LATEST REPORT: A mini-sub searching for missing Flight MH370 was again sweeping the Indian Ocean seabed Wednesday after aborting its first mission, officials said, as Malaysia vowed to reveal any ‘black box’ data found.
The unmanned submarine equipped with sonar gear was deployed Tuesday night after data analysis of the first failed foray drew a blank, Australia's Joint Agency Coordination Centre said.
After more than three weeks of hunting for black box signals, the autonomous sub had been deployed for the first time on Monday night from the Australian ship Ocean Shield, which has spearheaded the hunt for the Boeing 777 that vanished on March 8 with 239 people aboard.
"The autonomous underwater vehicle was again deployed last night (Tuesday) from ADV (Australian Defence Vessel) Ocean Shield," JACC said.
"The data from Bluefin-21's first mission has been downloaded and analysed. No objects of interest were found," JACC said.
The US navy explained that the Bluefin-21 had automatically aborted its first mission after six hours upon breaching its maximum operating depth.
JACC added that it had "exceeded its operating depth limit of 4,500 metres (15,000 feet) and its built-in safety feature returned it to the surface".
The sub was undamaged and had to be re-programmed, said US Navy Captain Mark Matthews.
"In this case the vehicle's programmed to fly 30 metres over the floor of the ocean to get a good mapping of what's beneath," he told CNN from Perth after the aborted dive.
"It went to 4,500 metres and once it hit that max depth, it said 'This is deeper than I'm programmed to be', so it aborted the mission."
Search zone adjusted
"To account for inconsistencies with the sea floor, the search profile is being adjusted to extend the sonar search for as long as possible," the US Navy statement said.
JACC chief Angus Houston announced Monday the end of listening for signals from the plane's black boxes and launch of the submarine operation.
The mini-sub is supposed to conduct a sonar survey of the silty ocean floor for 16 hours at a time looking for wreckage from the Malaysia Airlines flight which disappeared en route from Kuala Lumpur to Beijing.
Malaysia vows transparency
"It's about finding the truth. And when we... find out the truth, definitely we have to reveal what's in the black box," Hishammuddin Hussein told reporters.
"So there is no question of it not being released."
The Malaysian government has been tight-lipped about its ongoing investigation into the disappearance of the jet, adding to the anger and frustration of relatives.
It has come under fire for a seemingly chaotic initial response, while the scarcity of official information on MH370 has prompted questions over its transparency.
Hishammuddin said at the weekend that Malaysia's attorney general had been sent abroad to confer with the International Civil Aviation Organization and determine which country would have custody of the black box, if it is ever found.
But he shrugged off the importance of the custody issue on Tuesday.
"I don't think it's important who gets custody as far as I'm concerned," he told reporters.
Malaysian authorities insist they are hiding nothing but need to be cautious on commenting on ongoing investigations.
Hishammuddin also said an "international investigation team" that Malaysia plans to set up to probe MH370's disappearance would be transparent and operate in accordance with international standards.
Undersea drone hunt for plane may take two months
A US Navy underwater drone sent to search for a missing Malaysian jetliner on the floor of the Indian Ocean could take up to two months to scour a 600 sq km area where the plane is believed to have sunk, U.S. search authorities said on Tuesday.
The prediction coincided with the end to the abbreviated first mission by the Bluefin-21 autonomous underwater vehicle six hours into what was meant to be a 16-hour operation on Monday after it exceeded its 4.5 km (14,750 feet) depth limit and was automatically returned to the surface.
The introduction of the undersea drone marks a new slower paced phase in the search for Malaysia Airlines MH370 which disappeared on March 8 and is presumed to have crashed thousands of km (miles) off course with the loss of all 239 people on board.
Authorities, who soon plan to scale back the air and surface search, are confident they know the approximate position of wreckage of the Boeing 777, some 1,550 km (960 miles) northwest of Perth, and are moving ahead on the basis of four acoustic signals they believe are from its black box recorders.
But having not heard a "ping" for almost a week and with the batteries on the locator beacons two weeks past their 30-day expected life, the slow-moving "autonomous underwater vehicle" was launched on Monday to try and locate wreckage.
"The AUV takes six times longer to cover the same area as the towed pinger locator. It is estimated that it will take the AUV anywhere from six weeks to two months to scan the entire search area," Lt. J.G. Daniel S. Marciniak, a spokesman for the U.S. Seventh Fleet, said in a statement.
From its aborted first mission, the Bluefin-21 produced six hours of data which authorities analysed to find no objects of interest, Marciniak added. The drone was expected to embark on its second search mission late on Tuesday.
The robot, which takes two hours to descend another two to return to the surface, as well as several hours to download data, will build up a detailed acoustic image of the area using sophisticated "sidescan" sonar. It hopes to repeat its success in finding a F-15 fighter jet which crashed off Japan last year.
It is capable of spending up to 16 hours scouring the sea floor. If it detects possible wreckage, it will be sent back to photograph it in underwater conditions with extremely low light.
Officials are focusing their acoustic search on an area equivalent to a medium-sized city - 600 sq km (230 sq miles). But the much broader search area off the Australian coast covers about 60,000 sq km, according to the government.
The deep sea area now being searched, the Zenith Plateau, has never been mapped in detail because it is not in any country's economic zone.
However the sea floor is likely covered in "foraminiferal ooze", a sludge formed by microscopic marine organisms, which would show up any large metallic object clearly, James Cook University marine geologist Robin Beaman told Reuters.
"A sidescan is very good at detecting the difference in the acoustic return of a hard object versus a soft, muddy sea floor," he said. "This is quite a good environment for looking for wreck debris, albeit deep."
The Bluefin's main challenge was to remain within 50 metres (165 feet) of the seabed to ensure the best quality sidescan detection without exceeding its 4.5 km depth limit which could risk damaging it, Beaman said.
Malaysian authorities have still not ruled out mechanical problems as causing the plane's disappearance, but say evidence suggests it was deliberately diverted from its scheduled route from Kuala Lumpur to Beijing.
An aircraft's black box records data from the cockpit and conversations among flight crew and may provide answers about what happened to the missing plane.
The search for the missing plane is on track to be the most difficult and expensive search and recovery operation in aviation history.
EARLIER REPORT: A mini-sub hunting for Malaysian jet MH370 prepared to make a second mission to the remote Indian Ocean seabed Tuesday after aborting its first search as it encountered water deeper than its operating limits, officials said.
The unmanned submarine loaded with sonar to map the ocean floor deployed Monday night from the Australian ship Ocean Shield which has spearheaded the hunt for the Boeing 777 that vanished on March 8.
First search aborted
A mini-sub hunting for Malaysian jet MH370 aborted its first search of the remote Indian Ocean seabed after just six hours because the water was deeper than its operating limits, officials said Tuesday.
The unmanned submarine loaded with sonar to map the ocean floor deployed Monday night from the Australian ship Ocean Shield which has spearheaded the hunt for the Boeing 777 that vanished on March 8.
"After completing around six hours of its mission, Bluefin-21 exceeded its operating depth limit of 4,500 metres and its built in safety feature returned it to the surface," JACC said, without detailing the exact depth of operations.
"The six hours of data gathered by the Autonomous Underwater Vehicle is currently being extracted and analysed," JACC said. The AUV had been due to spend up to 16 hours collecting data.
US Navy Captain Mark Matthews explained the vehicle had exceeded its programmed operational limit and automatically resurfaced. "There's certain abort criteria that the vehicle has as it's executing its mission," he told CNN from Perth. "If there's certain conditions that occur, it stops and it comes to the surface.
"In this case the vehicle's programmed to fly 30 metres over the floor of the ocean to get a good mapping of what's beneath."
Charts put the depth at 4,200-4,400 metres, he said.
"It went to 4,500 metres and once it hit that max depth, it said this is deeper that I'm programmed to be, so it aborted the mission."
Matthews, a search and recovery expert, said the crew would now refine the task to cope with the depth encountered.
"It happend in the very far corner of the area it's searching. So they are just shifting the search box a little bit away from that deep water."
The US-made Autonomous Underwater Vehicle (AUV) Bluefin-21 would embark on a second mission during the day, weather permitting, Australia's Joint Agency Coordination Centre (JACC) said.
Malaysians' distrust
More than half of Malaysians believe their government is hiding information about missing flight MH370, according to survey results released by a news portal Monday.
Fifty-four percent of more than 1,000 people surveyed by Malaysia's leading independent polling firm said the government was not being transparent about the passenger jet's disappearance, the Malaysian Insider reported.
Only 26 percent said they believed the government was being truthful on the Malaysia Airlines plane, while 20 percent were unsure, the news portal said.
The Malaysian Insider said it commissioned the survey by the Merdeka Centre for Opinion Research, which conducted it from March 24-30.
AFP did not immediately have access to the original results.
The Malaysia Airlines plane carrying 239 people is believed to have veered off course March 8 en route from Kuala Lumpur to Beijing and crashed into the southern Indian Ocean.
A massive search is under way in waters off western Australia in hopes of finding the Boeing 777's flight data recorders to determine what befell the flight.
The ruling regime that has governed Malaysia since independence in 1957 already faced a major trust deficit at home.
Critics say that for decades it has abused power and its grip on key institutions such as the police and the courts to hide persistent corruption scandals and persecute opponents.
The Barisan Nasional (National Front) government stoked international criticism for a chaotic response to MH370, contradictory statements by various government officials, and an unwillingness to comment on an ongoing investigation.
Malaysian authorities have insisted, however, that they were not hiding anything but needed to be cautious on commenting on ongoing investigations.
Anguished Chinese families -- two-thirds of MH370's passengers were from China -- have accused Malaysia of covering up the truth.
In the survey 51 percent of respondents said they "were confident" in the government following the plane drama while 45 percent were not, the Malaysian Insider reported.
A separate Merdeka Centre survey released two weeks ago found that just 43 percent of Malaysians were satisfied with the government's handling of the mystery, while 50 percent were dissatisfied.
EARLIER REPORT
Australia has decided Monday to deploy a mini-submarine to scour the unmapped Indian Ocean seabed for Malaysian jet MH370 at a daunting depth of 4,500 metres (15,000 feet), ending the search for black-box signals.
Angus Houston, who heads the Joint Agency Coordination Centre, also revealed that an oil slick had been sighted in the area of the search led by the Australian vessel Ocean Shield far off Perth.
"Ocean Shield will cease searching with the towed pinger locator later today and deploy the autonomous underwater vehicle Bluefin-21 as soon as possible," Houston said, adding it could enter the water later Monday.
Oil slick
An oil slick has been detected in the Indian Ocean within the search area for missing Malaysia Airlines Flight MH370 but has yet to be analysed, the Australian leading the operation said Monday.
"I can report that (Australian ship) Ocean Shield detected an oil slick yesterday evening in her current search area," Angus Houston said.
Submarine robot
Australian officials leading the search for a missing Malaysia Airlines plane in the southern Indian Ocean are weighing when to deploy an underwater robot to aid in the hunt, now in its sixth fruitless week.
Malaysia Airlines Flight MH370 disappeared soon after taking off on March 8 from Kuala Lumpur bound for Beijing with 227 passengers and 12 crew on board, triggering a multinational search that is now focused on the Indian Ocean.
Searchers are confident they know the approximate position of wreckage of the Boeing 777, some 1,550 km (963 miles) northwest of Perth, after picking up several acoustic signals they believe are from its black box recorders.
With the batteries on the locators now two weeks past their 30-day expected life, the focus may soon shift to trying to find wreckage using sonar and cameras on a small unmanned "robot" known as an Autonomous Underwater Vehicle (AUV).
Australia's Ocean Shield, towing a sophisticated U.S Navy "towed pinger locator", and Britain's HMS Echo are still criss-crossing the zone where four signals or pings were picked up, but the last was almost a week ago.
"This work continues in an effort to narrow the underwater search area for when the Autonomous Underwater Vehicle is deployed," the Australian agency heading the search said in a statement on Sunday.
Up to a dozen planes and 15 ships will be searching in three separate areas on Monday, the furthest some 2,250 km (1,400 miles) from Perth, the agency added.
The AUV onboard the Ocean Shield, called a Blue-fin 21, could take months to scan and map the 600 sq km (230 sq miles) zone currently the focus of the acoustic search - an area the size of a medium city.
"Trying to locate anything 4.5 kilometres beneath the surface of the ocean about 1,000 kilometres from land is a massive, massive task and it is likely to continue for a long time to come," Australian Prime Minister Tony Abbott said at the weekend.
Pings rapidly fading
The search for a missing Malaysia Airlines jetliner resumed on Saturday, five weeks after the plane disappeared from radar screens, amid fears that batteries powering signals from the black box recorder on board were about to die.
Australian Prime Minister Tony Abbott said signals picked up during the search in the remote southern Indian Ocean, believed to be "pings" from the black box recorders, were "rapidly fading".
"While we do have a high degree of confidence that the transmissions that we've been picking up are from flight MH370's black box recorder, no one would underestimate the difficulties of the task still ahead of us," Abbott told a news conference in Beijing.
Search officials say they are confident they know the approximate position of the black box recorder, although they have determined that the latest "ping", picked up by searchers on Thursday, was not from the missing aircraft.
Batteries in the black box recorder are already past their normal 30-day life, making the search to find it on the murky sea bed all the more urgent. Once searchers are confident they have located it, they then plan to deploy a small unmanned "robot" known as an Autonomous Underwater Vehicle.
No confirmed acoustic detections
"Work continues in an effort to narrow the underwater search area for when the autonomous underwater vehicle is deployed," the Australian agency coordinating the search said on Saturday.
"There have been no confirmed acoustic detections over the past 24 hours," it said in a statement.
Narrowing search area
Once the search area is narrowed down to as small as possible "it is our intention to then deploy the submersible, conduct a sonar search of the sea bed and, based on the sonar search, attempt to get a visual of the wreckage," Abbott said.
The US supply ship USNS Cesar Chavez has joined the Australian-led task force to provide logistics support and replenish Australian navy ships, a Pentagon spokesman said.
Up to nine military aircraft, one civilian aircraft and 14 ships were scouring a 41,393 sq km patch of ocean 2,330 km northwest of Perth.
Experts say the process of teasing out the signals from the cacophony of background noise in the sea is slow and exhausting.
An unmanned submarine named Bluefin-21 is on board the Ocean Shield and could be deployed to look for wreckage on the sea floor some 4.5 km (2.8 miles) below the surface once a final search area has been identified.
Australian PM 'very confident' signals are from MH370
Australian Prime Minister Tony Abbott said Friday he was "very confident that signals detected in the search for missing Malaysia Airlines Flight MH370 were from the aircraft's blackbox.
"We have very much narrowed down the search area and we are very confident the signals are from the black box," Abbott said from China, the Australian Broadcasting Corporation reported.
New signal spurs search for missing MH370 black boxes
The logging of a fifth signal spurred Friday's hunt for missing Malaysian airliner MH370 as search crews work round-the-clock to find elusive wreckage in the southern Indian Ocean.
The Australian-led operation out of a Perth airbase is racing to gather as many signals as possible to determine an exact resting place for the Boeing 777 before sending down a submersible to plumb the depths.
The ping-emitting beacons on Flight MH370's data and cockpit voice recorders are expected to fade, more than a month after the plane vanished with 239 people on board.
With analysis of the latest ping underway, the Perth-based Joint Agency Coordination Centre (JACC) said Friday the search area had been further reduced to two zones totalling 46,713 square kilometres (18,06 square miles).
The core of the search is now 2,312 kilometres (1,436 miles) northwest of Perth.
An Australian air force P-3C Orion surveillance plane, which had been dropping dozens of sonar buoys into the remote waters of the search zone, captured the new signal on Thursday afternoon.
"The acoustic data will require further analysis overnight but shows potential of being from a made-made source," JACC chief Angus Houston said in a statement late Thursday.
The Orion was flying close to the area where two signals were detected at the weekend and two more on Tuesday by Australian navy ship Ocean Shield.
The vessel is dragging a US Navy "towed pinger locator" to listen for emissions from the black boxes.
Friday's weather forecast in the search zone was for 10-15 knot southerly winds with isolated showers, seas swells of one to 1.5 metres (three to five feet) and visibility of five kilometres during the showers.
US Seventh fleet spokesman Commander William Marks had earlier voiced optimism that the first two sets of signals showed the hunt was getting "closer and closer".
"When you put those two (sets of pings) together, it makes us very optimistic," Marks told CNN on Thursday.
"This is not something you find with commercial shipping, not something just found in nature -- this is definitely something that is man-made, consistent with what you would find with these black boxes."
Marks said he expected the pings to last "maybe another day or two" as the batteries powering the black box beacons fade after their normal lifespan of about 30 days.
- Still no debris spotted -
No floating debris from the Malaysia Airlines aircraft has yet been found, JACC said, despite the massive multinational air and sea operation.
JACC says the high-tech underwater surveillance is intended to define a reduced and more manageable search area in depths of around four kilometres (2.5 miles).
Houston has stressed the need to find the wreckage and urged repeatedly against unduly inflating hopes, for the sake of the families of missing passengers and crew who have endured a month-long nightmare punctuated by a number of false leads.
But he has voiced renewed optimism as day by day the search edges forward with new information.
No other ships are being allowed to sail near the Ocean Shield as it must work in an environment as free of noise as possible.
But JACC announced that up to 12 military aircraft, three civil aircraft and 13 ships will join Friday's hunt.
JACC says says it should not be long before a US-made autonomous underwater vehicle called a Bluefin-21 will be sent down to investigate, but has cautioned that it will have to operate at the very limits of its capability given the vast depths involved.
In Malaysia, Home Minister Zahid Hamidi said there was "no conclusive evidence yet" from the continuing investigation into what caused the plane to divert from its Kuala Lumpur-Beijing route.
Zahid said 180 people had been interviewed, including relatives of passengers and crew as well as airline ground staff and engineers.
Numerous theories have been put forward to explain MH370's baffling disappearance.
They include a hijacking or terrorist attack, a pilot gone rogue or a sudden catastrophic event that incapacitated the crew and left the plane to fly for hours until it ran out of fuel.
Malaysia Airlines has lost black box data before
Britain's air accidents investigator has criticized Malaysia Airlines for its lack of proper oversight in preserving flight recordings during an incident at London's Heathrow Airport in 2012.
A Boeing 747 bound for Kuala Lumpur, carrying 340 passengers, had to return to Heathrow soon after takeoff because of engine and electrical failures on Aug. 17, 2012. The pilots flew the plane manually and returned to the airport safely.
In a report issued Thursday, Britain's Air Accidents Investigation Branch said all the audio information relating to the incident was lost because the cockpit voice recorder ran on long after the landing. The body said the airline's "procedures for the preservation of flight recordings were not sufficiently robust."
The Heathrow incident was not related to Flight MH370, which went missing last month.
Hunt for MH370 closes in on 'final resting place'
The hunt for more black box "pings" from missing Malaysian airliner MH370 narrowed Thursday to a specific patch of remote ocean after the logging of fresh signals raised hopes wreckage will soon be found.
With dying batteries after more than a month since the Boeing 777 vanished, the head of the Australian-led search Angus Houston wants to pursue the listening operation to help pinpoint the plane's exact location before sending down a submersible.
Houston's Joint Agency Coordination Centre (JACC) announced Thursday the search area off western Australia was now 57,923 square kilometres (22,364 square miles) -- compared to more than 220,000 sq kms previously and 75,000 sq kms on Wednesday.
But Australian ship Ocean Shield is focused on a far smaller area of the Indian Ocean 2,280 kilometres (1,400 miles) northwest of Perth where it picked up two fresh signals Tuesday. They matched a pair of transmissions logged over the weekend.
"When you put those two (sets of pings) together, it makes us very optimistic," US Seventh fleet spokesman commander William Marks said Thursday, adding that the search was getting "closer and closer".
"This is not something you find with commercial shipping, not something just found in nature, this is definitely something that is man-made, consistent with what you would find with these black boxes."
"So we are looking pretty good now."
He told CNN he expected the pings to last "maybe another day or two".
No debris from the aircraft which disappeared on March 8 has yet been found although a large number of objects were spotted on the surface on Wednesday, JACC said.
"But only a small number were able to be recovered. None of the recovered items were believed to be associated with MH370."
Officials had feared that the signals which were initially picked up might not be detected again, particularly since the batteries on the black box tracking beacons have a normal lifespan of about 30 days.
"Yesterday's signals will assist in better defining a reduced and much more manageable search area on the ocean floor," Houston said Wednesday.
"I believe we are searching in the right area but we need to visually identify the aircraft before we can confirm with certainty that this is the final resting place of MH370."
Houston, however, again urged caution for the sake of the families of those aboard the flight which mysteriously vanished en route from Kuala Lumpur to Beijing with 239 people on board, and said the search for more signals would go on.
"Hopefully with lots of transmissions we'll have a tight, small area and... in a matter of days we'll be able to find something on the bottom," he said.
- Clock ticking -
Australia confirmed Wednesday that the fresh signals were consistent with black box recorders, boosting optimism after more than a month of fruitless searching for the missing jetliner.
Searchers are now focusing on tapping transmissions that are expected to be weaker than those signals as the batteries are soon expected to fail.
"With the batteries likely to fade or fail very shortly, we need to get as much positional data as we can so that we can define a very small search area," Houston said.
No other ships will be allowed near the Ocean Shield, as it must work in an environment as free of noise as possible.
With the clock ticking on how long the black boxes batteries, Houston said it would not be long before a US-made autonomous underwater vehicle called a Bluefin 21 would be sent down to investigate.
"I don't think that time is very far away," he said.
He noted that Ocean Shield can search six times the amount of area with a Towed Pinger Locator listening for evidence of the black boxes as can be done with the Bluefin sonar.
Once you put the Bluefin in the water, "there's really no time limit for that", said commander Marks.
Up to 10 military aircraft, four civil planes and 13 ships would take part in the search on Thursday, JACC said.
Fair visibility was predicted for the day with moderate southeasterly winds and isolated showers.
Earlier, experts analysing the first two pulse signals detected by an Australian ship searching for Malaysia Airlines Flight MH370 believe they are consistent with a flight data recorder, search chief Angus Houston said Wednesday.
"They believe the signals to be consistent with the specification and description of a flight data recorder," Houston told reporters.
Australian ship Ocean Shield has detected two more signals in the search for missing Malaysian flight MH370, a senior official said Wednesday.
"Ocean Shield has been able to reacquire the signals on two more occasions, late yesterday afternoon and later last night," said Angus Houston, head of the Joint Agency Coordination Centre.
Australia's MH370 search chief Angus Houston said Wednesday that he believes the Malaysian jet could be found within days -- raising hopes that the agonising wait could soon be over for relatives of the 239 people on board.
Consistent Signals
The hunt for more black box "pings" from missing Malaysian airliner MH370 was narrowing Thursday to a specific patch of remote ocean after two more signals were detected.
The head of the Australian-led search Angus Houston raised hopes Wednesday that wreckage will be found within days even as the black box batteries start to expire.
Houston's Joint Agency Coordination Centre (JACC) announced Thursday the search area off western Australia was now 57,923 square kilometres (22,364 square miles) -- some 20,000 square kilometres down on Wednesday.
But Australian ship Ocean Shield is focused on an area of the Indian Ocean 2,280 kilometres (1,400 miles) northwest of Perth where it picked up two fresh signals Tuesday to match a pair of transmissions logged over the weekend as searchers try to pinpoint the exact crash zone.
No debris from the Boeing 777 which disappeared on March 8 has yet been found.
A large number of objects were spotted on the surface on Wednesday, JACC said, "but only a small number were able to be recovered.
"None of the recovered items were believed to be associated with MH370."
Officials had feared that the signals which were initially picked up might not be detected again, particularly since the batteries on the black box tracking beacons have a normal lifespan of about 30 days.
"Yesterday's signals will assist in better defining a reduced and much more manageable search area on the ocean floor," Houston told a press conference.
"I believe we are searching in the right area but we need to visually identify the aircraft before we can confirm with certainty that this is the final resting place of MH370."
Houston, however, again urged caution for the sake of the families of those aboard the flight which mysteriously vanished en route from Kuala Lumpur to Beijing with 239 people on board, and said the search for more signals would go on.
"Hopefully with lots of transmissions we'll have a tight, small area and... in a matter of days we'll be able to find something on the bottom that might confirm that this is the last resting place of MH370," he said.
Bluefin-21 poised... but 'pings' have stopped
Ships searching for underwater signals from Flight MH370 have heard no more "pings" and will spend several more days trying to pinpoint a crash site before launching a mini-sub to scour the ocean floor, authorities say.
A month to the day since the Boeing 777 vanished with 239 people on board, time is running out to detect further signals as the batteries in beacons on the jet's black box data recorders reach their expiry date.
Transmissions picked up by Australia's Ocean Shield ship consistent with those from aircraft black boxes had raised hopes that a robotic submersible would soon be sent down to look for debris.
But search chief Angus Houston clarified Tuesday that while the pings were an exciting development, further transmissions were needed before scouring the ocean floor.
"We need to continue that (search) for several days to the point at which there is absolutely no doubt that the pinger batteries will have expired," Houston said.
"Until we stop the pinger search we will not deploy the submersible."
He said that no further transmissions had been detected in the remote search area off western Australia which could help pinpoint where the jet carrying 239 people might have crashed.
The plane went missing en route from Kuala Lumpur to Beijing on March 8 and the search is now focusing on a 600-kilometre (370-mile) arc of the remote southern Indian Ocean.
Houston had indicated that the time was nearing for the Ocean Shield, which is criss-crossing the area to try to home in on the signals again, to launch the US-made autonomous underwater vessel Bluefin-21.
But he put a more definitive timeframe on it Tuesday, saying the five-metre (16-feet) long submersible sonar device would not be put into the water unless more transmissions were detected.
"If we go down there now and do the visual search it will take many, many, many days because it's very slow, very painstaking work to scour the ocean floor," he said.
Families of MH370 passengers in Beijing marked the one-month anniversary of the plane's disappearance with a tearful candlelit vigil Tuesday, desperately trying to comfort each other as their agonising wait for news continues.
About two-thirds of the 239 people on board were Chinese.
Sub-marine hunter
The hunt for missing Malaysian Flight MH370 could soon head to the ocean floor using an autonomous sonar vessel after possible black box signals were detected, the head of the Australian-led search operation said Tuesday.
A month to the day since the Boeing 777 disappeared, retired Air Chief Marshal Angus Houston warned that hopes of finding surface debris were fading and that sonic "pings" detected by the Australian naval ship Ocean Shield were the best lead.
Houston told ABC radio Tuesday that once the position of the signals was pinpointed, autonomous underwater vessel Bluefin-21 would be deployed to the ocean floor to search for wreckage.
And this could happen soon.
"I haven't had the discussion this morning, we'll be having that discussion a little later on," he told ABC radio.
"I imagine we'd be getting very close to that point."
The search is now focusing on a 600-kilometre (370-mile) arc of the southern Indian Ocean, far off the West Australian coast.
Houston announced Monday that Ocean Shield had detected underwater signals consistent with aircraft "black boxes", calling it the "most promising lead" so far.
The apparent signals breakthrough came as the clock ticks past the 30-day lifespan of the emergency beacons of the two data recorders from the Malaysia Airlines jet, which vanished on March 8 with 239 people on board en route from Kuala Lumpur to Beijing.
"As a consequence there is a chance the locator beacon is about to cease transmission, or has ceased transmission," Houston said.
"I think it's absolutely imperative to find something else and hopefully when we put the autonomous vehicle down, its capability is such that it'll be able to find wreckage.
"Unfortunately with the passage of time, oceanic drift and all the rest of it -- particularly as a cyclone went through that area in the last few days -- the chances of finding anything on the surface are diminishing with time."
Houston explained that the 4,500m depth of the ocean floor was the absolute operating limit for a Bluefin-21, which is designed for deep sea surveying and can carry video cameras.
"It can't go deeper than that, so it's quite incredible how finely balanced all of this is," he said.
"It's a long, painstaking process, particularly when you start searching the depths of the ocean floor."
Up to eleven military planes, three civilian planes and 14 ships were Tuesday set to take part in the unprecedented search 2,200 kilometres northwest of Perth.
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