Frantic search for Titanic submersible continues

More "banging" noises have been heard from the ocean in the search for a missing submersible that had been visiting the wreck of the Titanic, but authorities still don't know what the sounds are. Rescuers are now focusing their search on a remote area of the Atlantic Ocean where the undersea noises were detected. Search and rescue teams are in a race against time to find the vessel with five people on board - it's estimated their oxygen will run out by tonight. A massive operation led by the US Coastguard is underway, but they are describing it as "extremely complicated". Kathryn speaks to Stefan Williams, a professor of Marine Robotics at the University of Sydney.