GRIM footage shows the grisly mess cleaners had to deal with after a passenger left diarrhoea "all the way through the plane".
The pilot was forced to make an emergency landing as the muck was deemed a biohazard.
The long haul Delta flight from Atlanta to Barcelona descended in chaos just two hours in as a passenger got the trots.
They left a vile trail of their mess throughout The Airbus A350 - which fully loaded can carry 330 people - in front of horrified travellers.
Speaking to air traffic control, the captain said: "This is a biohazard issue.
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"We’ve had a passenger who’s had diarrhea all the way through the airplane, so they want us to come back to Atlanta."
Footage shared on X claimed to be from the tainted jet shows the mess up and down the aisle on the carpet.
A number of paper towels appear to have been hastily put on the floor in a bid to clear up.
Flight attendants on board are also understood to have attempted to scrub the muck before the plane landed.
But according to those on board, the disinfectant spray didn't quite do the trick.
One woman whose partner was on board tweeted: "It was pretty bad.
"It was dribbled down the aisle, smelled horrible.
"The vanilla scented disinfectant used on it only made it smell like vanilla s***.
"After the plane landed, it was thoroughly cleaned."
Passengers were transferred from the Airbus A350 aircraft to another jet and made it to Spain eight hours later than scheduled, Flightradar24 data shows.
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The plane was subject to a deep clean after the emergency landing, and has since been used for another journey, flight records show.
Delta Airlines confirmed a passenger suffered a "medical incident", but did not elaborate.
A spokesman told Insider: "Delta flight 194 from Atlanta to Barcelona returned to Atlanta following an onboard medical issue.
"Our teams worked as quickly and safely as possible to thoroughly clean the airplane and get our customers to their final destination.
"We sincerely apologise to our customers for the delay and inconvenience to their travel plans."
