CNN Wolf March 14, 2014 17:18:00
Traffic control or others on the ground where the plane was? >> the transponders very easy because of the fact that when youre on the ground you are supposed to turn it off. youre no longer needing radar. so thats why the on/off switch is so accessible. the other equipment you talk about, whether it be the radios, and there are many frequencies that they could be using, whether they use the acars system, thats the system that basically transmits what the airplane is do, even the engines are repo...
Source: archive.org