What could an APU temperature warning light indicate?

The APU temperature warning light is a critical indicator that helps monitor the health and safety of the Auxiliary Power Unit. When this light illuminates, it typically signifies an overheating condition within the APU. Overheating can occur due to various reasons, including low coolant levels, a malfunctioning cooling system, or excessive operational demands placed on the APU beyond its designed capabilities. This warning is essential because if addressed promptly, it can help prevent more severe damage to the APU, ensuring operational reliability and safety.

In contrast, normal operational conditions would not trigger the temperature warning light. A fuel system malfunction might lead to different symptoms or warnings related to fuel delivery or combustion but would not specifically indicate a temperature issue. An electrical circuit failure might affect the APU's operation as well but would more likely manifest through different warning systems or indicators, not directly through a temperature warning. Hence, when the APU temperature warning light activates, it is a clear and direct indicator of an overheating condition, necessitating immediate attention.