With External Power Available, selecting EXT PWR switch to ON will __________

With External Power Available, selecting EXT PWR switch to ON will __________

• A. Disconnect the APU power source and apply External Power to both sides.
• B. Apply External Power to the APU only.
• C. Keep the APU power source connected and apply External Power to one side.
• D. External Power has no effect on APU.

Answer: (A)

When external power is available, turning EXT PWR ON routes the external source to the aircraft’s electrical system and isolates the APU generator. This ensures there’s no backfeed between the external power and the APU, while the external power is distributed to both AC buses so all systems on the left and right sides can be powered without using the APU. The other options don’t fit because the APU isn’t kept connected to power nor supplied alone, and external power does affect the system by providing power to both sides.

When external power is available, turning EXT PWR ON routes the external source to the aircraft’s electrical system and isolates the APU generator. This ensures there’s no backfeed between the external power and the APU, while the external power is distributed to both AC buses so all systems on the left and right sides can be powered without using the APU. The other options don’t fit because the APU isn’t kept connected to power nor supplied alone, and external power does affect the system by providing power to both sides.