An army Taipan helicopter that crashed in NSW’s Jervis Bay was flying without upgraded engine blades recommended by the aircraft’s manufacturer six years earlier, newly released documents show.

None of those aboard died in the March 2023 incident but four soldiers were killed when one of the same helicopters crashed months later in Queensland during the Talisman Sabre military exercise.

Documents tabled in the Senate reveal one of the turbine blades ruptured in the helicopter’s left-hand, causing a “catastrophic” failure.

The air safety investigation found the army had not complied with a 2017 Airbus recommendation, issued after several failures across the global MRH-90 Taipan fleet, for modified blades to be installed.

Investigators found the Australian Defence Force conducted a “hazard analysis” of the manufacturer’s recommendation, finding the risk of engine failure when flying with the unmodified engine was “extremely small”.

But the investigation “did not reveal definitive evidence” that the ADF finalised a safety assessment to determine the likelihood of engine failure.

An assessment conducted after the crash, the Army’s aviation branch determined the risk of blade failure would have been eliminated if all of the service’s MRH-90 helicopters had been fitted with the modified blades.

The helicopters were retired in September last year, after the July 2023 crash in the Whitsundays that killed Corporal Alex Naggs, Captain Danniel Lyon, Lieutenant Max Nugent and Warrant Officer Phil Laycock.

Defence has confirmed the pilots in the fatal crash were using a helmet-mounted display system at the time despite internal warnings the equipment carried an “increased risk”.

The Army Aviation Test and Evaluation Section had deemed the TopOwl helmet-mounted display an “unacceptable risk to flight safety” due to ambiguous and inconsistent data projected onto the pilot’s visor, an inquiry heard.

One Nation senator Malcolm Roberts, who requested the documents on the Jervis Bay crash, said they showed “Defence was willing to overlook serious risks when it came to this helicopter”.

“How many other problems with the MRH-90 helicopter did Defence overlook?” he told the Senate.

“How many times did they allow this thing back in the air, knowing it would unnecessarily put our defence personnel at needless risk? How many potentially catastrophic issues, like the TopOwl headset, were supposedly mitigated or did Defence just explain away?”

Senator Roberts said the aircraft should have been pulled from service a year earlier, declaring “blood is on the hands of the Defence leadership and successive defence ministers who kept this helicopter in the air when it belonged on the ground”.

The government is yet to release its official findings on the cause of the July 2023 Taipan crash near Lindeman Island.