An American Airlines plane. (Ted S. Warren/AP)

An American Airlines plane was forced to turn around Wednesday when multiple people on board the London-to-Los Angeles flight were struck by a mysterious illness.

Passengers on the plane became fearful after one flight attendant collapsed and rumors of airborne contamination spread throughout the cabin, according to accounts from several people on board. The plane was in the air for more than two hours and was flying close to Keflavik in southwest Iceland and when it turned around and headed back to London, according to CBS News.

“It was probably as tense as anyone wants to be 30,000 feet in the air,” passenger Eric Winter told CBS.

“I saw an older gentleman — unfortunately, he had thrown up all over himself,” he added.

One flight attendant “literally just fainted … just fell forward, put her hand out and hit the floor,” passenger Kris Evans told ABC News. “It was crazy.”

As word of the illness spread, a pilot announced that the crew at the front of the plane was safe and had made the decision to go back to London, Winter said.

Lee Gunn, who claimed to be a passenger on board Flight AA109, tweeted updates from the air.

The Boeing 777, which had 172 passengers on board, took off from London at 12:05 p.m. local time and landed in the same city about five hours later, according to ABC News.

Once it on the ground, emergency personnel met the plane, according to a statement released by American Airlines.

“Yesterday, two passengers and some of our flight attendants complained of lightheadedness during the flight,” the statement read. “The captain elected to return the Boeing 777-300 to London. The aircraft landed safely, where it was met by paramedics who evaluated passengers and crew. None requested further medical attention. Our maintenance team conducted a thorough inspection of the aircraft, including a test flight, and found no issues with the Boeing 777-300. Out of an abundance of caution, all of the air filters on the aircraft were replaced.”

The New York Times reported that dizziness and loss of consciousness are symptoms that have been associated with “jet engine fumes leaking into the cabin.”

Experts told the Daily Mail that the incident could have stemmed from multiple issues inside the cabin, including a problem with the plane’s air-conditioning system, an oven giving off fumes in the galley, or “a chemical leak from a passenger’s bag.”

“Any time there is a problem in flight when passengers are ill — especially five or six — the captain will most likely turn the plane around to land it at the closest place,” aviation expert Bruce Rodger told the Daily Mail. “It sounds like it was bad and this could have been a situation that the air quality was possibly compromised somehow.”

Winter, the passenger, praised the crew members for their professionalism and said the hardest part of the flight was the unknown.

“In the absence of information, your mind can go crazy, but I think they did a tremendous job,” he told CBS News. “They communicated to us every step of the way.

“And here we are. We’re sitting on the ground and we’re fine.”

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