PERTH, Australia (Reuters) - Hopes that a deep sea drone scouring the Indian Ocean floor might soon turn up a missing Malaysian jetliner were fading on Friday, as the remote-controlled submarine embarked on a fifth mission with still no sign of wreckage.
Sonar footage by the U.S. Navy owned Bluefin-21 has become the focal point of the search some 2,000 kms (1,200 miles) west of the Australian city of Perth, where authorities believe Malaysia Airlines flight MH370 hit the ocean after disappearing from radars on March 8 with 239 people on board.
The search has centred on a city-sized area where a series of "pings" led authorities to believe the plane's black box may be located. But after more than a week without a signal, and almost two weeks past the black box battery's life expectancy, authorities have now turned to the Bluefin-21.
But after four missions to depths of about 4.5 kms (2.8 miles), two of those aborted early for technical reasons, Australian search authorities said on Friday that the drone had yet to turn up a meaningful lead.
"Bluefin-21 has searched approximately 110 square kms to date. Data analysis from the fourth mission did not provide any contacts of interest," the Joint Agency Coordination Centre said in a statement.
The centre said the Bluefin-21's search area had been reduce based on further analysis of the initial black box signals. It said a U.S. Navy warning that the Bluefin-21's examination may take two months was now incorrect and the drone was focusing on a "reduced and more focused underwater search area" without specifying the size.
NO END IN SIGHT
On Monday, the search coordinator, retired Air Chief Marshal Angus Houston, said the air and surface search for debris would likely end in three days as the operation shifted its focus to the largely unmapped area of ocean floor.
But on Friday, the JACC said up to 11 military aircraft and 12 ships would join in the search across 52,000 square kms (32 square miles) of ocean.
That would suggest searchers, under pressure from the families of those on board the plane, still hold some hope of finding floating wreckage.
Australian Prime Minister Tony Abbott was quoted by the Wall Street Journal on Wednesday as saying that "we believe that (underwater) search will be completed within a week or so. If we don't find wreckage, we stop, we regroup, we reconsider".
Asked by Reuters to clarify Abbott's comments to the newspaper, his office said he was only suggesting that authorities may change the area being searched by the Bluefin-21 drone, not that the search would be called off.
Malaysia's defence minister, Hishammuddin Hussein, vowed that the search would continue even if there could be a pause to regroup and reconsider the best area to scour.
"The search will always continue. It's just a matter of approach," he told a news conference in Kuala Lumpur.
He said Abbott remained in close contact with Malaysian Prime Minister Najib Razak and the two had spoken on Thursday to discuss the search.
(Additional reporting by Al-Zaquan Amer Hamzah in Kuala Lumpur; Editing by Michael Perry)