Documents assessing the potential risks for a fleet of helicopters involved in a fatal crash will not be released by Defence, which claims confidentiality is "vital" to aviation safety.
But the Greens say a lack of transparency from the Australian Defence Force poses a safety risk.
The Taipans were withdrawn from service after a catastrophic crash in July during military Exercise Talisman Sabre in Queensland.
Captain Danniel Lyon, Lieutenant Maxwell Nugent, Warrant Officer Class Two Joseph Laycock and Corporal Alexander Naggs were killed in the accident.
A freedom of information request made by the office of Greens senator David Shoebridge into flight test reports and the airworthiness of the MRH-90 choppers was rejected by the Department of Defence.
The FOI decision maker wrote the "confidential aspect of aviation safety is vital" for quickly finding issues and preventing incidents from happening again.
"Any erosion of that process could be expected to diminish the quality and level of information available for the investigators to determine the cause of any aviation incident," the statement reads.
"I do not consider that releasing the information could reasonably be expected to improve Defence's aviation safety investigation processes."
The Taipans were dumped by the Australian Defence Force a decade earlier than scheduled, their service plagued with fleet-wide groundings and serious incidents.
They will be replaced with Black Hawks imported from the US.
Greens' defence spokesman David Shoebridge slammed the department for its secrecy and called on Defence leadership to tell the public what concerns they had about the choppers and what decisions were made about them.
"Very basic questions about accountability and transparency are treated by the government and Defence leadership with disdain," Senator Shoebridge said.
"The claim by Defence that 'confidentiality is a key aspect of aviation safety' would be almost funny if it were not for the devastating impacts this secrecy has on people's safety."
The ADF's top brass was grilled during tense Senate estimates hearings this year about the aircraft, with many questions taken on notice.
Senator Shoebridge pointed to aviation industry standards which deem the sharing of safety information is a key tenet of the air transport system.
"Secrecy and confidentiality hide incompetence and hide systemic problems and that's just what Defence wants," he said.
"The only reason they are denying this information is to protect decision-makers from public scrutiny."
