Robotic submarine Bluefin-21 will be deployed for the first time to search for the missing Malaysia Airlines plane.
Air Chief Marshal Angus Houston said the Bluefin-21 drone would be sent down as soon as possible to search for wreckage on the sea floor.
Teams have been using a towed pinger locator to listen for signals from the plane’s “black box” flight recorders.
But no new signals have been heard since April 8, amid concerns the flight recorders’ batteries have expired.
Flight MH370 went missing on March 8 with 239 people on board. It was flying from Kuala Lumpur to Beijing when it lost contact with air traffic controllers over the South China Sea.
Malaysian officials believe, based on satellite data, that it ended its flight in the southern Indian Ocean, thousands of kilometres off course.
An international search has focused on waters west of the Australian city of Perth, with teams racing against time to detect signals before the flight recorder batteries – which last about one month – run out.
ACM Angus Houston, who heads the joint agency coordinating the search effort, said that given no signals had been detected in six days, it was time to go underwater.
The Bluefin-21 – an almost 5m-long underwater autonomous vehicle that can create a sonar map of the sea floor – will search for wreckage in an area defined by four signals heard last week.
Officials believe those signals – picked up by the pinger locator towed by an Australian vessel – are consistent with flight recorders.
“Analysis of the four signals has allowed the provisional definition of a reduced and manageable search area on the ocean floor,” ACM Angus Houston said.
“The experts have therefore determined that the Australian Defense Vessel Ocean Shield will cease searching with the towed pinger locator later today and deploy the… Bluefin-21 as soon as possible.”
Angus Houston warned that the submersible search would be a long, “painstaking” process that might, in the end, yield no results.
Each Bluefin-21 mission will last 24 hours, with 16 hours spent on the ocean floor, four hours’ diving and resurfacing time, and four hours to download data.
Australian vessel Ocean Shield had also spotted an oil slick in the same area where the signals had been heard, ACM Angus Houston said, and a sample was being sent for testing.
“I stress the source of the oil is yet to be determined but the oil slick is approximately 5,500m downwind… from the vicinity of the detections picked up by the towed pinger locator,” he said.
Australian officials have said previously that they are confident they are searching in the right area for the missing plane.
Officials have no idea yet why the plane diverted so far from its intended flight path. Investigators are looking at options including hijacking, mechanical failure, sabotage and pilot action.
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