Australian authorities searching for missing Malaysia Airlines flight MH370 are gearing up to send in much more powerful sonar equipment to scan for debris on the seabed.

Search co-ordinators said on Wednesday that nothing had been found by the US navy robotic submarine Bluefin 21, which has covered more than 80% of a zone off the Australian west coast.

The area of 310 square kilometres (120 square miles) is thought to be where the plane is most likely to have gone down, based on "ping" signals that match those from an airliner's black box. Those signals were picked up by search vessels but are thought to have ceased when the beacons' batteries ran out.



Australia's defence minister, David Johnston, said more powerful towed side-scan commercial sonar equipment would probably be deployed, similar to the system that found the Titanic 3,800m (12,500f) under the Atlantic Ocean in 1985 and the Australian second world war wreck HMAS Sydney in the Indian Ocean, north of the current search area, in 2008.

"The next phase, I think, is that we step up with potentially a more powerful, more capable side-scan sonar to do deeper water," Johnston said.

Australia was consulting with Malaysia, China and the US on the next phase of the search for the plane, which went missing on 8 March after veering off course between Kuala Lumpur and Beijing, Johnston said



The search area is a circle 20km (12 miles) wide around an area where sonar equipment picked up a signal on 8 April consistent with a plane's black box.



The Bluefin had less than one-fifth of the search area left to complete but that could take another two weeks, the minister said. "We want to be very thorough."

The Bluefin's first 16-hour seafloor mission last week was aborted because the water depth exceeded its 4.5km safety limit. Johnston said it was possible wreckage had been missed in that deep water.

Analysis was continuing of flight data and the apparent black box beacon signals, Johnston said. "We are currently gathering all of the facts together to mount a further assault on the most likely location, given all the facts," he said.

"A lot of this seabed has not even been hydrographically surveyed before ... we're flying blind," he said, adding that there were waters 7km deep in the area.

The air search for debris would likely continue until the announcement of a new search phase next week, Johnston said.

Radar and satellite signals have shown the jet carrying 239 passengers and crew veered far off course for unknown reasons during its flight from Malaysia to China. Analysis indicates it would have run out of fuel in the remote section of ocean where the search has been focused, but no debris has yet been recovered.



The Associated Press contributed to this report