The hunt for missing MH370 entered a new phase today when officials said they would deploy the unmanned submarine Bluefin 21 to scan the ocean floor "as soon as possible".
The "towed pinger locator", being pulled along by Australia's Ocean Shield in an attempt to trace signals from the plane's black boxes, will be taken out of the water after picking up four possible detections between April 5 and 8.
Angus Houston, who is heading the search said no signals had been heard for six days, adding: "It's time to go underwater."
Houston revealed that the Ocean Shield had last night detected an oil slick, but cautioned that it would take several days before a two-litre sample could be analysed to determine whether it was from the Malaysia Airlines jet, missing since March 8.
The Bluefin 21 sub will use sonar to create a map of the ocean floor. Houston said its deployment would not automatically "result in the detection of the aircraft", adding that the search with the submarine would be "a slow and painstaking process".
Each time the submarine is deployed it will cover just 40 square kilometres, with one mission taking 24 hours - two to reach the ocean floor, 16 gathering data, two to return to the surface, and four hours to download and analyse the data.
It will taken the sub six times longer to cover the same area as the towed pinger locator, and will take about six weeks to two months to canvass the current underwater search area.
Signals picked up last week were believed to have come from 4,500 metres below the surface - the deepest the sub can dive.
Authorities yesterday said they had expanded a visual search for the missing jet as failure to detect further electronic signals deepened concern that the devices' battery power had expired.
Australia deployed more planes to comb a 57,506 square kilometre area, while a seabed-scanning robot submarine remained unused.
Two sounds heard a week ago by Ocean Shield were determined to be consistent with the signals emitted from the black boxes. Two more pings were detected in the same general area on Tuesday, but no new ones have been picked up since then.
"We're now into day 37 of this tragedy," said aviation expert Geoffrey Thomas.
"The battery life on the beacons is supposed to last 30 days. We're hoping it might last 40 days. However, it's been four or five days since the last strong pings. What they're hoping for is to get one more, maybe two more pings so they can narrow the [search] area."
Once officials are confident that no more sounds will be heard, a robotic submersible will be sent down to slowly scour for wreckage.
Recovering the flight data and cockpit voice recorders is essential if investigators are to solve the mystery of flight MH370, which vanished on March 8.
Watch: British Royal Navy aids in search for missing airliner MH370
Additional reporting by Associated Press