The Plane Stupid demonstration on 13 July led to delays and the cancellation of 22 flights.
The activists, who were protesting against plans to expand the airport, allegedly cut a hole in a fence and chained themselves to railings.
Supporters chanted "No ifs, no buts, no third runway!" outside the court.
Sheila Menon, one of the accused, read a statement outside Uxbridge Magistrates' Court. She said the pollution and noise caused by air traffic at Heathrow was already blighting the area.
She said the proposed expansion - recommended by the Airports Commission in its final report last month - was driven by "wealthy frequent flyers" rather than ordinary holidaymakers.
Plane Stupid's actions were "reasonable, justifiable and necessary", said Ms Menon.
The activists were charged with aggravated trespass and entering a restricted area of the airport without permission.
They were bailed on condition that they do not enter Heathrow or its perimeter, with a trial expected to begin on 18 January.
Thirteen climate change activists have pleaded not guilty to charges of trespassing on Heathrow's north runway.