Crews to test submersible's limits in push to find MH370

Perth (Australia) (AFP) - A US Navy submersible will be taken past its recommended depth limit in hopes of locating missing flight MH370, Australian authorities said Thursday, after Prime Minister Tony Abbott set a one-week deadline to spot wreckage.

Australian organisers of the MH370 search said the device, which aborted its first dive earlier this week after hitting a pre-programmed maximum depth of 4.5 kilometres (2.8 miles), would be taken lower after its manufacturer advised there was an "acceptable" risk.

"This expansion of the operating parameters allows the Bluefin-21 to search the sea floor within the predicted limits of the current search area," the Perth-based Joint Agency Coordination Centre (JACC) said in a statement.

It gave no details on how deep the advance sonar device would be sent.

The Malaysia Airlines Boeing 777 is believed to have crashed in the remote Indian Ocean after mysteriously vanishing March 8 with 239 people aboard.

Hopes for finding the plane have come to rest upon the Bluefin-21 after signals believed to be emanating from the plane's flight data recorders on the seabed fell silent in recent days before their source could be pinpointed.

The submersible is being deployed from an Australian naval vessel for the difficult task of scanning an uncharted seafloor at extreme depths in hopes of spotting wreckage from the plane.

But the effort launched on Monday has started slowly -- it only completed a full mission Thursday morning -- and Abbott said the Bluefin-21 would be given about one week.

"We believe that search will be completed within a week or so," Abbott was quoted telling the Wall Street Journal in an interview.

"If we don't find wreckage, we stop, we regroup, we reconsider."

Both Abbott and Malaysia's Transport Minister Hishammuddin Hussein vowed Thursday not to give up looking for the plane.

- Huge costs -

But suggestions have emerged that more sophisticated -- and highly expensive -- deep-diving equipment may be needed for the challenging search at such extreme depths.

"We have to look at contractors, and the cost of that will be huge," Hishammuddin told reporters in Kuala Lumpur, though he indicated that such concerns were not yet testing the resolve of search partners.

"But in any event, the search will always continue. It's just a matter of approach."

The Bluefin-21 has been deployed three times in hopes of eventually locating the plane's data recorders and determining what caused it to divert.

But the unmanned torpedo-shaped sonar device is operating at the extent of its depth range. Nothing has yet been detected.

There are fears that wreckage could have been enveloped in a thick layer of mud-like silt on the ocean floor, complicating detection and eventual recovery.

Extensive scouring of the sea surface in the area has failed to find any floating debris that could confirm the plane's fate, and the JACC said Thursday an analysis of samples from an oil slick found at the weekend had determined it was not from MH370.

"My determination for Australia is that we will do whatever we reasonably can to resolve the mystery," Abbott said.

"If the current search turns up nothing, we won't abandon it, we will simply move to a different phase," he was quoted as saying.

Neither Abbott nor Hishammuddin specified what a new phase might entail.

- Search 'significantly narrowed' -

But JACC chief Angus Houston said earlier this week that possible alternatives, including devices that can go deeper than the Bluefin-21, were "being looked at", but he gave no specifics.

Houston has repeatedly warned that the search will be protracted and require patience on the part of authorities and the distraught families of passengers, who still have no confirmation of what happened to their loved ones.

The JACC said the Bluefin-21 had "searched approximately 90 square kilometres (35 square miles) to date". Data from its mission completed Thursday was still being analysed.

The JACC also said an earlier US Navy estimate that it would take the Bluefin-21 between six weeks and two months to scan the search area was incorrect.

The area had been "significantly narrowed" due to analysis of the now-faded signals believed to be from the plane's data recorders, the JACC said, but it gave no updated time frame.

MH370 has drawn increasing comparisons to the effort to locate the underwater resting place of Air France flight 447, which crashed in the Atlantic in 2009.

It took nearly two years for AF447's flight data recorders to be recovered.

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