Water too deep for sub hunting MH370

The search area for the missing Malaysian jet has proved too deep for a robotic submarine which was hauled back to the surface of the Indian Ocean less than half way through its first seabed hunt for wreckage and the all-important black boxes, authorities said on Tuesday.

Search crews sent the Bluefin 21 deep into the Indian Ocean on Monday to begin searching the seabed for the missing Malaysia Airlines Boeing 777 after failing for six days to detect any signals believed to be from its black boxes.

But after only six hours of its planned 16-hour mission on the seabed, the autonomous underwater vehicle exceeded its maximum depth limit of 15,000 feet and its built-in safety feature returned it to the surface, the search coordination center said in a statement on Tuesday.

What if anything it might have discovered during the six-hour search was still being analyzed, searchers said, adding that the craft will resume the search Tuesday when weather conditions permit.

Search authorities knew that the primary wreckage from Flight MH370 was likely lying at the limit of the Bluefin's dive capabilities. Deeper diving submersibles have been evaluated, but none is yet available in the search area.

The search moved below the surface after crews picked up a series of underwater sounds over the past two weeks that were consistent with signals from an aircraft's black boxes, which record flight data and cockpit conversations.

The devices emit "pings" so they can be more easily found, but their batteries only last about a month and are now believed dead.

Meanwhile, officials were investigating an oil slick about 3.4 miles from the area where the last underwater sounds were detected, said Angus Houston, the head of a joint agency coordinating the search off Australia's west coast.

"Today is day 38 of the search," Houston told a news conference on Monday. "We haven't had a single detection in six days, so I guess it's time to go under water."

But Houston warned that while the signals are a promising lead, the public needs to be realistic about the challenges facing search crews in the extremely remote, deep patch of ocean — an area he called "new to man."

Flight 370 disappeared March 8 during a flight from Kuala Lumpur, Malaysia, to Beijing with 239 people on board, mostly Chinese.

The submarine takes 24 hours to complete each mission: two hours to dive to the bottom, 16 hours to search the seafloor, two hours to return to the surface, and four hours to download the data, Houston said.

The black boxes could contain the key to unraveling the mystery of what happened to Flight 370.

Investigators believe the plane went down in the southern Indian Ocean based on a flight path calculated from its contacts with a satellite and an analysis of its speed and fuel capacity. But they still don't know why.

The Associated Press