HONG KONG (CNN) -- The next phase in the search for Malaysia Airlines Flight 370 will be a more intense underwater search that will use private contractors, take months and cost about $56 million, officials said Monday.



"I regret to say that thus far none of our efforts in the air, on the surface or under sea, have found any wreckage," Australian Prime Minister Tony Abbott said Monday.



Because it's "highly unlikely" that any debris will be found on the ocean surface, authorities will be suspending aerial searches. By now, most of the debris will have become waterlogged and will have sunk, he said.



Crews will now conduct a thorough search of the ocean floor over a much larger area -- 60,000 square kilometers. The process could take at least six to eight months.



"The aircraft plainly cannot disappear. It must be somewhere," Abbott said. "We do not want this crippling cloud of uncertainty to hang over this family and the wider traveling public."



Demanding answers



It wasn't immediately known how family members of the missing passengers greeted Monday's news.



Furious with Malaysian officials, whom they fault for doing a poor job communicating, many family members plan to take their concerns to Boeing when the aircraft giant holds its annual shareholders meeting in Chicago on Monday morning.



MH370 is a Boeing 777, disappeared March 8 as it flew from Kuala Lumpur, Malaysia, to Beijing. It was carrying 239 people.



"The briefings are a joke," said Sarah Bajc, whose partner, Philip Wood, was a passenger on the plane. "The patience level of the families group is just gone."



"Boeing is a publicly traded company in the United States, and that puts them in a position of a little bit more fiduciary responsibility," she said.



Malaysian authorities need to do a better job of communicating with the families and answering their questions during briefings, she said, rather than treating passengers' loved ones "as if we are the enemy, as opposed to an interested party in helping to solve this mystery."







Shift in focus



For 52 days, an international coalition has been searching for the plane, focusing its effort in the southern Indian Ocean, where the plane is believed to have gone down.



Bluefin-21, a submersible on contract to the U.S. Navy, had been scouring the ocean floor for traces of the plane.



But despite multiple missions searching 400 square kilometers (154.44 square miles), it has found no evidence of the missing aircraft's data recorders.



Bluefin will continue to operate. But it will now be joined by sonar devices towed by ships.



The new equipment will be able to perform broad sweeps and provide feedback from the ocean floor. The Bluefin had to be brought up after each mission to have its data downloaded.



The Australian government will continue to work with Malaysian and Chinese authorities. But "one or more" private companies will be contracted to assist, Abbot said.



Further technology, including a number of other underwater vehicles both private and public, could also be pressed into service.



Some of them can go miles deeper than the Bluefin and remain underwater for weeks at a time.



'We're in the right area'



The Bluefin was put to work after officials detected signals they believed were from the jet's flight recorders.



Retired Air Chief Marshal Angus Houston, the head of Australia's Joint Agency Coordination Centre, said Monday the pings detected remained "the best lead we've got."



"I think we're in the right area," Houston said.



Asked whether it was possible that thick silt on the seabed may have buried the aircraft, Houston said some wreckage would still be on top of the silt.



"This is an extraordinary mystery," Prime Minister Abbott said. "We will do everything we reasonably can to resolve it."