Jet Search: Pings Have Gone Silent Submersible ready to investigate underwater, but field of search needs to be narrowed By Matt Cantor, Newser User Posted Apr 8, 2014 6:24 AM CDT 10 comments Comments In this photo taken on Tuesday, April 1, 2014, provided by the US Navy, the Bluefin 21 is hoisted back on board the Australian Defense Vessel Ocean Shield after successful buoyancy testing. (AP Photo/U.S. Navy, Specialist 1st Class Peter D. Blair) (Newser) – When an Australian ship heard pings possibly from Malaysia Airlines Flight 370, officials saw a big lead open up in the search—but since then, investigators haven't been able to recapture the signal, Reuters reports. That's particularly worrying since the batteries on the jet's black boxes have likely just about run out. But "we need to continue (searching) for several days right up to the point at which there's absolutely no doubt that the batteries will have expired," says Angus Houston, the Australian official leading the search, per CBS News. "If we don't get any further transmissions, we have a reasonably large search area of the bottom of the ocean to prosecute and that will take a long, long time," Houston says. The ship is carrying an autonomous underwater vehicle that can search the depths for the plane, "literally crawling along the bottom of the ocean," Houston notes. Trouble is, findings so far point to "a large area for a small submersible that has a very narrow field of search." Once the vehicle, called Bluefin-21, does head downward, it will conduct 20-hour sonar missions to try to find the plane.