A protester lay on top of a plane while another forced a jet to turn around on the runway as climate change activists descended on London City Airport on Thursday, causing some disruption but ultimately failing to cancel flights.
Protest organizers Extinction Rebellion had vowed to occupy the airport's terminal and shut down operations for three days as part of its action in the British capital.
London City is the capital's fifth-biggest - and most central - airport, popular with business travelers, bankers and politicians for short-haul and regional routes.
A Reuters photographer saw one man, former paralympian cyclist James Brown, lay himself across the top of the body of a British Airways Embraer 190 jet. "I managed to get on the roof," Brown said in a video he posted online.
"This is all about the climate and ecological crisis. We're protesting against government inaction."
He was eventually removed. A spokeswoman for BA said "we are investigating what happened as a matter of urgency".
The group said they were protesting plans to expand the airport, which aims to have 6.5 million passengers a year by 2022 compared to the 4.8 million in 2018, and which has said there could be demand for as many as 11 million by 2035.
On Thursday, 18,000 passengers were due to arrive or depart from the airport, with 286 flights scheduled. While some protesters got inside the terminal building, flights were continuing, though some were delayed.
An Aer Lingus plane was forced to stop taxiing and return to its gate when a passenger got up to give a speech about climate change.
"I'm extremely sorry to disturb everybody here. We have two generations of human civilization left if we carry on doing what we're doing," the unnamed man said in a video of the incident, as he politely declined efforts by staff and passengers to get him to sit down.
Aer Lingus said that a passenger was removed from the flight to Dublin due to "disruptive behavior on board."
Extra security measures at the airport meant that most of the protesting happened well away from the runway.
Protesters glued themselves to the terminal building, occupied a nearby Docklands Light Railway (DLR) station and blocked roads around the airport.
Police have made hundreds of arrests so far this week as the protesters have sought to shut down London with two weeks of civil disobedience.
"We continue to work closely with the Metropolitan Police to ensure the safe operation of the airport, which remains fully open and operational," a spokesman for London City Airport said.
Police said that they had arrested one person on a flight on the runway with a number of people arrested outside the airport, without specifying how many.
The airport said it is "committed to building a more sustainable future for the airport and the aviation industry" and has said it will achieve net zero carbon emissions by 2050. British Airways owner IAG also pledged on Thursday to meet that emissions target.