A United Airlines plane flying above Wales declared a general emergency mid-air and was forced to return to London.
A Chicago-bound flight 929 from Heathrow turned back as it flew above Cardiff and Newport after reports of smoke in the cabin.
United Airlines said on their website they are addressing a "technical error" on the Boeing 767 but did not elaborate on the problem.
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They said on their website: "We want you to know your flight is departing late because we are addressing a technical issue on your plane. Your safety is our priority and we're sorry for the inconvenience. (Estimated departure two hours 13 minutes late)."
The flight left London Heathrow at 8.35am this morning and was due to arrive into Chicago O'Hare International Airport at 11.20am. It arrived back at Heathrow at 9.43am.
Jonathan Vasdekas was on the flight and tweeted United Airlines saying: "Hey @united, we just landed back at Heathrow because of the smell of smoke in the cabin... could we please get a newer plane?? Props to the captain and crew for getting us back on the ground safely."
They replied: "Hello Jonathan, we apologize for this experience. Please know that safety is always our priority, and our teams will all work to get you back on the way as quickly as possible."
WalesOnline have approached United Airlines for comment.
