General Authority of Civil Aviation (GACA) Aeronautical Information Publication (AIP) Practice Exam

What does the APU fire switch achieve when pulled?

1. Closes all fuel and bleed air valves

2. Arms APU fire extinguishers

3. Closes APU air inlet door only

4. Disconnects APU from aircraft electrical system

The correct answer is: Arms APU fire extinguishers

The action of pulling the APU fire switch primarily serves to arm the fire extinguishing systems associated with the Auxiliary Power Unit (APU). When this switch is engaged, it activates the mechanisms necessary to ensure that the fire extinguishers can discharge and effectively combat a fire within the APU. This function is critical for safety, as it allows the crew to respond quickly to a potential fire threat, enhancing the overall emergency protocol. The fire extinguishing system is designed to suppress or extinguish a fire that might occur in the APU compartment, thereby protecting the aircraft and its occupants. The other options do not accurately represent the primary function of the APU fire switch. For example, while closing fuel and bleed air valves is an important safety measure in the context of fire prevention, it is not the direct outcome of pulling the fire switch. Additionally, while it might be important to close the APU air inlet door during certain emergency procedures, this is not specifically achieved by pulling the fire switch. Moreover, disconnecting the APU from the aircraft's electrical system is a separate function that is not directly related to the operation of the fire switch. Thus, the action of arming the fire extinguishers stands as the correct understanding of the A