What does the APU warning horn indicate when in the cargo compartment?

The APU warning horn in the cargo compartment is an important safety feature designed to alert the crew to critical conditions related to the Auxiliary Power Unit (APU). When the warning horn sounds, it specifically indicates an APU fire. This warning is crucial because an APU fire can pose serious risks not only to the aircraft but also to personnel working in or around the cargo compartment.

Timely recognition of this warning allows the flight crew to take immediate action to mitigate potential hazards, such as activating fire suppression systems or preparing for emergency procedures. The ability to respond quickly to an APU fire warning is essential in maintaining the safety of the aircraft and the safety of those onboard.

Understanding this alert ensures pilots and crew members are well-prepared to handle emergencies effectively, highlighting the importance of familiarity with the APU's operational parameters and associated warnings.