investigators are maximizing their options, but it will still be tough. look back at some of the major crashes in recent contemporary history, it would seem implausible to be able to find two black boxes without having any form of even slight indication that there was debris nearby. reporter: the signals can only be detected from one to two miles away. but this could be futile if the pingers are no longer working. that s why the surface search is still critical. you don t get smoke without fire. so looking at the lower probabilities, i would still be highly vested in what information the aircraft assets can be ascertaining over that area, the p-3 orion, the p-8 poseidon, the 76. these aircraft can travel at 240 knots plus which is four mile ps a minute. it can search areas a lot greater than a ping locator can. reporter: the bluefin 21, an
four weeks after malaysian flight 370 disappeared, the surface below surface. the pinger locator trying to detect sounds from up to two nautical miles away, around the clock with no break. this is assuming the beacons are still emitting a signal at all. the batteries could be dead or it could be malfunctioning. there is also dating in the search an underwater robot ready to search the seabed for wreckage if the ping locator picks up a signal. there is a chance they could be looking in the wrong area. searchers are making educated guesses. we have not searched everywhere where the aircraft might have gone. we are concentrating in an area that above the surface, meanwhile, 14 planes in the air,
motive? hello, there, everyone. i m john berman. i am michaela pereira. it is 11:00 out east and 8:00 a.m. where you are. i am already in trouble. we are four weeks in after malaysia airlines flight 370 disappeared. the search turns in another direction, below the surface. crews have dropped a pinger locator in the water. it is trying to pick up the chirps from the missing jet s flight data recorders. it canic p up sound from two nautical miles away. even if the boxes are 20,000 feet under the water. the technology should detect the pings. this, of course, all assuming tho tha tho that those beacons are emitting any signals at all. the batteries could be dead. there is also an underwater robot getting ready to go. it will search the seabed for wreckage if the ping locator
me crash further when i find out the real truth, which we re all expecting will be that the plane has crashed. reporter: you know, torture going through this. i mean, when she describes in terms of talking about the search and everything being done, you can imagine how difficult it is. kyra, she has two young boys. you know how they keep your spirits up. she s doing as well as she can. she feels in terms of speaking for all the families out there, they want something to be found as soon as possible. they re very hopeful now that the search has moved underwater. paula, you talked with the u.s. navy s top ocean engineer. we heard from him right there saying that he s confident, but there has to be challenges also. what did he tell you? reporter: well, you know, he s been very blunt with me for the entire week as we ve been going through this. he s happy to get the towed ping locator in the water. he has the blue fin out there. i asked him, kyra, i said, is this a shot in the dark?
no, sooner. i think we have until sunday. but they ve got up to about 40 days best case scenario. if they were stored well, and by the way they ll be pinging quieter and quieter. best case scenario we will have that. but once that goes then all the ping locator and the hms echo but michael the positive side is they are moving closer in towards the coast of australia. they re at 900 miles, i believe, out. so i think the water is shallower, the ocean currents are also different. they re going north at this point. so they could be following a debris field. they could have more luck, if you will, in that they re narrowing the search zone to i hope there s something more to this that i don t know that does make people in the search feel more optimistic. like i said, every time they change the search location it frustrates me more than christine dennison, colonel michael kay. thank you. the authorities by the way have been doing a lot to try to