here are new developments. the search area shifts and moves a little bit every day. this is where the focus is, what the focus is on now on sunday. you'll also see the spot marked pulse signal detected where chinese state-run media report a crew picked up pings from deep below the surface. planes are in the air again. just a short time ago the u.s. military aircraft took off from perth to join planes and ships representing eight countries controlling those search areas. that flight originated in kuala lumpur, malaysia, more than four weeks ago, where cnn's nic robertson is now. nic, something unusual happened this weekend. officials heard some people outside the investigation to hear some specific control tower recordings. who was that? >> reporter: that's right, don. well, these are friends and colleagues of the first officer and the captain. this is to try to determine who made that very important last communication, the "good night malaysian 370" indicating who would have been in control of