Mini-sub on second mission after first MH370 search aborted

PERTH: A mini-sub searching for missing Flight MH370 was again sweeping the Indian Ocean seabed Wednesday after drawing a blank on a first mission aborted at daunting depths in a laborious operation that could take months.

The unmanned submarine equipped with sonar gear was deployed Tuesday night after data analysis of the first failed foray produced nothing of interest, Australia´s Joint Agency Coordination Centre said.

After more than three weeks of hunting for black box signals, the autonomous sub had been deployed for the first time on Monday night from the Australian ship Ocean Shield, which has spearheaded the hunt for the Boeing 777 that vanished on March 8 with 239 people aboard.

"The autonomous underwater vehicle was again deployed last night (Tuesday) from ADV (Australian Defence Vessel) Ocean Shield," JACC said.

"The data from Bluefin-21´s first mission has been downloaded and analysed. No objects of interest were found," JACC said.

The US navy explained that the Bluefin-21 had automatically aborted after six hours upon breaching its maximum operating depth.

JACC added that it had "exceeded its operating depth limit of 4,500 metres (15,000 feet) 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.

"In this case the vehicle´s programmed to fly 30 metres over the floor of the ocean to get a good mapping of what´s beneath," he told CNN from Perth after the aborted dive.

"It went to 4,500 metres and once it hit that max depth, it said ´This is deeper than I´m programmed to be´, so it aborted the mission."