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(CNN) – Inside the cockpit of a Boeing 777, there are multiple ways pilots communicate with the ground. There is a system called ACARS, which automatically beams down information about the health of the plane.
Until Thursday, the last transmission from missing Malaysia Airlines Flight 370 was believed to be at 1:07 a.m. local time. Now, there is word the plane may have been transmitting data hours beyond that.
"Commonly what's downloaded (by ACARS) is engine parameters, temperatures, the amount of fuel burned, any maintenance discrepancies," said Tom Haueter, former director of the National Transportation Safety Boar's office of aviation safety.
Airlines monitor the real time data.
Another way to communicate is by radio.
"All right, good night" was the final call from the pilots, as flight 370 left Malaysian air space. It's a common phrase when changing controllers.
In Alaska Airlines Flight 261, when the plane dived out of control, pilots radioed what was happening, saying "Alaska 261, we are in a dive here."
But there was no mayday from flight 370.
In the event of an emergency, communication is secondary says Haueter.
"The first thing is to fly the airplane, navigate the airplane, then communicate. That's the order of precedence," said Haueter.
A third way to communicate is via transponder, which transmits the plane's location, speed, altitude and position.
At 1:21 a.m., flight 370's transponder signal went dead.
There is no good reason why a pilot would switch the transponder off, says Haueter.
"Clearly if all the power was lost to the aircraft, or something happened to take out that part of the electrical system, that would turn it off. But certainly one aspect of turning it off, is because you don't want to be seen," said Haueter.
Radar tracks flight 370 flying for another nine minutes. At 1:30 a.m. local time, the plane vanishes.
But the one piece of the plane that is likely still communicating are the flight recorders. Only sonar equipment can detect their pings, and time is of the essence – the signal only lasts for about 30 days.