Why is it crucial to monitor the APU fuel level?

Monitoring the APU fuel level is crucial primarily because it helps avoid APU shutdowns and potential disruptions to ground operations. The Auxiliary Power Unit (APU) provides essential power and air for starting the main engines and for various electrical and pneumatic functions while the aircraft is on the ground. If the fuel level drops too low, the APU can shut down unexpectedly, leading to inconvenience and operational delays. These shutdowns can hinder procedures like engine starts and equipment operation, affecting the overall efficiency and readiness of ground operations.

While ensuring efficiency and assessing fuel usage are important, they serve more as secondary considerations in comparison to the immediate operational impacts of an APU shutdown. Additionally, increased overall aircraft weight is not a relevant factor in this context since the APU is only concerned with its operational capability rather than affecting the total aircraft weight in a meaningful way. Therefore, monitoring the fuel level primarily safeguards against unintended interruptions during critical ground operations.