The Bluefin 21 autonomous submarine will be sent to search for the wreckage of MH370 as investigators fear the black box beacon batteries have likely expired.
The fact that no new signals have been detected since 8 April despite the presence of two ships equipped with highly sensitive equipment in the area seems to confirm the flight data recorder beacons are no longer transmitting any signal. The systems are only designed to last for 30 days and have already been within their margins.
The search crews will probably today sent the American Bluefin 21 to scan the depths of the southern Indian Ocean and create a detailed map of the seabed.
The unmanned submarine will be launched from the Australian ship Ocean Shield that has previously detected four signals, believed to be the black box pings, using a towed pinger locator made available by the US military.
The advanced sonar equipment carried by the Bluefin should be able to distinguish unusual objects on the seabed, such as aircraft debris.
"We haven't had a single detection in six days, and I guess it's time to go under water," said retired air chief marshal Angus Houston, the head of a joint agency co-ordinating the search off Australia's west coast.
"Analysis of the four signals has allowed the provisional definition of a reduced and manageable search area on the ocean floor. The experts have therefore determined that the Australian Defence Vessel Ocean Shield will cease searching with the towed pinger locator later today and deploy the autonomous underwater vehicle Bluefin 21 as soon as possible," he told a news conference in Perth.
But Mr Houston warned the switch to the submarine will not automatically "result in the detection of the aircraft wreckage. It may not".
The submarine takes six times longer to cover the same area as the ping locator and will need about six weeks to two months to canvass the current underwater zone. The signals are also coming from 4,500 metres below the surface, which is the deepest the sub can dive.
Recovering the plane's flight data and cockpit voice recorders is essential for investigators trying to figure out what happened to Flight 370, which vanished on 8 March. It was carrying 239 people, mostly Chinese, while en route from Kuala Lumpur, Malaysia, to Beijing.
A visual search for debris is also planned over 18,400 square miles of ocean centred 1,400 miles north west of Perth. A total of 12 planes and
15 ships will join the two searches.
Meanwhile officials are investigating an oil slick not far from the area where the underwater sounds were detected. Crews have collected a sample of the oil and are sending it back to Australia for analysis, a process that will take several days.
The oil does not appear to be from any of the ships in the area, but Mr Houston warned against jumping to any conclusions about its source.
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