What are the warning signals for APU system faults?

The warning signals for APU system faults are indicated by warning lights and fault messages. These visual and textual alerts are specifically designed to inform the crew of any irregularities or issues with the Auxiliary Power Unit, allowing for timely diagnosis and response. The APU control system continuously monitors its performance, and when a fault is detected, it activates warning lights or displays fault messages on the control panel. This is crucial for maintaining safety and ensuring the proper function of the aircraft's systems, as it provides the crew with immediate awareness of problems that may affect operation.

In contrast, while increased fuel flow, vibrations in the airframe, and silence from the APU control panel could be indicators of various operational conditions, they do not serve as standardized or direct warnings specific to APU faults. Increased fuel flow might occur due to normal operational demands rather than a fault. Vibrations could indicate a range of mechanical issues, but they are not unique to the APU. Silence from the APU control panel may imply normal operation or a different type of issue, but it lacks the clarity and specificity provided by the dedicated warning lights and fault messages.