Under what condition would the APU GEN ON advisory appear?

Under what condition would the APU GEN ON advisory appear?

• A. When the main generators are online
• B. When it is the sole source of AC power
• C. When the aircraft is on the ground
• D. When the battery voltage is high

Answer: (B)

The APU is used to supply AC power when other generators aren’t providing it. The advisory appears specifically to flag that the APU’s generator is the only source feeding the electrical system. That means both main engine generators are not online (or not delivering AC) and the APU is running and connected to the bus. So this advisory is shown when the APU is the sole AC power source, alerting you to the fact that if the APU were to fail or be shut down, there would be no AC power available.

The APU is used to supply AC power when other generators aren’t providing it. The advisory appears specifically to flag that the APU’s generator is the only source feeding the electrical system. That means both main engine generators are not online (or not delivering AC) and the APU is running and connected to the bus.

So this advisory is shown when the APU is the sole AC power source, alerting you to the fact that if the APU were to fail or be shut down, there would be no AC power available.