Searchers hunting for the crashed Malaysian jet today said they will deploy a robotic underwater drone for the first time to locate the plane's "final resting place" in the Indian Ocean at a depth of 4,500 metres after failing to detect any signals from the black boxes in a week.
"Ocean Shield will cease searching with the towed pinger locater later today and deploy the autonomous underwater vehicle Bluefin-21 as soon as possible," Australian chief search coordinator Angus Houston said.
"We haven't had a single detection in six days so I guess it's time to go underwater," he told a news conference.
In another significant development in the search, Houston said two litres of the newly spotted oil slick had been collected for testing.
"I stress the source of the oil is yet to be determined but the oil slick is approximately 5,500 metres downwind...from the vicinity of the detections picked up by the towed pinger locater on Ocean Shield," he said.
Houston said he did not think the oil slicks were from one of the many ships involved in the search but it would take a number of days before the oil could be conclusively tested.
"It's very close to where the transmissions are coming from and we'll investigate it and that will take a little bit of time, given that we're in the middle of the Indian Ocean.
We don't think it's from the ships, so where is it from? So it's another lead to pursue," he said.
The Bluefin-21, a US Navy probe equipped with side-scan sonar, will be deployed today. Side-scan sonar is an acoustic technology that creates pictures from the reflections of sound rather than light.
Multi-nation search teams have been using a towed pinger locater to listen for signals from the plane's black box flight recorders till now. But no new signals have been heard since April 8, amid concerns the flight recorders' batteries have expired.
Flight MH370 with 239 people, including five Indians, on board went missing 38 days ago. The Malaysia Airlines Boeing 777-200 was flying from Kuala Lumpur to Beijing when it lost contact with air traffic controllers over the South China Sea.
The search teams, armed with sophisticated naval aircraft and ships, have focused on waters west of the Australian city of Perth, with teams racing against time to detect signals before the flight recorder batteries - which last about one month - run out.
Though the discovery of four pings believed to be from the missing jet's black boxes -- its flight data recorder and its cockpit voice recorder -- have helped investigators narrow the search area, they would still face a formidable task, Houston said.
Houston cautioned against hopes that the underwater vehicle will find wreckage.
"It may not," he said. "This will be a slow and painstaking process."
Each deployment of the Bluefin-21 underwater drone will last 24 hours.
It will take two hours for the device to get down to the bottom of the ocean. Then it will scour the ocean bed for 16 hours and take another two hours to resurface. It will take take another four hours to download and analyse the data collected, Houston said.
The first mission will cover an area 5 kilometres by 8 kilometres.
The bottom of the search area is not sharply mountainous -- it's more flat and almost rolling, Houston said. But he said the area is likely to have a lot of silt on the bottom, which can "complicate" the search.
"As I have said before, aircraft wreckage needs to be visually identified before we can say with certainty that this is the final resting place of MH370," Houston said.
"I would caution you against raising hopes that the deployment of the Autonomous Underwater Vehicle will result in the detection of the aircraft wreckage. It may not. However, this is the best lead we have and it must be pursued vigorously. Again, I emphasise that this will be a slow and painstaking process," he said.
"The chances of any floating material being recovered have greatly diminished and it will be appropriate to confer with Australia's partners to decide the way ahead later this week," Houston said.
He said the four underwater signals previously received are "most promising lead we have in the search for MH370." "We need to pursue this lead as far as possible. Analysis of the four signals has allowed the provisional definition of a reduced and manageable search area on the ocean floor," he added.