Day 38 of the search for the missing Malaysian Airlines flight MH370 sees a change in strategy from the multinational team tasked with uncovering its remains. Angus Houston, chief of the Joint Agency Coordination Centre, has today announced that the next phase in the search will begin "as soon as possible" with the deployment of a Bluefin-21 autonomous underwater vehicle. The drone — which has already been in testing to prepare for its deployment in the Indian Ocean — will map out the ocean floor using sonar, scanning an area of 40 square kilometers every 24 hours.

Narrowing down the likely location of the MH370 wreckage has been an immense challenge, owing to the vastness of the area in which the plane may have crashed. A recent set of four signals that may have come from the airplane's black boxes has helped this effort, and today Air Chief Marshal Houston has noted the discovery of an oil slick in the vicinity as well. Because the oil slick is both "down-wind and down-sea" from the location of the detected pings, it could corroborate the searchers' present estimates. Samples of it have been collected and will be analyzed over the coming days.

"We've got a good lead, the most promising lead that we've had through the entire search."

Houston cautions against reading too much into today's announcement. The batteries on the MH370 black boxes are only rated to last for 30 days, so continuing to listen out for their pings would now be more hopeful than helpful. While he describes the current information as "the most promising lead that we've had through the entire search," he also cautions that "it may be very difficult to find something and you don't know how good any lead is until you get your eyes on the wreckage." Rated for a depth of 4.5 kilometers, the Bluefin drone appears to be the best available method for extending the search in the absence of any further signals from the black boxes. It will have to operate at the very edge of its range, too, since the relevant signals picked up by investigators came from roughly the same depth last week.