Submersible reached maximum depth of 4,500m and may not be able to return to the ocean, US navy captain said

Australian search officials may need to use a different underwater vehicle to scan the ocean floor for the missing Malaysia Airlines flight, after the first submersible mission was cut short because the ocean floor appears to be more than 4,500m deep.



The head of Australia’s joint coordination centre, Angus Houston, announced on Monday that the Australian defence vessel Ocean Shield would no longer be using the towed pinger to attempt to locate noises from the black box of flight MH370 and would instead deploy a remote submersible, the Bluefin-21, to continue the search.



But the submersible’s mission was cut short after it exceeded the limits of its operation - 4,500m below sea level - and was forced to return to the surface, according to a release from the centre on Tuesday morning.



“After completing around six hours of its mission, Bluefin-21 exceeded its operating depth limit of 4,500 metres and its built in safety feature returned it to the surface,” the release said.



“The six hours of data gathered by the autonomous underwater vehicle is currently being extracted and analysed.”

The release indicates the water may be deeper than has been previously thought. On Monday Mark Matthews, the United States navy captain who oversees the use of the Bluefin-21, told Guardian Australia that if the vehicle exceeded its limits more than once it would no longer work.



“It could probably go down further than that once, but it wouldn’t be functional after that,” he said.



Matthews said the vehicle was “chosen for its speed of deployment, and principally the mission right now is to localise. It’s got a tactical capability to do those debris fields but it’s certainly not the tool I would use to do a very, very broad area sonar scan”.



Matthews added that the search using the underwater vehicle was likely to unfold slowly: “If we find it on day one I would be shocked … People need to realise these searches typically unfold over months and years, certainly not hours and days.”



Houston said on Monday that there were other vehicles that could be used in the event Bluefin-21 did not have the capabilities to undertake the search.



The submersible will be sent out again later on Tuesday, although weather conditions may cause issues. There are sea swells of up to two metres and scattered showers and thunderstorms forecast.



Up to nine military aircraft, two civil aircraft and 11 ships are assisting the search on Tuesday.

