Flight AA57 from Heathrow to Miami performed a u-turn over northern France on Tuesday (May 3) morning, shortly before 11am, due to what the airline described as a water pressure issue.
The aircraft landed at Heathrow at 11.37am and American Airlines has said it is due to leave again at around 1pm, following maintenance work.
The airline tweeted at 11.23am to say: "We'll be arriving shortly and then we'll do Maintenance on it and leave now around 1pm."
American Airlines said it had returned as a result of a mechanical issue and had declared an emergency due to an overweight landing.
It said the mechanical issue was a water pressure issue.
"We apologize for the inconvenience to our passengers for the disruption to their travel plans," added a spokesman for the airline.
Last week, we reported how planes had been hit by lightning as they approached Heathrow amid an electrical storm on Wednesday (April 28) night.
You can watch footage of lightning striking one of the planes, which landed safely, below.