PERTH (Reuters) - 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. On Monday it will be 30 days since the Malaysia Airlines flight MH370 lost communications and disappeared from civilian radar less than an hour into an overnight flight from Kuala Lumpur to Beijing on March 8. Most of the 239 people on board the flight were Chinese. "The area of highest probability as to where the aircraft might have entered the water is the area where the underwater search will commence," Retired Air Chief Marshal Angus Houston, the head of the Australian agency coordinating the operation, told reporters in Perth. Australian authorities said the so-called Towed Pinger Locator will be pulled behind navy ship HMAS Ocean Shield, searching a converging course on a 240 km (150 miles) track with British hydrographic survey ship HMS Echo. "On best advice the locator beacon will last about a month before it ceases its transmissions so we're now getting pretty close to the time when it might expire." The black box is equipped with a locator beacon that transmits "pings" when underwater, but which only has an expected battery life of around 30 days. The Boeing 777 was briefly picked up on military radar on the other side of Malaysia and analysis of subsequent hourly electronic "handshakes" exchanged with a satellite led investigators to conclude the plane crashed far off the west Australian coast hours later. HUGE SEARCH AREA 
 
 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. ACM Houston said there was still a "great possibility of finding something on the surface [of the ocean]". "There's lots of things in aircraft that float," he said, citing previous searches where life jackets from planes were found.
– Two ships have begun a race against time to try to find the black boxes of Malaysia Airlines Flight 370 before the data recorder's battery-powered pinger ceases transmission. An Australian navy ship towing a pinger locator and a British survey vessel are searching a 150-mile track where the plane could have gone down, reports Reuters. "The area of highest probability as to where the aircraft might have entered the water is the area where the underwater search will commence," search chief Angus Houston told reporters. "On best advice the locator beacon will last about a month before it ceases its transmissions so we're now getting pretty close to the time when it might expire." The Boeing 777 disappeared on March 8, so the search teams may now have just a few days to locate the signal, the BBC notes. Some 14 planes and nine ships are still searching an area of the southern Indian Ocean for floating wreckage, and Houston says there is still a strong possibility of finding debris like lifejackets. "This is a vast area, an area that’s quite remote, and we’ll continue the surface search for a good deal more time," he says. "If we find a piece of wreckage on the surface ... that gives us a much better datum to start the underwater search than we’ve currently got."