How does the APU assist with engine starts and electrical power on the ground?

• A. Provides pneumatic bleed air for engine starting and electrical power when external power is unavailable or on the ground
• B. Supplies hydraulic pressure for landing gear
• C. Provides cabin pressurization only
• D. Provides fuel to engines

Answer: (A)

The APU’s job on the ground is to supply two essential services: bleed air for engine starts and electrical power for the aircraft when external power isn’t available. The bleed air from the APU drives the engine’s air-start units (air turbine starters), spinning the engines until they can take over their own air and fuel supply. At the same time, the APU’s generator provides electrical power to the aircraft’s systems, keeping avionics, lighting, air conditioning, and other loads energized without needing ground power. This role does not include providing hydraulic pressure or fuel to the engines.