In the case of ASI data failure, which system should be referenced to diagnose the issue?

Referencing the Air Data Computer (ADC) to diagnose an ASI (Airspeed Indicator) data failure is appropriate because the ADC is responsible for processing the raw data from the pitot static system, which feeds into the ASI. The ADC gathers information related to airspeed, altitude, and vertical speed, converting this data into usable information for various cockpit displays and systems.

When the ASI displays an error or failure, checking the ADC allows for verification of the data being provided to the ASI. If the ADC itself is functioning correctly, it can help identify whether the problem lies in the ASI or in the data being sent from the ADC.

The other systems mentioned, while important in their respective functions, do not directly correlate to the diagnosis of ASI data issues. The Primary Flight Display (PFD) presents data but does not diagnose the source of the problem. Similarly, the Radio Altimeter and Flight Management System (FMS) serve different purposes and would not provide the pertinent information necessary to troubleshoot an ASI malfunction. Thus, the ADC is the most logical choice for diagnosing ASI data failures.