After the plane vanished. Sources also tell us that investigators are confident it was the flights captain who radioed in that last message and there was no sign of stress or possible third party when he said good night malaysian flight 370. This morning search crews discover a possible new signal, raising hopes that they may be closing in on the flights socalled black boxes which could explain exactly what happened. Lets begin with that new signal. Cnns will ripley is in perth, australia. Good morning, will. Reporter good morning, carol. We know that Data Analysis is happening as we speak on that fifth possible ping that was detected, not by that towed pinger locater. This was actually detected by whats called the sonar bu es. The Australian Military was dropping these into the ocean. It has an under water microphone that goes down about 1,000 feet. It listens as well. And were told one of these microphones picked up what they believe could be a signal from an in flight data recorder. They need to check it out. Thats why theres Data Analysis that will be happening through the overnight hours in perth. We also got a new tidbit of new info. We know the british ship, the hms echo that was with the chinese ship that thought they heard something, they cleared that area. The british ship is moving to join the ocean shield. We know that ship will be in the area as well listening to see if they can get a lock on more possible signals. A lot to follow here, carol. That means, will, the search area has shrunk yet again, right . Reporter thats right. We know the actual visual search area, the area where theyre looking for debris is now down to 22,000 square miles or so. That is the smallest that it has been yet. Still, though, no debris sighted. It will be interesting to see what happens as they corporate to narrow the search area. The other big developments i told you about this morning, investigators say it was captain Zawahiri Shah who said good night malaysian flight 370. They believe the plane dropped to between 4,000 and 5,000 feet. Nic robertson is in kuala lumpur with more of these developments. Hi, nic. Reporter hi, carol. What we know is investigators played the air traffic recording, they played that to five pilots who knew both the first officer and the captain. They say they were able to identify the first officer speaking when the aircraft was on the ground, but that last communication at 1 19 in the morning was given by the captain. They say there was no third party in the cockpit, no sign or sound of distress coming from the cockpit at that time. Of course, who was in control, who was talking through that last communication, a very important thing for investigators. Were also learning after the aircraft did that loop back, flew back across the malaysian peninsula, it dipped below military radar, reappeared 120 nautical miles further away and came up again. What were being told is the belief is from all the data that the aircraft was dropping down to an altitude between 4,000 to 5,000 feet, possibly they say because it was trying to dodge what is a busy commercial air lane in the sky there. Again, this is what theyre putting together from the best data they have at the moment, carol. So why didnt they tell us this information before . Reporter investigators have been keeping this very close to their cleft. We understand one of the reasons they didnt, in fact, announce the aircraft had made that dip in altitude is because they were aware if they had said that, that would tell people that somebody was in control of the aircraft. It does seem to be something very closely held. They have taken a lot of time to get the information, not only about the change in altitude. Remember we were talking about flying around radar control. All these different indications showing somebody was controlling the aircraft. That sort of information the investigators have been not willing to put forward. Were getting it only now from sources, carol. Nic robertson reporting live from kuala lumpur. Lets bring in mary schiavo, cnn aviation analyst and former Inspector General. And peter goal, former ntsb investigator. Investigators now say the plane took off from kuala lumpur, made that strange westward turn back over the malaysian peninsula. At some point they say the plane dipped in altitude to as low as 4,000 feet and disappeared from military radar. Mary, care to tackle that . What does it tell us . It can tell us three things. We still dont know why, but we know three things that could have accomplished. Once, if you had a loss of pressurization, youd want to get down below 10,000 feet so you didnt have to rely on oxygen and you could live in a depressurized cabin or cockpit. Two, you want to get out of other traffic. Thats where you have to do it because commercial airliners fly at much higher attitudes, 18,000 feet and above. Three, if you dont have any communications, you need to get out of other traffic because if your transponder is off or broken or dont work, you dont have cligs avoidance. Three reasons to get out of harms way. Peter, if the plane did dip low and dis disappeared from radar, might that mean those fishermen on the other side of the country, on the other side of malaysia, did they really see flight 370. Remember this . Translator i was fishing when i saw the plane. It looked strange, flying low. I told my friend thats not normal. Normally it flies at 35,000 feet. But that night it touched the clouds. I thought the pilot must be crazy. Does that lend more credence to what those fishermen say they saw, peter . Certainly you have to take their eyewitness statement more seriously now because apparently the malaysians have some evidence that theyre confident in that the plane was down at 4,000 or 5,000 feet. I think, as much as mary wants to point towards the aircraft, the real issue is it looks like more and more somebody in the cockpit was directing this plane and directing it away from land. And it looks as though they were doing it to avoid any kind of detection. Thats a very disturbing but thats where the evidence is leading. Lets have that debate between you two. Mary, you seem to think that maybe something mechanical went wrong with the plane. As captain shah radioed in the last transmission, he sounded calm. There was no sign of distress. Could something catastrophic happen that fast after that last transmission . Well, it can. And the point is we still dont have any motive and any evidence of a crime yet. By the way, if youre trying to get away from radar, although apparently malaysian military radar didnt go below 5,000 feet, for most civilians radars, they take you down almost to the runway threshold. Youd have to get down a lot lower than 5,000 feet to avoid radar. The fishermen story is problematic. If they were at 5,000 feet, they wouldnt have seen the detail on the plane. They said they could see the doors and windows. 4,000 to 5,000 feet is still way up there this the sky. If anything, its just more mystery. You cant say its a crime and cant point to the mechanical failure. We have a lot more evidence now which is always helpful in the investigation. Peter, malaysian investigators say they do think its possible that this was a criminal act, that someone on board that plane deliberately made that turn and the altitude changed in a way that didnt make sense. They seem to think it was deliberate, may have been criminal. That is the governments position. I think weve all been skeptical that there isnt quite enough evidence to indicate that. As mary said, theres nothing in the captains background or in his Flight Simulator that indicates anything amiss. But there is this the performance of the aircraft, how it got into the ocean hopefully 1,000 miles, if were looking in the right place, from perth, is inexplicable and has to involve some degree of human kror. Mary, when they do find the black boxes and i think they will. Five separate signals have been picked up in one general area, although its a large area. It seems like theyre going to find those black boxes, what will they tell us . Will they fill in all the blanks for us . They might fill in all the blanks at the very first attempt to download. If, as the malaysian authorities are claiming, someone committed the perfect crime, certainly youd pull the Circuit Breaker on the recorders. If they go to download it and find the Circuit Breakers are empty, then we know. I suspect well have a lot of data certainly on the flight data recorder. Thats why its going to be imperative to find it. There was a south African Airways that went down in the indian ocean in 87. That was found in 16,000 feet and it was still good, one of the recorders. Theres hope theyll find it all soon. Mary schiavo, peter goelz, thanks for joining me. Appreciate it. Thank you, carol. Still to come, not a single piece of debris has been found, but a possible debris field depends heavily on how the plane might have entered the water. A look at what searchers are a look at what searchers are hoping to find next. So ameriprise created the exclusive. Confident retirement approach. Now you and your ameripise advisor can get the real answers you need. Well, knowing gives you confidence. Start building your confident retirement today. Im dave and i have copd. Im kate and i have copd, but i dont want my breathing problems to get in the way my volunteering. 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Ford technicians are ready to find the right tires for your vehicle. Get up to 120 in mailin rebates on four select tires when you use the Ford Service Credit card at the big tire event. See what the ford experts think about your tires. At your ford dealer. Welcome back to our special coverage of the search for Malaysia Flight 370. A number of new important developments unfolding. Sources tell us when the flight took the mysterious turn and fell from the radar it must have plunged in altitude to between 4,000 and 5,000 feet. 34 days after the flights disappearance, malaysia is confirming that it did, in fact, dispatch search aircraft soon after the plane disappeared. Sources also tell us investigators are now confident it was indeed the flights captain who radioed in that last message and there was no sign of stress or a possible third party when he said those final words to air traffic controllers, good night, malaysian flight 370. This morning search crews discover a possible new signal, raising hopes they may be closing in on the flights socalled black boxes which could explain exactly what happened. Even as searchers continue to hear pings believed to be from the black boxes, not a single piece of debris has been found in the search. Is it possible the plane stayed intact while sinking to the bottom of the ocean . Some experts believe no matter how the plane might have come down, there should be at least some sort of debris floating on top of the water. Gary tuchman has more. Reporter not a spec of wreckage has been found from Malaysian Airlines flight 370 raising the question is it possible all the wreckage is under water . The chances of not having debris very, very remote. Reporter jim tillman is an aviation expert with decades of experience as a lpilot for American Airlines and army corps of engineers. He says if amount of debris on top of the water would vary based on the scenario of how the plane went down. If it went down at a steep dive at high speeds, thats what happens to an Alaskan Airlines jet that plunged into the pacific in 2000 killing every one on board. Midwest of the wreckage would go under water, but not all. Its not like sticking your hand into the water, its like slamming your car into a brick wall. Thats the more likely result of that kind of situation. Youre going to have lots of debris. Reporter what if there was a catastrophic explosion in the planes last few seconds. Thats what happens with twa flight 800 off the coast of long island in 1996 and pan am 193 over lockerbie, scotland. In any case while an airplane breaks up while in the air, youll have a wider debris field. You may well have small fraegmentes of the aircraft that are going to be identifiable. Reporter then the hijacking of an Ethiopians Airline flight in 1986. In that case the pilots ran out of gas and were forced to make an intentional landing. Even that resulted in significant debris on top of the water. Water is like concrete. If you hit it regard enough, it destroys the planes integrity. It will open up things like compartments and sections of the airplane that have items that will float. The best Case Scenario for the Malaysia Airlines plane would be the type made by captain Sully Sullenberger on the hudson river in new york city. That is by far the most unlikely scenario. Sully did an incredible job of flying, but he landed on a river. The river is pretty relaxed, lets say, by comparison with the ocean where youve got swells of 10, 12, 16 feet. Its pretty difficult to make that kind of a landing on water. Reporter the search continues for the wreckage. The landing scenarios just mentioned, all part of the investigation. Gary tuchman, cnn atlanta. Still to come in newsroom, the heroes from yesterdays school stabbing. Were hearing from those who rushed to help. Were working that live from pennsylvania. Reporter carol, in the midst of all the sadness, incredible stories of composure and teamwork at a time of crisis. Well have that and more after the break. [ male announcer ] what if a Small Company became big business overnight . Like, really big. Then expanded . Or their new product tanked . Or not . What if they embrace new technology instead . Imagine a companys future with the future of trading. Company profile. A Research Tool on thinkorswim. From td ameritrade. A Research Tool on thinkorswim. Thoughtful combinations, artfully prepared. Fancy feast elegant medleys. Inspired dishes like primavera, florentine and tuscany. Fancy feast. A medley of love, served daily. But with medcare, i dont have to waiting to get my diabetic supplies is such a hassle. They deliver everything i need right to my door with Free Shipping plus, medcare takes private policies, medicaid, even my medicare now we have the time to do the things we love. Medcare. We deliver a better life. Well koopt our coverage on the search for flight 370. First several students and faculty at Franklin Regional High School are being hailed adds heroes this morning. Many held a prayer vigil last night to honor the victims and the heroes. There are more stories of har w harrowism among the students. One told Anderson Cooper how she tried to save her best friend. As soon as the three boys got stabbed in 30 seconds, i let out i dont know what to do so i led out a blood curdling scream. At that moment there was somebody that pulled the fire alarm. I was just trying to keep people alive. I was trying to keep the one kid alive that i was applying pressure to. I was telling him to keep talking to me, keep awake, that he needs to stay awake, that the emts are going to be here soon and youre going to be fine and everything. So many stories of heroism. Elizabeth cohen is here to tell us more. Reporter carol, when you think about that kind of composure from a teenager with no training, its really amazing. Minutes before gracie did what she described, a boy helped her by protecting her from the assailant. Gracies boyfriend wrote on the Facebook Page to this young man, he said i cant thank you enough for everything you did for gracie. This boy that protected her is now in the hospital. The other stories were hearing is when the assailant was allegedly stabbing people, that some of the kids took off their hood kis and used them as tourniquets. Were hearing about the assistant principal who helped wrestle the alleged assailant down to the ground. Were hearing about the Security Guard who acted very quickly and got kids away from the crime scene. So as awful as everything is that happens here yesterday, there were so many people who did their best under terrible circumstances to minimize the damage. Carol . The other hero in this that should be mentioned, this teenager who pulled the fire alarm, got all the students to run out of the school. He was injured himself. Reporter right, exactly. Thats really, really quick thinking. Here he is, hes injured and he thinks quickly enough to pull the fire alarm to alert people that they need to get out of the building. Its the kind of thing you hope you would do under those circumstances, but until it actually happens, you dont know if youre going to have the composure. That young man had the composure. Elizabeth cohen reporting live this morning. Thank you. Lets turn our attention to the suspect, alex hribal, 16 years old. Yes, he will be charged as an adult. He faces four counts of attempted homicide, one for each person critically injured. The total number of victims reflected in the 21 counts of aggravated assault. Hes also charged with possession of a weapon on school property. Earlier on new day, the teenagers Attorney Says both families and classmates are dumbstruck. He has never had any Mental Health problems whatsoever. Hes never been in the Juvenile Court system. He was a wellliked student. He