LUBBOCK, TX -- There are still lots of questions about what happened to Malaysia Airlines flight 370, and big piece of the puzzle is why the transponder stopped transmitting.
We spoke with Hub City Aviation owner Louie Hilliard about what a transponder is, and what its used for.
"A transponder is a two way radio that airplanes use to relay their location to air traffic control," said Hilliard.
He says transponders are used to track a plane's location and altitude.
Hilliard took us for a ride to show us how it works. The transponder showed air traffic controllers where our plane was during the flight.
Hilliard says there are multiple things that could have shut down the transponder on Flight 370.
"If they had a failure of their electrical system, that could turn off the transponder, however those airplanes have so many redundant systems I I find that to be fairly unlikely. The pilots could have turned it off or somebody else could have turned it off the transponder but they would have to physically turn it off or interrupt the power supply to the transponder," said Hilliard.
"The transponder has an off button they also have back up power supplies so to totally disable the transponder you would have to turn it off or pull a circuit breaker to cause power to stop from the transponder," he said.
Hilliard says pilots are taught standardized codes they can send to air traffic controllers in times of distress including ones for high jacking, radio failure and mayday.
Thursday the search for the missing airliner expanded to the Indian Ocean. The US Navy is now assisting.