you haven't got the luxury of time. you've got pingers that may expire, so you've got to say, this is our best guess now. >> their best guess is a remote area more than twice the size of california. >> good morning. these are all the aircraft flying today. >> the australians take over the search. and soon after the australian ship lowers its pinger locator into the water, pings are detected. >> clearly this is a most promising lead. >> it was wow again. >> it was miraculous. they had just put the pinger locator in the water. >> i was convinced this is it. they've got the answer. it's a matter of days. >> a robotic submarine scours the 329 square mile area where the pings were heard. it's painstakingly slow work. then two months later --