Three US Marines died in the August 27 crash after the crew lost control of their MV-22B Osprey during war games near a remote tropical island off Australia.

The deadly accident was one of several involving Ospreys in the past few years, prompting renewed scrutiny of the tilt-rotor aircraft, a mix between a helicopter and a plane.

"Ultimately, based on the evidence available, the primary cause for this mishap was pilot error and complacency," the report said.

But the probe also found "several concerning maintenance practices" by the squad, including falsified paperwork about the aircraft's weight and load, and incomplete turnaround inspections prior to flight.

While "there is no evidence to indicate these practices caused the mishap on 27 August 2023, ultimately, the aircraft should not have been certified as safe-for-flight," it said.

As a result of the Australia crash, Pentagon investigators recommended all Marine Osprey squadrons hold a safety standdown to review the incident.

They also urged disciplinary action against the leadership involved, including the former commanding officer "for permitting a culture that disregarded safety of flight and aviation maintenance procedures."

The three Marines killed in the crash, Major Tobin Lewis, Captain Eleanor LeBeau and Corporal Spencer Collart, were among 23 people onboard the Osprey as it headed towards the sparsely populated Melville Island.

It averted a near mid-air collision with another Osprey but two near 90-degree turns saw the aircraft nosedive into the ground where it skidded and then burst into flames.

The hybrid aircraft, which can take off and land vertically like a helicopter and rotate its propellers forward to fly like an airplane, has been involved in several recent deadly crashes.

In late November, a US Osprey crashed off the coast of Japan, killing all eight people on board and prompting the military the following month to ground the aircraft worldwide.

Ospreys resumed flight operations in limited capacity in March, but military officials overseeing the program told US lawmakers in June that the aircraft would not fully return until 2025.

Four US Marines were killed in Norway in 2022 when their Osprey went down during NATO training exercises.

Three Marines were killed in 2017 when an Osprey crashed after clipping the back of a transport ship while trying to land at sea off Australia's north coast.

The United States had previously temporarily grounded the aircraft in Japan in 2016 after an Osprey crash-landed off Okinawa.