Which power source can supply power for engine start if engine-driven generators are not available?

• A. External power only
• B. Hydraulic system
• C. APU generator GA
• D. Battery only

Answer: (C)

When engine-driven generators aren’t available, the onboard source designed to supply start power is the auxiliary power unit’s generator. The APU is a self-contained power source that, once running, can provide the electrical power needed to operate the engine start motors and other essential systems, allowing you to start the engines without external power. External power could be used if a ground power unit is connected, but it isn’t always available, so the APU generator offers a reliable onboard option. The hydraulic system doesn’t generate electrical power for starting engines, and a battery alone can’t provide the sustained high current required for reliable two-engine starts.