Which three systems are explicitly listed as continuing to operate when both generators and batteries are inoperative?

• A. Passenger O2, the pressurization controller, and the ESIS
• B. Aircraft inertial system, weather radar, and transponder
• C. Cockpit lights, hydraulic pump, and fuel pump
• D. Navigation lights, autopilot, and audio panel

Answer: (A)

When electrical power is completely lost, the systems that keep functioning are the ones that have their own independent power or don’t rely on the main electrical system to operate. In this case, the three that continue to operate are the passenger oxygen system, the cabin pressurization controller, and the Electronic Standby Instrument System (ESIS).

Passenger oxygen is a self-contained supply that doesn’t require the aircraft’s electrical power to deliver oxygen to passengers, so it remains available even if generators and batteries aren’t providing power. The pressurization controller is designed to regulate cabin pressure using a backup mechanism that does not depend on the main electrical system, ensuring the cabin can stay within safe pressure limits during a power failure. The ESIS has its own standby power pathway, so essential flight information—attitude, altitude, and airspeed—remains readable even when the primary instruments and power are down.

Other systems listed rely on the aircraft’s electrical power to operate, so without generators and batteries they would not continue functioning.