Flight 370 search -- 'most difficult in human history' -- moves under water

The Bluefin 21, the Artemis autonomous underwater vehicle (AUV), is hoisted back on board the Australian navy's Ocean Shield in the southern Indian Ocean. (U.S. Navy)

The search for Flight 370 has moved to the depths of the Indian Ocean, as time is running out on the missing Malaysian jetliner’s ability to send signals from its black box.

British and Australian ships are plumbing the vast ocean, using sophisticated equipment on loan from the U.S., to listen for pings from the plane’s black box, but nearly a month after the plane and its 239 passengers and crew vanished, there may not be enough time. The box, or flight data recorder, may soon lose the ability to transmit.

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"It is a very difficult search — the most difficult in human history,” Australian Prime Minister Tony Abbott told reporters this week. “But as far as Australia is concerned, we are throwing everything we have at it."

Malaysia has been criticized from the beginning of the hunt, which so far has turned up only unrelated junk in the massive search area some 1,500 miles west of Australia. With Australia now in charge of the search, its naval supply ship Ocean Shield and the British navy’s HMS Echo are scouring a 100,000-square-mile field where authorities believe the plane went down. They are towing the U.S. Navy’s underwater microphone, the TPL-25, to listen for the pings from the flight data recorder, and using the American the Bluefin-21, an underwater robot, to scour the ocean bed for wreckage.

The ocean is between 6,500 and 13,000 feet deep in the area where the search is now concentrated.

So far, the hunt for the Boeing 777, which disappeared March 8 after taking off from Beijing bound for Kuala Lumpur, as proven utterly fruitless.  More than a dozen planes and ships have scanned the area, and even crowd-sourced sifting through millions of satellite images have turned up nothing.

The search area has hopscotched over the last month, first centering off the coast of Vietnam, then to the other side of Malaysia and Indonesia and finally out to the remotest area of the Indian Ocean, near the bottom of the globe.

But authorities acknowledge that even that location is at best a guess, as there is no tell-tale debris field and the plane’s communications systems were mysteriously shut off some seven hours before the plane is believed to have gone down.

"The area of highest probability as to where the aircraft might have entered the water is the area where the underwater search will commence," said Angus Houston, the head of a joint agency coordinating the search. "It's on the basis of data that arrived only recently, and it's the best data that is available."

With wire service