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First sub deployed in MH370 search

At the same time, officials were investigating an oil slick not far from
the area where the last underwater sounds were detected, said Angus
Houston, the head of a joint agency co-ordinating the search off
Australia's west coast.

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 Houston
cautioned against jumping to conclusions about its source.

The unmanned underwater vehicle, the Bluefin 21, was launched Monday
evening from the Australian navy ship Ocean Shield, the joint agency
said. The autonomous sub can create a three-dimensional sonar map of any
debris on the seafloor.

The move comes 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 contain flight data and cockpit voice recordings. The
devices emit "pings" so they can be more easily found, but their
batteries last only about a month, and it has been more than a month
since the plane vanished.

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

Australian Prime Minister Tony Abbott raised hopes last week when he
said authorities were "very confident" the four underwater signals that
have been detected were from the black boxes on Flight 370, which
disappeared March 8 during a flight from Kuala Lumpur, Malaysia, to
Beijing with 239 people on board.

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 dubbed "new to
man."

"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," Houston said. "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."

The Ocean Shield had been dragging a U.S. Navy device called a towed
pinger locator through the water to listen for any sounds from the black
boxes' beacons.

The Bluefin sub takes six times longer to cover the same area as the
ping locator, and the two devices can't be used at the same time. 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.

The submarine will take 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. In its first deployment, it will search a 40-square kilometre
section of seafloor.

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.

A visual search for debris on the ocean surface continued Monday over
47,600 square kilometres of water about 2,200 kilometres northwest of
the west coast city of Perth. A total of 12 planes and 15 ships joined
the searches.

But Houston said the visual search operation will end in the next two
to three days. Officials haven't found a single piece of debris
confirmed to be from the plane, and Houston said the chances that any
would be found have "greatly diminished."

"We've got no visual objects," he said. "The only thing we have left
at this stage is the four transmissions and an oil slick in the same
vicinity, so we will investigate those to their conclusion."

Complicating matters further is the depth of the ocean in the search
area. The seafloor is about 4,500 metres below the surface, which is the
deepest the Bluefin can dive. Officials are looking for other vehicles
that could help to retrieve any wreckage, should the Bluefin find any.

Searchers are also contending with a thick layer of silt on the
bottom that is tens of meters deep in places, which could hide debris
that has sunk.

U.S. Navy Capt. Mark Matthews said the silt may not have hidden everything, however.

"Our experience shows that there will be some debris on top of the
silt and you should be able to see indications of a debris field,"
Matthews said. "But every search is different."

A British vessel, the HMS Echo, has equipment that can help map the
seafloor in the area, which is more flat than mountainous, Houston said.