Autonomous underwater vehicle Bluefin 21, a US Navy probe equipped with side-scan sonar, has focused the search on an area in the southern Indian Ocean where four acoustic signals were detected that led authorities to believe that the black box of Malaysia Airlines Flight MH370 may be found there.
"Overnight Bluefin-21 AUV completed another mission in the underwater search area and has commenced mission five," the Perth-based Joint Agency Coordination Centre (JAAC) said on the 42nd day of the search for the plane Boeing 777-200.
Searchers have extended the search beyond the normal 4,500 metre depth range of the mini-submarine.
"The AUV reached a record depth of 4,695 metres during mission four. This is the first time the Bluefin-21 has descended to this depth," the US Navy said.
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"Diving to such depths does carry with it some residual risk to the equipment and this is being carefully monitored," a statement said.
Meanwhile, Malaysia's acting transport minister Hishammuddin Hussein, in a Twitter post, said Malaysian authorities are now considering the possibility of deploying more autonomous underwater vehicles (AUVs).
"The most difficult part of any investigation of this nature is having to deal with the families in our case," he said in Kuala Lumpur.
Hishammuddin said his country will not back down from searching for the plane, despite Australia announcing that the Bluefin-21 may cease scouring the Indian Ocean, if no trace of the aircraft is found within a week.
Authorities probing the criminal aspects of the missing Malaysian jet have conducted a "chronological re-enactment" of the flight before it took off from here six weeks ago.
The Beijing-bound Malaysia Airlines flight MH370 - carrying 239 people, including five Indians, an Indo-Canadian and 154 Chinese nationals - had mysteriously vanished on March 8 after taking off from Kuala Lumpur.