FAA Development in Aircraft Data Communications

The application of digital techniques to aeronautical air traffic control communications has been under study in the United States for more than fifteen years. During the past four years active development and evaluation programs have been conducted by the Federal Aviation Agency (FAA) on specific experimental equipment intended to provide guidance in the establishment of parameters for a universal system. Equipment has been developed using both low data rates and relatively high data rate approaches. Both systems utilize existing airborne voice communication equipment. The major effort was spent on the development and evaluation of an experimental "Automatic Ground-Air Communication System" referred to as AGACS. This two-way time division multiplex system was designed primarily for operation at 750 bits per second, and provided both frequency-shift keyed carrier (FSK) and tone-shifted amplitude-modulation (FSK-AM) options. The second equipment was developed under a program for "Analysis of Advanced Data Transmission Techniques" and utilized data rates in the range from approximately 30 to 200 bits per second. Audio tone-shifted (FSK-AM) modulation was used. The equipment developed is described and the results of the test evaluation is given. Guidelines are presented for future efforts.