Unmanned sub to search ocean bed for jetliner

The search for Flight MH370 and its black box data and voice recorders has reached a critical point and must not ease up, President Xi Jinping said on Monday.   [Special coverage]

Chinese personnel involved in the Australia-led multinational search will strengthen their efforts and coordination to help find the plane, Xi told members of the People's Liberation Army air force at its base in Beijing.

Xi, who said the plane's disappearance was a very unfortunate incident, received an update on the air force's involvement in the search in the Indian Ocean west of Perth.

Flight MH370 disappeared on March 8 en route from Kuala Lumpur to Beijing with 239 people on board, including 154 Chinese passengers. Why the plane veered so far off course remains a mystery.

Australia decided on Monday to deploy a mini-submarine to scour the Indian Ocean seabed at a depth of 4,500 meters for the Boeing 777 , ending the search for black-box signals.

Angus Houston, who heads the Joint Agency Coordination Center, also said an oil slick had been sighted in the search area far off Perth led by Ocean Shield, an Australian vessel.

"Ocean Shield will cease searching with the towed pinger locator later today and deploy the autonomous underwater vehicle Bluefin-21 as soon as possible," Houston said, adding that it could enter the water later on Monday.

"We haven't had a single detection in six days, so I guess it's time to go underwater," Agence France-Presse quoted him as saying at a news conference.

No debris has been found despite an enormous search effort involving ships and planes from 26 nations. But Houston said about 2 liters of oil from a newly spotted slick had been collected for testing.

It would be several days before the oil could be conclusively tested ashore, but he did not think it came from one of the many ships involved in the search.

"It's very close to where the transmissions were coming from and we'll investigate it, but that will take a little bit of time, given that we're in the middle of the Indian Ocean."

Houston said it was 38 days since the Boeing 777 vanished, and the batteries powering the black-box tracker beacons have a life of only 30 days.

Ocean Shield has detected four signals consistent with those from aircraft black boxes, helping to narrow the vast search zone. But the last confirmed ping came on Tuesday last week, and officials suspect the batteries are now dead.

The Bluefin-21, a 4.93-meter-long unmanned vehicle with sonar that weighs 750 kg, can operate at depths of 4,500 meters - about the depth of the ocean floor where the pings were detected.

A Chinese Ministry of Transport official, who wanted to be identified only as Peng, told China Daily on Monday that the search by Chinese ships and aircraft "will continue in the way we are doing it now".

Peng said the search would not end until a new arrangement was made.