PERTH, Australia (AP) -- A robotic submarine has completed its first full 16-hour mission scanning the floor of the Indian Ocean for wreckage of the missing Malaysian airliner after two previous missions were cut short by technical problems and deep water, authorities said on Thursday.
The Bluefin 21 had covered 90 square kilometers (35 square miles) of the silt-covered sea bed off the west Australian coast in its first three missions, the search coordination center said on Thursday. While data collected by the sub from its latest mission, which ended overnight, was still being analyzed, nothing of note had yet been discovered, the center said.
A total of 12 planes and 11 ships were to join what could be the final day of the surface ocean search for debris from the Malaysia Airlines Boeing 777.
Thursday's search would cover a 40,300-square-kilometer (15,600-square-mile) patch of sea about 2,200 kilometers (1,400 miles) northwest of the Australian city of Perth, the center said.
When the sea bed search began this week, authorities announced that the days of the fruitless surface search were numbered as the chances of success dwindled.
But a sample of an oil slick found this week about 5.5 kilometers (3.4 miles) from where underwater sounds that could be from an aircraft black box beacon were heard has been shipped to Perth for analysis, the center said.
The analysis could provide further evidence that the hunt for Flight 370 was headed in the right direction. Searchers have yet to find any tangible proof that the sounds that led them to the sea floor were from the ill-fated jet.
On Wednesday, Chinese relatives stormed out of a teleconference meeting in Beijing to protest the Malaysian government for not addressing them in person.
More than 100 relatives of Chinese passengers on the plane walked out of a teleconference meeting with senior Malaysian officials, an act of defiance over a lack of contact with that country's government and for taking so long to respond to their demands.
They had gathered at a hotel where Malaysia Airlines had provided lodging and food but filed out shortly before the call with Malaysia's civil aviation chief, Azharuddin Abdul Rahman, was about to start.
"These video conference meetings often don't work, the sound stops and it's constantly disrupted. Is that how we are going to communicate?" said Jiang Hui, one of the family members, after the walkout. "Do they need to waste our time in such a way?"
Jiang said the Malaysian government had not met demands the relatives had presented to them weeks ago in Malaysia — an apology for the way they've handled the matter along with meetings with the Malaysian government and airline officials. They also asked to sit down with executives from Boeing and Rolls-Royce, the manufacturer of the plane and its engines.
The Boeing 777 vanished March 8 with 239 people on board while en route from Kuala Lumpur, Malaysia to Beijing. Radar and satellite data show it flew far off-course for an unknown reason and would have run out of fuel over the southern Indian Ocean west of Australia.
A ship-towed device detected four signals underwater that are believed to have come from the airliner's black boxes shortly before the beacons' batteries died. The sounds helped narrow the search area to the waters where the Bluefin 21 is now operating.
The U.S. Navy's unmanned sub cut short its first mission on Monday because it exceeded its maximum operating depth of 4,500 meters (15,000 feet). Searchers moved it away from the deepest waters before redeploying the sub to scan the seabed with sonar to map a potential debris field.
In addition to finding the plane itself, investigators want to recover the black boxes in hopes the cockpit voice and flight data recorders contain answers to why the plane lost communications and flew so far off-course before disappearing.
Associated Press writers Kristen Gelineau in Sydney, Rod McGuirk in Canberra, Australia and videojournalist Aritz Parra in Beijing, contributed to this report.