The search for missing Malaysia Airlines Flight MH370 in remote seas off Australia headed underwater on Friday, with a U.S. Navy high tech "black box" locator deployed for the first time as the battery life of the cockpit data recorder dwindles.

Sonar may help find the plane's black box voice and data recorders that are key to unlocking what happened on the flight.

Houston said the start of the underwater search in earnest did not override the need to keep searching for surface wreckage of the plane, as a find would be the most effective way to pinpoint a sub-sea hunt.

On Friday, up to 14 planes and nine ships were scouring the search area of about 223,000 sq km (86,000 sq miles) -- roughly the size of the U.S. state of Minnesota -- some 1,680 km (1,040 miles) west-north-west of Perth, he said.

...