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

When does the APU fire switch unlock automatically?

1. When the APU reaches operational temperature

2. Upon receiving a fire warning

3. During a routine system check

4. When the APU generator is tripped

The correct answer is: Upon receiving a fire warning

The correct answer relates to the safety protocols surrounding auxiliary power units (APUs) and their fire suppression systems. The APU fire switch is designed to enhance safety by automatically unlocking when a fire warning is received. This feature allows for immediate access to the fire suppression controls, enabling crew members to respond swiftly to an emergency situation. In the case of a fire warning, the immediate response is crucial; hence, the system is engineered to provide easy access to the necessary controls at that critical time. This proactive measure helps to ensure that any potential fire risks associated with the APU can be managed effectively and without delay. Other options, while relevant to APUs, do not accurately describe situations where the fire switch would automatically unlock. For instance, APU operational temperature does not trigger this specific safety mechanism, nor does a routine system check or the tripping of an APU generator directly relate to the fire warning protocol. Understanding this distinct function of the fire switch is essential for comprehending APU operations and safety measures in aviation.