What is indicated when the standby attitude indicator shows an incorrect reading?

The standby attitude indicator is designed to provide critical information regarding the aircraft's orientation in space, specifically its pitch and bank angles. When this indicator presents an incorrect reading, it is likely due to a malfunction in the Air Data Computer (ADC), which processes data from various sensors, including those related to attitude. An inoperable ADC means that the primary source of attitude data is compromised, leading to the standby indicator displaying incorrect information.

In contrast, if power systems were functioning properly, inaccuracies in the standby attitude indicator could not be guaranteed. Therefore, while all power systems might appear to operate normally, they could mask issues with the ADC, which is crucial for providing accurate attitude information.

Inaccurate secondary pitot/static data might affect other instruments rather than the standby attitude indicator directly, as the latter primarily relies on the ADC for its readings. Similarly, while a failing auxiliary battery can affect certain electronic systems, it does not directly correlate with a discrepancy in the attitude indication unless it specifically impacts the ADC's power supply. Thus, the most direct link to an incorrect reading on the standby attitude indicator is indeed an inoperable ADC.