NSW kit plane wreckage tough to move: cops

Police admit it may prove a challenge to extricate the full wreckage of a light plane that crashed into a national park on the NSW-Queensland border killing two brothers.

Robert Bryan Dull, 68, and Owen Stanley Dull, 61, died when their small kit aircraft went down on Sunday in the Koreelah National Park.

Rescuers entered the park on foot on Monday after the Wittman Tailwind's wreckage was spotted in rugged terrain by the Westpac Rescue Helicopter.

NSW police rescue and SES volunteers arrived at the crash site about 3pm and confirmed the two men had died.

The Australian Transport and Safety Bureau will investigate the crash but police on Monday acknowledged removing all of the wreckage may be impossible.

"The terrain is that difficult and dense," Inspector Bill McKenna told reporters.

"Our plan is to get back into the scene ... to record that scene for the coroner, as you would expect, and then make a determination in relation to the wreckage.

"We will be heavily guided by ATSB investigators."

The bureau will examine any recorded data, weather information and potential witnesses.

Police on Tuesday said a plan to extricate the wreckage was yet to be formulated.

The single-engine, two-seat aircraft left Casino Airport on Sunday afternoon but never reached its scheduled destination of Boonah in Queensland.

The brothers' family said in a statement that Robert and Owen were both pilots with more than three decades of experience.

The family said the Wittman Tailwind - usually constructed with a steel tubing fuselage, wooden wings and fabric covering - had passed all safety requirements and won awards for "experimental amateur-built aircraft".

"Robert had built the plane as a labour of love," the family said.

"Robert is survived by his wife, three adult sons, their spouses and four grandchildren. Owen is survived by his wife.

"We would like to thank all of those involved in the search and recovery efforts for Robert and Owen in difficult conditions."

Aviators need to have kit planes checked by an engineer and complete test flights away from populated areas before they can be flown regularly, Civil Aviation Safety Authority spokesman Peter Gibson told AAP.

"It's a basic plane ... but it is regulated," Mr Gibson said on Monday.