During an electrical failure, standby power supplies should power which systems?

• A. Essential systems
• B. All systems
• C. Only cabin lighting
• D. Only flight controls

Answer: (A)

Standby power is there to keep the aircraft safe during an electrical failure by preserving power to the most safety-critical systems. This ensures the crew retains situational awareness and the ability to control the airplane until a safe landing can be made. The focus is on essential items such as the flight instruments and the minimal avionics needed to understand the aircraft’s attitude, speed, altitude, and heading, along with any other critical systems necessary for safe operation. Nonessential items, like cabin lighting or comfort systems, are not supplied by standby power to conserve energy. So the standby power should power essential systems to maintain safe flight, rather than powering everything, or just cabin lighting, or only flight controls.