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.

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Gabbiadini scored twice to bring Saints level at 2-2, but had what would have been the opener incorrectly ruled out.
"Gabbiadini's first was a good goal, it should have stood. He scored three good goals," Puel said.
"It's a lot of disappointment. We deserved better," the Frenchman added.
"I would like the video for the future for this situation, but at the moment we are without. Sometimes there is a bad decision against us, it is important to accept this.
"The memories are always for the winner. It's football and congratulations for Manchester. I'm proud of my players because we played very well."
Zlatan Ibrahimovic collected the 32nd trophy of his career after heading an 87th-minute winner at Wembley on Sunday, having earlier given United the lead with a brilliant 19th-minute free-kick.
Jesse Lingard put United 2-0 in front before Gabbiadini struck twice - his fourth and fifth goals in three games since joining from Napoli for £14m.
"Puel has reason to be really sad and disappointed because he did fantastic work and his team deserved extra time,'' United manager Jose Mourinho said.
"To lose in minute 87 with very little time to try to react, as they did in the first half, is a little bit unfair on them."
Goalline technology - to determine whether the ball has crossed the line - was brought in to the Premier League for the start of the 2013-14 season.
And a trial - possibly in Britain - using video assistant referees for "game-changing decisions" will begin no later than the 2017-18 campaign, the International Football Association Board (IFAB) has said.

Ovidio Gonzalez was suffering from terminal throat cancer and said he had been suffering unbearable pain.
Colombia's Catholic Church has said euthanasia is morally unacceptable and it has threatened to close its hospitals across the country.
Colombia is one of the few countries in the world, and the only one in Latin America, where euthanasia is allowed.
Assisted suicide was approved by the Constitutional Court in the 1990s. But no procedures had been performed because the measure had not been regulated.
It was only in May that the health ministry intervened and issued a set of guidelines for hospitals.
Mr Gonzalez died in a clinic in the western city of Pereira, after a legal battle.
His son Julio Cesar is a cartoonist with one of Colombia's top newspapers, El Tiempo.
"My father received the news [that the procedure had been approved] with relief," said Mr Gonzalez, better known by his pen name Matador, or The Killer.
"It is a pity that it had to be like that. My dad deserved to go with less publicity," he added.
Euthanasia is highly controversial in the predominantly Roman Catholic country.
Critics also point out that the measure has not been voted by Congress.
Thirteen climate change activists have pleaded not guilty to charges of trespassing on Heathrow's north runway.
[NEXT_CONCEPT]
Southampton manager Claude Puel says he would like to see video technology used for offside after Manolo Gabbiadini's disallowed goal in the 3-2 EFL Cup final defeat by Manchester United.
[NEXT_CONCEPT]
A 79-year old Colombian man has become the first person in the country to die legally by euthanasia.