A British Airways flight, which was two hours into its journey from London to Chicago, had to turn back to Heathrow due to "technical reasons".
Passengers on the plane posted on Twitter that the fault was with the aircraft's landing gear.
Journalist Ben de Pear, who was on the flight, said the captain explained to those onboard that the plane landed on three sets of wheels instead of five.
Heathrow Airport apologised to passengers after the incident meant it could only use one runway for a time, causing disruption to flights.
British Airways has not issued a statement about the incident.