A Paralympic medallist climbed on top of a British Airways plane at London City Airport as part of ongoing protests by Extinction Rebellion.
James Brown, who is visually impaired, filmed himself clinging to the fuselage as he streamed a live message online.
Metropolitan Police Commissioner Dame Cressida Dick described the action as “reckless, stupid and dangerous”. About 50 arrests were made at the airport.
Another man refused to sit in his seat, delaying a flight by nearly two hours.
On the fourth day of climate change protests, disruption in the UK has centred around London City Airport.
Earlier, police arrested people blocking the airport entrance as others glued themselves to the floor.
Flights have largely run on time or with slight delays in and out of London City Airport. As of 12:15 BST, a spokesman for the airport said more than 100 flights had either arrived or departed.
Meanwhile in Westminster, tents and protesters have been cleared from the roads leading to Parliament Square.
Police said they were working to clear a camp in St James’ Park, with Trafalgar Square the only other site still occupied in central London.
BBC Newsnight’s Nicholas Watt was on a Dublin-bound flight when a “smartly dressed man” stood up and walked down the aisle, delivering a lecture on climate change.
Cabin crew “calmly and very politely” asked the protester to retake his seat and, when he declined, they alerted the pilot, Watt said in a tweet.
He said the plane then taxied back to the gate, where police escorted the protester off the plane.
Aer Lingus said the passenger was removed “due to disruptive behaviour on board” and a full security check of the aircraft was completed before the delayed flight could depart.
At lunchtime, James Brown, a Paralympian cyclist from Northern Ireland, filmed himself sitting on top of an Amsterdam-bound plane which had been due to take off just after 13:00 BST. He was booked on to the flight.
In a live stream posted on Facebook, he said it was “scary” because he hated heights, felt cold and hoped they would get him down soon.
“Oh man I’m shaking,” he went on. “This is all about the climate and ecological crisis. We’re protesting at government inaction on climate and ecological breakdown. They declare climate emergency and do nothing about it.”
Met Commissioner Dame Cressida said: “My early understanding is somebody has been arrested after they presumably bought a ticket, went through security perfectly normally, went up the steps of a plane and hurled themselves on top of a plane.
“Actually, that was a reckless, stupid and dangerous thing to do for all concerned.
“But I think you can see that is quite a hard thing to predict or stop from happening.”
She said a full review of security at the airport would be carried out.
Police said more than 1,000 people have been arrested since Monday, including about 50 at the airport on Thursday.
Twenty-nine people have been charged with various offences, police said, including seven who were due to appear at Westminster Magistrates’ Court on Thursday.
Activists are attempting a three-day “Hong Kong-style occupation of the terminal building” to highlight what they claim is the “incompatibility” of the east London airport’s planned £2bn expansion with meeting the government’s legally-binding commitment to go net carbon neutral by 2050.
However, by Thursday afternoon, the number of protesters at the airport was beginning to dwindle, and an Extinction Rebellion spokesman said they would decide later whether to stay there overnight and continue their protest on Friday.
Former Metropolitan Police detective John Curran was among those arrested, after he glued himself to the pavement outside the airport.
An 83-year-old man, Phil Kingston, was also arrested, as hundreds of people blocked the main passenger entrance.
It is the third time he has been arrested as part of the Extinction Rebellion protests this week.
An activist who gave her name as Claire told the PA news agency that protesters wanted “to make the statement that there are many areas of our lives that are going to have to change because of the climate crisis we’ve created, and one of them is flying”.
“We can’t carry on with life, with business as usual,” the 51-year-old said.
Protesters also caused disruption outside the terminal, as several sat down on the zebra crossing, blocking traffic going in and out of the passenger drop-off zone.
Cars and buses were backed up in both directions before the demonstrators were cleared from the roads by police.
Taxi driver Jason Lempiere said the protests had disrupted his work in and around the city.
“It’s disturbing everyone’s everyday life; working, travel in and out of the airport,” he said.
“Yeah, have a voice, but not disrupt people’s lives like this.”
A spokesman for London City Airport said: “We continue to work closely with the Metropolitan Police to ensure the safe operation of the airport, which remains fully open and operational.”
The airport advised passengers to check the status of their flight before travelling.