Police say aircraft debris has been found in the search area where the pilot, identified as Tasmanian man Bob Bramley, crashed in the air charter plane on Tuesday.
Northern Territory Police Assistant Commissioner Peter Malley told reporters in Darwin on Thursday that authorities believed Mr Bramley died in the crash, but they had yet to find a body.
The Air Frontier twin-engined Beechcraft Baron aircraft went missing after taking off from Gove airport at Nhulunbuy on the Northern Territory coast with only the pilot aboard.
The plane was due to land at the remote Indigenous community of Numbulwar at 11.50am on Tuesday but never arrived.
A search led by NT Police began after a witness on a vessel reported seeing the plane crash into the sea near Isle Woodah in the Gulf of Carpentaria.
The search on Thursday involved police and Aboriginal ranger vessels, a helicopter and a police plane.
Police divers have also been deployed to conduct searches of the sea floor in the vicinity of the crash site.
Search mission co-ordinator, Acting Sergeant Nathan Conelius, told ABC Radio that aircraft debris had been found in the search area on Wednesday.
"That's helped refine our search planning so we are more hopeful today of finding something else," he said.
In a statement on Thursday Mr Bramley's family described him as courageous and inspirational, saying they could not "comprehend this great loss in our lives".
"There are no words, deeds or silver linings that make this any easier, but our beloved Bob is gone," they said.
"Bob was a courageous individual, who inspired those around him with his infectious enthusiasm.
"He was a dreamer, who never let fear, problems or pessimists stop him from reaching his goals."
As a 16-year-old in 2019, Mr Bramley circumnavigated Australia in a small plane to raise awareness of youth suicide, saying he was motivated to do so after almost losing two very close friends.
He went on to found the youth suicide prevention initiative Surviving Turbulence and featured on Australian Story in 2021 for his record-breaking solo flight.
Air Frontier CEO Kylie Hunt said the company was "deeply saddened" by the accident and her thoughts were with the pilot and his family.
As a precautionary measure, the company has grounded all five of its Beechcraft Baron aircraft pending advice from authorities.
The Australian Transport Safety Bureau has initiated a crash investigation.
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