The plane was about two and a half hours into its trip from London to Los Angeles, near Iceland, reports The Telegraph, when several passengers and crew were felled by the mystery malady.
A member of the cabin crew reportedly fainted, and five others said they didn’t feel well, along with three passengers.
One passenger said he saw a flight attendant faint.
“It was at that point the captain said he was turning the plane around,” he told the Mail Online. “He said he wasn’t willing to take the risk to keep going and hadn’t got the crew to do it.”
Upon landing, emergency vehicles greeted the plane and escorted it down the taxiway. Officials came on board to test the air, before paramedics arrived to check out the ill. No passengers required additional medical help, American said.
American Airlines said the decision to return to London, more than 1,000 miles away, instead of landing in Iceland, was made by the cabin crew. The aircraft was inspected by maintenance engineers, the airline said.
“We apologize to our customers for the inconvenience,” American said in an emailed statement to the New York Times.
It’s still unclear what happened on board, but some of the symptoms — dizziness and loss of consciousness — are among those that have been tied to jet engine fumes leaking into the cabin, the NYT notes. This happens when heated air drawn from the engines, which is used for cabin pressurization and air-conditioning systems, can be contaminated with traces of engine oil or hydraulic fluid. This can cause aerotoxic syndrome, a condition that goes away once you’re away from that air.