Protesters angry about climate change damaging our planet have climbed on to a plane at London's Heathrow airport.
Two men and two women from the campaign group Greenpeace clambered on top of the aircraft after it landed on a flight from Manchester on Monday.
Greenpeace doesn't want another runway to be built at the airport, which is Europe's busiest. Planes use a lot of fuel, which harms the environment.
The protesters had a banner saying: "Climate emergency - no third runway."
Heathrow bosses described the protest as "unlawful and irresponsible" and said things were operating normally elsewhere at the airport.
It will be holding an investigation to find out how the protesters got on to the plane.
A Greenpeace spokesman said the protesters had targeted this flight because it came from Manchester, which is easy to reach by train from London.
"These unnecessary flights, where there's a train that takes two hours, are the flights that are fuelling this push for a third runway," he said.