What indicates that APU is running properly?

The indication of a properly running Auxiliary Power Unit (APU) includes both normal oil temperature and stable Exhaust Gas Temperature (EGT) readings. Normal oil temperature suggests that the lubrication system within the APU is functioning correctly, ensuring that moving parts are adequately lubricated and that the engine is not overheating. Conversely, stable EGT readings provide insight into the combustion process within the APU; fluctuations in EGT could indicate combustion irregularities or other operational issues.

Together, these indicators confirm that the APU is operating within its intended parameters, ensuring reliability and efficiency during operations. Thus, both normal oil temperature and stable EGT readings are essential for assessing the health of the APU.