Robot sub returns to water after 1st try cut short

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Robot sub returns to water after 1st try cut short
In this map provided on Wednesday, April 23, 2014, by the Joint Agency Coordination Centre, details are presented in the search for the missing Malaysia Airlines Flight 370 in the southern Indian Ocean. The hunt for the missing Malaysia Airlines jet will likely soon deploy more powerful sonar equipment that can delve deeper as the current search of the most likely crash site in the Indian Ocean has failed to yield any clues, Australia's defense minister said Wednesday. (AP Photo/Joint Agency Coordination Centre) EDITORIAL USE ONLY
In this map provided on Monday, April 14, 2014, by the Joint Agency Coordination Centre details are presented in the search for the missing Malaysia Airlines Flight 370 in the southern Indian Ocean. The hunt for the missing Malaysian airliner continued on Monday to focus on a search for weakening radio signals from deep beneath the waves despite evidence mounting that the batteries in the plane’s all-important black boxes may finally have died. (AP Photo/Joint Agency Coordination Centre) EDITORIAL USE ONLY
In this map provided on Monday, April 14, 2014, by the Joint Agency Coordination Centre details are presented in the search for the missing Malaysia Airlines Flight 370 in the southern Indian Ocean. The hunt for the missing Malaysian airliner continued on Monday to focus on a search for weakening radio signals from deep beneath the waves despite evidence mounting that the batteries in the plane’s all-important black boxes may finally have died. (AP Photo/Joint Agency Coordination Centre) EDITORIAL USE ONLY
In this map provided on Monday, April 14, 2014, by the Joint Agency Coordination Centre details are presented in the search for the missing Malaysia Airlines Flight 370 in the southern Indian Ocean. The hunt for the missing Malaysian airliner continued on Monday to focus on a search for weakening radio signals from deep beneath the waves despite evidence mounting that the batteries in the plane’s all-important black boxes may finally have died. (AP Photo/Joint Agency Coordination Centre) EDITORIAL USE ONLY
Ben Pelletier, marine operations engineer for Bluefin Robotics, attempts to retrieve a submarine in Quincy, Mass., Wednesday, April 9, 2014. Bluefin Robotics shipped a version of their submarine to help locate the missing Malaysian Airlines Flight 370, by using its side-scan sonar. (AP Photo/Scott Eisen)
Cheryl Mierzwa, left, systems engineer for Bluefin Robotics, helps guide a submarine onto the deck of a boat in Quincy, Mass., Wednesday, April 9, 2014. Bluefin Robotics shipped a version of their submarine to help locate the missing Malaysian Airlines Flight 370, by using its side-scan sonar. (AP Photo/Scott Eisen)
A submarine built by Bluefin Robotics is lowered into the water by systems engineer Cheryl Mierzwa in Quincy, Mass., Wednesday, April 9, 2014. Bluefin Robotics shipped a version of their submarine to help locate the missing Malaysian Airlines Flight 370, by using its side-scan sonar. (AP Photo/Scott Eisen)
A submarine built by Bluefin Robotics is lowered down onto a boat at their headquarters in Quincy, Mass., Wednesday, April 9, 2014. Bluefin Robotics shipped a version of their submarine to help locate missing Malaysian Airlines Flight 370, by using its side-scan sonar. (AP Photo/Scott Eisen)
In this Tuesday, April 8, 2014 photo, Leading Aircraftman Andrew Smith works on a propeller of a Royal Australian Air Force P-3 Orion at RAAF Base Pearce after it arrived back from the ongoing search operations for the missing Malaysia Airlines Flight 370 in Perth, Australia. The ground crews typically work on the tarmac through the night so the planes are ready to fly again by daylight, as the international effort to find some trace of the missing jetliner continues. (AP Photo/Rob Griffith)
In this photo taken March 30, 2014, ground crew repair a window on a Royal Australian Air Force P-3 Orion at RAAF Base Pearce after the aircraft returns from the search for the missing Malaysia Airlines Flight 370 in Perth, Australia. The ground crews typically work on the tarmac through the night so the planes are ready to fly again by daylight, as the international effort to find some trace of the missing jetliner continues. (AP Photo/Rob Griffith)
In this photo taken March 25, 2014, ground crew work on a Royal Australian Air Force P-3 Orion at RAAF Base Pearce after the aircraft returns from the search for the missing Malaysia Airlines Flight 370 in Perth, Australia. The ground crew typically work on the tarmac through the night so the planes are ready to fly again by daylight, as the international effort to find some trace of the missing jetliner continues. (AP Photo/Rob Griffith)
FILE - In this April 3, 2014 photo, Malaysian Prime Minister Najib Razak, right, greets a Royal Australian Air Force P-3 Orion captain Lt. Russell Adams and his crew involved in the search for wreckage and debris of the missing Malaysia Airlines Flight 370, at RAAF Base Pearce near Perth, Australia. The ground crews at this air force base near Perth typically work on the tarmac through the night so the planes are ready to fly again by daylight, as the international effort to find some trace of missing Flight 370 continues. (AP Photo/Rob Griffith, Pool, File)
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 in the Indian Ocean, West of Australia, 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)
PERTH, AUSTRALIA - APRIL 08: Defence Minister David Johnston (R) responds to a reporters question together with Air Chief Marshal Angus Houston (Ret'd) during a press conference over the continuing search for missing Malaysia Airlines Flight MH370 at RAAF Base Pearce on April 8, 2014 in Perth, Australia. ACM Angus Houston advised the towed pinger by ADV Ocean Shield is still trying to re-locate the signals previously detected, which were believed to be consistent with aircraft black boxes. The airliner disappeared on March 8 with 239 passengers and crew on board and is suspected to have crashed into the southern Indian Ocean. (Photo by Paul Kane/Getty Images)
A Chinese relative (R) of passengers on the missing Malaysia Airlines flight MH370 holds a candle as she takes part in a prayer service at the Metro Park Hotel in Beijing on April 8, 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)
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)
A U.S. Navy P8 Poseidon waits at the end of the runway before it takes off from Perth Airport en route to rejoin the ongoing search operations for missing Malaysia Airlines Flight 370 in Perth, Australia, Monday, April 14, 2014. The hunt for the missing Malaysian airliner continued to focus Monday on a search for weakening radio signals from deep beneath the waves despite mounting evidence that the batteries in the plane's all-important black boxes may finally have died. (AP Photo/Rob Griffith)
A screen inside of a Bluefin Robotics research vessel shows side-scan sonar data retrieved from one of their submarines in Quincy, Mass., Wednesday, April 9, 2014. Bluefin Robotics shipped a version of their submarine to help locate missing Malaysian Airlines Flight 370, by using its side-scan sonar. (AP Photo/Scott Eisen)
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By MARGIE MASON
Apr. 15, 2014 10:22 AM EDT

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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Follow Margie Mason on Twitter at twitter.com/MargieMasonAP


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