PSA Airlines Canadair Regional Jet Systems (PSA-CRJ) Practice Exam

The automatic shutdown of the Auxiliary Power Unit (APU) with a fire indication is designed to enhance safety by preventing potential fire hazards from escalating. When the APU detects a fire condition, it prioritizes crew and passenger safety. This shutdown typically occurs on the ground because the APU is often running during ground operations to provide electrical power, air conditioning, and bleed air. In-flight scenarios do not trigger an automatic shutdown; instead, the crew would follow specific emergency procedures to deal with the fire indication. If the temperature exceeds certain limits, the APU may shut down, but this is not specifically tied to a fire indication. During maintenance operations, the APU may be in a controlled environment where risks can be managed differently, and thus its operation does not follow the same protocols as during normal operation either on the ground or in flight. Therefore, it is specifically on the ground where the automatic reaction to a fire indication is implemented to ensure immediate safety measures can be activated.