A Qantas flight from Perth to London was forced to turn around because of a disruptive passenger.
The Boeing 787-9 Dreamliner was around two hours into the 17-hour trip on Sunday when the captain decided to fly back to its departure airport.
A male passenger was taken off the flight in handcuffs.
He was banned from all Qantas flights pending an investigation.
Clare Hudson, who was travelling on the plane with her baby, said the disruptive passenger locked himself in a toilet for about an hour.
She told The West Australian: "When he came out he started acting really aggressive and it looked like he was going to attack another one of the passengers.
"Luckily they did manage to calm him down after a few minutes and took him up the back of the plane."
After passengers were put up in hotels for the night, they reboarded the plane and it took off for a second time, 18 hours behind schedule.
It was originally due to land at London Heathrow shortly after 5am on Sunday, but did not touch down until 10.30pm (local time).
A Qantas spokesman said: "This type of disruption inconveniences our customers, and we take a zero tolerance approach to disruptive behaviour on board.
"The safety of our crew and customers is our number one priority.
"The passenger has been issued with an interim 'no fly ban' which means they are unable to travel on Qantas Group flights until the investigation into the matter is completed."
Perth-London is the longest non-stop scheduled passenger route serving UK airports.