The underwater drone hunting for clues to the fate of flight MH370 returned six hours into a planned 16-hour mission because it was out of its depth, officials said on Tuesday.

The submersible is programmed to resurface rather than go beyond its safe maximum operating limit of 4,500 metres.

“The six hours of data gathered by the Autonomous Underwater Vehicle is currently being extracted and analysed,” searchers said.

The Bluefin-21 vehicle was sent down for the first time on Monday to scour a 40 sqkm patch of the Indian Ocean about 2,170 kilometres north-west of Perth, the search team said.

A week has gone by without any signals being picked up that could be from the flight recorders on the missing Malaysia Airlines Boeing 777.

Search leader Angus Houston said “aircraft wreckage needs to be visually identified before we can say with certainty that this is the final resting place of MH370.” The plane vanished an hour into a night flight March 8 from Kuala Lumpur to Beijing with 239 people on board.

In a downbeat assessment of search results, Mr. Houston said it would “be appropriate to consult with Australia’s partners to decide the way ahead later this week.” The search for aeroplane wreckage has been assessed as the most costly ever mounted.

Mr. Houston said “it’s very expensive and all the countries contributing to this are running up big costs.” No debris has been recovered and the chances of wreckage still remaining on the surface are slim. It is also likely that any wreckage could be submerged in the silt on the ocean floor.

More In: World | International | News