it's believed the communications system was automatically sending out electronic hand shakes to a satellite, even though the transponder was dark. this allows authorities to plot the mysterious course. >> reporter: the search area moves again in late march. >> mh370 flew at a higher speed than previously thought, which in turn means it used more fuel and could not travel as far. the authorities have indicated they have searched the area approximately 1100 kilometers to the northeast. >> high-tech listening devices are deployed along the bottom of the sea listening for sounds from the pinger attached to the black box. they pick up a signal. it's the first sign of hope. >> we have very much narrowed down the search area and we are very confident that the signals that we are detecting are from the black box.