Yet the fleet wasn't officially grounded until July 11 this year, when an Australian Army aircraft was forced to undertake a precautionary landing due to a tail rotor vibration.

Defence said a modification program was being progressively rolled out across the ADF's 47-strong MRH90 fleet when the incident happened, but the "affected helicopter had not undergone the modification at the time".

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The aircraft had been en route to Brisbane Airport on July 11 when the vibration was detected with the aircraft captain aborting the mission and returning to HMAS Adelaide for a precautionary landing.

Defence said the full circumstances that led to the precautionary landing were under investigation and grounded all its MRH90 aircraft pending further technical investigation and advice.

"The failure of a small component on the tail rotor assembly of a MRH90 led to excessive vibrations on a flight, during Exercise Talisman Sabre and resulted in a precautionary grounding of the ADF's fleet pending a technical investigation," a spokesperson said.

"All operating nations (of the aircraft) were advised of the modifications required in October 2018.

"A modification program was already being progressively rolled out across the ADF's MRH90 fleet."

The Australian aircraft were due to be back in the air from August 19.

Defence said the ADF's CH-47F Chinook heavy-lift helicopters, which were also participating in the exercise, compensated for the absence of MRH90, however, it is understood ADF was also forced to use aircraft from New Zealand and the US.

Similar incidents have occurred on the German armed forces NH90 helicopters in 2014 and 2017, which led the original equipment manufacturer, NH Industries, to develop a modification of a component on the tail rotor assembly.

"As the modification issue affects the worldwide NH90 fleet, other nations either have or are expected to complete the same modification," the defence spokesperson said.

"Within the international NH90 community, several [forums] exist for nations to share information relating to the airworthiness, sustainment and ongoing development of this modern platform.

"The ADF is actively engaged in these [forums]."

Talisman Sabre is a bilateral training exercise focused on the planning and conduct of mid-intensity "high end" warfighting between Australian and the US military.

Historically Talisman Sabre exercises have been conducted across northern and eastern Australia, and within Australia's Exclusive Economic Zone, with additional participants from third party nations participating or observing the exercise

The majority of TS19 exercise activities took place in the existing ADF Shoalwater Bay Training Area and surrounding State Forests, near Rockhampton in Central Queensland from late June to early August with the initial surge of equipment and people and their subsequent departure after the exercise. Peak activities were between July 11-24.

Australia spent $3.5 billion on 47 new MRH90s - a multi-role helicopter to be used by both navy and army, replacing the retired Sea King and ageing Black Hawk fleets.

The Royal Australian Navy operates six MRH90s permanently.

They are based out of 808 Squadron at HMAS Albatross with a number embarked on ships across the RAN fleet.

The MRH-90, as the name suggests, is a multi-role helicopter, capable of troop transport, search and rescue, special operations and counter-terrorism missions.