A robotic U.S. submarine that aborted its first attempt to locate the missing Malaysian jetliner in the Indian Ocean when it strayed into excessively deep waters was launched Tuesday on a second mission as searchers face dwindling options for finding the plane.

Malaysia Airlines Flight 370 from Kuala Lumpur to Beijing, with 239 people aboard, disappeared soon after takeoff March 8, sparking a major, multinational search effort in the air and on the seas.

The first attempt to use the U.S.-made Bluefin 21 in the search but was cut short Monday after just six hours when it reached its maximum depth of 15,000 feet. Safety devices on board the sub, which is programmed to hover 100 feet above the seabed, returned it to the surface automatically, according to Australia's Joint Agency Coordination Center (JACC), which is responsible for the search and recovery effort.

CNN reports that the Bluefin was redeployed again on Tuesday to try to comb the seabed west of Australia.

Search teams have given up attempts to pick up any more possible acoustic signals from the jet's two black boxes, surmising that their batteries have already expired. The last "pings" possibly from the data and voice recorders were heard seven days ago.

Now, the air and surface search for debris is also winding down and will be completed in the next two to three days as chances of finding wreckage "have greatly diminished," said Angus Houston, who leads the JACC.

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The slow-moving, unmanned submersible, or "autonomous underwater vehicle," is fitted with sonar equipment that can map the ocean floor, said Houston. Officials say it could take two months to cover the 230-square-mile area where the plane likely went down.

A mission normally takes 24 hours to complete: two hours to dive to the bottom, 16 hours to search the seabed, two hours to return to the surface, and four hours to upload the data.

The limited data collected by the Bluefin on Monday in its brief run was analyzed after it returned to the surface but nothing of interest was found, the U.S. Navy said in a statement.

Officials had held off launching the little yellow sub until they were convinced that batteries from the jet's black boxes had expired. The sub's own noises could have interfered with acoustic equipment listening for any new signals from the plane.

Authorities are also awaiting an analysis of a 2-liter sample of oil that was collected from an oil slick found Sunday in the area where four strong underwater signals were detected last week.


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