Defence has admitted the door on its multi-role Taipan helicopters is too narrow to allow its gun to fire while troops are descending from the aircraft.
During a Senate Estimates hearing, officials have confirmed a third round of work is being carried out on the MRH-90 Taipan fleet that was bought from Airbus for $3.8 billion.
Head of helicopter capability and sustainment for Defence, Shane Fairweather, told the committee the problems were due to the width of the door, not the gun mount design.
"The door isn't wide enough to enable the safe exit while firing is taking place," he said.
"The Taipan gun mount minimises the time at which that firing can take place because you can deploy it and stow it quickly."
The Chief of Army, Lieutenant General Rick Burr, said "tactical workarounds" were allowing the aircraft to complete its duties.
"There are some technical issues and safety issues that prevent that from occurring but there are tactical workarounds that are in place," General Burr said.
The inability of the European-designed Taipan to fire its gun while soldiers are rappelling means the Army must fly the helicopters in pairs to carry out certain missions.
Senate Estimates was also told the cargo hook on the Navy's MRH-90s had been an "ongoing problem", but a solution was expected soon.
"We're very close to resolution on that … and I accept to be able to certify that into operational service very soon," Navy Chief Vice-Admiral Mike Noonan said.
Defence Chief General Angus Campbell defended the Airbus-made product as an "extraordinary helicopter" but conceded there were problems.
"I would like a perfect helicopter — it would be all things to all people," General Campbell said.
"It requires a careful planning of the employment of our aircraft. We never fly an aircraft on its own."
Australia's acquisition of the MRH-90 for Army and Navy commenced in 2004 and on Tuesday remains on the Defence Department's "projects of concern" list.
Last year, the ADF grounded its entire fleet of 47 MRH-90 helicopters after one of the Taipans made a precautionary landing caused by a tail rotor vibration.
