so for the first 40 minutes of this flight, up to that point, everything has been routine. >> mm-hmm, yes. >> everything was routine until now. two minutes after talking with air traffic control, 40 minutes into the flight, the plane's transponder goes dark. >> the plane's transponder is effectively the instrument by which sends out a signal to air traffic control. it tells you what height it's at, which direction, and what speed it's traveling. suddenly, this giant 777 is blind to the world. >> and there's no easy explanation for why it happened. >> either it was intentional and someone tried to turn all of those systems off at once, or the pilot was unable to communicate, kept from communicating, or there was a mechanical failure of some kind that took all those systems out at one time. >> then, muninutes after the transresponder stops, the 777 makes an unexpected turn,