Which feature distinguishes a well-maintained APU?

A well-maintained Auxiliary Power Unit (APU) is characterized by increased operational stability. This means the APU can function reliably under varying conditions, supporting the aircraft's electrical and environmental systems without experiencing interruptions or failures. Consistent performance is critical for the APU to effectively supply power and serve as a backup when the main engines are not operational.

This stability arises from regular maintenance practices, which ensure that components such as the fuel system, lubrication, and electrical circuits are in good condition. By maintaining the APU properly, its responses to load changes remain predictable, and it continues to meet operational demands without excessive wear or unexpected breakdowns.

While lower fuel consumption is generally a benefit of an efficient APU, it can also be influenced by operational conditions or design efficiencies rather than maintenance alone. Higher RPM readings do not necessarily indicate better performance or maintenance; they could result from various factors, including operational demands. Greater noise levels typically suggest underlying issues or inefficiencies, rather than being an indicator of good maintenance.