The HT717-1 is a convenient easy-to-use tool for test and maintenance of aircraft systems that are tied to the Digital Flight Data Recorder (DFDR). It is a self contained handheld tester that displays the user specified data received from a Digital Flight Data Acquisition Unit (DFDAU) or DFDR output databus.
In an aircraft the DFDAU samples, conditions, and digitizes or reformats the analog and digital signals representing flight data. This data passes from the DFDAU to the DFDR and back on special ARINC 573 or 717 Harvard biphase encoded serial databuses. The HT717-1 provides access to the flight data by reading these Harvard biphase databuses or the bipolar auxiliary output for a Quick Access Recorder (QAR).