If G1 and G2 fail, how is power maintained?

• A. The standby battery powers all buses
• B. There is no alternate power source
• C. The APU generator GA or external power maintains essential buses, and nonessential loads can be shed
• D. The aircraft shuts down essential systems

Answer: (C)

When the two engine-driven generators fail, the aircraft relies on an alternate power source to keep the essential systems alive. The APU generator (GA) can be started and used to power the essential electrical buses, and if the aircraft is on the ground, external power can also supply those buses. Because the available power may be limited without the main generators, nonessential loads—such as certain cabin services or non-critical systems—are shed to conserve power for the essential systems. This keeps the flight-critical equipment operating while normal power is restored or the APU takes over.