A prolonged undersea search for the missing Malaysia Airlines Flight 370 could cost nearly a quarter of a billion U.S. dollars if private companies are used, Australia's top transport official said Thursday.

Martin Dolan emphasized that the $234 million price tag is a "ballpark rough estimate" of an extended search and salvage mission that includes an underwater vehicle that has come up empty in its first four missions.

The Bluefin-21 is back at work Friday morning on a fifth trip into the southern Indian Ocean. Authorities said the vessel has scanned a total of 110 square kilometers (42.5 square miles) without making any "contacts of interest."

Searchers seem to be preparing for the possibility that an underwater drone scan of the southern Indian Ocean may not yield debris from the plane immediately.

Officials might consider searching along a large portion of sea highlighted by a partial digital "handshake" between the jetliner and an Inmarsat PLC satellite, Dolan said.

That arc of sea is over 370 miles long and 30 miles wide.

Underwater search

Officials didn't indicate whether Bluefin's fourth mission was a lengthy one.

The Bluefin was forced to abort its mission twice this week; the first time after it exceeded its original depth limit and the second time over a technical issue. After the latter was resolved, officials dipped it into the ocean again.

Phoenix International Holdings, which owns and operates the equipment under a contract for the U.S. Navy, called the third dive "very productive," saying that the underwater drone spent nearly 13 hours at the sea bottom.

But after four dives, "there has been no debris or aircraft wreckage discovered," the company said.

The underwater vessel takes two hours to get near the ocean floor and another two hours to return to the surface. It aims to map the ocean floor for 16 hours to retrieve data, which then take four hours to analyze.

The vessel searches maximum depths of 4,500 meters (14,764 feet). The U.S. Navy has determined the seafloor in the search area reaches a maximum depth of 4,600 meters (15,092 feet).

Bluefin operators said they can reprogram it to operate at 5,000 meters (16,404 feet), giving it more leeway.

New setbacks

Officials believe a recent ping heard in the search area has the right frequency to belong to the flight data recorder's emergency beacon.

The quality of the "ping" led authorities to focus the underwater search in the area.

A preliminary analysis of an oil sample collected in the southern Indian Ocean shows that it is not aircraft engine oil or hydraulic fluid, Australia's Joint Agency Coordination Centre said Thursday.

Malaysia Airlines Flight 370 vanished on March 8 with 239 people aboard after taking off from Kuala Lumpur, Malaysia, bound for Beijing.

With no debris found so far and no possible pings from the plane's "black boxes" detected in a week, officials shifted the focus of the search underwater.

Air and sea surface searches continued Friday across three areas northwest of Perth, Australia, officials said.

Those searches are probably nearing an end, officials said.

Disgruntled families

A technical glitch during a video conference to update Chinese families on the search Wednesday turned into a screaming match.

"You're all bloody liars, and you're lying to us again," one man yelled.

Families of the passengers attending the Beijing briefing exploded in anger and stormed out.

Chinese relatives of those aboard the flight have accused Malaysia of withholding information. They demanded an apology from the Malaysian diplomat behind the botched briefing.

"We will request their team of experts to come to Beijing to conduct face-to-face communications and fulfill their commitment," said Jing Hui, a spokesman for some of the families. "What is the truth? What problem do they want to cover up?"

The families have 26 questions they want answered. They included requests for shared evidence, including the flight's logbook and recordings of air traffic control the night the plane disappeared.

Most of the people on the plane were Chinese. Their relatives have become distrustful of Malaysian authorities and airline officials.

Hishammuddin defended his government's handling of the operation and accused the media of focusing on the Chinese families. He said relatives of other nations represented have not had problems.

"The most difficult part of any investigation of this nature is having to deal with the families in our case," he said.

A Malaysian delegation will travel to Beijing in a few days to advise families on the ongoing search.

Malaysia has put together a committee to work with the relatives, Hishammuddin said.

CNN