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TODAY   |  April 08, 2014

No new pings heard; Flight 370 search reduced

Officials struggle to detect new pings that could be coming from the plane’s data recordings. But they’ve reduced the size of the Flight 370 search area. NBC’s Tom Costello reports.

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>>> latest on the hunt for malaysia flight 370, and the tantalizing pings that naval search teams heard coming from the targeted search zone. they were looking for them again today. nbc's tom costello has got the latest from washington. tom, good morning.

>> good morning. this is the area that they're listening for these pings right here. among one of these arcs. the trouble, today they didn't hear anything at all. this is what they're listening for. that's the pinging that would come from the black boxes . now, again, they didn't hear it today. that may be because the batteries are dying. or perhaps the thermal layers in the ocean. but they need to triangulate that sound. they need to get a fix on that pinger so they can then drop down an unmanned submarine. 32 days since flight 370 disappeared and search teams are now working their most promising lead yet. those pings picked up by the australian naval ship ocean shield, which sound very much like the pings black boxes emit when they're submerged in water.

>> we have a positive lead. this is an herculean task . the water is extremely deep.

>> reporter: while the pinger batteries are supposed to last 30 days , the manufacturer says they could go longer.

>> they do vary. 30 days is the minimum. they can operate as much as 45 days.

>> reporter: now ocean shield is towing a u.s. pinger locator, and methodically traversing an area three miles by three miles listening for the pings. each sweep takes eight hours. complicating matters, the indian ocean in that area is two to three miles deep. if they can triangulate the signals, the next step would be to drop the blue fin 21 unmanned submarine into the water to map the ocean's floor and search for possible wreckage.

>> we have a reasonably large search area on the bottom of the ocean to prosecute, and with the device we've got, that will take a long, long time.

>> reporter: if search teams spot the wreckage, they will eventually deploy a remotely operated robot to retrieve the plane's black boxes , much as they did with air france 447. crucially, the flight data recorder holds more than a thousand measurements of the plane's last 24 hours . even if it sits in salt water for years, the ntsb's aaron gormley says the data should survive.

>> we should be able to build the information back, so you won't lose the entire one last hour of the flight or all of the air speed data like one parameter.

>> reporter: all of it critical to piecing together what happened to flight 370. but first, they have to find the wreckage. making matters even more complicated, they don't have any debris on the ocean's surface here. that may be because it's drifted several hundred miles. or, remember, there was a typhoon that moved here. in a best case scenario, assuming they pick up the pings again and then they drop the submersible down and they identify wreckage, best case scenario, it could be a month or more before they retrieve the black boxes . guys, back to you.