Robot sub resumes search for plane
A robotic submarine looking for the lost Malaysian jet has continued its second seabed search as up to 14 planes are taking to the skies for some of the final sweeps of the Indian Ocean for floating debris.
The US Navy's Bluefin 21 submarine began its second 20-hour underwater mission after cutting short its first because the ocean waters where it was sent were too deep, officials said.
The unmanned sub is programmed to hover 100ft above the seabed, but it started searching in a patch that was deeper than the sub's maximum operating depth of 15,000ft, the search co-ordination centre said.
A built-in safety feature returned the Bluefin to the surface and it was not damaged, officials added.
The data collected by the sub was later analysed and no sign of the missing plane was found, the US Navy said.
Crews shifted the search zone away from the deepest water before sending the Bluefin back, the Navy added.
The search co-ordination centre said 11 military planes and three civilian planes would search a 21,000 square mile expanse of ocean centred 1,300 miles north west of the Australian west coast city of Perth. Eleven ships will also join the search.
Isolated showers are forecast in the search area with sea swells up to 6ft 7in and visibility of three miles, the centre said.
With no wreckage from the Boeing 777 yet found, authorities said this week that the days of the surface search were numbered as the hunt for the remains of Flight 370 moved under the waves.
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 programme to protect the device from harm if it went a bit deeper than its 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 are investigating an oil slick about 3.4 miles from the area where the last underwater sounds were detected.
Crews collected an oil sample and sent it back to Perth for analysis, a process that will take several days, said Angus Houston, the head of the joint agency co-ordinating 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.
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 do not know why.
Malaysia's defence minister Hishamuddin Hussein yesterday 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."