What are the indications of an ADHARS failure?

An indication of an ADHARS (Air Data and Heading Reference System) failure is represented by both the attitude fail and heading fail alerts shown on the Primary Flight Display (PFD). The ADHARS is crucial for providing accurate data regarding the aircraft's pitch, roll, and heading. When these functions become compromised, the PFD will alert the pilot through specific fail messages, indicating that the reliability of attitude and heading information cannot be assured, which directly affects the overall situational awareness during flight operations.

This failure is critical because it can impact navigation and control of the aircraft. As such, pilots must be trained to recognize these alerts in order to take appropriate actions to maintain safety and control during flight.

Other choices, while related to aircraft systems, do not directly correlate with an ADHARS failure. Altitude and speed failures pertain more to the air data components rather than heading and attitude. Engine and fuel fails relate to powerplant operation, while navigation and communication failures pertain to systems that are separate from those monitored by ADHARS, highlighting the importance of the specific contextual understanding of failure indications in aircraft systems.