HMAS Albatross MRH-90 helicopters grounded

The helicopters flown by 808 Squadron, which are also operated by army have been grounded as a precaution after a tail rotor vibration was detected during a flight.

Defence said an Australian Army MRH-90 aircraft conducted a precautionary landing on HMAS Adelaide on July 11.

"The MRH-90 aircraft sustained a tail rotor vibration en route to Brisbane Airport," the defence spokesperson said.

"The aircraft captain aborted the mission and returned to HMAS Adelaide for a precautionary landing.

"No personnel were injured during the incident."

Defence said the full circumstances that led to the precautionary landing were under investigation.

"While the investigation is underway, the Australian Defence Force (ADF) has ceased all MRH-90 flying pending further technical investigation and advice," the spokesperson said.

The spokesperson said no other ADF aircraft had been affected by the temporary cessation.

It was revealed last month the MRH-90s had been included in a secret Australian Defence Force "project of concern" document.

Obtained by the ABC under Freedom of Information, the quarterly performance report from the Department of Defence's Capability and Sustainment Group, listed two major projects, the ADF's MRH-90 helicopters and the Deployable Defence Air Traffic Management and Control System as areas of concern.

Although much of the detail has been redacted on "national security" grounds, the protected 86-page document marked "sensitive" confirms the projects remained on the concern list.

The report said Australia was spending $3.5 billion on 47 new MRH-90s - a multi-role helicopter to be used by both navy and army, replacing the retired Sea King and ageing Black Hawk fleets.

A number of MRH-90s helicopters are embarked on various RAN ships, while the aircraft's home squadron is 808 at the Nowra based Fleet Air Arm station.

Defence said there were concerns over the delivery and service release of the enhance cargo hook system on the MRH-90s but rebuked claims in the ABC report that the aircraft also has issues with the auxiliary power unit on board, which limits the fleets' capability on certain missions because it cannot shut down its main engines due to problems with the power unit.