Deep dive for MH370

After aborting its first dive on Monday after reaching pre-programmed depth limits, the unmanned mini-sub "Bluefin-21" was scheduled to make a second dive on Tuesday to search the ocean floor for any sign of the Boeing 777 that vanished on March 8.

The initial dive of the US Navy's Autonomous Underwater Vehicle (AUV) was automatically aborted when the vessel, programmed to operate 30 meters (98 feet) above the ocean floor, reached its maximum operating depth of 4,500 meters below the surface. At that point, the AUV was programmed to automatically resurface.

Signals silent

Despite turning back just six hours into the 16-hour mission, the 5-meter-long AUV still collected large amounts of data, which have now been retrieved and are being analyzed by searchers.

Officials have determined that an underwater search is the only option left for finding MH370. Signals originally thought to be coming from the plane's black box recorders have ceased, possibly due to the fact that the batteries emitting the acoustic signals are only designed to last about a month.

The submersible drone records sonar or video from the ocean floor, which is then taken back to the surface for analysis.

Long search likely

Angus Houston, the head of the search operation being conducted by Australia's Joint Agency Coordination Center, said on Tuesday that any "aircraft wreckage needs to be visually identified before we can say with certainty that this is the final resting place of MH370."

Despite using the most recent acoustic signals - the strongest lead regarding the plane's location - and information about the plane's suspected final trajectory to limit the size of the search area, rescuers are still tempering expectations that the missing plane will be found soon. Houston noted that the black boxes from Air France Flight AF447, which crashed in the Atlantic Ocean in June 2009, took over two years to retrieve.

"However, this is the best lead we have and it must be pursued vigorously," he said of the current search for MH370. "Again I emphasize that this will be a slow and painstaking process."

mz/pfd (AFP, dpa, AP)