The Australian Maritime Safety Authority said the robotic sub Bluefin-21 was deployed on Tuesday night after deep ocean water ended its initial dive after just six hours.
The sub had been expected to search for 16 hours on Monday, but a built-in safety mechanism cut the journey short after the sub's depth limit of about 2.8 miles was reached, officials said.
Bluefin-21 is searching in the southern Indian Ocean about 1,000 miles off Australia’s west coast, an area of about the size of a medium city — 230 square miles — that officials think is the likeliest place the plane went down.
Acoustical signals believed to be from the aircraft’s black box or flight data recorder led searchers to the remote search area.
Bluefin-21 is capable of creating a three-dimensional sonar map of the area to chart debris on the sea floor. Still, no wreckage or physical trace of the plane has been found.
16/04/14 NBC News