What must be accomplished if there is no external power available for an APU start?

When starting the Auxiliary Power Unit (APU) without external power available, having a fire truck standing by is a critical safety measure. This is due to the potential risks involved in the APU start sequence, especially if the procedure does not go as planned. APUs can produce significant heat and include fuel systems that could pose a fire hazard, particularly in confined spaces or in situations where there is a malfunction during start.

Having a fire truck on standby ensures that emergency response resources are immediately available to deal with any issues that may arise, such as an engine fire or other emergency conditions that might occur during the start-up process. This proactive approach helps ensure the safety of personnel and equipment during operations where external power is not available.