The activists unfurled two banners and threw paper planes from the roof
Five activists have been found guilty of trespass after unfurling banners on the House of Commons' roof in protest at Heathrow's proposed expansion.
Leo Murray, Graham Thompson, Alexander George, Tamsin Omond, all from London, and Olivia Chessell, from Cambridge, are in protest group Plane Stupid.
Omond was given a conditional discharge and ordered to pay £150 costs. The other four were each fined £150.
They sneaked the banners past security then climbed onto the roof in February.
All protesters except Omond must also pay costs of £200 plus a £15 surcharge.
They had denied a charge of trespass, at Westminster Magistrates' Court.
The group put forward a defence under Section 3 of the Criminal Law Act which allows force to be used to stop a crime being committed.
But district judge Nicholas Evans ruled it was not applicable.
Once on the House of Commons roof the group unfurled banners and threw paper aeroplanes onto people gathered below.
Two of the protesters also handcuffed themselves to railings on the roof.
Sentencing, the judge said: "You caused no damage, you made no threat to anybody and it was a peaceful demonstration."
He added: "It has no doubt caused embarrassment to those charged with the security of the House of Commons."
It was part of a series of protests against a proposed third runway at Heathrow airport.
In a separate case, six Greenpeace activists were cleared in September of causing £30,000 damage to Kingsnorth power station in Hoo, Kent, in a protest over coal-fired power.
They successfully argued in court that they had a "lawful excuse" to damage the power station to prevent even greater damage caused by climate change, under the Criminal Damage Act 1971.