC that one of the crew members onboard “literally just fainted... just fell forward, put her hand out and hit the floor. It was crazy.”

The Boeing 777 landed safely in London at 5:05 p.m. local time, and was met by emergency crews and ambulances. Paramedics on the scene examined the six people who had fallen ill, and discharged them all without any need for further medical assistance.

In a report from the New York Times, the cause of the sickness for the passengers and crew members was still a mystery as of Thursday. With that said, the report acknowledges the possibility that it could have been jet engine fumes leaking into the cabin.

The plane was inspected by maintenance workers after the passengers disembarked, and American Airlines released a statement to the New York Times, saying, “We apologize to our customers for the inconvenience.”

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