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

What is the primary and secondary purpose of the APU?

1. Only for electrical power

2. Supply electrical power; bleeding air as secondary

3. Only for bleed air

4. Supply bleed air; electrical power as secondary

The correct answer is: Supply electrical power; bleeding air as secondary

The correct choice identifies that the Auxiliary Power Unit (APU) serves as a source for electrical power while also capable of providing bleed air as a secondary function. The APU primarily functions to generate electrical power once the main engines have not yet started or are idle. This is crucial for powering essential onboard systems and ensuring operations like lighting, avionics, and other electrical demands. In addition to its electrical generation capabilities, the APU can also supply bleed air, which is used for various purposes such as engine starting and environmental control systems. This versatility allows the APU to be invaluable during ground operations, where the aircraft may not have access to the main engine power or external ground power sources. The other options do not accurately capture the dual role of the APU. Some suggest it’s solely for electrical power or bleed air, overlooking the comprehensive functionality of the unit. Understanding the correct choice emphasizes the importance of the APU in managing aircraft systems effectively during pre-flight operations and ground servicing.