information is being beamed down? >> commonly what's downloaded is engine parameters, engine burn, discrepancies. >> reporter: airlines monitor the realtime data. another way to communicate, radio. all right, good night. the final call from the pilots as the theft malaysian air space. a common phrase when changing controllers. >> we are in a dive here. >> in alaska airlines flight 261 when the plane dived out of control, pilots radioed what was happening. but no may day from flight 370. in the event of an emergency, is communication secondary? >> yeah, the first thing is to fly the airplane, navigate the airplane, then communicate. that's the order of precedence. >> reporter: a third way to communicate, by transponder. 1:21 a.m. flight 370's transponder signal goes dead. it transmits the plane's location, speed, altitude and