( CNN ) -- Once investigators looking for Malaysia Airlines Flight 370 decide to shift from listening for pings emanating from the floor of the Indian Ocean to poring over its terrain , they will begin drawing from a whole new set of tools . Among them will be the Bluefin-21 , a probe equipped with side-scan sonar -- an acoustic technology that creates pictures from the reflections of sound rather than light . `` That is a piece of equipment that does assist in locating where the wreckage may be , '' said Sylvia Earle , an oceanographer from National Geographic who was chief scientist for the National Oceanic and Atmospheric Administration . A 'massive , massive task ' Though the discovery of four pings believed to be from the jet 's so-called 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 . `` It 's a lot of terrain to cover , '' given that the Bluefin-21 moves at the pace of a leisurely stroll , she told CNN . Though it moves slowly , it creates good images -- so good that they are `` almost a picture of what 's there ... but it 's imaged with sound instead of with a camera . '' Listen for a ping , and the water may play tricks on you . Once the debris field is found , then other equipment -- such as remotely operated vehicles -- would be brought in to recover the black boxes , Earle said . ROVs working at depths of three miles would require power conveyed down a cable from a ship above , she said . `` There are not many pieces of equipment in the world able to do this . '' And there are only a handful of countries that have manned submarines capable of descending to such depths , she said , citing the United States , Russia , Japan , France and China . `` Having the human presence there can make a big difference , '' she said . It `` can give you a real edge in terms of understanding what 's there . '' The scarcity of resources `` shows how ill-prepared we are to operate in the deep sea , '' Earle said . `` We 've invested in aviation and aerospace , and we 've been neglecting the ocean . '' The time to move from listening for pings to looking for debris is fast approaching , said Alan Diehl , a former Air Force accident investigator . `` We 're right on the cusp where we need to go from passive listening to active ( looking ) with the Bluefin , '' he told CNN . That 's because the batteries powering the black boxes ' locator devices are probably already dead , said Mary Schiavo , former inspector general for the U.S. Department of Transportation , who noted that more than four days had elapsed since any pings were detected . `` I 'm surprised that they lasted as long as they did , '' she said . The failure of searchers to find any debris linked to the plane has not surprised CNN Aviation Analyst David Soucie , author of `` Why Planes Crash . '' The model used for tracking the debris could be incorrect , he said , noting that that was the case when investigators were searching for evidence of Air France Flight 447 , which plunged into the southern Atlantic Ocean in 2009 , killing all 228 people aboard . `` They spent weeks looking for debris in the wrong area , '' he said . The lack of debris could also mean that the plane did not break apart on impact , but instead sank largely intact , he said . If that was the case , it could complicate the effort to retrieve the black boxes , since they were stored inside the tail of the plane . Investigators would have to dismantle the tail in order to extract them and whatever secrets they may hold . Lessons from past air disasters . Where 's the debris ? How deep is deep ?
Probe of the ocean floor will move from ping locators to sonar . The Bluefin-21 is equipped with side-scan sonar . This is a very interesting project and I hope it goes well. An intact plane could complicate the search effort , CNN analyst says .