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Missing MH370: Sub to Scour 'New to Man' Section of Ocean Floor

The pinger locator will be replaced by the Bluefin 21 sub, which can create a three-dimensional sonar map of the area to chart any debris on the sea floor.

The air search for signs of missing MH370 will be called off within 72 hours as a robotic submarine begins to scan and map a "new to man" section of ocean floor, the official in charge of the operation said Monday.

“It is time to go underwater,” said Angus Houston, the head of the joint agency coordinating the search far off Australia's coast.

The U.S. Navy's pinger locator was replaced in the southern Indian Ocean by the Bluefin 21 autonomous sub, which can create a three-dimensional sonar map of the area to chart any debris on the sea floor.

The Bluefin sub takes six times longer to cover the same area as the pinger locator, and the two devices can't be used at the same time. It was launched around 5:20 a.m. ET.

Officials believe batteries in the missing jet's black box recorders have probably died. Crews had been hoping to detect additional signals before sending down the sub, so they could triangulate the source and zero in on where exactly the black boxes may be.

Complicating matters further is the depth the sea floor which at 15,000 feet below the surface, is at the deepest the Bluefin can dive. Officials are looking for other vehicles that could help to retrieve any wreckage if the submarine detects any sign of the Boeing 777.

Officials haven't found a single piece of debris linked to the plane and Houston said Monday that the visual search operation would be ending in the next two to three days.

The submarine will take 24 hours to complete each mission: two hours to dive to the bottom, 16 hours to search the sea floor, two hours to return to the surface, and four hours to download the data, Houston said. In its first deployment, it will search a 15-square-mile section of sea floor.

"The current depth that the system will be operating in is right at its rated maximum, so that is certainly a concern," Houston said. "That's what it's rated to operate into but anytime we push something to its limits you're always concerned about how the performance is going to be."

He also warned of the need to be realistic about the challenges ahead, dubbing the waters being searched as “new to man.”

Houston added: "I would caution you against raising hopes that the deployment of the autonomous underwater vehicle will result in the detection of the aircraft wreckage. It may not. However, this is the best lead we have, and it must be pursued vigorously. Again, I emphasize that this will be a slow and painstaking process."

Officials are currently focusing their acoustic search on an area about the size of a medium city - around 230 square miles - and say it could take the underwater robot months to scan and map the whole search zone.

A visual search for debris on the ocean surface was continuing on Monday over 18,400 square miles of water about 1,400 miles northwest of Perth, Australia.

The Associated Press and Reuters contributed to this report.