What could indicate potential fuel contamination in the APU?

When assessing the health of the Auxiliary Power Unit (APU) in the C-130J, unusual engine sounds or performance inconsistencies can be significant indicators of potential fuel contamination. Contaminants in fuel, such as water, dirt, or microbial growth, can disrupt the combustion process, leading to rough engine operation, fluctuations in power output, or a failure to maintain consistent speeds.

These performance discrepancies can often manifest as abnormal noises from the engine, including sputtering or intermittent power loss, which are often directly related to the quality of the fuel being used. Unregulated fuel quality can lead to insufficient combustion, affecting not only the APU's operational reliability but also potentially damaging the engine components over time if not addressed.

While increased fuel consumption, a lack of visible fuel supply, and frequent electrical failures might suggest other operational issues or maintenance concerns, they do not specifically indicate the presence of contaminated fuel as clearly as performance anomalies do.