from the coast of australia. we're operating at the range towards the limits of the equipment that's available to us, which is the best equipment available. >> in may 2015, after the initial efforts turned up nothing, they doubled the size of the priority search area. >> it is a huge area, and it's a complicated area with valleys and ocean mountains and crevices. >> complex terrain is not the only challenge they faced. >> you're grinding through high seas, strong winds, incredible difficult conditions. >> they've had to winterize the ships so they could keep searching throughout the brutal winter. >> it wasn't easy, and it wasn't cheap. >> the most expensive search in human history, period. this is all uncharted territory,