Richard Green, 74, his graphic artist wife Carolyn, 71, and filmmaker John Davis, 72, were killed on their way back to the northern beaches from an anti-mining festival at Breeza, near Tamworth, on Saturday.

The highly regarded environmentalists were working on a documentary capturing the environmental destruction wrought by mining.

Mr Green's modified Eurocopter 135, described by him as his "flying campervan", was found in rugged, bushland near Cessnock on Monday evening.

A witness, Jim Bloomfield, said he saw the helicopter fly into a valley near his Hunter Valley home as a severe storm rolled in on Saturday evening. He said the helicopter landed but then took off again and looked in trouble.

"I actually said to my wife I hope that guy is an instrument-rated pilot because he's in trouble if he's not," he told Sky News.

The experienced pilot had his license suspended for six months in 2013 over four incidents in one year where he almost collided with other aircraft and one incident in which he struck powerlines and tore off part of his helicopter.

In a submission to an air safety inquiry in 2013, Mr Green had demanded the sacking of the Civil Aviation Safety Authority (CASA) board and other officials.

The submission reveals that Mr Green had been the first to import the high-performance Eurocopter into Australia and had immediately struggled to find qualified technicians to keep the machine flying. As a result he maintained it himself.

He complained bitterly about being investigated by CASA as far back in 2006 after he hit a tree branch while flying in Cape York in far north Queensland and how the incident had severely affected his authority to maintain the machine.

"I had a minor blade strike on a tree branch in a wilderness area in Cape York. In order to get the helicopter out of that location, I made a repair to the rotor blades," he wrote in the submission to the federal government's Aviation Safety Regulation Review.

"CASA's concern was not the fact I had a blade strike but what happened afterwards.

"My wife and I were stranded in the Cape York wilderness. Drawing on my training and an experienced-based evaluation, I made the sensible decision to effect a temporary repair that would permit a safe two hour flight to Cairns."

Mr Green said his alternative was to leave it "stuck in the wilderness" where it would have been difficult to repair and recover.

He said when he reported his actions to CASA an airworthiness inspector tried to revoke his pilot's licence, deeming the flight "dangerous and illegal".

He said CASA had "dramatically embellished the incident by listing a whole slew of alleged technical breaches of the regulations that flowed on from this primary incident".

Mr Green said he was required to show cause why his licence should not be revoked.

He then appealed to CASA's then head of aviation Greg Vaughan who instead increased Mr Green's authorities to conduct and certify maintenance on his helicopter.

However when the authority required renewal two years later, CASA refused to renew it.

Mr Green then successfully appealed through the Administrative Appeals Tribunal. He also said he faced further allegations of safety breaches as a result of his dispute with CASA.

He lashed out at CASA, saying "in my case alone well over 1000 man hours have been expended in trying to clip the wings of one private pilot who flies his own private helicopter about 100 hours a year and almost exclusively in wilderness areas of Australia".

He finished his submission by calling for "all the senior management in CASA ... to be replaced and the CASA board disbanded".

NSW Greens MP Jeremy Buckingham said the trio "were committed environmentalists who spent their lives making amazing films and taking incredible photographs of our incredible country – and fighting tooth and nail to defend it".

"It is a very dark day for anyone who loves the environment of Australia," he said on Tuesday.

Former independent MP Tony Windsor, who spoke at the Breeza festival on Saturday and met all three crash victims, said Mr Davis, a former Greens candidate for Davidson, interviewed him that afternoon about political lobbying and mining.

"I had a long conversation with John and probably did the last interview John ever did," said Mr Windsor.

"He wanted to have a yarn on a few things, mostly the influence of paid lobbyists in Canberra, particularly in the mining sector. He gave me his card and I'd put it on the beside table."

He said the three victims were keen and passionate environmentalists.

"About 800 people came to that event over the weekend, people travelled from near and far and the three of them really represented that body of people," Mr Windsor said.

"They had come to learn about this magnificent piece of country. They went out of their way to do that so it's tragic to think [the crash] happened on the back of their concerns for other people."

The twin-turbine Eurocopter had been used by Mr Green and his wife as aerial campervan to explore Australia and as part of his photography business and hobby.

He said when he first imported the machine there was nobody in the country who had certification to maintain it and he was the only pilot in the country endorsed to fly it.

A scientist and engineer by training, Mr Green said he purchased his helicopter in the late 1990s as an early unit off the production line in Germany.

He also noted he had flown with the chief flying instructor of Eurocopter Germany.

"Based on my training and experience (after a rigorous) flight test I was given endorsement to train other pilots to fly the machine," he said. He also noted that he had a maintenance hangar at his own home.