Media caption Richard Westcott reports on the use of a pinger locator to find a black box 
 
 The hunt for missing Malaysia Airlines flight MH370 moved into a new phase on Friday with the deployment of a towed pinger locator to find the black box. 
 
 Two ships with locator capabilities are searching a 240km (150 mile) path in a bid to retrieve the data recorder. 
 
 But Australia's search chief said it was a race against time as the battery-powered signal fades after 30 days. 
 
 The plane disappeared on 8 March en route from Kuala Lumpur to Beijing. It was carrying 239 people. 
 
 It is believed to have crashed in the southern Indian Ocean, although no confirmed debris has been found from the plane. 
 
 The search is being co-ordinated from the city of Perth in Western Australia. 
 
 Fourteen aircraft and 11 ships were involved in Friday's search activities. 
 
 Ships sighted a number of objects in the area but none were associated with the missing plane, the coordination agency said. 
 
 'Highest probability' 
 
 Angus Houston, head of the Joint Agencies Coordination Centre (JACC) leading the search, said that two ships had "commenced the sub-surface search for emissions from [the] black box pinger". 
 
 Australia naval vessel Ocean Shield was using a towed pinger locator from the US Navy, while HMS Echo, which had similar capabilities, was also searching. 
 
 But the former military chief now coordinating the eight-nation search said it was "getting pretty close to the time when it might expire." 
 
 Beacons in the black box emit "pings" so they can be more easily found but the batteries only last for about a month. 
 
 Image copyright Reuters Image caption Officials said there was "some hope" the locators would be able to find the black box 
 
 "The two ships will search a single 240km track converging on each other," Air Chief Marshal Houston, who is retired, said. 
 
 ACM Houston said that the area had been picked on the basis of analysis of the satellite data. 
 
 MH370 - Facts at a glance 8 March: Malaysia Airlines Kuala Lumpur-Beijing flight carrying 239 people disappears 
 
 Malaysia Airlines Kuala Lumpur-Beijing flight carrying 239 people disappears Plane's transponder, which communicates with ground radar, was switched off as it left Malaysian airspace 
 
 Satellite 'pings' indicate plane was still flying seven hours after satellite contact was lost 
 
 24 March: Based on new calculations, Malaysian PM says "beyond reasonable doubt" that plane crashed in southern Indian Ocean with no survivors What we know The search for flight MH370 
 
 It was based on work regarding "how the aircraft might have performed and how it might have been flown", to choose the "area of highest probability as to where it might have entered the water". 
 
 He pointed out that this data was continuing to be refined, but the current search was based on the "best data that is available". 
 
 Given the progress in data evaluation and calculation, "there is some hope we will find the aircraft in the area we are searching", he added. 
 
 The two ships will be moving at reduced speeds, of around three knots, in their attempt to detect any signal from the pinger. 
 
 Commodore Peter Leavy, Commander of Joint Task Force 658, said that search operations generally preferred to use "physical evidence" and "drift modelling" to locate a plane. 
 
 However, "no hard evidence has been found to date so we have made the decision to search a sub-surface area on which the analysis has predicted MH370 is likely to have flown," he said. 
 
 In a statement, JACC said the focus was now on a search area of about 217,000 sq km (84,000 sq miles), 1,700 km (1,000 miles) north west of Perth. 
 
 Media caption Malaysia Airlines ex-steward Patrick Chow says the cabin crew he knew could not be responsible for the plane's disappearance 
 
 Meeting staff involved in the search on Friday, Australian Prime Minister Tony Abbott said: "It is probably the most difficult search that's ever been mounted." 
 
 "A large aircraft seems like something that would be easy enough to locate - but a large aircraft that all but disappeared and disappeared into inaccessible oceans is an extraordinary, extraordinary challenge that you're faced with." 
 
 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. ||||| 1 of 7. Japan's Maritime Self-Defence Force Commander Hidetsugu Iwamasa is pictured in front of one of their P-3C Orion aircraft currently at RAAF Base Pearce near Perth, April 4, 2014. 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. 
 
 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. 
 
 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. 
 
 "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. 
 
 "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." 
 
 On Monday it will be 30 days since the jetliner lost communications and disappeared from civilian radar less than an hour into an overnight flight from Kuala Lumpur to Beijing on March 8. 
 
 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. 
 
 Sonar may help find the plane's black box voice and data recorders that are key to unlocking what happened on the flight. 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. 
 
 Experts have warned the Towed Pinger Locator may be of little use unless investigators can get a much better idea of exactly where the plane went into water, because its limited range and the slow speed at which it must be pulled behind the ship mean it cannot cover large areas of ocean quickly. 
 
 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. 
 
 "This is a vast area, an area that's quite remote. We will continue the surface search for a good deal more time," he said. 
 
 "I think there's still a great possibility of finding something on the surface," he said. "There's lots of things in aircraft that float. In previous searches life jackets have appeared which can be connected to the aircraft that was lost." 
 
 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. 
 
 Britain is also sending HMS Tireless, a Trafalgar-class nuclear submarine with sonar capabilities and a Malaysian frigate was due to arrive in the search area on Saturday. 
 
 Malaysian Prime Minister Najib Razak on Thursday joined his Australian counterpart Tony Abbott in a tour of RAAF Base Pearce, near Perth, where aircrews from seven countries have been flying dozens of missions deep into the southern Indian Ocean. 
 
 Malaysian authorities have faced heavy criticism, particularly from China, for mismanaging the search, now in its fourth fruitless week, and holding back information. Most of the 239 people on board the flight were Chinese. 
 
 "The world expects us to do our level best, and I'm very confident we will indeed show what we can do together as a group of nations; that we want to find answers, that we want to provide comfort to the families and we will not rest until answers are indeed found," Najib said. 
 
 Authorities have not ruled out mechanical problems as causing the disappearance, but say all the evidence suggests the plane was deliberately diverted from its scheduled route. 
 
 Malaysia's police chief said the investigation was focusing on the cabin crew and pilots, after clearing all 227 passengers of possible involvement in hijacking, sabotage or having personal or psychological problems that could have been connected to the disappearance. 
 
 (Additional reporting by Niluksi Koswanage in KUALA LUMPUR and Jane Wardell in SYDNEY; Writing by Jane Wardell; Editing by Alex Richardson)
– 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."