welcome back. breaking news, the bluefin 21 has nearly completed its 12th mission, 90% of the search zone scanned. and yet another deadend when sheet metal with rivets washed ashore has been ruled out as debris from this plane. it raises the question, is it time to rethink the search vat gee? jean casaras has more now. australia will not rest until we have done everything we humanly can to get to the bottom of this mystery. >> reporter: it is a mystery no closer to being solved. the bluefin 21 autonomous underwater vehicle has searched the targeted area with no luck. experts are preparing for the next phase of the recovery effort. >> this requires deep sea ascents. this requires more probably bluefin 21s. this requires probably