On the ground with engines off, which power source commonly supplies essential systems?

On the ground with engines off, which power source commonly supplies essential systems?

• A. APU generator
• B. External power unit
• C. Battery only
• D. Standby power system

Answer: (A)

On the ground with engines off, the aircraft’s on-board auxiliary power unit generator powers the essential systems. The APU is designed to supply electrical power to the essential buses so cockpit avionics, lighting, and other critical systems stay powered while the engines aren’t running and during engine start. An external ground power unit can provide power when connected, but it isn’t always available at every airport. The standby power system is reserved for emergency operation, typically in flight, and it only supports a limited set of critical items. A battery alone doesn’t have enough capacity to power all essential systems for normal ground operations.

On the ground with engines off, the aircraft’s on-board auxiliary power unit generator powers the essential systems. The APU is designed to supply electrical power to the essential buses so cockpit avionics, lighting, and other critical systems stay powered while the engines aren’t running and during engine start. An external ground power unit can provide power when connected, but it isn’t always available at every airport. The standby power system is reserved for emergency operation, typically in flight, and it only supports a limited set of critical items. A battery alone doesn’t have enough capacity to power all essential systems for normal ground operations.