Robot sub returns to water after 1st try cut short

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Robot sub returns to water after 1st try cut short
This photo illustration shows a journalist looking on the data communication logs from British satellite operator Inmarsat and released by Malaysia's Department of Civil Aviation (DCA) in Kuala Lumpur on missing Malaysia Airlines flight MH370 on May 27, 2014. Malaysia's aviation authority released on May 27 the satellite data used to determine that flight MH370 went down in the southern Indian Ocean following demands from sceptical relatives of those on board. AFP PHOTO / MOHD RASFAN (Photo credit should read MOHD RASFAN/AFP/Getty Images)
A man stands in front of a billboard in support of missing Malaysia Airlines flight MH370 as Chinese relatives of passengers on the missing Malaysia Airlines flight MH370 have a meeting at the Metro Park Hotel in Beijing on April 23, 2014. The hunt for physical evidence that the Malaysia Airlines jet crashed in the Indian Ocean more than three weeks ago has turned up nothing, despite a massive operation involving seven countries and repeated sightings of suspected debris.. AFP PHOTO / WANG ZHAO (Photo credit should read WANG ZHAO/AFP/Getty Images)
In this picture taken May 14, 2014 a Malaysia Airlines staff walks up to a flight prior to departure at the Kuala Lumpur International Airport in Sepang. Malaysia Airlines is expected to announce its first quarter earnings after a bruising period since Flight 370 vanished. AFP PHOTO/ Manan VATSYAYANA. (Photo credit should read MANAN VATSYAYANA/AFP/Getty Images)
In this photo taken on May 5, 2014 the Phoenix Autonomous Underwater Vehicle Artemis Bluefin-21, is shown on the deck of the Australian navy ship Ocean Shield berthed at Fleet Base West near Perth as it prepared to resupply and undertake routine maintenance. Ocean Shield, with the Autonomous Underwater Vehicle on board, was due to head back on May 10 to the remote area of ocean off Western Australia to continue searching for missing Malaysia Airlines Flight MH370. AFP PHOTO / Greg WOOD (Photo credit should read GREG WOOD/AFP/Getty Images)
The attached map shows MH370’s flight path, based on the best available knowledge of the investigation team. There are a number of possible flight paths to the southern Indian Ocean, and three boxes indicating where MH370 likely ended. These flight paths differ based on different projections of the aircraft’s speed, shown on the map in knots.
The attached map shows MH370’s flight path, based on the best available knowledge of the investigation team. There are a number of possible flight paths to the southern Indian Ocean, and three boxes indicating where MH370 likely ended. These flight paths differ based on different projections of the aircraft’s speed, shown on the map in knots.
The attached map shows MH370’s flight path, based on the best available knowledge of the investigation team. There are a number of possible flight paths to the southern Indian Ocean, and three boxes indicating where MH370 likely ended. These flight paths differ based on different projections of the aircraft’s speed, shown on the map in knots.

Photo of a map provided by GeoResonance, which claimed on Tuesday April 29, 2014, that it found wreckage thought to possibly be from missing Flight MH370. The photo was posted to Twitter by user Cristina Lombardi.

GeoResonance A graphic shows images depicting underwater "anomalies" suggesting deposits of various metals #MH370 http://t.co/qi2aUlzE1z

Photo of a map provided by GeoResonance, which claimed on Tuesday April 29, 2014, that it found wreckage thought to possibly be from missing Flight MH370. The photo was posted to Twitter by user Jickson Johnson.

PERTH, AUSTRALIA - APRIL 17: A South Korean P3 Orion aircraft takes off from Pearce Airbase, in Bullsbrook, 35 kms north of Perth to help in the search for missing Malaysia Airlines flight MH370 on April 17, 2014 in Perth, Australia. Twenty-six nations have been involved in the search for Malaysia Airlines Flight MH370 since it disappeared more than a month ago. The Malaysian Airways aircraft went missing on 8th March 2014 whilst on a flight between Kuala Lumpur and Beijing. (Photo by Greg Pool - Pool/Getty Images)
AT SEA - APRIL 17: In this handout image provided by Commonwealth of Australia, Department of Defence, Phoenix Autonomous Underwater Vehicle (AUV) Artemis begins its dive in the search for the missing Malaysia Airlines Flight MH370 on April 17, 2014. Twenty-six nations have been involved in the search for Malaysia Airlines Flight MH370 since it disappeared more than a month ago. The Malaysian Airways aircraft went missing on 8th March 2014 whilst on a flight between Kuala Lumpur and Beijing. (Photo by LSIS Bradley Darvill/Australia Department of Defence via Getty Images)
KUALA LUMPUR, MALAYSIA - MARCH 26: Malaysia's Minister of Defence and acting Minister of Transport Hishammuddin Hussein (C) is viewed through a lens as he speaks during a press conference on March 26, 2014 in Kuala Lumpur, Malaysia. The search for flight MH370 resumes today after rought winds and high swells prevented crews from searching for debris yesterday. Six countries have joined the search, now considered to be a recovery effort, after authorities have announced that airliner crashed in the Southern Indian Ocean and that there are no survivors. (Photo by Rahman Roslan/Getty Images)
Malaysia's Minister of Defence and Acting Transport Minister, Hishammuddin Hussein (L) looks at maps as Director General of Civil Aviation Department (DCA) Azharuddin Abdul Rahman (R) answers questions during a press conference at a hotel near Kuala Lumpur International Airport in Sepang on March 17, 2013. An investigation into the pilots of missing Malaysia Airlines flight 370 intensified on March 17 after officials confirmed that the last words spoken from the cockpit came after a key signalling system was manually disabled. AFP PHOTO/ MANAN VATSYAYANA (Photo credit should read MANAN VATSYAYANA/AFP/Getty Images)
US navy captain Mark Matthews (C) speaks with journalists following a media conference involving Angus Houston, head of the Joint Agency Coordination Centre in Perth on April 9, 2014 on the search for missing Malaysia Airlines flight MH370. Australian ship Ocean Shield detected two more signals on April 8 to match a pair of transmissions picked up earlier in the week that have been analysed as consistent with flight data recorder emissions, Angus Houston said. AFP PHOTO / POOL / Greg WOOD (Photo credit should read GREG WOOD/AFP/Getty Images)
Flight MH370's pilot, Capt. Zaharie Ahmad Shah
CANBERRA, AUSTRALIA - APRIL 10 : A handout image released by the Australian Maritime Safety Authority (AMSA) in Canberra, Australia, 10 April 2014, shows the search area and Sonobuoy search area where 14 planes and 13 ships are scouring a 57,923 square km area of ocean for the wreckage of flight MH370 on 10 April 2014.Flight MH370 went missing after losing radio contact with Malaysian and Vietnamese air traffic control after leaving Kuala Lumpur International Airport on March 8. The Beijing-bound flight carried 239 passengers including 12 flight crew from 14 different countries. (Photo by AMSA/Anadolu Agency/Getty Images)
Angus Houston (2nd-L), head of the Joint Agency Coordination Centre leading the search for missing Malaysia Airlines flight MH370 speaks at a media conference in Perth on April 9, 2014. Australian ship Ocean Shield detected two more signals on April 8 to match a pair of transmissions picked up earlier in the week that have been analysed as consistent with flight data recorder emissions, Houston said. AFP PHOTO / POOL / Greg WOOD (Photo credit should read GREG WOOD/AFP/Getty Images)
A graphic of the area being searched for missing Malaysia Airlines flight MH370, is displayed during a media conference involving Angus Houston, head of the Joint Agency Coordination Centre in Perth on April 9, 2014. Australian ship Ocean Shield detected two more signals on April 8 to match a pair of transmissions picked up earlier in the week that have been analysed as consistent with flight data recorder emissions, Houston said. AFP PHOTO / POOL / Greg WOOD (Photo credit should read GREG WOOD/AFP/Getty Images)
Angus Houston, head of the Joint Agency Coordination Centre leading the search for missing Malaysia Airlines flight MH370, points to a graphic of the search area during a media conference in Perth on April 7, 2014. An Australian navy ship has detected new underwater signals consistent with aircraft black boxes, Houston said on April 7, describing it as the 'most promising lead' so far in the month-old hunt for missing Flight MH370. AFP PHOTO / Greg WOOD (Photo credit should read GREG WOOD/AFP/Getty Images)
Angus Houston, head of the Joint Agency Coordination Centre leading the search for missing Malaysia Airlines flight MH370, displays a graphic of the search area during a media conference in Perth on April 7, 2014. An Australian navy ship has detected new underwater signals consistent with aircraft black boxes, Houston said on April 7, describing it as the 'most promising lead' so far in the month-old hunt for missing Flight MH370. AFP PHOTO / Greg WOOD (Photo credit should read GREG WOOD/AFP/Getty Images)
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PERTH, Australia (AP) -- A robotic submarine looking for the lost Malaysian jet began its second mission Tuesday after cutting short its first because the ocean waters where it was sent were too deep, officials said.

Monday's planned 16-hour search lasted just six and none of the data collected by the U.S. Navy's Bluefin 21 submarine offered clues to the whereabouts of the plane.

The unmanned sub is programmed to hover 30 meters (100 feet) above the seabed, but it started searching atop a patch that was deeper than the sub's maximum operating depth of 4,500 meters (15,000 feet), the search coordination center and the U.S. Navy said.

A built-in safety feature returned the Bluefin to the surface and it was not damaged, they said.

The data collected by the sub was later analyzed and no sign of the missing plane was found, the U.S. Navy said.

Crews shifted the search zone away from the deepest water before sending the Bluefin back for Tuesday's mission, the U.S. Navy said.

Search authorities had known the primary search area for Flight 370 was near the limit of the Bluefin's dive capabilities. Deeper-diving submersibles have been evaluated, but none is yet available to help.

A safety margin would have been included in the Bluefin's program to protect the device from harm if it went a bit deeper than its 4,500-meter limit, said Stefan Williams, a professor of marine robotics at the University of Sydney.

"Maybe some areas where they are doing the survey are a little bit deeper than they are expecting," he said. "They may not have very reliable prior data for the area."

Meanwhile, officials were investigating an oil slick about 5,500 meters (3.4 miles) from the area where the last underwater sounds were detected.

Crews collected an oil sample and sent it back to Perth in western Australia for analysis, a process that will take several days, said Angus Houston, the head of the joint agency coordinating the search off Australia's west coast.

He said it does not appear to be from any of the ships in the area, but cautioned against jumping to conclusions about its source.

The submarine is programmed to take 24 hours to complete each mission: two hours to dive to the bottom, 16 hours to search the seafloor, two hours to return to the surface, and four hours to upload the data.

The Bluefin can create a three-dimensional sonar map of any debris on the ocean floor. But the search is more challenging in this area because the seabed is covered in silt that could potentially cover part of the plane.

"What they're going to have to be looking for is contrast between hard objects, like bits of a fuselage, and that silty bottom," Williams said. "With the types of sonars they are using, if stuff is sitting up on top of the silt, say a wing was there, you could likely see that ... but small items might sink down into the silt and be covered and then it's going to be a lot more challenging."

The search moved below the surface after a U.S. Navy device towed by an Australian ship detected underwater sounds consistent with signals from an aircraft's black boxes, which record flight data and cockpit conversations. The devices emit "pings" so they can be more easily found, but their batteries last only about a month and are now believed to have failed.

Australian Prime Minister Tony Abbott raised hopes last week when he said authorities were "very confident" the signals were from the black boxes on Flight 370, which disappeared March 8 during a flight from Kuala Lumpur, Malaysia, to Beijing with 239 people on board, mostly Chinese.

Houston said the signals were a promising lead, but that finding aircraft wreckage in the remote, deep patch of ocean remains extremely difficult.

The black boxes are key to finding the wreckage itself but also could reveal what happened on Flight 370. Investigators believe it crashed in the southern Indian Ocean based on a flight path calculated from its contacts with a satellite and an analysis of its speed and fuel capacity. But they still don't know why.

On Tuesday, Malaysia's defense minister, Hishamuddin Hussein, pledged to reveal the full contents of the black boxes if they are found.

"It's about finding out the truth," he told reporters in Kuala Lumpur. "There is no question of it not being released."

Up to 11 planes and as many ships were scouring a 62,000-square kilometer (24,000-square mile) patch of ocean about 2,200 kilometers (1,400 miles) northwest of Perth on Tuesday, hunting for any floating debris.

The weekslong surface search is expected to end in the next two days. Officials haven't found a single piece of debris confirmed to be from the plane, and Houston said the chances that any would be found have "greatly diminished."

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Associated Press writers Kristen Gelineau in Sydney and Rod McGuirk in Canberra, Australia, contributed to this report.

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Flight 370: How the BlueFin-21 Sonar Sub Works

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