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

How many operating modes are there for the APU?

1. One mode

2. Two modes

3. Three modes

4. Four modes

The correct answer is: Two modes

The APU, or Auxiliary Power Unit, typically has two operating modes: ground mode and flight mode. In ground mode, the APU provides electrical power and pneumatic air to support various aircraft systems while on the ground, such as air conditioning and starting main engines. This mode ensures that the aircraft can maintain its systems without needing to rely on external ground power sources. In flight mode, the APU continues to provide electrical power and can be used to supply bleed air for engine starting or environmental control system needs at altitude. This capability is particularly valuable in scenarios where main engines may not be available to perform these functions, enhancing operational safety and efficiency. Understanding these two modes is crucial for pilots and ground crew in effectively managing aircraft systems and ensuring proper APU operation under different conditions.