Don started by pointing out that most people think only of air to ground voice communications as being the sum total of the use of radio. There are, however, many other types of radio signals in use, beside voice there is radar and data.
Don went through the communications used to help the pilot know his location and point to the destination. Following that, Don detailed radio used for instrument landings indicating the aircraft position with regard to the runway, the glide slope and markers at three critical distances to landing. But, it was also pointed out that important information can be automatically transmitted to indicate position, aircraft operating parameters and aircraft ‘health’ to ground stations. During long flights, including overseas trips, automatic transmissions can be made to satellites designed to work with the aircraft information.
The question was asked as to why signals of this sort couldn’t be used to locate a plane that had gone off the radar map. The answer being that the transmitting units, in this case, must have been turned off. The next question was why be able to turn the system off and the answer is that they must be turned off when on the ground to stop multi transmissions from various planes interfering with those in the air.
Don showed a diagram of a typical airliner pointing out the locations of various antennas, there can be over twenty!