Media playback is unsupported on your device Media caption Air Chief Marshal Angus Houston: "Until we stop the pinger search, we will not deploy the submersible" 
 
 An Australian vessel searching for the missing Malaysia Airlines plane has detected signals consistent with those from "black box" flight recorders. 
 
 The Ocean Shield ship picked up the signal twice, once for more than two hours, said Angus Houston, a retired air chief marshal leading the search. 
 
 He called it the "most promising lead" so far. 
 
 But he said more information was needed: "We haven't found the aircraft yet and we need further confirmation." 
 
 Malaysia's acting transport minister, Hishammuddin Hussein, said he had been briefed by Air Chief Marshal Houston and was "cautiously hopeful that there will be a positive development in the next few days if not hours". 
 
 The plane, carrying 239 people, was flying from Kuala Lumpur to Beijing on 8 March when it disappeared. Malaysian officials say they believe it crashed in the southern Indian Ocean. 
 
 'Two distinct returns' 
 
 ACM Houston said the signals were detected using the towed pinger locator deployed on the Ocean Shield. 
 
 Image copyright Reuters Image caption The signals were heard by the towed pinger locator deployed by the Ocean Shield 
 
 Two separate detections occurred, he said. The first was held for two hours and 20 minutes before being lost. 
 
 Analysis "Lottery odds" is how one oceanographer described to me how incredible it would be if they had actually stumbled over distress signals from the black boxes. This listening equipment trickles along at just a few miles an hour and they were searching an area the size of Britain. Now they are racing against the clock to try to pick up the signals again so they can pinpoint a better location, and send a drone down to look for parts of the aircraft. The battery on this pinger will be starting to go flat, which cuts the range. One very interesting part of these findings is the fact that they seemed to hear two separate pings on one of their sweeps. There are two pingers on board the plane, one for each black box. Could the noise be something else? Well, the frequency of black box pings, 37.5 kHz, is designed to be unique in the water. It's an unusual frequency, so that it's easier to find. But the ocean's an incredibly noisy place and people and equipment can make mistakes. 
 
 The ship then turned around and on the return leg detected the signal again for 13 minutes. 
 
 "On this occasion two distinct pinger returns were audible. Significantly this would be consistent with transmissions from both the flight data recorder and the cockpit voice recorder," ACM Houston said. 
 
 "I'm much more optimistic than I was a week ago," he said. 
 
 "We are now in a very well defined search area, which hopefully will eventually yield the information that we need to say that [Malaysia Airlines flight] MH370 might have entered the water just here." 
 
 The Ocean Shield was still in the area, about 1,040 miles (1,680 km) north-west of the Australian city of Perth, but had not been able to reacquire the signals since, he said. 
 
 The position of the signals needed to be fixed, ACM Houston said. Once that happened, the Ocean Shield could lower the Bluefin 21 underwater autonomous vehicle to try to locate wreckage on the sea floor. 
 
 The signal had been heard in sea with a depth of 4,500m, he added, which was at the limit of the capability of the Bluefin 21. 
 
 He cautioned that the next steps would take time. 
 
 "It could take some days before the information is available to establish whether these detections can be confirmed as being from MH370," he said. "In very deep oceanic water, nothing happens fast." 
 
 The search operation is in a race against time as the flight recorders' batteries are due to run out, meaning a signal would no longer be emitted. 
 
 A Chinese search vessel, Haixun 01, also said it briefly heard signals over the weekend in a different search area. 
 
 Media playback is unsupported on your device Media caption Navy divers searched the area near the signal - courtesy Australian Defence Force 
 
 Media playback is unsupported on your device Media caption Families hold a candle-lit vigil in Kuala Lumpur, as the "black box" hunt continues 
 
 Those signals are now being investigated with the help of a British naval vessel, HMS Echo, which is equipped with sophisticated sound-locating equipment. 
 
 Reports said the crew of the Chinese ship had been using a sonar device called a hydrophone to pick up sounds. 
 
 Experts said it was technically possible but unlikely that the sounds heard with this equipment related to the missing plane. 
 
 Chris Portale, a director of the US company Dukane which makes the device that emits signals from flight recorders, said looking for the Malaysian plane's "black boxes" was like "looking for a suitcase on the side of a mountain" but under water. 
 
 But he said he thought searchers were now in the right area and had a "very good hope" of spotting debris, if the signal was from the aircraft. 
 
 "I believe they have got three to four more days of good, solid output [from the flight recorders]," he told the BBC's Today Programme. 
 
 Media playback is unsupported on your device Media caption Richard Westcott reports on the use of a pinger locator to find a black box 
 
 So far, not a single piece of wreckage has been found from the missing plane, but officials have concluded - based on satellite data - that it ended its flight in the sea to the west of Perth. 
 
 Officials do not know why it lost contact with air traffic controllers and ended up so far from its intended path. 
 
 The backgrounds of both passengers and crew have been investigated but to date officials are not thought to have discovered any concrete evidence about what might have caused the plane to disappear. ||||| An Australian ship scouring the Indian Ocean for missing flight MH370 has detected two further pings consistent with the plane's two black boxes, in a "great lead", bolstering hopes for wreckage discovery. 
 
 The Australian Defence Vessel Ocean Shield, towing a US pinger locator, detected two sets of pings, on Tuesday afternoon and then again about five hours later. 
 
 The signal detected on Tuesday afternoon was held for about five minutes and 32 seconds; followed by a second signal on Tuesday night, which was held for seven minutes. 
 
 The Australian vessel Ocean Shield is towing a pinger locator in the search for MH370. Photo: AP 
 
 The development came more than two days after Ocean Shield first detected the month-long search's most promising lead: two acoustic events on Saturday. 
 
 Advertisement 
 
 Retired air chief marshal Angus Houston, the head of the search's Joint Agency Co-ordination centre, announced the "promising" development during a press conference in Perth on Wednesday afternoon. 
 
 It revives hope the missing Malaysia Airlines plane's black box is still transmitting data days after its batteries were due to run dead. 
 
 Crew on the Ocean Shield deploy the towed pinger locator. Photo: AP 
 
 Mr Houston said expert data analysis on previously detected signals had found they were not of natural origin, further boosting hopes of a breakthrough. 
 
 Mr Houston said experts believed the signals were consistent with those of a flight data recorder. 
 
 He said the first two pings - detected on April 5 at 4.45pm and at 9.27pm Perth time - had been analysed by the Australasian Joint Acoustic Analysis Centre, based at HMAS Albatross in Nowra, on the NSW south coast. 
 
 "The analysis determined that a very stable, distinct and clear signal was detected at 33.331 kilohertz, and that it consistently pulsed at a 1.106-second interval," Mr Houston said. 
 
 ''They therefore asses that the transmission was not of natural origin, and was likely sourced from specific electronic equipment. They believe the signals to be consistent with the specification and description of a flight data recorder.'' 
 
 He said two latest pings were detected on Tuesday - at 4.27pm and 10.17pm, Perth time. 
 
 Mr Houston said up to 11 military aircraft, four civil aircraft and up to 14 ships would assist in Wednesday's search, while the Ocean Shield would also conduct a sonar voice search. 
 
 The search area has been refined to a single zone, about 75,423 square kilometres in size, 2261 kilometres north west of Perth, which was a considerably smaller area than in previous days, he said. 
 
 ''Based on Ocean Shield's detections, we are now searching a much more concentrated area, based on the drift predications made possible by Ocean Shield's detections,'' Mr Houston said. 
 
 ''The smaller area has also allowed us to plan much tighter search patterns based entirely on visual search principles. In other words, we have intensified our search in the visual search area. 
 
 "There's no second chances," he said. 
 
 "It looks like the signals we picked up recently have been much weaker than the original signals we picked up ... we're either a long away from it or in my view more likely the batteries are starting to fade." 
 
 Although authorities have previously said the autonomous underwater vehicle Bluefin-21 would be dropped to the ocean floor once they received a third ping, they have yet to deploy the asset. 
 
 "By triangulating this data we will be able to come up with a much smaller search area under water," Mr Houston said. 
 
 "Time spent on the surface, we're covering six times more area than we would be able to do when we get under water. With the batteries due to fail shortly, we need to get as much positional data as we can." 
 
 An RAAF aircraft has been diverted to Ocean Shield to drop buoys around the field to lay a "sonar buoy pattern", which will involve underwater and floating components transmitting data back to the aircraft. 
 
 "That will provide a range of sensors, 1000 feet down, which is 1000 feet closer to the pinger locator on the ocean floor," Commodore Leavy, the operational head of the Australian search, said. 
 
 The Malaysia Airlines Boeing 777 vanished without a trace during en route to Beijing from Kuala Lumpur on March 8. 
 
 Despite an extensive and costly international search operation off the West Australian coast, the effort has failed to turn up a single piece of evidence to confirm the plane's final resting place. ||||| PERTH, Australia -- Search crews hunting for the missing Malaysia Airlines jet have failed to relocate faint sounds heard deep below the southern Indian Ocean that officials said were consistent with a plane's black boxes, the head of the search operation said Tuesday. 
 
 Angus Houston, the retired Australian air chief marshal who is heading the search far off Australia's west coast, said sound locating equipment on board the Ocean Shield has picked up no trace of the signals since they were first heard late Saturday and early Sunday. 
 
 Time may have already run out to find the devices, whose locator beacons have a battery life of about a month. Tuesday marks one month since the plane vanished. Once the beacons blink off, locating the black boxes in such deep water would be an immensely difficult, if not impossible, task. 
 
 Up to 14 planes and 14 ships are scouring the 30,000-square-mile search zone. 
 
 The wait has been devastating for weary families, CBS News correspondent Seth Doane reports. Many insist the search continues at all costs, despite the frustrations. 
 
 It is unclear whether a sub on board the Ocean Shield will be deployed to try to chart out any debris on the sea floor when searchers are certain the black boxes' locator beacons have gone silent. If the sub maps out a debris field, the crew will replace the sonar system with a camera unit to photograph any wreckage. 
 
 
 
 Houston's comments about deploying the sub contradicted an earlier statement from Australia's acting prime minister, Warren Truss, who said search crews would launch the Bluefin 21 autonomous sub on Tuesday. 
 
 The towed pinger locator detected late Saturday and early Sunday two distinct, long-lasting sounds underwater that are consistent with the pings from an aircraft's "black boxes" - the flight data and cockpit voice recorders, Houston said, dubbing the find a promising lead in the month-long hunt for clues to the plane's fate. 
 
 Still, officials warned it could take days to determine whether the sounds were connected to Flight 370, which vanished March 8 on a flight from Kuala Lumpur, Malaysia, to Beijing with 239 on board. 
 
 "This is an herculean task - it's over a very, very wide area, the water is extremely deep," Defense Minister David Johnston said. "We have at least several days of intense action ahead of us." 
 
 Houtson said finding the sound again was critical to narrowing down the search area before the sub can be used. If the vehicle went down now with the sparse data collected so far, it would take "many, many days" for it to cover all the places the pings might have come from. 
 
 "It's literally crawling at the bottom of the ocean, so it's going to take a long, long time," Houston said. 
 
 Despite the excitement surrounding the Ocean Shield's sound detections, Houston warned that the search had previously been marred by false leads - such as ships detecting their own signals. Because of that, other ships cannot be sent in to help with the underwater search, as they may add unwanted noise. 
 
 "We're very hopeful we will find further evidence that will confirm the aircraft is in that location," Houston said. "There's still a little bit of doubt there, but I'm a lot more optimistic than I was one week ago." 
 
 Finding the black boxes is key to unraveling what happened to the Boeing 777, because they contain flight data and cockpit voice recordings that could explain why the plane veered so far off-course. 
 
 "Everyone's anxious about the life of the batteries on the black box flight recorders," said Truss, who is acting prime minister while Tony Abbott is overseas. "Sometimes they go on for many, many weeks longer than they're mandated to operate for - we hope that'll be the case in this instance. But clearly there is an aura of urgency about the investigation." 
 
 The first sound picked up by the equipment on board the Ocean Shield lasted two hours and 20 minutes before it was lost, Houston said. The ship then turned around and picked up a signal again - this time recording two distinct "pinger returns" that lasted 13 minutes. That would be consistent with transmissions from both the flight data recorder and the cockpit voice recorder. 
 
 The black boxes normally emit a frequency of 37.5 kilohertz, and the signals picked up by the Ocean Shield were both 33.3 kilohertz, U.S. Navy Capt. Mark Matthews said. But the manufacturer indicated the frequency of black boxes can drift in older equipment. 
 
 Houston said the frequency of the sounds heard was considered "quite credible" by the manufacturer, and noted that the frequency from the Air France jet that crashed several years ago was 34 kilohertz. Pressure from being so deep below the surface and the age of the batteries can also affect the transmission level, he said. 
 
 The frequency used by aircraft flight recorders was chosen because no other devices use it, and because nothing in the natural world mimics it, said William Waldock, a search-and-rescue expert who teaches accident investigation at Embry-Riddle Aeronautical University in Prescott, Ariz. 
 
 But these signals are being detected by computer sweeps, and "not so much a guy with headphones on listening to pings," said U.S. Navy spokesman Chris Johnson. So until the signals are fully analyzed, it's too early to say what they are, he said. 
 
 "We'll hear lots of signals at different frequencies," he said. "Marine mammals. Our own ship systems. Scientific equipment, fishing equipment, things like that. And then of course there are lots of ships operating in the area that are all radiating certain signals into the ocean." 
 
 The Ocean Shield is dragging a ping locator at a depth of 1.9 miles. It is designed to detect signals at a range of 1.12 miles, meaning it would need to be almost on top of the recorders to detect them if they were on the ocean floor, which is about 2.8 miles deep. 
 
 Meanwhile, the search for any trace of the plane on the ocean's surface continued Tuesday. It is taking place 1,400 miles northwest of the Australian west coast city of Perth, with good weather predicted, said the Joint Agency Coordination Center, which is overseeing the operation. 
 
 One-hundred-thirty-three missions have been completed so far in the hunt from the air for debris that could be from Flight 370, but no debris from the plane has been found.
– Australian officials have sounded a fresh note of confidence in the search for Malaysia Airlines Flight 370, saying they've reacquired underwater signals following a lapse into silence. Search chief Angus Houston says an Australian navy vessel detected two sets of pings yesterday in the same area that signals were detected over the weekend, reports the Sydney Morning Herald. "I'm now optimistic that we will find the aircraft, or what is left of the aircraft, in the not too distant future—but we haven't found it yet, because this is a very challenging business," Houston told reporters. The signals are getting weaker, which could be a sign that searchers are getting further away, or, more likely, a sign that the data recorder batteries are starting to fade, explained Houston. He says they have delayed deploying the autonomous underwater vehicle Bluefin-21 to search for wreckage because with time running out, they don't want anything to get in the way of the signals. In another promising development, authorities have analyzed the pings detected over the weekend and confirmed that they came from electronic equipment, with signals consistent with those of flight data recorders, CNN reports.