Thirteen activists who cut through a fence at Heathrow Airport and chained themselves together on a runway have been told to "expect jail sentences".
The protesters, part of action group Plane Stupid, were found guilty at Willesden Magistrates' Court of aggravated trespass and entering a security restricted area.
They oppose Heathrow's planned expansion and its environmental impact.
Twenty-five flights were cancelled after the protest on 13 July last year.
District Judge Deborah Wright said all of the defendants were people of integrity who were concerned about climate change and Heathrow expansion.
But she said the cost of the disruption had been "absolutely astronomical".
When the verdict was read out one person yelled "this is a farce" and another shouted "shame on you" at the judge.
The activists previously admitted to being on the runway but said such action was necessary to stop people dying from the effects of pollution and climate change.
Supt Andy Jones, of the Metropolitan Police, said: "When protestors encroach into the airside environment they not only cause major disruption but also significant danger to themselves and aircraft.
"These convictions send out a clear message that such behaviour will not be tolerated."
Owen Greenhall, representing five of the demonstrators, said they were "honest, sincere in their beliefs and genuine in their intentions".
Plane Stupid issued a statement saying: "When the democratic, legislative processes have failed it takes the actions of ordinary people to change them.
"Climate change and air pollution from Heathrow are killing people now and the government's response is to spend millions making the problem bigger."
But Rob Gray, director of the Back Heathrow campaign, said the protesters' actions were "undemocratic".
"Plane Stupid do not represent the majority of local residents who want to see a bigger, better Heathrow - or the millions of people who simply want to use the airport uninterrupted and unmolested."
The protestors will be sentenced on 24 February.
- Rebecca Sanderson, 28, from Newton Road, Machynlleth, Powys
- Richard Hawkins, 32 and Kara Moses, 32, both from Heol y Doll, Machynlleth, Powys
- Ella Gilbert, 23, from Magdalen Street, Norwich
- Melanie Strickland, 32, from Borwick Avenue, Waltham Forest
- Danielle Paffard, 28, from Blenheim Grove, Peckham
- Graham Thompson, 42, from Durlston Road, Hackney
- Sheila Menon, 44, from Pellerin Road, Hackney
- Cameron Kaye, 23, Edward Thacker, 26, Alistair Tamlit, 27 and Sam Sender, 23, from Kenwood Close, Sipson, West Drayton
- Robert Basto, 67, from Blackborough Road, Reigate, Surrey