Australian army chief Lieutenant General Simon Stuart said on Sunday that Australia's 45-strong fleet of MRH-90 Taipan helicopters would cease flying until further notice after one crashed into the ocean during multinational military exercises on Friday.
The ageing Taipans have repeatedly been grounded in the past, with officials complaining that they are difficult to maintain and that spare parts are not readily available.
The crash was the second emergency involving an Australian Taipan this year. In March, a helicopter of that type ditched into the search off the coast of the state of New South Wales while on a training exercise. All 10 people on board were rescued.
What did Australia's army chief say?
"We are not flying the MRH-90 today and won't until we think it is safe to do so," Stuart told reporters in the eastern city of Sydney.
Stuart said the army was currently planning to keep the Taipans in service until 2024 but that the crash might cause some reconsideration.
"What happens between now and then, from what we learn from this incident, is yet to be determined," he said.
The Australian government has in the past already spoken of plans to replace the Taipan fleet with US-made Black Hawks.
Stuart also identified the four missing crew and said they were all from the 6th Aviation Regiment, based in Sydney.
"You have to feel for their families and their mates," he said.
What are the details of the crash?
The aircraft that crashed was taking part in Talisman Saber, a biennial joint US-Australian military exercise. It went down in waters near the Whitsunday Islands off Australia's subtropical northeast in the state of Queensland, where the exercise is largely based.
A search for the missing pilot and three other crew members is ongoing, with hundreds of Australian, US and Canadian military personnel taking part.
Debris from the the aircraft was reportedly recovered on Saturday.
This year's Talisman Saber exercise involves 13 nations and more than 30,000 military personnel. It was interrupted briefly on Saturday but some activities were later started up again away from the crash site.
The crash came as US Secretary of State Antony Blinken and US Defense Secretary Lloyd Austin are in Australia for ministerial talks.
"Our hearts go out to their loved ones during this terribly difficult time," Austin said of the missing crew.
