What occurs when the APU FIRE switch light is depressed?

What occurs when the APU FIRE switch light is depressed?

• A. APU Generator drops offline
• B. Squib Armed
• C. Fuel SOV closes
• D. All of the above

Answer: (D)

Depressing the APU FIRE switch starts the APU fire suppression sequence: it shuts down the APU by closing the fuel shutoff valve to stop fuel flow and taking the APU generator offline to remove power and heat from the compartment. At the same time, the extinguishing system is armed so that if a fire is present, the extinguishing agent can be discharged into the APU area. This coordinated action—removing fuel, removing power, and arming the extinguishing agent—is designed to rapidly suppress an APU fire and protect the airplane.

Depressing the APU FIRE switch starts the APU fire suppression sequence: it shuts down the APU by closing the fuel shutoff valve to stop fuel flow and taking the APU generator offline to remove power and heat from the compartment. At the same time, the extinguishing system is armed so that if a fire is present, the extinguishing agent can be discharged into the APU area. This coordinated action—removing fuel, removing power, and arming the extinguishing agent—is designed to rapidly suppress an APU fire and protect the airplane.