What is an indicator of APU system failure in the C-130J?

High temperatures are a significant indicator of APU system failure in the C-130J. In a well-functioning Auxiliary Power Unit (APU), the temperature readings should stay within a specific operational range. When the APU experiences internal failures or malfunctions, it may lead to overheating, which can cause damage to the unit and affect its performance.

Monitoring temperatures is crucial because excessive heat can indicate issues such as insufficient lubrication, a malfunctioning coolant system, or electrical failures. Operators are trained to observe these variables closely to ensure safety and functionality. In contrast, low oil pressure and normal RPMs, while important metrics, do not directly indicate an APU failure in the same way high temperatures do. Similarly, stable voltage readings suggest that the APU is providing consistent power, which does not correlate with system failure.