Upon detecting an APU fire in flight, what action does the APU automatic fire protection take?

When an APU fire is detected in flight, the APU automatic fire protection system is designed to respond by shutting down the APU to prevent further operation, which could exacerbate the situation or lead to additional hazards. However, while the system efficiently terminates APU operation in an emergency, it is designed not to discharge the fire bottle automatically. This decision is based on the operational procedures and safety protocols, which may require flight crew confirmation or manual intervention to discharge the fire bottle.

By shutting down the APU, the system minimizes the risk of an uncontrolled fire spreading or leading to more serious consequences. In-flight operations prioritize crew safety and aircraft integrity, thus requiring that the decision to use the fire-extinguishing system is evaluated appropriately by the pilots based on the specific conditions in the moment.