During approach, ACSC switches from Engines to APU when Gear Down or Flaps Down occurs. Which statement describes the conditions?

• A. Gear Down OR Flaps Down
• B. Gear Up and Flaps Up
• C. Gear Down and Flaps Up
• D. Gear Up OR Flaps Down

Answer: (A)

The situation tests bleed-air source selection during approach. The system is designed to switch from engine bleed to APU bleed as soon as either gear is down or flaps are down. In other words, if the landing gear is extended or the flaps are extended, the ACSC will automatically use the APU bleed instead of engine bleed. This helps ensure uninterrupted bleed air for the environmental control system and packs when the aircraft configuration changes for landing, without requiring both conditions to occur. The other options imply requiring both conditions or using the other configuration in situations that aren’t how the system is intended to operate.