Australian and Chinese vessels have both picked up acoustic "pings" that could be from the black box of missing Malaysia Airlines flight MH370, search officials have announced.  The hunt for Malaysia Airlines flight MH370 continued as Australian authorities responded to reports that a Chinese patrol ship had detected ultrasonic “pings” matching the frequency put out by the beacon on a flight recorder. Angus Houston, the Australian retired air chief marshal in charge of the search, announced on Sunday that underwater detection gear towed behind an Australian navy ship, the Ocean Shield, had also detected a sound.  Up to 12 aircraft and 13 ships were sent out on Sunday, focused on three large stretches of ocean about 2,000km from Perth.  News that a black-box detector aboard a Chinese patrol ship, the Haixun 01, might have detected an ultrasonic pulse first emerged late on Saturday night via the Chinese state media agency, Xinhua. The ping had a frequency of 37.5kHz – the same as that emitted by flight recorders – and was detected at about 25 degrees south and 101 degrees east, within the 216,000 square kilometre search zone. A reporter for Xinhua said the signal was heard for about 90 seconds.  Houston said on Sunday that there had been another “fleeting” signal picked up 24 hours earlier by the Haixun 01, on Friday afternoon. The two detections took place about two kilometres apart.  “In an ocean that size two kilometres is not a large distance,” Houston said, adding that the lead was “encouraging [but] unverified until such time as we can provide unequivocal determination”.  The third signal was detected on Sunday morning by the Australian navy ship Ocean Shield, located around 300 nautical miles away from the Chinese ship.  Houston said he did not know at this stage whether the acoustic signal detected by Ocean Shield was 37.5kHz, the frequency emitted by a black box locator beacon, but the lead was “something that needs to be investigated”.  The HMAS Echo, a British navy ship carrying a towed pinger locator, was being sent to assist Haixun 01 but would take 14 hours to arrive at the rendezvous, said Commodore Peter Leavy of the Australian navy.  The Ocean Shield would further investigate the signal in its own area before heading to join the Haixun 01 and Echo, Leavy said.  On Saturday China's state media reported that a Chinese air force aeroplane involved in the search had photographed several white objects floating in the search zone. Houston said the sightings were 90km from the area of the pings detected by Haixun 01 but no connection to the plane had been confirmed.  Houston said the area being searched by Haixun 01 was extremely deep – “four and a half kilometres straight down” – and any recovery operation would be “incredibly challenging”.  If the black box recorder beacon was close then the signal picked up by ships would be uninterrupted. “If you get close to the device we should be receiving [the signal] for a long period of time, not just a fleeting encounter,” Houston said.  “Underwater the environment is quite difficult. There will be lots of occasions when noises will be transmitted over long distance, depending on the temperature layers in the water."  Houston said a correction to satellite data being used to calculate the possible flight path of the missing plane had steered the search towards a southern part of the zone of interest in the Indian Ocean. The two detections by Haixun 01 had taken place inside this higher-priority southern search zone.  Pinger locators are being used by several ships scouring the remote stretch of the southern Indian Ocean where investigators believe the aircraft crashed after disappearing from civilian radar screens en route to Beijing on 8 March.  Relatives of the 239 people on board have repeatedly had their hopes raised and dashed by reported sightings of debris and other clues as to the aircraft’s fate – first in the South China Sea, the initial focus of the search, and now the Indian Ocean. Almost a month after the aircraft vanished, no confirmed trace of it has been found.  Houston on Saturday warned it was “getting pretty close” to the point at which a signal from a black box might be picked up. There should have been enough battery power to emit pulses for 30 days, although experts have said they often continue for another 14 days or so.  Anish Patel, president of Dukane Seacom – which says it manufactured the black box beacons used on MH370 – told CNN that the signal reportedly detected by the Haixun 01 was “identical” to the standard frequency emitted by its pingers.  David Gallo, an oceanographer who helped in the search for Air France flight 447 in the Atlantic Ocean in 2009, said the pulse detected was unlikely to occur naturally. “It could very well be one of the beacons,” he told the Observer.  It would not be unusual for the sound to come and go, he said, because of factors such as thermal currents.  Even if pinger locators could not detect the precise location, they might narrow it to an area of about 10 square kilometres, at which point teams would map the seafloor using robots and towed systems, Gallo said. “When you find [recorders] there is a sense of satisfaction but it is also a very sombre moment … it brings the end that the families and loved ones of passengers have been praying and hoping would not come.”  The Australian prime minister, Tony Abbott, on Sunday reiterated that the search was the most difficult in “human history”. “While we certainly are throwing everything we have at it, and while the best brains and the best technology in the world will be deployed, we need to be very careful about coming to hard and fast conclusions too soon,” he told reporters in Tokyo.
Australia announces one of its vessels picked up possible underwater signal, adding to two detections by Chinese ship