PERTH - A mini-submarine hunting for wreckage of a missing Malaysian airliner has completed its first full mission at the third attempt, officials said Thursday, as seabed data it retrieved was being analysed.
The first two attempts to scan the deep Indian Ocean off western Australia failed to produce any results.
The first dive began Monday night but aborted automatically after breaching the sub's maximum operating depth of 4,500 metres (15,000 feet).
The second was launched Tuesday night and cut short Wednesday morning due to unspecified "technical" troubles.
"Overnight Bluefin-21 AUV completed a full mission in the search area and is currently planning for its next mission," Australia's Joint Agency Coordination Centre (JACC) said.
"Bluefin-21 has searched approximately 90 square kilometres (35 square miles) to date and the data from its latest mission is being analysed."
The statement gave no other detail about the next dive or the technical issues of the previous forays.
Before the device was put in the water for the third time, data was downloaded from the vehicle while on the deck of the Australian vessel Ocean Shield, which has led the search for the Malaysia Airlines Boeing 777 that vanished on March 8 with 239 people aboard.
But initial analysis of the data indicated no significant detections, JACC said.
The Bluefin's first mission, cut short after just six of an intended 16 hours mapping the seabed with sonar, had also drawn a blank.
After more than three weeks of hunting for black box signals, the autonomous sub was deployed for the first time on Monday night.
The US navy explained that the Bluefin-21 had automatically aborted its first mission after six hours.
JACC added that it had "exceeded its operating depth limit of 4,500 metres 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.
Two months to scan area
Questions have been raised about how deep the seabed may be in the search area where silt is also expected to be a problem.
JACC chief Angus Houston has stressed that the mini-sub cannot operate below 4,500 metres and that other vehicles would have to be brought in to cope with greater depths.
Houston had announced Monday the end of listening for signals from the plane's black box flight recorders and the launch of the submarine operation.
The mini-sub is supposed to conduct a sonar survey of the ocean floor for 16 hours at a time, looking for wreckage from Malaysia Airlines Flight MH370 which mysteriously disappeared en route from Kuala Lumpur to Beijing. The dive takes two hours as does re-surfacing.
The US Navy has estimated it would take the Bluefin-21 "anywhere from six weeks to two months to scan the entire search area".
The area has been narrowed down using satellite data and the detection of electronic pulses from the black box which were last heard more than a week ago.
Houston has described those detections as the best lead in the hunt for the plane, and added Monday that an oil slick had also been sighted in the search area.
JACC said Thursday the oil sample had arrived in Perth for detailed analysis.
The cause of the plane's disappearance, after being diverted hundreds of kilometres off course, remains a mystery. No debris has been found despite an enormous search involving ships and planes from several nations.
The visual search for debris also continued Thursday, JACC said, with as many as 12 aircraft and 11 ships involved over an area of 40,349 square kilometres (15,579 square miles) more than 2,170 kilometres (1,345 miles) northwest of Perth.