What indicates a malfunction if starting the APU?

When starting the Auxiliary Power Unit (APU), the indication of a malfunction can be reflected by an Exceeding Gas Temperature (EGT) reading. This is crucial because EGT is a key parameter that monitors the performance and health of the engine. An EGT that exceeds acceptable limits usually signifies that the engine is operating outside its safe operational parameters, which may lead to overheating or potential damage to the APU.

Monitoring the EGT is critical during the start-up phase, as it helps ensure the engine is functioning properly and within the designed thermal limits. If the temperature rises excessively, it indicates that there might be underlying problems such as poor airflow, excessive fuel flow, or a malfunctioning component within the APU, all of which require immediate attention to prevent further damage or operational failure.

In contrast, while low fuel pressure, incorrect load meter readings, and fire detection failures are also important indicators of APU functionality, they relate to specific operational aspects rather than the immediate health of the engine during start-up like the EGT does. The EGT is a direct measure of engine performance during critical phases, emphasizing its role in indicating potential malfunctions more effectively in this scenario.