hours in to a 20 1/2 hour dive. that s part of the plan to protect it from being lost. you speak to it acoustically and while it s operating you re talking to it but it has a program that tells it to run certain heights and lengths off the bottom. reporter: officials at phoenix say even though the bluefin had a much shorter run than it did the first time, it was able to scan eight square miles. at that rate, it could take months to map the search area. tonight one search specialist says having only one autonomous underwater vehicle in the area that cannot go as deep as the ocean floor is not enough. that s a little bit like you losing your key on the way to your car at night and then backtracking and only searching under the well-lit areas. you need a tool that can do the entire search area. reporter: there is such a tool.
bluefin, is any of it preprogrammed or do they do it freelance style? they do a little bit of both. it s got a program to run a certain distance, a certain length and height off the ocean floor. for other certain movemens, they speak to it acoustically. they have to bring the data up and analyze it and then send it back down. good explanation, brian todd. thank you. if the searchers are right, the wreckage for flight 370 may be under three miles of water. we re joined by oceanographer ellen preager joining us from miami. was it right to send the bluefin down now and give up on the batteries for the two black boxes? well, i think the team really didn t have a choice. at this point, if those pings are really coming from the black box, they need to start looking