MH370 search goes underwater

An Australian and a British navy ship on Friday began a targeted hunt for the missing plane towing sensitive sonic detectors that are equipped to pick up "pinging" signals from the aircraft's black box.

The Ocean Shield from Australia (pictured above with a sonic detector) and the HMS Echo from Britain have been deployed 240 kilometers (150 miles) apart in the southern Indian Ocean on gradually converging courses, search coordinator Angus Houston told reporters in the western Australian city of Perth.

Houston said two submarines were now also engaged in the search for the plane, which went missing nearly four weeks ago while flying from Kuala Lumpur to Beijing with 239 people on board.

He also said that a surface search would continue at the same time, as there was still a chance of finding wreckage or other debris floating in the water.

Urgent hunt

The search for the black box - a plane's cockpit data recorder - has a sense of urgency, with the battery on the device expected to run out some time after April 7, though it could last until mid-April.

Locating the plane after that will become an even more difficult, or perhaps even virtually impossible task, as data from satellites and radar have allowed only an extremely approximate estimate as to where it may have come down. The search zone at present measures 217,000 square kilometers, though investigators say they are working to narrow the area down.

Ships and planes from a number of countries have been taking part in the search, which is now in its 18th day.

Authorities have not ruled out mechanical problems as causing the plane to vanish, but say evidence suggests that it was deliberately diverted from its scheduled route.

tj/dr (AP, dpa)