Thirteen anti-Heathrow expansion activists who blocked a runway face jail after being found guilty of aggravated trespass.
The climate change protestors, who have been on trial for the past week at Willesden Magistrates' Court, were also found guilty of entering a security restricted area.
JULY 2015: Heathrow protesters removed from runway
All have been told that an "immediate custodial sentence" was "almost inevitable".
However, the judge did say the defendants were principled and that Heathrow is in breach of EU emission regulations.
The protestors made their way onto the north runway by cutting through a perimeter fence line on July 13, 2015.
They built a metal tripod structure and locked themselves to it.
Superintendent Andy Jones, from the Met's Aviation Policing, said: "While it is the role of the police to facilitate peaceful protest it is also our role to uphold the law and to allow businesses and the public to go about their lawful business.
"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.
"I appreciate that airport expansion will trigger protest but I would urge those considering such action, to do so peacefully and within the bounds of the law."
Green Party MP Caroline Lucas added: "Sending the Heathrow 13 to prison would be utterly unwarranted.
"They took a principled and non-violent stand against the colossal environmental cost of expanding an airport that already breaches air pollution laws - yet they’re being treated is if they are somehow a danger to society.
"The real danger we face are the toxic fumes emitted by airports and the looming threat of catastrophic climate change.
"Sending these committed activists to jail would be deeply unjust."
Officers were called at about 3.45am to reports of suspicious activity at the perimeter fence.
Police found the fence cut and several bolt-cutters discarded at the scene, with the protestors found at the eastern end of the north runway.
They had built a tripod out of scaffolding poles and surrounded themselves with 6ft high metal fencing.
The protestors, campaigning against expansion at Heathrow, had then locked themselves onto the structure or in pairs with arm locks filled with expanding quick set foam.
The design of the structure and 'lock-ons' meant that neither the metalwork nor the protestors could easily be moved.
Specialist officers then called in to safely remove them.
A number of items were seized, including superglue, locks, chains and pieces of steel pipe.
The northern runway was finally cleared for full use at 10.02am.
THE HEATHROW RUNWAY 13
- Rebecca Holly Sanderson, 28 (10.01.88) of Newton Road, Machynlleth, Powys;
- Melanie Strickland, 32 (17.02.83) of Borwick Avenue, Waltham Forest, E17;
- Richard Steven Hawkins, 32 (29.01.83) of Heol y Doll, Machynlleth, Powys;
- Ella Gilbert, 23 (16.07.92) of Magdalen Street, Norwich, Norfolk;
- Danielle Louise Paffard, 28 (25.02.87) of Blenhiem Grove, Southwark, SE15;
- Graham Edward James Thompson, 42 (27.09.73) of Durlston Road, Hackney, E5;
- Robert Anthony Basto, 68 (13.09.47) of Blackborough Road, Reigate, Surrey;
- Kara Lauren Moses, 33 (25.10.83) of Heol y Doll, Machynlleth, Powys;
- Cameron Joseph Kaye, 23 (11.02.92) of Kenwood Close, Sipson, West Drayton;
- Edward Thacker, 26 (24.06.89) of Kenwood Close, Sipson, West Drayton;
- Alistair Craig Tamlit, 27 (16.05.88) of Kenwood Close, Sipson, West Drayton;
- Sheila Menon, 44 (22.10.71) of Pellerin Road, Hackney, N16;
- Sam Sender, 23 (25.01.92) of Kenwood Close, Sipson, West Drayton.
The sentencing will take place at the same court on February 24.